original design and construction of forms are: Economy in lumber,
economy in carpenter work, and economy in taking down, carrying and
re-erecting. Economy in lumber is not merely the matter of using the
least amount of lumber that will serve the purpose considering the form
as an isolated structure. It may be possible to build a column form, for
example, of very light material which will serve to mold a single
column, but it is evident that we could better afford to use twice this
amount of lumber if by doing so we obtained a form which could be used
over again to mold a second column; no more lumber per column would be
used while the cost of erecting a form already framed is less than the
cost of framing a new form. Economy in lumber in form construction
involves, therefore, recognition of the economies to be gained by
repeated use of the lumber. A certain amount of additional sturdiness is
required in the shape of heavier form lumber and stronger framing to
provide for the wear and tear of repeated use, and it is always economy
to provide it when repeated use is possible. The thing can be overdone,
however; there is an economical limit to repeated use, as we demonstrate
further on. In the matter of economy in carpenter work, a certain amount
of extra work put into framing the forms to withstand the stress of
repeated use is economically justifiable. Also carpenter work put into
framing which substitutes clamps and wedges for nails is sound economy;
generally speaking a skillful form carpenter is recognized by the
scarcity of nails he uses. The possibility of reducing carpenter work by
ordering lumber to length and width from plans has already been
mentioned. It is possible often to go a step further by having certain
standard panels, boxes, etc., made in regular shops. Piece work is often
possible and will frequently reduce framing costs. In designing for
economy in taking down, carrying and re-erecting forms a cardinal point
should be that the work be such that it can be executed by common
laborers. This result can be very nearly approached by careful design,
even for form work that is quite complex, if a special gang is devoted
to the work and trained a little in the various operations. Design the
forms so that they come apart in units by simply removing bolts, clamps
and wedges. They can then be taken down, carried and erected by common
laborers with a skilled man in charge to meet emergencies and to true
and line up the work.
In the matter of details the joints deserve particular attention. In
column and girder forms, generally, joints will be square or butt
joints, and to get them tight the lumber must be dressed true to edge.
Tight joints are considered essential by many not only to avoid joint
marks but for the more important reason that otherwise, with wet
mixtures, a honeycombed concrete is produced by leakage. Where tight
joints are desired tongue and groove stock or stock cut with one edge
beveled and the other square give the best results. The authors believe
that the best general satisfaction will be got from the bevel edge stock
placed so that the bevel edge of one board comes against the square edge
of the next board; undue swelling then results in the bevel edge cutting
into the adjacent square edge without bulging. Tongues and grooves
suffer badly from breakage. As a matter of fact square edged stock, if
well dressed and sized and well filled with moisture, can be used and is
used with entire success in nearly all kinds of work. The leakage will
be very slight with ordinarily good butt joints and so far as surface
appearance goes joint marks are more cheaply and more satisfactorily
eliminated by other means than attempting to get cabinet work in form
construction. Where girder forms join columns or beams connect with
girders and at the angles of floor slabs with beams the edges or corners
of the forms should be rounded. The edges of beams and column corners
will appear better if beveled; a triangular strip in the corners of the
forms will provide this bevel. Forms and mold construction for
ornamental work call for and are given special consideration in Chapter
XXIII. In conclusion, the reader should study the specific examples of
form construction for different purposes that are given throughout the
book for hints as to special practice and details.
~UNIT CONSTRUCTION OF FORMS.~--Unit construction has a somewhat variable
meaning in form work. In wall and tank work and in some other kinds of
work unit construction means the use of form units which are gradually
moved ahead or upward as the concreting progresses or of form units
which are used one after another in continuous succession as the
concreting progresses. In column, girder and floor work unit
construction means the division of the form work as a whole and also of
the individual forms into independent structural units; thus in forms
for a building the column forms may be independent of the girder forms
and also each column and girder form be made up of several separate
units. In all cases unit construction has for its purpose the use of the
same form or at least the same form lumber over and over for molding
purposes. Every time the use of the same form is repeated, the cost of
form work per cubic yard of concrete placed is reduced. The theoretical
limit of economical repetition is then the limit of endurance of the
form, the practical limit, however, is something quite different. Most
concrete work varies in form or dimensions often enough to prevent the
use of the same forms more than a few times, and even if these
variations did not exist the time element would enter to prevent the
same form or form lumber being used more than a certain number of times.
Unit construction to give repeated use of forming has, therefore, its
economic limits. The significance of this conclusion does not lie in any
novelty that it possesses but in the fact that for any piece of work it
determines the labor that may profitably be expended in working out and
constructing form units.
~LUBRICATION OF FORMS.~--All forms for concrete require a coating of some
lubricant to prevent the concrete from adhering to the wood with which
it comes in contact. Incidentally this coating tends to give a smoother
surface to the concrete and to preserve the wood against damage by its
alternate wetting and drying. The great value of lubrication is,
however, that it reduces the cost of removing forms. The requisite of a
good coating material is that it shall be thin enough to spread evenly
and to fill the pores and grain of the wood. Crude oil or petroline
makes one of the best coatings, but various other greasy substances will
serve. Where the forms are not to be removed until the concrete has set
hard a thorough wetting of the wood just before the concrete is placed
is all the coating necessary. Any concrete adhering to forms should be
thoroughly cleaned off before they are used again and the wood
underneath given a special heavy coating.
~FALSEWORKS AND BRACING.~--The falseworks which support the forms proper
and stagings for workmen, runways, material hoists, etc., do not call
for any striking differences in construction and arrangement from such
work elsewhere. For wall forms inclined props reaching from ground to
studding are used for walls of moderate height such as retaining walls,
wing walls, and abutments. For building walls of some height a gallows
frame arrangement or the common braced staging used by masons and
carpenters is used. In building construction, however, movable forms are
commonly employed for walls more than one story high and should always
be employed above one story to save staging timber. Column forms are
seldom braced unless erected without connecting girder or floor forms at
their tops, and then only by diagonal props to the floor or ground.
Girder and floor supports usually consist of uprights set under the
girder form at intervals and occasionally under floor slab forms. The
spacing of props and uprights will be regulated by the judgment of the
foreman and boss carpenter; no general rule is applicable, except that
enough lumber must be used to hold the forms rigid and true to line and
level. The various illustrations of actual formwork which follow are the
best guides to good practice.
~TIME FOR AND METHOD OF REMOVING FORMS.~--No exact time schedule for
removing forms is wise in concrete work. Concrete which is mixed wet
sets slower than dry concrete and concrete sets slower in cold weather
than it does in warm weather. Again the time of removal is influenced by
the risk taken by too early removal, and also by the nature of the
stresses in the member to be relieved of support. In all cases the forms
should be removed as soon as possible so that they can be used over
again and so that the concrete may be exposed to the air to hasten
hardening. The following suggestions as to time of removal are general
and must be followed with judgment.
Using dry concrete in warm weather the forms for retaining walls,
pedestals, isolated pillars, etc., can be removed in 12 hours; using wet
or sloppy concrete the time will be increased to 24 hours. In cold
weather the setting is further delayed and inspection is the only safe
guide to follow. Very cold weather delays setting indefinitely. Forms
for small arch work like sewers and culverts may be removed in 18 to 24
hours if dry concrete is used, and in 24 to 48 hours if wet concrete is
used. The time for removing large arch centers should not be less than
14 days for spans up to 50 ft. if the arch is back-filled at once; when
the center is not to be used again it is better to let it stand 28 days.
For very large arches the problem becomes a special one and is
considered in Chapter XVII. In building construction the following
schedule is a common one. Remove the column forms in 7 days and the
sides of the girder forms and the floor lagging in 14 days leaving the
bottom boards of the girder forms and their supports in place for 21
days.
As an example of individual practice the following requirements of a
large firm of concrete contractors are given:
Walls in mass work, 1 to 3 days, or until the concrete will bear
pressure of the thumb without indentation.
Thin walls, in summer, 2 days; in cold weather, 5 days.
Slabs up to 6-ft. span, in summer, 6 days; in cold weather, 2 weeks.
Beams and girders and long span slabs, in summer, 10 days or 2 weeks; in
cold weather, 3 weeks to 1 month. If shores are left without disturbing
them, the time of removal of the sheeting in summer may be reduced to 1
week.
Column forms, in summer, 2 days; in cold weather, 4 days, provided
girders are shored to prevent appreciable weight reaching columns.
Conduits, 2 or 3 days, provided there is not a heavy fill upon them.
Arches, of small size, 1 week; for large arches with heavy dead load, 1
month.
The method of removing forms will vary in detail with the character of
the structure. With proper design and lubrication of forms they will
ordinarily come away from the concrete with a moderate amount of sledge
and bar work. If the work will warrant it, have a special gang under a
competent foreman for removing forms. The organization of this gang and
the procedure it should follow will vary with the nature of the form
work, and they are considered in succeeding chapters for each kind of
work.
~ESTIMATING AND COST OF FORM WORK.~--It is common practice to record the
cost of forms in cents per cubic yard of concrete, giving separately the
cost of lumber and labor. This should be done, but the process of
analysis should be carried further. The records should be so kept as to
show the first cost per 1,000 ft. B. M. of lumber, the number of times
the lumber is used, the labor cost of framing, the labor cost of
erecting and the labor cost of taking down, all expressed in M. ft. B.
M. In this way only is it possible to compare the cost of forms on
different kinds of concrete work, and thus only can accurate predictions
be made of the cost of forms for concrete work having dimensions
differing from work previously done. It is well, also, to make a note of
the number of square feet of exposed concrete surface to which the forms
are applied.
Some of the items mentioned demand brief explanation. Framing and
erecting costs are kept separate for the reason that the framing is done
only once, whereas the erecting occurs two or more times. The lumber
cost, where the material is used more than once, can be computed in two
ways. An example will illustrate the two modes of procedure. In one of
the buildings described in Chapter XIX the lumber cost $30 per M. ft. B.
M. and was used three times. As 34,000 ft. B. M. were required to encase
the 200 cu. yds. of concrete in one floor, including columns, it would
have required 34,000 ÷ 200 = 170 ft. B. M. of lumber at $30 per M. per
cubic yard of concrete if it had been used only once. But since it was
used three times we may call it 170 ft. B. M. at $10 per M. per cubic
yard of concrete, or we may call it 170 ÷ 3 = 57 ft. B. M. at $30 per M.
per cubic yard of concrete. The authors prefer the first method, due to
the fact that it is 170 ft. B. M. that is handled and taken down each
time and it is more consistent to have the lumber cost on the same basis
thus:
170 ft. B. M. of lumber at $10 per M $1.70
170 ft. B. M. handled at $2 per M 0.34
170 ft. B. M. erected at $7 per M 1.19
-----
Total 170 ft. B. M. per cu. yd $3.23
Returning to our main thought, there are three ways of recording the
cost of form work: (1) In cents per cubic yard of concrete; (2) in cents
per square foot of concrete face to which forms are applied, and (3) in
dollars per 1,000 ft. B. M. of lumber used. In all cases the cost of
materials and of labor should be kept separate. It is well if it can be
done to attach a sketch of the forms to the record. So much for the
general method of recording costs in form work.
In estimating the probable cost of forms for any job the following
method will be found reliable: Having the total cubic yards of concrete
in the work and the time limit within which the work must be completed
determine the number of cubic yards that must be placed per day, making
liberal allowances for delays. Next estimate the number of thousands of
feet board measure of forms required to encase the concrete to be placed
in a day. This will give the minimum amount of lumber required, for it
is seldom permissible to remove the forms until the concrete has
hardened over night. Now we come to the very important and puzzling
question of the time element, particularly in work where it is possible
to use the same forms or the same form lumber two or more times.
It has already been pointed out that wet concrete sets more slowly than
dry concrete; that all concrete sets more slowly in cold than in warm
weather, and that the support of forms is necessary a longer time for
pieces subject to bending stress like arches and girders. General
suggestions as to specific times for removing forms have also been
given. Where the specifications state the time of removal the contractor
has a definite guide, but where they do not, as is most often the case,
he must depend very largely on judgment and previous experience. Another
matter which deserves consideration is the use of the forms as staging
for runways or tracks. Such use may result in forms having to stand on
work for sake of their service as trestles much longer than there is any
necessity so far as supporting the concrete is concerned. A derrick or
cableway may often prove cheaper than tieing up form lumber by trying to
make it serve the double purpose of a trestle.
The possibilities of repeated use of forms and of unit construction of
forms have already been noted. This is the next point to be considered
in estimating form lumber. At the expense of a little planning movable
forms can be used to materially reduce the amount of lumber required.
The reader is referred particularly to the chapters on retaining wall,
conduit and building work for specific data on movable form work.
Having estimated the amount of lumber required and the number of times
it can be used the labor cost of framing, erecting and taking down can
be figured. In ordinary retaining wall work forms will cost for framing
and erection from $6 to $7 per M. ft. B. M. To tear down such forms
carefully and to carry the lumber a short distance will cost some $1.50
to $2 per M. ft. B. M. We have then a cost of $7.50 to $9 per M. ft. B.
M. for each time the forms are erected and torn down. Where movable
panels are used and the forms not ripped apart and put together again
each time there is of course only the cost of moving, which may run as
low as 50 cts. per M. ft. B. M. Framing and erecting centers for piers
will run about the same as for retaining wall. At this point it may be
noted that in estimating the cost of forms for plain rectangular piers
the following method will give very accurate results. Ascertain the
surface area of the four sides of the pier. Multiply this area by 2, and
the product will be the number of feet board measure of 2-in. plank
required. Add 40 per cent. to this, and the total will be the number of
feet board measure of 2-in. plank and of upright studs (4×6), spaced 2½
ft. centers. Sometimes 3×6-in. studs are used, and spaced 2 ft. centers,
which requires practically the same percentage (40 per cent.) of timber
for the studs as where 4×6-in. studs are used and spaced 2½ ft. centers.
No allowance is made for timber to brace the studs, since, in pier work,
it is customary to hold the forms together either with bolts or with
ordinary No. 9 telegraph wire, which weighs 0.06 lb. per foot. The
foregoing data can be condensed into a rule that is easily remembered:
_Multiply the number of square feet surface area of the sides and ends
of a concrete pier by 2.8, and the product will be the number of feet
board measure required for sheet plank and studs for the forms._
If the form lumber can be used more than once, divide the number of feet
board measure by the number of times that it can be used, to ascertain
the amount to be charged to each pier. Forms can be erected and taken
down for $8 per M. carpenters being paid $2.50 and laborers $1.50 a day.
Since there are 2.8 ft. B. M. of forms per square foot of surface area
of concrete to be sheeted, it costs 2¼ cts. for the labor of carpenters
per square foot of surface area to be sheeted. If lumber is worth $24
per M., and is used three times, then the lumber itself also costs 2¼
cts. per sq. ft. of surface area of concrete. By dividing the total
number of cubic yards of concrete into the total number of square feet
of area of surface to be sheeted with forms, the area per cubic yard is
obtained. Multiply this area by 4½ cts., and the product is the cost per
cubic yard for material in the forms (assumed to be used three times)
and the labor of erecting it and taking it down.
The cost of framing and erection of forms for building work and of
centers for large arches is a special problem in each case and is
considered in the chapters devoted to those classes of work.
CHAPTER X.
METHODS AND COST OF CONCRETE PILE AND PIER CONSTRUCTION FOR FOUNDATIONS.
Two general methods of concrete pile construction are available for
engineering work. By one method a hole is formed in the ground by
driving a steel shell or by other special means and this hole is filled
with concrete. By the other method the pile is molded in suitable forms
and after becoming hard is driven as a wood or steel pile is driven.
Piles constructed by the first method may be either plain or reinforced,
but piles constructed by the second method are always reinforced to
strengthen them for handling and driving. Concrete piers for foundation
work are simply piles of enlarged diameter.
~MOLDING PILES IN PLACE.~--Molding piles in place requires the use of
special apparatus, and this apparatus is to a very large degree
controlled by patents. Pile work of this kind is thus generally done by
concerns which control the use of the apparatus employed and the general
contractor can undertake it only by permission of the proprietary
companies. The methods of work followed and the cost of work are thus of
direct interest only as general information.
~Method and Cost of Constructing Raymond Piles.~--The machinery and
processes employed in the construction of Raymond concrete piles are
patented and all piling work by this method is controlled by the Raymond
Concrete Pile Co. As detail costs of construction are not given out by
the company the following figures collected by the authors are subject
to revision. They are believed to be fairly approximate, having in one
case been obtained by personal watch on the work and in the other case
from authentic records of the engineers on the work.
The pile is made as follows: A collapsible steel core 30 ft. long, 20
ins. diameter at the top and 6 ins. diameter at the bottom, encased in
a thin sheet steel shell, is driven into the ground by an ordinary pile
driver. When it has reached the proper depth, a wedge is loosened,
permitting the two sections of the core to come closer together so that
the core can be pulled out of the hole, leaving the steel shell behind
as a casing to prevent the sides from caving in. The shell is made of
No. 20 gage steel, usually in four or more sections, which telescope one
over the other. A nest of sections is slipped over the lower end of the
core as it hangs in the leads, a rope is hitched around the outer
section and the engine hoists away until the sections are
"un-telescoped" and drawn snug onto the core. The rope is then
unfastened and the driving begins. Figure 49 shows the usual pile
driving rig used. The following are examples of pile construction in
actual work:
_Example I._--In this work, for a building foundation in New York City,
the pile driver was mounted on a turntable, the framework of the
turntable in turn resting on rollers traveling on timbers laid on the
ground. The driver was moved along and rotated when necessary by ropes
passing around the winch head of the engine. The driver had 50-ft. leads
and a 3,100-lb. hammer operated by an ordinary friction clutch hoisting
engine. The hammer blow was received by an oak block fitting into a
recess at the top of the steel core. This block was so battered by the
blows that it had to be renewed about every five or six piles driven. A
¾-in. wire rope passing over a 10-in. sheave lasted for the driving of
130 piles and then broke. When the work was first begun the crew
averaged 10 piles per 10-hour day, but the average for the job was 13
piles per day, and the best day's work was 17 piles. The cost of labor
and fuel per pile was as follows:
5 men on driver at $1.75 $ 8.75
2 men handling shells at $1.75 3.50
1 engineman 3.00
6 men mixing and placing concrete 10.50
1 foreman 5.00
Coal and oil 2.50
-------
Total, 13 piles, at $2.55 $33.25
[Illustration: Fig. 49.--Pile Driver Rigged for Constructing Raymond
Concrete Piles.]
Deducting the cost of placing the concrete we get a cost of $1.75 for
driving the cores. The pile, 25 ft. long, 6 ins. at the point and 18
ins. at the head, contains 21¼ cu. ft., or 0.8 cu. yd., of concrete, and
has a surface area of 77 ft. As No. 20 steel weighs 1.3 lbs. per sq.
ft., each shell weighed approximately 100 lbs. The cost per pile may
then be summarized as follows:
1.2 bbls. cement in 0.8 cu. yd., at $1.75 $2.10
0.8 cu. yd. stone at $1.25 1.00
1/3 cu. yd. sand at $1.05 0.35
100 lbs. steel in shell at 3½ cts. 3.50
Labor and fuel as above 2.55
-----
Total per pile (38 cts. per lin. ft.) $9.50
_This cost, it should be carefully noted, does not include cost of
moving plant to and from work or general expenses._
_Example II._--In constructing a building at Salem, Mass., 172
foundation piles, 14 to 37 ft. long, 6 ins. diameter at the point and 20
ins. diameter at the top, were constructed by the Raymond process. The
general contractor made the necessary excavations and provided clear and
level space for the pile driver, braced all trenches and pier holes, set
stakes for the piles and gave all lines and levels. The piles were
driven by a No. 2 Vulcan steam hammer with a 3,000-lb. plunger having a
drop of 3 ft., delivering 60 blows per minute. Figure 49 shows the
driver at work. Sixteen working days were occupied in driving the piles
after the driver was in position. The greatest number driven in one day
was 20, and the average was 11 piles per day. When in position for
driving, the average time required to complete driving was 12 minutes.
The total number of blows varied from about 310 to 360, the average
being about 350. The piles were driven until the penetration produced by
8 to 10 blows equaled 1 in. When in full operation, a crew of 5 men
operated the pile driver. Seven men were engaged in making the concrete
and 5 men working upon the metal shells.
Assuming the ordinary organization and the wages given below, we have
the following labor cost per day:
1 foreman at $5 $ 5.00
1 engineman at $3 3.00
4 laborers on driver at $1.75 7.00
6 laborers making concrete at $1.75 10.50
5 laborers handling shells at $1.75 8.75
------
Total $34.25
As 172 piles averaging 20 ft. in length were driven in 16 days, the
total labor cost of driving, given by the figures above, is 16 × $34.25
= $548, or practically 16 cts. per lineal foot of pile driven.
The concrete used in the piles was a 1-3-5 Portland cement, sand and
1½-in. broken stone mixture. A 20-ft. pile of the section described
above contains about 20 cu. ft. of concrete, or say 0.75 cu. yd. We can
then figure the cost of concrete materials per pile as follows:
0.85 bbl. cement at $1.60 $1.36
0.36 cu. yd. sand at $1 0.36
0.60 cu. yd. stone at $1.25 0.75
-----
Total per pile $2.47
The steel shell has an area of about 72 sq. ft., and as No. 20 gage
steel weighs 1.3 lbs. per sq. ft., its weight for each pile was about 94
lbs. Assuming the cost of coal, oil, etc., at $2.50 per day, we have the
following summary of costs:
Per lin. ft.
of pile.
Labor driving and concreting $0.16
Concrete materials 0.123
94 lbs. steel shell at 3 cts. 0.145
Coal, oil, etc. 0.011
------
Total $0.439
_The cost does not include interest on plant, cost of moving plant to
and from work and general expenses._
[Illustration: Fig. 50.--Sketch Showing Method of Constructing Simplex
Concrete Piles.]
~Method of Constructing Simplex Piles.~--The apparatus employed in driving
Simplex piles resembles closely the ordinary wooden pile driven, but it
is much heavier and is equipped to pull as well as to drive. A 3,300-lb.
hammer is used and it strikes on a hickory block set in a steel drive
head which rests on the driving form or shell. This form consists of a
¾-in. steel shell 16 ins. in diameter made in a single 40-ft. length.
Around the top of the shell a ½-in. thick collar or band 18 ins. deep is
riveted by 24 1-in. countersunk rivets. This band serves the double
purpose of preventing the shell being upset by the blows of the hammer
and of giving a grip for fastening the pulling tackle. The bottom of the
form or shell is provided with a point. Two styles of point are
employed. One style consists of two segments of a cylinder of the same
size as the form, so cut that they close together to form a sort of clam
shell point. In driving, the two jaws are held closed by the pressure of
the earth and in pulling they open apart of their own weight to permit
the concrete to pass them. This point, known as the alligator point, is
pulled with the shell. It is suitable only for driving in firm, compact
soil, in loose soil the pressure inward of the walls keeps the jaws
partly closed and so contracts the diameter of the finished pile. The
second style of point is a hollow cast iron point, 10 ins. deep and 16½
ins. in diameter, having a neck over which the driving form slips and an
annular shoulder outside the neck to receive the circular edge of the
shell. The projected sectional area of this point is 1.4 sq. ft. It is
left in the ground when the form is withdrawn. The form is withdrawn by
means of two 1-in. cables fastened to a steel collar which engages under
the band at the top of the form. The cables pass in the channel leads on
each side over the head of the driver and down in back to a pair of
fivefold steel blocks, the lead line from which passes to one of the
drums of the engine. In this manner the power of the drum is increased
ten times and it is not unusual to break the pulling cables when the
forms are in hard ground. The general method of construction is about as
shown by Fig. 50, being changed slightly to meet varying conditions. The
form resting on a cast iron point is driven to hard ground. A heavy
weight is then lowered into the form to make sure the point is loose.
While the weight is at the bottom of the form a target is placed on its
line at the top of the form, the purpose of which will be apparent
later. The weight is then withdrawn. Given the length of the pile and
sectional area, it is an easy matter to determine the volume of concrete
necessary to fill the hole.
This amount is put into the form by means of a specially designed bottom
dump bucket, which permits the concrete to leave it in one mass,
reaching its destination with practically no disintegration. It will be
noticed that when the full amount of concrete is in the form its surface
is considerably above the surface of the ground. This is due to the fact
that the thickness of the form occupies considerable space that is to be
occupied by the concrete. The weight is now placed on top of the
concrete and the form is pulled. The target previously mentioned now
becomes useful. As the form is withdrawn the concrete settles down to
occupy the space left by the walls of the form. Obviously this
settlement should proceed at a uniform rate, and as it is difficult to
watch the weight, the target on its line further up is of considerable
help. By watching this target in connection with a scale on the leads of
the driver, it can be readily told how the concrete in the form is
acting. As another check, the target, just as the bottom of the form is
leaving the ground should be level with the top of the form. This would
indicate that the necessary amount of concrete has gone into the ground
and that, other conditions being all right, the pile is a good one. In
some grounds where the head of concrete in the form exerts a greater
pressure than the back pressure or resistance of the earth, the concrete
will be forced out into the sides of the hole, making the pile of
increased diameter at that point and necessitating the use of more
concrete to bring the pile up to the required level.
~Method of Constructing Piles with Enlarged Footings.~--A pile with an
enlarged base or footing has been used in several places by Mr. Charles
R. Gow of Boston, Mass., who has patented the construction. A single
pipe or a succession of pipes connected as the work proceeds is driven
by hammer to the depths required. The material inside the shell is then
washed out by a water jet to the bottom of the shell and then for a
further distance below the shell bottom. An expanding cutter is then
lowered to the bottom of the hole and rotated horizontally so as to
excavate a conical chamber, the water jet washing the earth out as fast
as it is cut away. When the chamber has been excavated the water is
pumped out and the chamber and shell are filled with concrete. The
drawings of Fig. 51 show the method of construction clearly. The
chambering machine is used only in clay or other soil which does not
wash readily. In soil which is readily washed the chamber can be formed
by the jet alone. The practicability of this method of construction is
stated by Mr. Gow to be limited to pipe sizes up to about 14 ins. in
diameter.
[Illustration: Fig. 51.--Sketch Showing Method of Constructing Concrete
Piles with Enlarged Footings.]
~Method of Constructing Piles by the "Compressol" System.~--The compressol
system of concrete pile or pillar construction is a French invention
that has been widely used abroad and which is controlled in this country
by the Hennebique Construction Co., of New York, N. Y. The piles are
constructed by first ramming a hole in the ground by repeatedly
dropping a conical "perforator" weighing some two tons. This perforator
is raised and dropped by a machine resembling an ordinary pile driver.
The conical weight gradually sinks the hole deeper and deeper by
compacting the earth laterally; this lateral compression is depended
upon so to consolidate the walls of the hole that they do not cave
before the concrete can be placed. The concrete is deposited loose in
the hole and rammed solid by dropping a pear-shaped weight onto it as it
is placed. The view Fig. 52 shows the "perforator" and the tamping
apparatus at work. Very successful work has been done abroad by this
method.
[Illustration: Fig. 52.--View of Apparatus Used in Constructing
Compressol Piles.]
~Method of Constructing Piers in Caissons.~--For piles or pillars of
diameters larger than say 18 ins. the use of driving shells and cores
becomes increasingly impracticable. Concrete pillars of large size are
then used. They are constructed by excavating and curbing a well or
shaft and filling it with concrete. This construction has been most used
in Chicago, Ill., for the foundations for heavy buildings, but it is of
general application where the sub-soil conditions are suitable. The
method is not patented or controlled by patents in any particular,
except that certain tools and devices which may be used are proprietary.
_General Description._--The caisson method of construction is simple in
principle. A well is dug by successive excavations of about 5 ft. each.
After each excavation of 5 ft. is completed, wood lagging is placed
around the sides and supported by internal steel rings, so that the soft
ground around the excavation is maintained in its former position. The
methods of excavating and removing the soil and of constructing the
lagging are considered in detail further on. The caissons vary in
diameter according to the load; some as large as 12 ft. in diameter have
been sunk, but the usual diameter is 6 ft.; a caisson of 3 ft. in
diameter is as small as a man can get into and work. When the pier goes
to bed rock the caisson is made of uniform diameter from top to bottom,
but where the pier rests on hardpan the bottom portion of the well is
belled out to give greater bearing area. It is customary to load the
piers about 20 tons per square foot.
[Illustration: Fig. 53.--Curbing for Concrete Piers (Usual
Construction).]
_Caisson Construction._--The caisson construction, or more correctly the
form of curbing most commonly used, is that indicated by the sketch,
Fig. 53. The lagging is 2×6 in. or 3×6 in., stuff 5 ft. 4 ins. or 4 ft.
long set vertically around the well and held in place by interior
wrought iron rings. For a 6-ft. diameter caisson these hoops are ¾ by 3
ins.; they are made in two parts, which are bolted together as shown by
Fig. 53. Generally there are two rings for each length of lagging; for
5-ft. lagging they are placed about 9 ins. from each end. In some
cases, however, engineers have specified three rings for the upper
sections in soft clay and two rings for the sections in the hard ground
lower down. The lagging used is not cut with radial edges, but is rough,
square cut stuff; the rings, therefore, take the inward pressure
altogether.
[Illustration: Fig. 54.--Curbing for Concrete Piers (Jackson Patent).]
In some recent work done by the inventor use has been made of the
caisson construction shown by Fig. 54 and patented by Mr. Geo. W.
Jackson. In place of the plain rings a combination of T-beam ribs and
jacks is used; this construction is clearly shown by the drawing. The
advantages claimed for the construction are that it gives absolute
security to the workmen and the work, that the lagging can be jacked
tightly against the outer walls of the well, that the braces form a
ladder by which the workmen can enter and leave the well, and that the
possibility of shifting the bracing easily permits the concrete to be
placed to the best advantage. On the other hand the braces abstruct the
clear working space of the caissons.
[Illustration: Fig. 55.--Layout of Plant for Concrete Pier Construction.
Cook County Court House Foundations.]
_Excavating and Handling Material._--The excavation of the wells is done
by hand, using shovels and picks, and, in the hardpan, special grubs
made by A. J. Pement and George Racky, Chicago blacksmiths. The
excavated material is hoisted out of the well in buckets made by the
Variety Iron Works, of Chicago. For caissons which are not specified to
go to rock it is considered more economical to do the hoisting by
windlass derricks operated by hand. These derricks have four 6×6-in.
legs and a 3×6-in. top piece. When the caissons go to rock the hoisting
is done by power, so-called "cable set-ups" being used in most cases. To
illustrate this method the following account of the foundation work for
the Cook County Court House is given:
The Cook County Court House foundations consist of 126 caissons varying
from 4 ft. to 10½ ft. in diameter and averaging$ 7½ ft. in diameter.
They were sunk to rock at a depth of 115 ft. below street level. The
work involved 22,000 cu. yds. of excavation and the placing in the
caissons of 17,000 cu. yds. of concrete. Over 1,000 piles about 40 ft.
long, that had formed the foundation of the old Court House built in
1875, were removed. These piles were found to be in good condition. The
work was done by the George A. Fuller Co., of Chicago, Ill.,
Contractors, with Mr. Edgar S. Belden Superintendent in Charge. The
details which follow have been obtained from Mr. Belden.
[Illustration: Fig. 56.--Section Showing Arrangement of Hoist for
Concrete Pier Construction.]
The foundation area was 157×375 ft., and was excavated to a depth of 15
ft. below the street surface before the caissons were started. The
caissons, of which there were 126, were arranged in rows across the lot,
there being from six to eight caissons in a row. The arrangement of the
plant for the work is indicated by Fig. 55. One row of caissons formed a
unit. A platform or "stand" was erected over each caisson and carried in
its top a tripod fitted with a "nigger head" operated by a rope sheave.
This arrangement is shown by Fig. 56. An engine on the bank operated by
a rope drive all the tripod sheaves for a row of six or eight caissons.
The arrangement is indicated by Fig. 55. The clay hoisted from the pits
was dumped into 1 cu. yd. hoppers with which the stands were fitted, as
shown by Fig. 56; when a hopper was full it was dumped into a car
running on a 24-in. gage portable track. Side dump Koppel cars of 1 cu.
yd. capacity were used; they dumped their load into an opening connected
with the tracks of the Illinois Tunnel Co., where the material passed
into tunnel cars and was taken to the lake front about one mile away. As
soon as one row of caissons was completed the stands, tripods, etc.,
which were made portable, were shifted to another row. At times as many
as five units were in operation, sinking 40 caissons.
[Illustration: Fig. 57.--Details of Working Platform for Concrete Pier
Construction.
Side Elevation.
End Elevation.
Bottom Plan.
Section.]
Fig. 56 shows the arrangement in detail at one caisson. In this work the
lagging used was 3×6-in. maple, 5 ft. 4 ins. long, and was supported by
3×¾-in. steel hoops. The lagging was matched and dressed. The "nigger
head," as will be seen, is operated by a rope sheave on the same axle.
As stated above, an endless rope drive operated all the "nigger heads"
on a row of caissons. A 26-in. driving sheave was attached to an
ordinary hoisting engine equipped with a governor. The driving rope was
5/8-in. steel. It was wrapped twice around the driving sheave and once
around the "nigger head" sheaves. These latter were 18 ins. in diameter.
For the hoists 1-in. Manila rope was used. The other details, the
bucket, bucket hook, swivel block, etc., are made clear by the drawing.
The platforms, tripods, etc., were of the standard dimensions and
construction adopted by the contractors of the work. Detail drawings of
the standard platform are given by Fig. 57. One of these platforms
contains about 1,000 ft. B. M. of lumber. As will be seen, all
connections are bolted, no nails being used anywhere. A platform can
thus be taken down and stored or shipped and erected again on another
job with very little trouble.
The plant described handled some 22,000 cu. yds. of excavated material
on this work. Work was kept up night and day, working three 8-hour
shifts. It took an average of 35 shifts to excavate one row of caissons.
No figures of the working force or the cost of excavation of this work
are available.
_Mixing and Placing Concrete._--The placing of the concrete in the
excavated wells is done by means of tremies, or, which is more usual, by
simply dumping it in from the top, workmen going down to distribute it.
The manner of mixing the concrete and of handling it to the caisson
varies of course with almost every job. As an example of the better
arranged mixing and handling plants the one used on the Cook County
Court House work may be described. This plant is shown by the sketch,
Fig. 58.
Bins for the sand and stone were built at one side of the lot on the
sloping bank; their tops were level with the street surface and their
bottoms were just high enough to permit their contents to be delivered
by chutes into 1 cu. yd. cars. Wagons dumping through traps in the
platform over the bin delivered the sand and stone. The sketches
indicate the arrangement of the bins and mixer and the car tracks
connecting them. The raw material cars were first run under the stone
bin and charged with the required proportion of stone, and then to the
sand bin, where the required proportion of sand was chuted on top of the
stone. The loaded car was then hauled up the incline and dumped into the
hopper, where cement and water were added. A No. 2½ Smith mixer was used
and discharged into cars which delivered their loads on tracks leading
to the caissons. The same cars and portable tracks were used as had been
used to handle the excavated material. In operation a batch of raw
materials was being prepared in the hopper while the previous batch was
being mixed and while the concrete car was delivering the still previous
batch to the caissons. An average of 40 batches an hour mixed and put
into the caissons was maintained with a force of 25 men. In all some
17,000 cu. yds. of concrete were mixed and deposited.
[Illustration: Fig. 58.--Arrangement of Concrete Making Plant, Concrete
Pier Construction.]
_Cost of Caisson Work._--The following attempt to get at the cost of
caisson work is based largely upon information obtained from Mr. John M.
Ewen, John M. Ewen Co., Engineers and Builders, Chicago, Ill. Mr. Ewen
says:
"My experience has taught me that it is almost impossible to determine
any definite data of cost for this work. This is due to the fact that no
two caisson jobs will average the same cost, notwithstanding the fact
that the cost of material used and the labor conditions are exactly the
same. This condition is due to the great variety in texture of the soil
gone through. For instance, it has come under my experience that in
caissons of the same diameter on the same job it required but fifteen
8-hour shifts to reach bedrock in some of these, while it required as
many as 21 to 25 shifts to reach rock in the others, rock being at the
same elevation. In fact, the digging all the way to rock in some was the
best that could be wished for, while in the others boulders and
quicksand were encountered, and the progress was slower, and the cost
consequently greater.
"Again, we have known it to require eight hours for two men to dig 8
ins. in hardpan in one caisson, while on a job going on at the same time
and on the opposite corner of the street two men made progress of 2 ft.
in 8 hours through apparently the same stuff, the depth of hardpan from
grade being 61 ft. 6 ins. in both instances, and the quality of labor
exactly the same.
"There have been more heavy losses among contractors due to the
unexpected conditions arising in caisson digging than in any other item
of their work, and I predict a loss to some of them that will be serious
indeed if an attempt be made to base future bids for caisson work
entirely upon the data kept by them on past work. If a contractor is
fortunate enough to find the ordinary conditions existing in his caisson
work, and by ordinary conditions I mean few boulders, no quicksand,
ordinary hardpan and no gas, the following items may be considered safe
for figuring caisson work:
"Figure that it will require from 22 to 25 shifts of 8 hours each to
strike bedrock, bedrock being from 90 to 95 ft. below datum, and datum
being 15 ft. below street grade; figure 2 diggers to the shift in all
caissons over 5 ft. in diameter, 45 cts. per hour for each digger;
figure 1 top man at 40 cts. per hour, and 1 mucker or common laborer at
30 cts. per hour for all caissons in which there are two diggers, and 1
top man less if 1 digger is in the caisson, which condition exists
generally in caissons less than 5 ft. in diameter. Add the cost of
5/8-in. cable, tripods, sheaves, 1-in. Hauser laid line, nigger heads,
ball-bearing blocks, etc., for rigging of the job. Lagging, which is 2×6
ins. and 3×6 ins. hemlock or some hard wood, in length of 5 ft. 4 ins.
and 4 ft., is priced all the way from $20 to $22.50 and $21 to $24.50
per M. ft. B. M., respectively. The price of caisson rings is $2.40 per
100 lbs. The cost of specially made grubs for digging in hardpan is
about $26 per dozen. Shovels are furnished by the diggers themselves in
Chicago, Ill. The cost of temporary electric light is $10 per caisson.
This includes cost of cable, lamps, guards, etc. Add the cost of or
rental of engine or motors for power.
"Some engineers specify three rings to be used to each set of lagging
below the top set until hardpan is reached, then two rings for each of
the remaining sets from hardpan to rock. This is, of course, to insure
against disaster from great pressure of the swelling clay above the
hardpan strata, and may or may not be necessary. These rings are ¾×3
ins. wrought iron.
"For caissons which are not specified to go to rock, it is not
considered economical to rig up cable set-ups, but rather to use
windlass derricks. In this case 1-in. Hauser laid line is used as the
means of hoisting the buckets of clay out of the caisson, as is the case
in cable set-ups, hand power being used on the windlass derricks instead
of steam or electricity. The windlass derricks are made with four legs
out of 6×6-in. yellow pine lumber. The top piece is generally a piece of
3×6-in. lagging. The cost of windlass and boxes is about $35 per dozen.
Hooks for caisson buckets cost 45 cts. each. Caisson buckets cost $8
each.
"With the above approximate units as a basis, I have seen unit prices
given per lineal foot in caisson work which ranged all the way from $12
to $16.50 for 6-ft. diameter caissons, larger and smaller sized caissons
being graded in price according to their size. This unit price included
rings, lagging, concrete, power, light, labor, etc."
From the above data the following figures of cost can be arrived at,
assuming a 6-ft. caisson:
Labor. Per day.
2 diggers in caisson, at $3.60 $ 7.20
1 top man, at $3.20 3.20
1 mucker, at $2.40 2.40
------
$12.80
The depth sunk varies from 3½ to 8 ft. per 8-hour day, depending on the
material. Assuming an average of 4 ft., we have then 4 lin. ft. of
caisson, or 2.8 cu. yds. excavated at a labor cost of $12.80, which is
at the rate of $3.20 per lin. ft., or $4.57 per cu. yd. We now get the
following:
Per lin. ft.
Caisson.
40 ft. B. M. (2×6-in. lagging) at $25 $1.00
60 lbs. iron (¾×3-in. rings) at 2½ c. 1.50
0.7 cu. yd. excavation at $4.57 3.20
0.7 cu. yd. muck hauled away at $1 0.70
0.7 cu. yd. concrete at $5 3.50
Electric light 0.10
------
Total $10.00
If 3×6-in. lagging is used add 50 cts. per lin. ft. of caisson.
~MOLDING PILES FOR DRIVING.~--Piles for driving are molded like columns in
vertical forms or like beams in horizontal forms. European constructors
have a strong preference for vertical molding, believing that a pile
better able to withstand the strain of driving is so produced; such
lamination as results from tamping and settling is, in vertical molding,
in planes normal to the axis of the pile and the line of driving stress.
Vertical molding has been rarely employed in America and then only for
molding round piles. The common belief is that horizontal molding is the
cheaper method. In the ordinary run of work, where comparatively few
piles are to be made, it is probably cheaper to use horizontal molds,
but where a large number of piles is to be made, the vertical method has
certain economic advantages which are worth considering.
[Illustration: Fig. 59.--Plant for Vertical Molding of Concrete Piles.]
Vertical molding necessitates a tower or staging to support the forms
and for handling and placing the concrete; an example of such a staging
is shown by Fig. 59. To counterbalance this staging, horizontal molding
necessitates a molding platform of very solid and rigid construction if
it is to endure continued and repeated use. In the matter of space
occupied by molding plant, vertical molding has the advantage. A tower
40 ft. square will give ample space around its sides for 80 vertical
forms for 12-in. piles and leaves 1 ft. of clear working space between
each pair of forms. The ground area occupied by this tower and the forms
is 1,764 sq. ft. With the same spacing of molds a horizontal platform
at least 25 × 160 ft. = 4,000 sq. ft., would be required for the molds
for the same number of piles 25 ft. long. For round piles, vertical
molding permits the use of sectional steel forms; horizontal forms for
round piles are difficult to manage. For square piles vertical molding
requires forms with four sides; horizontal forms for square piles
consist of two side pieces only, the molding platform serving as the
bottom and no top form being necessary. Thus, for square piles
horizontal molding reduces the quantity of lumber per form by 50 per
cent. The side forms for piles molded on their sides can be removed much
sooner than can the forms for piles molded on end, so that the form
material is more often released for reuse. The labor of assembling and
removing forms is somewhat less in horizontal molding than in vertical
molding. Removing the piles from molding bed to storage yard for curing
requires derricks or locomotive cranes in either case and as a rule this
operation will be about as expensive in plant and labor in one case as
in the other. In the ease and certainty of work in placing the
reinforcement, horizontal molding presents certain advantages, the
placing and working of the concrete around the reinforcement is also
easier in horizontal molding. Mixing and transporting the concrete
materials and the concrete is quite as cheap in vertical molding as in
horizontal molding. If anything, it is cheaper with vertical molding,
since the mixer and material bins can be placed within the tower or
close to one side where a tower derrick can hoist and deposit the
concrete directly into the molds. Car tracks, cars, runways and
wheelbarrows are thus done away with in handling the concrete from mixer
to molds. Altogether, therefore, the choice of the method of molding is
not to be decided off-hand.
~DRIVING MOLDED PILES.~--Driving molded concrete piles with hammer drivers
is an uncertain operation. It has been done successfully even in quite
hard soils and it can be done if time is taken and the proper care is
exercised. The conditions of successful hammer driving are: Perfect
alignment of the pile with the line of stroke of the hammer; the use of
a cushion cap to prevent shattering of the pile-head, and a heavy hammer
with a short drop. The pile itself must have become well cured and
hardened. At best, hammer driving is uncertain, however; shattered piles
have frequently to be withdrawn and the builder is never sure that
fractures do not exist in the portion of the pile that is underground
and hidden. The actual records of concrete pile work given in succeeding
sections illustrate successful examples of hammer driving. The plant
required need not vary from that ordinarily used for driving wooden
piles, except that more power must be provided for handling the heavier
concrete pile and that means must be provided for holding the pile in
line and protecting its head.
Sinking concrete piles by means of water jets is in all respect a
process similar to that of jetting wooden piles. Examples of jetting are
given in succeeding section. In rare cases, driving shells, or sheaths
have been used for driving molded piles.
~Method and Cost of Molding and Jetting Piles for an Ocean Pier.~--In
reconstructing in reinforced concrete the old steel pier at Atlantic
City, N. J., some 116 reinforced concrete piles 12 ins. in diameter were
molded in air and sunk by jetting. The piles varied in length with the
depth of the water, the longest being 34½ ft. Their construction is
shown by Fig. 60, which also shows the floor girders carried by each
pair of piles and forming with them a bent, and the struts bracing the
bents together. In molding and driving the piles the old steel pier was
used as a working platform.
[Illustration: Fig. 60.--Concrete Pile for Pier at Atlantic City, N. J.]
The forms for the piles were set on end on small pile platforms located
close to the positions to be occupied by the piles and were braced to
the old pier. The forms were of wood and the bulb point, the shaft and
the knee braces were molded in one piece. Round iron rods were used for
reinforcement. The concrete was composed of 1 part Vulcanite Portland
cement, 2 parts of fine and coarse sand mixed and 4 parts of gravel 1
in. and under in size. The mixture was made wet and was puddled into the
forms with bamboo fishing rods, which proved very efficient in working
the mixture around the reinforcing rods and in getting a good mortar
surface. The concrete was placed in small quantities; it was mostly all
hand mixed. The forms were removed in from 5 to 7 days, depending on the
weather.
The piles were planned to be sunk by water jet and to this end had
molded in them a 2-in. jet pipe as shown. They were sunk to depths of
from 8 ft. to 14 ft. into the beach sand. Water from the city water
mains at a pressure of 65 lbs. per sq. in. was used for jetting; this
water was furnished under special ordinance at a price of $1 per pile,
and a record of the amount used per pile was not kept. The piles were
swung from the molding platforms and set by derricks and block and fall.
The progress of jetting varied greatly owing to obstructions in places
in the shape of logs, old iron pipes, etc. In some cases several days
were required to get rid of a single pipe. In clear sand, with no
obstruction, a 12-in. pile could be jetted down at the rate of about 8
ft. per hour, working 1 foreman and 6 men. The following is the itemized
actual cost of molding and sinking a 26-ft. pile with bulb point and
knee braces complete:
Cost per
Forms-- pile.
Lumber, 340 ft. B. M. @ $30 $10.20
Labor (carpenters @ $2.50 per day) 12.00
Oil, nails, oakum, bolts, clamps, etc. 1.20
-------
$23.40 $ 3.90
Times used 6
Reinforcement--
275 lbs. of plain ¾-in. steel rods @ 2 cts. per lb. $ 5.50
Preparing and setting, 4/10 ct. per lb. 1.10 6.60
Jet Pipe--
26½ ft. of 2-in. pipe @ 10 cts. per ft. in place. 2.65
Setting Forms--
6 men @ $2.50 per day = $15, set 4 piles 3.75
Material--
90/100 Cu. yds. gravel @ $1.50 per yd. 1.35
45/100 cu. yds. sand @ $1.50 per yd. .67
1.50 bbls. cement @ $1.60 2.40 4.42
Labor--
Concrete and labor foreman 3.00
6 laborers, mixing and placing by hand, $1.75
each 10.50
-------
$13.50 3.38
Average number of piles concreted per day 4
Removing Forms--
4 men @ $2.50 remove and clean in half day 4
columns 1.25
1 man @ $2.25 plastering column with cement
grout (4 per day) .56
Jetting 10 ft. into Sand--
Foreman $ 3.00
4 men, $2.25 each, handling hose and traveler 9.00
-------
$12.00 3.00
Average number of piles jetted per day 4
City water pressure used for jetting @ $1 per pile 1.00
Superintendence @ $5.00 per day 1.25
Caring for trestle, traveler, material, etc. 4.84
-------
Total cost per pile $36.60
The pile being 26 ft. long, the cost in place was $1.41 per foot.
Subtracting the cost of sinking amounting to $7.09 per pile, we have the
cost of a 26-ft. pile molded and ready to sink coming to about $1.10 per
foot. It should be noted that this is the cost for a pile of rather
complicated construction; a plain cylindrical pile should be less
expensive.
~Method of Molding and Jetting Square Piles for a Building
Foundation.~--The foundation covered about an acre. The soil was a
deposit of semi-fluid mud and quicksand overlying a very irregular rock
bottom and encircled by a ledge of rock. The maximum depth of the mud
pocket was 40 ft., and interspersed were floating masses of hard pan.
Soundings were made at the locations of all piles; a ½-in. gas pipe was
coupled to a hose fed by city pressure and jetted down to rock, the
depth was measured, the sounding was numbered and the pile was molded to
length and numbered like the sounding. In all 414 piles were required,
ranging in length from 1½ to 40 ft.; all piles up to 6 ft. were built
in place in wooden forms. The piles were 13 ins. square and were of
1-2½-4 concrete reinforced with welded wire fabric. A tin speaking tube
was molded into each pile at the center. This tube was stopped about 10
ins. from the head and by means of an elbow and threaded nipple
projected through the side of the pile to allow of attaching a pressure
hose. The piles were handled to the pile driver, the hose attached and
water supplied at 100 lbs. pressure by a pump. Churning the pile up and
down aided the driving. A hammer was used to force the piles through the
hard pan layers. A wooden follower was used to protect the pile head. A
2,800-lb. hammer falling 20 ft. did not injure the piles. One pile was
given 300 blows with a 2,800-lb. hammer falling 12 ft., and when pulled
was unbroken. It was found that 30 ft. piles and under could be picked
up safely by one end; longer piles cracked at the center when so
handled. These long piles were successfully handled by a long chain, one
end being wrapped around the pile at the center and the other end
similarly wrapped near the head; the hook of the hoisting fall was
hooked into the loop of the chain and as the pile was hoisted the hook
slipped along the chain toward the top gradually up ending the pile. The
piles weighed 175 lbs. per lin. ft. It was attempted to mold the piles
directly on the ground by leveling it off and covering it with tar
paper, but the ground settled and the method proved impracticable.
~Method of Molding and Jetting Piles for Building Foundations.~--In a
number of foundations Mr. Frank B. Gilbreth has used a polygonal pile,
either octagonal or hexagonal, with the sides corrugated or fluted as
indicated in Fig. 61. In longitudinal section these piles have a uniform
taper from butt to point and have flat points. Each pile is cored in the
center, the core being 4 ins. in diameter at the top and 2 ins. at the
bottom end. On each of the octagon or hexagon sides the pile has a
half-round flute usually from 2½ to 3 ins. in diameter. The principal
object of these flutes or "corrugations" is to give passage for the
escape to the surface of the water forced through the center core hole
in driving the pile. They are also for the purpose of increasing the
perimeter of the pile and thereby gaining greater surface for skin
friction.
The piles are reinforced longitudinally and transversely. On this
particular job the reinforcement was formed with Clinton Electrically
Welded Fabric, the meshes being 3 ins.×12 ins.; the longer dimension
being lengthwise with the pile and of No. 3 wire; the horizontal or
transverse reinforcement being of No. 10 wire. The meshes being
electrically welded together, the reinforcement was got out from a wide
sheet taking the form of a cone. No part of the reinforcement was closer
than 1 in. from the outside of the concrete. In general only sufficient
sectional area of material is put in the reinforcement to take the
tensile stresses caused by the bending action when handling the pile
preparatory to driving; more reinforcement than this only being
necessary when the piles are used for wharves, piers or other marine
structures, where a considerable length of pile is not supported
sidewise or when they are subjected to bending stresses.
[Illustration: Fig. 61.--Cross-Section of Corrugated Reinforced Concrete
Pile.]
_Molding._--The forms for molding the piles are made from 2-in. stuff,
gotten out to the required dimensions, the corrugations being formed by
nailing pieces on the inside whose section is the segment of a circle.
The sides of the octagon are fastened to the ends through which the core
projects some 6 or 8 ins. At times while the molding of the pile is in
progress, the central core is given a partial turn to prevent the
setting of the cement holding it fast and thereby preventing the final
removal.
The stripping of the forms from the piles is usually done from 24 to 48
hours after molding, and from this time on great care is taken that
there is a sufficient amount of moisture in the pile to permit of the
proper action for setting of the cement. This is usually accomplished by
covering the piles over with burlaps and saturating with water from a
hose; the operation of driving the pile not being attempted until the
concrete is at least ten days old.
_Driving._--The operation of driving corrugated concrete piles is
somewhat similar to that for driving ordinary wooden piles by water jet,
but a much heavier hammer with less drop is used. The jetting is
accomplished by inserting a 2-in. pipe within the pile. This pipe is
tapered at the bottom end to 1-in. diameter, forming a nozzle, and the
water pressure used is about 120 lbs. per sq. in. As a rule, this
pressure is obtained by the use of a steam pump which may be connected
with the boiler which operates the pile driver, or with a separate steam
supply. At the upper end of this 2-in. pipe an elbow is placed and a
short length of pipe is connected to this and to the hose from the water
supply.
[Illustration: Fig. 62.--Cushion Cap for Driving Gilbreth Corrugated
Pile.]
As it is not practicable to drop the hammer directly on the head of the
concrete piles, the driving is accomplished by the use of a special cap,
Fig. 62. This cap is about 3 ft. in height and the bottom end fits over
the head of the pile. In one side of this cap is a slot from the outside
to the center, which permits the 2-in. pipe, which supplies the water
jet for driving the pile, to project. The outside of this cap is formed
with a steel shell, the inside has a compartment filled with rubber
packing and the top has a wooden block which receives a blow from the
hammer. In this way the head of the pile is cushioned, which prevents
the blow of the hammer from bruising or breaking the concrete.
During the operation of driving, the water from the jet comes up on the
outside of the pile and carries with it the material which it displaces
in driving. This, with the assistance of the hammer, allows the pile to
be driven in place, and, contrary to what might be supposed, after the
operation of driving when the water has saturated into the ground or
been drained away, this operation puddles the earth around the pile, so
that after a few hours' time the skin friction is much more than it
would be with the pile driven into more compact soil without the use of
a jet.
[Illustration: Fig. 63.--View Showing Method of Fabricating
Reinforcement for a Round Pile with Flattened Sides.]
~Method of Molding and Driving Round Piles.~--In constructing a warehouse
at Bristol, England, some 600 spirally-reinforced piles of the Coignet
type were used. Coignet piles are in section circles with two
longitudinal flat faces to facilitate guiding during driving; this
section is the same as would be found by removing two thin slabs from
opposite sides of a timber pile. The reinforcement consists of
longitudinal bars set around the periphery and drawn together to a point
at one end and then inserted into a conical shoe; these longitudinal
bars are wound spirally with a ¼-in. rod wire tied to the bars at every
intersection. This spiral rod has a pitch of only a few inches, but to
bind it in place and give rigidity to the skeleton it is wound by a
second spiral with a reverse twist and a pitch of 4 or 5 ft. As thus
constructed, the reinforcing frame is sufficiently rigid to bear
handling as a unit. The piles used at Bristol were 14 to 15 ins. in
diameter and 52 ft. long, and weighed about 4 tons gross each. The
mixture used was cement, river sand and crushed granite.
_Molding._--In molding Coignet piles the reinforcement is assembled
complete as shown by Fig. 63 and then suspended as a unit in a
horizontal mold constructed as shown by the cross-section Fig. 64. The
concrete is deposited in the top opening and rammed and worked into
place around the steel after which the opening is closed by the piece
A. After 24 hours the curved side pieces B and C are removed and
the pile is left on the sill D until hard enough to be shifted; a pile
is considered strong enough for driving when about six weeks old.
[Illustration: Fig. 64.--Form for Molding Round Pile with Flattened
Sides.]
_Driving._--Coignet piles at the Bristol work were handled by a
traveling crane. The material penetrated was river mud and they were
driven with a hammer weighing 2 tons gross; in driving the pile head was
encircled by a metal cylinder into which fitted a wooden plunger or
false pile with a bed of shavings and sawdust between plunger and pile
head.
~Molding and Driving Square Piles for a Building Foundation.~--The Dittman
Factory Building at Cincinnati, O., is founded on reinforced concrete
piles varying from 8 to 22 ft. in length. The piles were square in
cross-section, with a 2-in. bevel on the edges; a 16-ft. pile was 10
ins. square at the point and 14 ins. square at the head, shorter or
longer piles had the same size of point, but their heads were
proportionally smaller or larger, since all piles were cast in the same
mold by simply inserting transverse partitions to get the various
lengths. Each pile was reinforced by four ¾-in. twisted bars, one in
each corner, bound together by ¼-in hoops every 12 ins.. The bars were
bent in at the point and inserted in a hollow pyramidal cast iron shoe
weighing about 50 lbs. The concrete was a 1-2-4 stone mixture and the
pile was allowed to harden four weeks before driving. They were cast
horizontally in wooden molds which were removed after 30 hours.
_Driving._--Both because of their greater weight and because of the care
that had to be taken not to shatter the head, it took longer to adjust
and drive one of these concrete piles than it would take with a wooden
pile. The arrangement for driving the piles was as follows: A metal cap
was set over the head of the pile, on this was set the guide cap having
the usual wood deadener and on this was placed a wood deadener about 1
ft. long. The metal cap was filled with wet sand to form a cushion, but
as the pile head shattered in driving the sand cushion was abandoned and
pieces of rubber hose were substituted. With this rubber cushion the
driving was accomplished without material damage to the pile head. The
hammer used weighed 4,000 lbs. and the drop was from 4 to 6 ft. The
blows per pile ranged from 60 up. The average being about 90. In some
cases where the driving was hard it took over 400 blows to drive a
14-ft. pile. An attempt to drive one pile with a 16-ft. drop resulted in
the fracture of the pile.
~Method of Molding and Driving Octagonal Piles.~--The piles were driven in
a sand fill 18 ft. deep to form a foundation for a track scales in a
railway yard. They were octagonal and 16 ins. across the top, 16 ft.
long, and tapered to a diameter of 12 ins. at the bottom. They were also
pointed for about a foot. The reinforcement consisted of four ½-in.
Johnson corrugated bars spaced equally around a circle concentric with
the center of the pile, the bars being kept 1½ ins. from the surface of
the concrete. A No. 11 wire wrapped around the outside of the bars
secured the properties of a hooped-concrete column. The piles were cast
in molds laid on the side. They were made of 1:4½ gravel concrete, and
were seasoned at least three weeks before being driven.
An ordinary derrick pile driver, with a 2,500-lb. hammer falling 18 ft.,
was used in sinking them. A timber follower 6 ft. long and banded with
iron straps at both ends was placed over the head of the pile to receive
directly the hammer blows. The band on the lower end was 10 ins. wide
and extended 6 ins. over the end of the follower. In this 6-in. space a
thick sheet of heavy rubber was placed, coming between the head of the
pile and the follower. Little difficulty was experienced in driving the
piles in this manner, although 250 to 300 blows of the hammer were
required to sink each pile. The driving being entirely through fine
river sand there is every probability that any kind of piles would have
been driven slowly. The heads of the first 4 or 5 piles were battered
somewhat, but after the pile driver crew became familiar with the method
of driving, no further battering resulted and the heads of most of the
piles were practically uninjured.
[Illustration: Fig. 65.--Cross-Section of Chenoweth Rolled Pile.]
[Illustration: Fig. 66.--Diagram Showing Method of Rolling Chenoweth
Pile.]
~Method and Cost of Making Reinforced Concrete Piles by Rolling.~--In
molding reinforced concrete piles exceeding 30 or 40 ft. in length, the
problem of molds or forms becomes a serious one. A pile mold 50 or 60
ft. long is not only expensive in first cost, but is costly to maintain,
because of the difficulty of keeping the long lagging boards from
warping. To overcome these difficulties a method of molding piles
without forms has been devised and worked out practically by Mr. A. C.
Chenoweth, of Brooklyn, N. Y. This method consists in rolling a sheet of
concrete and wire netting into a solid cylinder on a mandril, by means
of a special machine. Fig. 65 is a sketch showing a cross-section of a
finished pile, in which the dotted line shows the wire netting, the
hollow circle is the gas pipe mandril, and the solid circles are the
longitudinal reinforcing bars.
[Illustration: Fig. 67.--Machine for Rolling Chenoweth Piles.]
In making the pile the netting is spread flat, with the reinforcing bars
attached as shown at (a), Fig. 66, and is then covered with a layer of
concrete. One edge of the netting is fastened to the platform, the other
edge is attached to the winding mandril. The winding operation is
indicated by sketch (b), Fig. 66. Fig. 67 shows the machine for
rolling the pile. It consists of a platform and a roll. The platform is
mounted on wheels and is so connected up that it moves back under the
roll at exactly the circumferential speed of the roll; thus the forming
pile is under constant, heavy pressure between the roll and platform.
When the pile has been completely rolled it is bound at intervals by
wire ties; the wire for these ties is carried on spools arranged under
the edge of the platform at intervals of 4 ins. for the first 10 ft.
from the point and of 6 ins. for the remainder of the length. The
binding is done by giving the pile two or three extra revolutions and
then cutting and tying the wire; then by means of a long removable shelf
which contains the flushing mortar, as the pile revolves it becomes
coated on the outside with a covering that protects the ties and other
surface metal. Finally the pile is rolled onto a suitable table to
harden.
An exhibition pile rolled by the process described is 61 ft. long and 13
ins. in diameter. This pile was erected as a pole by hoisting with a
tackle attached near one end and dragging the opposite end along the
ground exactly as a timber pole would be erected. It was also suspended
free by a tackle attached at the center; in this position the ends
deflected 6 ins. Neither of these tests resulted in observable cracks in
the pile. The pile contains eight 1-in. diameter steel bars 61 ft. long,
one 2½-in. pipe also 61 ft. long, 366 sq. ft., or 40.6 sq. yds. ½-in.
mesh 14 B. & S. gage wire netting, and 2 cu. yds. loose concrete. Its
cost for materials and labor was as follows:
Materials--
Gravel, 28.8 cu. ft., at $1 per cu. yd. $ 1.05
Sand, 19.8 cu. ft., at $1 per cu. yd. .73
Cement, 3 bbls., at $1.60 per bbl. 4.80
Netting, 40.6 sq. yds., at 17½ cts. per sq. yd. 7.10
Rods, wire, etc., 1,826 lbs., at 2½ cts. per lb. 45.65
--------
Total $59.33
Mixing 2 cu. yds. concrete, four men one hour, at 15 cts.
per hour $ 0.60
Placing concrete and netting, four men 30 mins., at 15
cts. per hour .30
Winding pile, four men 20 mins., at 15 cts. per hour .20
Removing pile, four men 10 mins., at 15 cts. per hour .10
--------
$1.20
Grand total $60.53
This brings the cost of a pile of the dimensions given to about $1 per
lin. ft.
CHAPTER XI.
METHODS AND COST OF HEAVY CONCRETE WORK IN FORTIFICATIONS, LOCKS, DAMS,
BREAKWATERS AND PIERS.
The construction problem in building concrete structures of massive form
and volume is chiefly a problem of plant arrangement and organization of
plant operations. In most such work form construction is simple and of
such character that it offers no delay to placing the concrete as
rapidly as it can be produced. The same is true of the character of the
structure, it is seldom necessary for one part of the work to wait on
the setting and hardening of another part. As a rule, there is no
reinforcement to fabricate and place and where there is it is of such
simple character as not to influence the main task of mixing, handling,
and placing concrete. Stated broadly, the contractor in such work
generally has a certain large amount of concrete to manufacture,
transport and deposit in a certain space with nothing to limit the
rapidity of these operations, except the limitations of plant capacity
and management. Installation and operation of mixing and conveying
plant, then are matters to be considered carefully in heavy concrete
work.
In the following sections we have given one or more examples of nearly
every kind of heavy concrete work excepting bridge foundations and
retaining walls, which are considered in Chapters XII and XIII, and
except rubble concrete work, which is considered in Chapter VI. In each
case so far as the available records made it possible, we have given an
account of the plant used and of its operation.
~FORTIFICATION WORK.~--Concrete for fortification work consists very
largely of heavy platforms and walls for gun foundations and enclosures
and of heavily roofed galleries and chambers for machinery and
ammunition. The work is very massive and in the majority of cases of
simple form. A large number of data are to be found in the reports of
the Chief of Engineers, U. S. A., on all classes of fortification work,
but the manner in which they are recorded makes close analysis of
relative efficiencies of methods or of relative costs almost impossible.
The following data are given, therefore, as examples that may be
considered fairly representative of the costs obtained in fortification
work done under the direction of army engineers; these data are not
susceptible of close analysis because wages, working force, outputs,
etc., are nearly always lacking.
~Gun Emplacements, Staten Island, N. Y.~--The work comprised 5,609 cu.
yds. of concrete in two 12-in. gun emplacements, and 3,778 cu. yds. of
concrete in two 6-in. gun emplacements. Concrete was mixed in a
revolving cube mixer with the exception of 809 cu. yds. in the 6-in.
emplacements which were mixed by hand at a cost of 56 cts. more per
cubic yard than machine mixing cost. The body of the concrete was a
1-3-5 Portland cement, beach sand and broken trap rock mixture. The
floors and upper surface of the concrete had a pavement consisting of 6
ins. of 1-3-5 concrete surfaced with 2 ins. of 1-3 mortar. Wages are not
given, but for the time and place should have been about $1.50 per
8-hour day for common labor. The cost of materials was:
Alpha Portland cement, per bbl. $1.98
Broken trap rock, per cu. yd. 0.81
12-in. emplacement, hauling sand per cu. yd. 0.175
6-in. emplacement, hauling sand per cu. yd. 0.20
The cost of the concrete in place was as follows:
12-in., per 6-in., per
Body Concrete-- cu. yd. cu. yd.
Cement, at $1.98 per bbl. $2.546 $2.546
Broken stone, at 81 cts. per cu. yd. 1.041 1.041
Sand, at 17½ and 20 cts. per cu. yd. 0.225 0.257
Receiving and storing materials at 11.6 cts. per
cu. yd. and 8.4 cts. per bbl. 0.149 0.180
Mixing, placing and ramming 0.879 1.110
Forms, lumber and labor 0.477 0.950
Superintendence and miscellaneous 0.190 0.150
------ ------
Total $5.507 $6.234
Concrete Pavement--
Materials $2.97 $3.06
Labor 4.63 4.72
------ ------
Total $7.60 $7.78
[Illustration: Fig. 68.--Sketch Plans of Concrete Making Plant for
Mortar Battery Platform.]
~Mortar Battery Platform, Tampa Bay, Fla.~--The platform contained 8,994
cu. yds. of concrete composed of a mixture of Portland cement, sand,
shells and broken stone. The broken stone and cement were brought in by
vessel and the sand and shells were obtained from the beach near by. The
plant for the work was arranged as shown by the sketch, Fig. 68. Sand,
stone and shells were stored in separate compartments in the storage
bins. Box cars, divided into compartments of such size that when each
was filled with its proper material, the car would contain the proper
proportions for one batch of concrete, were pushed by hand under the
several compartments of the bin in succession until charged; then they
were hooked to a cable and hauled to the platform over the mixer and
dumped. The charge was then turned over with shovels and shoveled into
the hopper of a continuous mixer, located beneath. Two cars were used
for charging the mixer, running on separate tracks as shown. The mixer
discharged into buckets set on flat cars, which were hauled by mules
under the cableway, which then lifted and dumped the bucket and returned
it empty to the car. By using three bucket cars, one was always ready
to receive the mixer discharge as soon as the preceding one had been
filled, so that the mixer operated continuously. The cableway had a
working span of 270 ft., the cable being carried by traveling towers 69
ft. high; the cableway was very easily operated back and forth along the
work. The cableway complete, with 497 ft. of six-rail track for each
tower, cost $4,700. The cost of materials and labor for the 8,994 cu.
yds. of concrete was as follows:
Per cu. yd.
1 bbl. cement at $2.46 $2.46
0.89 cu. yd. stone, at $2.95 2.622
0.315 cu. yd. shells, at $0.45 0.142
0.51 cu. yd. sand, at $0.12 0.062
Mixing and placing 0.693
-------
Total $5.979
The above batch tamped in place to 30 cu. ft., or 1-1/9 cu. yds., which
gives the cost as follows:
Per cu. yd.
Cost of concrete tamped in place $5.381
Cost of form work 0.370
-------
Total cost $5.751
In the preceding prices of cement and stone, 59 cts. and 29 cts. per
cubic yard, respectively, are included for storage. The costs of sand
and shells are costs of screening and storing. Rough lumber for forms
cost $10.25, and dressed lumber $12.75 per M. ft. B. M.
~Emplacement for Battery, Tampa Bay, Fla.~--The emplacement contained
6,654 cu. yds. of Portland cement, sand, shells and broken stone
concrete. The plant arrangement is shown by Fig. 69. The sand and shells
were got near the site, using an inclined cableway running from a 40-ft.
mast near the mixer to a deadman at the shell bank. All the sand for the
fill around the emplacement was obtained in the same way. The other
materials were brought by vessel to a wharf, loaded by derrick onto cars
operated by an endless cable, and taken to the work. The storage bins
and mixing plant were operated much like those for the mortar battery
work, previously described. A cube mixer was used, and the concrete was
handled from it to the work by a crane derrick covering a circle of 100
ft. in diameter. The cost of materials and concrete was as follows:
Cement, plus 7 cts. for storage per bbl. $ 2.532
Stone, plus 38 cts. for storage per cu. yd. 3.047
Shells, excavating and storage. 0.481
Sand, excavating and storage. 0.250
Lumber, rough per M. ft. B. M. 10.25
Lumber, dressed per M. ft. B. M. 12.75
[Illustration: Fig. 69.--Sketch Plans of Concrete Making Plant for
Battery Emplacement.]
A batch made up as follows, tamped in place to a volume of 30 cu. ft. or
1-1/9 cu. yds.:
1 bbl. cement, at $2.532. $ 2.532
0.315 cu. yd. shells, at $0.481. 0.151
0.51 cu. yd. sand, at $0.25. 0.130
0.89 cu. yd. stone, at $3.047. 2.710
Mixing and placing. 0.761
--------
Total for 30 cu. ft. $ 6.284
This gives a cost per cubic yard of concrete in place as follows:
Concrete in place, per cu. yd. $ 5.655
Forms, per cu. yd. of concrete. 0.220
--------
Total cost of concrete per cu. yd. $ 5.875
~United States Fortification Work.~--The following methods and cost of
mixing and placing concrete by hand and by cubical mixers is given by
Mr. L. R. Grabill for U. S. Government fortification work done in 1899.
_Hand Mixing and Placing._--The work was done by contract, using a 1
cement, 2 sand, 2 pebbles and 3 stone mixture turned four times. A board
large enough for three batches at a time was used; one batch was being
placed, one being mixed and one being removed at the same time so that
the mixers moved without interval from one to the other. Two gangs were
worked, each mixing 64 batches of 0.75 cu. yd., or 48 cu. yds. of
concrete per day at the following cost:
Per Per
Hand Mixing 9,000 Cu. Yds.-- day. cu. yd.
6 men wheeling materials $ 7.50 $0.16
8 men mixing 10.00 0.21
8 men wheeling away 10.00 0.21
6 men placing and ramming 7.50 0.16
1 pump man 1.25 0.02
1 waterboy 1.00 0.02
1 foreman 2.00 0.04
------- -------
Totals $39.25 $0.82
The entire cost of plant for this work was about $500.
_Machine Mixing and Placing._--The concrete was mixed in a 4-ft. cubical
mixer operated by a 12 hp. engine which also hauled the material cars up
the incline to the mixer. These cars passed by double track under the
material bins where the compartments of the car body were filled through
trap doors; they then passed the cement house where the cement was
placed on the load, then up the incline to the mixer and dumped, and
then empty down an opposite incline. Seven turns of the mixer mixed the
charge which was discharged into iron tubs on cars hauled by horses to
two derricks whose booms covered the work. One gang by day labor mixed
and placed 168 batches of 0.7 cu. yd., or 117.6 cu. yds. per day at the
following cost:
Per Per
Machine Mixing 4,000 Cu. Yds.-- day. cu. yd.
32 men at $1.25 $40.00 $0.34
1 pumpman 1.25 0.01
1 teamster and horse 2.00 0.02
2 waterboys at $1 2.00 0.02
1 engineman 1.70 0.02
1 derrickman 1.50 0.01
1 fireman 1.50 0.01
1 foreman 2.88 0.03
Fuel (cement barrels largely) 1.25 0.01
------- -------
Totals $54.08 $0.47
The cost of the plant was about $5,000.
[Illustration: Fig. 70.--Concrete Making Plant for Constructing Lock
Walls, Cascades Canal.]
~LOCK WALLS, CASCADES CANAL.~--Four-fifths or 70,000 cu. yds. of lock
masonry was concrete, the bulk of which was mixed and deposited by the
plant shown by Fig. 70. The concrete was Portland cement, sand, gravel
and broken stone. Cement was brought in in barrels by railway, stored
and tested; from the store house the barrels were loaded onto cars and
taken 250 ft. to a platform onto which the barrels were emptied and from
which the cement was shoveled into the cement hopper and chuted to cars
which took it to the charging hopper of the mixer. The stone was crushed
from spalls and waste ends from the stone cutting yards, where stone for
wall lining and coping and other special parts was prepared. These
spalls and ends were brought in cars and dumped into the hopper of a
No. 5 Gates crusher, with a capacity of 30 tons per hour. From the
crusher the stone passed to a 2½-in. screen, the pieces passing going to
a bin below and the rejections going to a smaller Blake crusher and
thence to the bin. The dust and small particles were not screened out.
The sand and gravel were obtained by screening and washing pit gravel.
The gravel was excavated and brought in cars to the washer. This
consisted of a steel cylinder 2 ft. 6½ ins. in diameter and about 18 ft.
long, having an inclination of 1 in. per foot. An axial gudgeon
supported the cylinder at the lower end and it rested on rollers at the
other end and at an intermediate point. The gravel was fed by hopper and
chute into the upper end and into this same end a 3-in. perforated pipe
projected and extended to about mid-length of the cylinder. The cylinder
shell was solid and provided with internal fins for about half its
length from the feed end. For the remainder of its length nearly to the
end, the shell was perforated with 2½-in. holes. For a length of 4 ft.
beyond mid-point it was encircled by a concentric screen of 1/8-in.
holes, and this screen for 3 ft. of its length was encircled by another
screen of 30 meshes to the inch. The pit mixture fed into the cylinder
was gradually passed along by the combined inclination and rotation,
being washed and screened in the process. The sand fell into one bin and
the gravel into another, and the waste water was carried away by a
flume. The large stones passed out through openings at the lower end of
the shell and were chuted into cars. The cars came to the mixer as
clearly shown by Fig. 70.
The stone and gravel cars were side dump and the cement car was bottom
dump. The mixers were of the cube type 4 ft. on each edge and operated
by a 7×12-in. double cylinder engine at nine revolutions per minute. The
usual charge was 32 cu. ft. of the several ingredients, and it was found
that 15 revolutions requiring about 1½ minutes were sufficient for
mixing. The average work of one mixer was 17 batches or about 13 cu.
yds. per hour, but this could be speeded up to 20 batches per hour when
the materials were freely supplied and the output freely removed. Two
cars took the concrete from the mixer to the hopper, from which it was
fed to the work by chute. The hopper was mounted on a truck and the
chute was a wrought iron cylinder trussed on four sides and having a
45° elbow at the lower end to prevent scattering. The chute fed into a
car running along the wall and distributing the material. It was found
impracticable to move the chute readily enough to permit of feeding the
concrete directly into place. As the concreting progressed upward the
trestle was extended and the chute shortened. It was found that wear
would soon disable a steel chute so that the main trussed cylinder had a
smaller, cheaply made cylinder placed inside as a lining to take the
wear and be replaced when necessary.
The plant described worked very successfully. Records based on 9,614.4
cu. yds. of concrete laid, gave the following:
Cu. yds.
Concrete mixed by hand 1,777.0
Concrete mixed by machine 7,837.4
Total concrete laid 9,614.4
Concrete placed by derricks 2,372.0
Concrete placed by chute 7,242.4
Concrete 1-2-4 mixture 156.0
Concrete 1-3-6 mixture 1,564.0
Concrete 1-4-8 mixture 6,892.0
The average mixture was 1 cement, 3.7 sand, 4.8 gravel and 2.6 broken
stone. The average product was 1.241 cu. yds. concrete per barrel of
cement and 1.116 cu. yds. of concrete per cubic yard of stone and
gravel. The average materials for 1 cu. yd. of concrete were: Cement
0.805 bbl., sand 0.456 cu. yd., gravel 0.579 cu. yd., and stone 0.317
cu. yd.
The cost of these 9,614.4 cu. yds. of concrete in place was:
Hand Mixed and Placed by Derrick-- Per cu. yd.
Labor mixing 1,777 cu. yds $1,072
Repairs, fuel, etc 0.016
-------
Total cost mixing $1,088
Labor placing 2,372 cu. yds. 0.6025
Fuel, tramways, etc. 0.1958
-------
Total cost placing $0.7983
Machine Mixed and Placed by Chute--
Labor mixing 7,837 cu. yds. $0.388
Repairs, fuel, etc 0.046
------
Total cost mixing $0.434
Labor placing 7,242 cu. yds 0.414
Fuel, tramways, etc. 0.045
------
Total cost placing $0.459
Materials and Supplies 9,614 cu. yds.--
Timbering $0.145
Cement 3.289
Sand and gravel 1.073
Broken stone 0.536
Cement testing, repairs, etc. 0.223
------
Total $5,266
Plant and Superintendence, 9,614 Cu. Yds.--
Engineering, superintendence, repairs, etc. $1,508
20% cost of plant 0.165
------
Total $1,673
The comparative cost of hand and machine mixing and handling was thus:
Item-- Hand. Machine.
Mixing per cu. yd. $1.088 $0.434
Placing per cu. yd. 0.798 0.459
Materials, etc., per cu. yd. 5.466 5.466
Plant, etc., per cu. yd. 1.673 1.673
------ ------
Totals $9.025 $8.032
The average total costs of all the concrete placed were:
Mixing per cu. yd. $0.555
Placing per cu. yd. 0.543
Materials per cu. yd. 5.266
Plant, etc., per cu. yd. 1.673
------
Total $8.037
~LOCKS, COOSA RIVER, ALABAMA.~--The following methods and costs are given
by Mr. Charles Firth for constructing lock No. 31 for the Coosa River
canalization, Alabama. This lock is 420 ft. long over all, 322 ft.
between quoins, 52 ft. clear width, 14.7 ft. lift and 8 ft. depth of
water on sills; it contained 20,000 cu. yds. of concrete requiring
21,500 bbls. cement, half Alsen and half Atlas.
Figure 71 shows the concrete mixing plant, consisting of two 4×4 ft.
cube mixer, driven by a 10×16-in. engine. The top floor of the mixer
house stored the cement, 2,000 bbls. The concrete was a 1-3-5½ stone
mixture. Each mixer charge consisted of 3 cu. ft. cement, 9 cu. ft. sand
and 16.5 cu. ft. stone; the charge was turned over four times before and
six times after watering at a speed not exceeding eight revolutions per
minute. The average output of the plant was 200 cu. yds. per 8-hour day,
or 100 cu. yds. per mixer, but it was limited by the means for placing.
[Illustration: Fig. 71.--Concrete Mixing Plant for Lock Construction,
Coosa River, Alabama.]
The concrete was mixed dry, deposited in 6 to 8-in. layers, and rammed
with 30-lb. iron rammers with 6-in. square faces. For all exposed
surfaces a 6-in. facing of 1-3 mortar was placed by setting 2×12-in.
planks 4 ins. from the laggings, being kept to distance by 2×4-in.
spacers, placing and ramming the concrete behind them, then withdrawing
them, filling the 6-in. space with mortar and tamping it to bond with
the concrete. The walls were carried up in lifts, each lift being
completed entirely around the lock before beginning the next; the first
lift was 10.7 ft. high and the others 6 ft., except the last, which was
4.5 ft., exclusive of the 18-in. coping. The coping was constructed of
separately molded blocks 3 ft. long, made of 1-2-3 concrete faced with
1-1 mortar and having edges rounded to 3 ins. radius.
In constructing the forms a row of 6×8-in. posts 24 ft. long and 5 to 7
ft. apart was set up along the inside of each wall and a similar row of
posts 12 ft. long was set up along the outside. From the tops of the
short posts 6×8-in. caps reached across the wall and were bolted to the
long posts; these caps carried the stringers for the concrete car
tracks. The lagging consisted of 3×10-in. planks dressed on all sides.
The backs of the walls were stepped and as each step was completed the
rear 12-ft. posts were lifted to a footing on its top and carried in the
necessary distance. The front posts remained undisturbed until the wall
was completed. The lagging was moved up as the filling progressed. As no
tie bolts were permitted, these forms required elaborate bracing.
From the mixing plant, which was located on the bank above reach of
floods, the concrete cars were dropped by elevator to the level of the
track over the walls and then run along the wall and dumped onto
platforms inside the forms and just below the track. This arrangement
was adopted, because it was found that even a small drop separated the
stone from the mortar. The concrete was shoveled from the platforms to
place and rammed. The cars were bottom dumping with a single door hinged
at the side; this door when swinging back struck the track stringers and
jarred the form so that constant attention was necessary to keep it in
line. It would have been much better to have had double doors swinging
endwise of the car. Another point noted was that unless the track was
high enough to give good head room at the close of a lift the placing
and ramming were not well done.
The cost of 8,710 cu. yds. of concrete placed during 1895 by day labor
employing negroes at $1 per 8-hour day was as follows per cubic yard:
1 bbl. cement $2.48
0.88 cu. yd. stone at $0.76 0.67
0.36 cu. yd. sand at $0.34 0.12
Mixing, placing and ramming 0.88
Staging and forms 0.42
----
Total $4.57
~LOCK WALLS, ILLINOIS & MISSISSIPPI CANAL.~--The locks and practically all
other masonry for the Illinois & Mississippi Canal are of concrete. The
following account of the methods and cost of doing this concrete work is
taken from information published by Mr. J. W. Woermann in 1894 and
special information furnished by letter. The decision to use concrete
was induced by the fact that no suitable stone for masonry was readily
available (the local stone was a flinty limestone, usually without bed,
or, at best, in thin irregular strata, and cracked in all directions
with the cracks filled with fire clay) while good sand and gravel and
good stone for crushing were plentifully at hand. The concrete work done
in 1893-4 comprised dam abutments, piers for Taintor gates and locks.
_Dam Abutments._--Four dam abutments were constructed, three of which
were L-shaped, with sides next to the river 40 ft. long and sides
extending into the banks 20 ft. long; the top thickness was 3 ft., the
faces were vertical and the backs stepped with treads of 14 to 16 ins.,
and the width of base was 0.4 of the height. Each of these abutments was
built in four 30-cu. yd. sections, each section being a day's work. The
forms consisted of 2×8-in. planks, dressed on both sides, 2×8-in. studs
spaced 2 ft. on centers and 4×6-in. braces. For the first two of the
four abutments, the forms were erected in sections, the alternate
sections being first erected and filled. When these sections had
hardened the forms were shifted to the vacant sections and lined up to
and braced against the completed sections. This method did not give well
aligned walls, so in subsequent work the forms were erected all at once.
The concrete was mixed by hand. The sand and cement were mixed dry,
being turned four times and spread in a layer Pebbles and broken stone
previously wetted were spread over the sand and cement and the whole
turned four times, the last turn being into wheelbarrows; about five
common buckets of water were added during the mixing. The mixture sought
was one that would ram without quaking. Two forms of rammers were used;
for work next to forms a 4×6-in. rammer and for inside work 6-in
diameter circular rammer weighing 20 lbs. The gang mixing and placing
concrete consisted usually of:
Item. Per Day. Per Cu. Yd.
2 handling cement and sand $ 3.00 $0.10
3 filling barrows with aggregate 4.50 0.15
8 mixing concrete 12.00 0.40
2 shoveling concrete into barrows 3.00 0.10
5 wheeling concrete to forms 7.50 0.25
1 spreading concrete 1.50 0.05
5 tamping concrete 7.50 0.25
------ -----
Total, 26 men $39.00 $1.30
These cubic yard costs are based on 30 cu. yds. of wall completed per
8-hour day. The cost in detail of two abutments containing 254 cu. yds.
was per cubic yard as follows:
Item. Per Cu. Yd.
1.65 bbls. Portland (Germania) cement $ 5.60
0.5 cu. yd. crushed stone 2.07
0.24 cu. yd. gravel 0.59
0.53 cu. yd. sand 0.24
Lumber, forms, warehouses, platforms[D] 0.55
Carpenter work[E] ($9 per M.) 1.10
Mixing and placing 1.47
20 per cent. first cost of plant 0.31
Engineering and miscellanies 0.31
------
Total $12.24
[Footnote D: Charging ¼ of first cost of $18 per M. ft.]
[Footnote E: Carpenters $3.50, laborers $1.50 per day; there was one
laborer to two carpenters.]
The large amount of cement 1.65 bbls. per cubic yard was due to facing
the abutments with 8 ins. of 1-2 mortar. The concrete in the body of the
wall was 1 cement, 2 sand, 2 gravel and 2 broken stone mixture. A dry
mixture was used and this fact is reflected in the cost of ramming, 25
cts. per cu. yd. The cost of mixing was also high.
[Illustration: Fig. 72.--Concrete Mixing Plant for Lock Walls, Illinois
& Mississippi Canal.]
_Piers for Taintor Gates._--The masonry at this point consisted of three
piers 6×30 ft., and two abutments 30 ft. long, 6 ft. thick at base and 4
ft. thick at top, with wing walls; it amounted to 460 cu. yds. The feet
of the inclined braces were set into gains in the horizontal braces and
held by an 8-in. lag screw; after the posts were plumbed a block was
lag-screwed at the upper end of each brace. These forms proved entirely
satisfactory. The cost of the work per cubic yard was as follows:
Item. Per Cu. Yd.
1.45 bbls. Portland cement $4.330
0.55 cu. yd. crushed stone 0.604
0.252 cu. yd. pebbles 0.328
0.465 cu. yd. sand 0.419
40,000 ft. B. M. lumber (¼ cost of $16 per M.) 0.348
Carpenter work on forms 0.780
Mixing and placing concrete 1.909
20 per cent. cost of plant 0.090
Miscellaneous 0.182
-----
Total $8.99
_Mixing Plant._--The concrete for all the lock work of 1893-4 was mixed
by the plant shown by Figs. 72 and 73. The mixer plant proper consisted
of a king truss carried by two A-frames of unequal height; under the
higher end of the truss was a frame carrying a 4-ft. cubical mixer and
under the lower end a pit for a charging box holding 40 cu. ft. This
charging box was hoisted by ½-in. steel cable running through a pair of
double blocks as shown; the slope of the lower chord of the truss was
such that the cable hoisted the box and carried it forward without the
use of any latching devices. On two sides of the pit were tracks from
the sand and stone piles and on the other two sides were the cement
platform and water tank. The charging box dumped into the hopper above
the mixer and the mixer discharged into cars underneath. A 15-HP. engine
operated the hoist by one pulley and the mixer by the other pulley. Nine
revolutions of the mixer made a perfect mixture. The plant as
illustrated was slightly changed as the result of experience in
constructing the guard lock. The charging hopper was lowered 6 ins. and
the space between the mixer and lower platform reduced by 9 ins.;
diagonal braces were also inserted under the timbers carrying the mixer
axles. This plant cost for framing and erection $300 and for machinery
delivered $706. The crushing plant shown by Fig. 73 consisted of a No. 2
Gates crusher delivering to a bucket elevator.
[Illustration: Fig. 73.--Stone Crushing Plant for Lock Walls, Illinois &
Mississippi Canal.]
[Illustration: Fig. 74.--Forms for Guard Lock, Illinois & Mississippi
Canal.]
_Guard Lock._--The forms employed in constructing the guard lock are
shown by Fig. 74, and in this drawing the trestle and platform for the
concrete cars are to be noted. The walls were concreted in sections. A
batch of concrete consisted of 1 bbl. cement, 10 cu. ft. sand and 20 cu.
ft. crushed stone. The average run per 8-hour day was 40 batches of
facing and 60 batches concrete, representing 100 bbls. cement. The gang
worked was as follows:
Duty. No. Men. P. C. Cost.
Handling cement 3 5.26
Filling and pushing sand car 5 8.77
Filling and pushing stone car 9 15.79
Measuring water 1 1.75
Dumping bucket on top platform 3 5.26
Opening and closing door of mixer 1 1.75
Operating friction clutch 1 1.76
Attending concrete cars under mixer 1 1.76
Dumping cars at forms 2 3.51
Spreading concrete in forms 3 5.26
Tamping concrete in forms 10 17.54
Mixing mortar for facing 6 10.53
Finishing top of wall 2 3.51
Hauling concrete cars with 1 horse 1 3.51
Engineman operating hoist 1 3.51
Engineman operating engine 1 3.51
Foreman in charge of forms 1 3.51
General foreman 1 3.51
-- ------
Total 52 100.00
The percentages of cost in this statement have been calculated by the
authors upon the assumption that each laborer received one-half as much
wages as each engineman, foreman and horse and driver per 8 hours, which
would make the total daily wages equivalent to the wages of 57 men.
Wages of common labor were $1.50 per day. Considering the size of the
gang the output of 40 batches of mortar and 60 batches of concrete per
day was very small. The total yardage of concrete in the guard lock was
3,762 cu. yds., 2,212 cu. yds. in the walls and 1,550 cu. yds. in
foundations, culverts, etc. Its cost per cubic yard was made up as
follows:
Item. Total. Per Cu. Yd.
5,246 bbls. Portland cement $15,604}
} $4.170
152 bbls. natural cement 84}
2,910 cu. yds. stone 2,901 0.771
126 cu. yds. pebbles 113}
} 0.401
1,970 cu. yds. sand 1,398}
145,000 ft. B. M. lumber (¼th cost) 659 0.175
Iron for forms, trestles, etc. 90 0.024
Coal, oil, miscellaneous 327 0.087
Carpenter work 2,726 0.724
Mixing and placing concrete 6,693 1.780
Pumping, engineering, misc. 742 0.197
20 per cent of plant 550 0.146
------- ------
Total $31,887 $8.475
[Illustration: Fig. 75.--Forms for Regular Lock Walls, Illinois &
Mississippi Canal.]
_Lock No. 37._--The character of the forms used in constructing the lock
walls is shown by Fig. 75. The walls were built in sections and work was
continuous with three 8-hour shifts composed about as specified for the
guard lock work except that one or two men were added in several places
making the total number 58 men. The average output per shift was 65
batches of concrete and 31 batches of facing mortar. The cost of the
work, comprising 3,767 cu. yds., was as follows:
Item. Total. Per Cu. Yd.
4,564 bbls. Portland cement $14,181 $3.764
2,460 cu. yds. crushed stone 4,521 1.200
250 cu. yds. pebbles 325 0.086
1,750 cu. yds. gravel 2,335 0.619
450 cu. yds. sand 450 0.119
180,000 ft. B. M. lumber (¼th cost) 990 0.236
Fuel, light, repairs, etc. 1,171 0.311
Carpenter work 2,526 0.671
Pumping 270 0.071
Mixing and placing concrete 6,170 1.632
20% cost of plant 730 0.193
------- ------
Total $33,669 $8.902
_Lock No. 36._--The forms used were of the construction shown by Fig.
75. Three shifts were worked, each composed as specified for the guard
lock, except that the number of tampers and spreaders was doubled,
bringing the gang up to 65 men. The average output per gang per shift
was 76 batches of concrete and 35 batches of facing mortar. The cost of
2,141 cu. yds. of concrete in this lock was as follows:
Item. Total. Per Cu. Yd.
3,010 bbls. Portland cement $9,057 $4.23
1,377 cu. yds. broken stone 1,922 0.90
393 cu. yds. pebbles 354 0.17
459 cu. yds. gravel 310 0.15
500 cu. yds. sand 889 0.42
150,000 ft. B. M. lumber (¼th cost) 600 0.28
Fuel, light, repairs, etc. 253 0.68
Carpenter work 1,472 0.11
Mixing and placing concrete 3,897 1.82
20% cost of plant 650 0.30
------- -----
Total $19,404 $9.06
The preceding data, made public by Mr. Woermann in 1894, are
supplemented by the following information prepared for the authors:
"If any criticism was to be made of the concrete masonry erected in 1893
and 1894, it would probably be to the effect that it was too expensive.
The cost of the masonry erected during those two seasons was $8 to $9
per cu. yd. Our records showed that about 45 per cent. of this cost was
for Portland cement alone, and moreover, that 40 per cent. of the total
cement used at a lock was placed in the 8-in. facing and 5-in. coping.
So in the seven locks erected in 1895 on the eastern section, the facing
was reduced to 3 ins. and the proportions changed from 1-2 to 1-2½.
"In 1898 this cost received another severe cut, and Major Marshall's
instructions stated that the facing should not exceed 1½ ins. in
thickness nor be less than ¾-in., while the layer of fine material on
top of the coping was to be only sufficient to cover the stone and
gravel. The amount of sand was again increased so that the proportions
were 1-3.
"The cost of the Portland cement concrete was likewise cheapened by
increasing the amount of aggregates. On the earlier work the proportions
were 1-2-2-3, while on the work in 1898 the proportions were 1-4-4. The
cost of the walls was further cheapened by using Utica cement in the
lower steps of the wall, with 2 ft. of Portland cement concrete on the
face. The proportions used in the Utica cement concrete were 1-2½-2½.
This lower step is one-third of the height, or about 7 ft.
[Illustration: Fig. 76.--Sketch Showing Method of Attaching Lagging to
Studs, Illinois & Mississippi Canal.]
"The forms were of the same character as those used on the first locks,
except that for lining the inner face, 3×10-in. hard pine planks were
substituted for the 4×8-in. white pine. The hard pine was damaged less
by the continuous handling, and the cost was practically the same. There
was also an important change made in the manner of fastening the plank
to the 8×10-in. posts. A strip 1¾ ins. square was thoroughly nailed to
each post, once for all, with 20d. spikes, and the planking was then
nailed from the outside, as shown in Fig. 76. This kept the face of the
plank in a perfectly smooth condition, and prevented the formation of
the little knobs on the face of the concrete which represented all the
old nail holes. This style of forming was also easier to take apart
after the setting of the concrete. Rough pine planks, 2×12-in., were
used for the back of the form, the same as before.
"In order to keep ahead of the concrete force it was necessary to use
two gangs of carpenters, erecting the forms for the next two locks. Each
gang consisted of about 20 carpenters (at $2.25) and 10 helpers (at
$1.50); but men were transferred from one to the other, according to the
stage of completion of the two locks. In addition to these two gangs,
two carpenters were on duty with each concrete shift to put in the steps
in the back of the forms. Sufficient lumber was required for the forms
for three complete locks, and 14 locks (Nos. 8 to 21) were built.
"The same type of mixer has been used as on the earlier work at Milan,
namely, a 4-ft. cubical steel box mounted on corners diagonally
opposite. On account of the greater number of locks to be built on the
eastern section, however, two mixers were found necessary, so that while
the concrete force was at work at one lock, the carpenters and helpers
were erecting the mixer at the next lock. The facing was mixed by hand.
After turning over the dry cement and sand at least twice with shovels,
the mixture was then cast through a No. 5 sieve, after which the water
was incorporated slowly by the use of a sprinkling can so as to avoid
washing. The secret of good concrete, after the selection of good
materials, is thorough mixing and hard tamping. Each batch of concrete,
consisting of about 1.2 cu. yds. in place, was turned in the mixer for
not less than 2 mins. at the rate of 9 revolutions per minute. The
amount of tamping is indicated by the fact that about 16 men out of 72
on each shift did nothing but tamp. The rammers used were 6 ins. square
and weighed 33 lbs. The bottom of the rammer consisted of three ridges,
each 1-in. in height, so as to make more bond between the successive
layers.
"On the eastern section the top of the lock walls was higher above the
ground, as a rule, than at the Milan locks, and the cars were run up an
incline with a small hoisting engine. A 15-HP. portable engine and
boiler operated the bucket hoist from one pulley, the mixer from the
other pulley, and also furnished steam for the hoist which pulled the
cars up the incline. The incline made an angle of about 30° with the
ground. The practice of carrying on two sections at once was continued
the same as on the western section. Each main wall was systematically
divided into 11 sections, making each section about 20 ft. long. The
corners of the coping were dressed to a quadrant of about 3 ins. radius
with a round trowel like those used on cement walks. In fact, the whole
method of finishing the coping was the same as is used on concrete
walks. The mortar was put on rather wet and then allowed to stand for
about 20 mins. before finishing. This allowed the water to come to the
surface and prevented the formation of the fine water cracks which are
sometimes seen on concrete work. After its final set the coping was
covered with several inches of fine gravel which was kept wet for at
least a week.
"The last concrete laid during the season was in November, on Lock No.
21, and Aqueducts Nos. 2 and 3. Portions of these structures were built
when the temperature was below freezing. The water was warmed to about
60° or 70° F., by discharging exhaust steam into the tank. Salt was used
only in the facing, simply sufficient to make the water taste saline.
The maximum amount used on the coldest night when the temperature was
about 20° F. was 1½ per cent.
The concrete force on each shift was as follows:
Men.
Filling and pushing stone car 10
Filling and pushing gravel car 8
Measuring cement 3
Measuring water and cleaning bucket 2
Dumping bucket on top platform 2
Operating mixer 2
Loading concrete cars 1
Pushing and dumping cars on forms 3
Switchmen on forms 2
Spreading concrete in forms 12
Tamping concrete in forms 16
Mixing facing 3
Water boys 2
--
Total laborers 66
Operating hoists 2
Finishing coping 2
Fireman 1
Sub-overseers 2
Overseer 1
--
Total force 74
The cost of material and labor at Lock No. 15 (10-ft. lift), which
contains 2,559 cu. yds. of concrete, was as follows:
Materials. Per cu. yd.
0.56 bbl. Portland cement (0.96 per cu. yd.) $1.42
0.64 bbl. Utica cement (1.58 per cu. yd.) .30
0.58 cu. yd. stone 1.15
0.60 cu. yd. gravel .52
14 ft. B. M. lumber[F] at $15 per M. .21
0.6 lb. spikes .01
Coal (10 tons in all, at $1.70) .01
0.35 gal. kerosene .03
-----
Total materials $3.65
Labor.
Erecting forms ($7 per M.) .45
Removing forms ($2 per M.) .13
Erecting and removing mixer ($161) .06
Loading and unloading materials at yards and lock sites .23
Track laying ($86) .03
Train service (narrow gage road) .09
Delivering materials to mixer .28
Mixing concrete .11
Depositing concrete .21
Tamping concrete .21
Mixing, depositing and tamping, 69 cu. yds. face mortar
($160) .23
General construction ($553) .22
-----
Total labor $2.25
[Footnote F: The lumber was used nearly five times, which accounts for
its low cost per cu. yd.]
There were 1,430 cu. yds. of Portland cement concrete. 69 cu. yds. of
Portland cement mortar facing, and 1,059 cu. yds. of Utica cement
concrete. The Portland concrete cost $6.43 per cu. yd.; the Utica
concrete, $4.77 per cu. yd. The following is the cost of labor on Lock
No. 20 (11-ft. lift.; 2,750 cu. yds.):
Per cu. yd.
Erecting forms ($7 per M.) $.434
Removing forms ($1.70 per M.) .113
Erecting and removing mixer ($151) .058
Loading and unloading at yards, lock sites, etc. .614
Tracks .024
Train service (narrow gage) .016
Pumping .114
Delivering material to mixer .288
Mixing concrete .134
Depositing concrete .205
Tamping concrete .192
Mixing, depositing and tamping, 85 cu. yds. face
mortar .071
General construction .246
------
Total $2.509
~COST OF HAND MIXING AND PLACING, CANAL LOCK FOUNDATION.~--Mr. Geo. P.
Hawley gives the following record of mixing and placing 4,000 cu. yds.
of 1-4½ gravel concrete for the foundation of a lock constructed for the
Illinois and Mississippi Canal in 1897. The concrete was mixed on
14×16-ft. board platforms, from which it was shoveled directly into
place. The materials were brought to the board in wheelbarrows. Two
boards were used, the usual gang for each being 4 men wheeling gravel, 4
men mixing, 1 man sprinkling, 2 men depositing and leveling and 2 men
tamping. The two gangs were worked against each other. Ten hours
constituted a day's work, and the average time and cost per cubic yard
for mixing and placing were:
Cts.
Foreman, 0.21 hr., at 30 cts 6.30
Laborers, 3.339 hrs., at 15 cts 50.09
Pump runner, 0.129 hr., at 20 cts 3.58
Water boy, 0.087 hr., at 7½ cts 0.65
-----
Total labor per cu. yd., cents. 60.62
~BREAKWATER AT MARQUETTE, MICH.~--The breakwater extends out from the
shore and consists of a prism of concrete resting on timber cribs filled
with stone. Originally the cribs carried a timber superstructure; this
was removed to give place to the concrete work. A typical cross-section
of the concrete prism is shown by Fig. 77; the prism is 23 ft. wide on
the base. Farther in shore the base width was reduced to 20 ft., and in
the shore section the prism was changed to a triangular trapezoid by
continuing the first slope to the bottom cutting off the berm and second
slope. The wooden structure was removed to a level 1 ft. below mean low
water and on it a concrete footing approximately 2 ft. thick was
constructed for the prism proper. This footing reached the full width of
the crib and was constructed in various ways during the 5 years through
which the work continued. At first the footing concrete was deposited
loose under water by means of bottom dumping buckets; later the stone
filling of the cribs was simply leveled up by depositing concrete in
bags, and last toe and heel blocks were molded and set flush with the
sides of the crib and filled between. Methods of construction and
records of cost are reported for portions only of the work and these are
given here.
[Illustration: Fig. 77.--Cross Section of Marquette Breakwater.]
_Footing Placed under Water with Buckets._--Besides the material track
which was constructed along the old wooden structure the plant
consisted of a mixing scow and a derrick scow, which were moored
alongside the work. The sand, stone and cement were brought out in cars
between working hours and stored on the mixing scow, enough for one
day's work at a time. The derrick handled a 40-cu. ft. bottom dump
bucket, which sat in a well on the mixing scow with its top flush with
the deck. The concrete was mixed by hand on the deck and shoveled into
the bucket; the bucket was then handled by the derrick to the crib and
lowered and dumped under water. The gang consisted of 24 men, 1 foreman,
1 master laborer, 14 men shoveling and mixing, 3 men wheeling materials,
1 derrick man and 3 men placing and depositing concrete. No record of
output of this gang is available. The cost of the concrete in place with
wages $1.25 to $1.40 per day for common labor is given as follows:
Materials. Per cu. yd.
1.21 bbls. (459 lbs.) cement at $2.20 $2.657
1 cu. yd. stone at $1.58 1.580
0.5 cu. yd. sand at $0.50 0.250
2.02 lbs. burlap at $0.037 0.075
Twine and needles 0.005
------
Total materials $4.567
Labor.
Loading scow with materials $0.4114
Mixing concrete 0.8459
Depositing concrete 0.5242
-------
Total labor $1.7815
Grand total $6.348
These figures are based on some 757 cu. yds. of concrete footing. In
explanation of the items of burlap, etc., it should be said that the
cribs were carpeted with burlap to prevent waste of concrete into the
stone fill.
[Illustration: Fig. 78.--Cross Section of Marquette Breakwater Showing
Manner of Constructing Footing with Bags of Concrete.]
_Leveling Off Cribs with Concrete in Bags._--The sketch, Fig. 78, shows
the method of leveling off the cribs with concrete in bags. The concrete
was mixed by hand on shore and filled into 8-oz. burlap bags, 6 ft. long
and 80 ins. around, holding 2,000 lbs. The bags were filled while lying
in position in a skip holding one bag. A skip was lifted by gallows
frame and tackle onto a car and run out to the work where the derrick
scow handled the skip to the crib, lowered it into the water and dumped
the bag. The cost of making and placing some 375 cu. yds. of concrete in
bags is given as follows:
Materials. Total. Per cu. yd.
453 bbls. cement at $2.627 $1,190.03 $3.173
375 cu. yds. stone at $1.619 607.13 1.619
180 cu. yds. sand at $0.392 70.56 0.188
3,220 yds. burlap at $0.03304 106.39 0.283
Twine and needles 6.36 0.017
--------- ------
Total materials $1,980.47 $5.280
Labor Mixing.
108 hrs. master laborer at $0.21-7/8 $ 23.42 $0.062
1,750 hrs. labor at $0.175 306.25 0.816
Superintendence 12.55 0.033
-------- ------
Total labor mixing $ 342.22 $0.911
Labor transporting.
306 hrs. labor at $0.175 $ 53.55 $0.142
Superintendence 5.25 0.014
-------- ------
Total labor transporting. $ 58.80 $0.156
Labor Depositing.
108 hrs. engineman at $0.25 $ 27.00 $0.072
108 hrs. master laborer at $0.21-7/8 23.42 0.062
510 hrs. labor at $0.175 89.25 0.238
Superintendence 13.25 0.035
-------- ------
Total labor depositing $ 152.92 $0.407
Grand total labor $ 553.94 $1.477
Grand total materials and labor $2,534.41 $6.757
_Molding Footing Blocks._--The blocks used at the toe of the prism were
of the form and dimensions shown by Fig. 79. They were molded in a
temporary shed heated to 50° to 65° F., and provided with a 2×8-in.
dressed plank floor on 12×12-in. sills. The floor formed the bottoms of
the block molds. Four molds were used, each consisting of four sides.
Three laborers molded one block, 2.22 cu. yds. per day, wheeling,
mixing, erecting and removing forms, placing concrete and doing all
other work. The cost of making 40 blocks was recorded as follows:
Materials. Total. Per cu. yd.
126 bbls. cement at $2.75 $346.50 $3.893
88.9 cu. yds. screenings at $1.10 97.79 1.098
40.1 cu. yds. sand at $0.45 18.04 0.203
5 gals. oil at $0.65 3.25 0.036
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Total materials $465.58 $5.230
Labor.
1,000 hrs. labor at $0.125 $125.00 $1.404
Watchman 29.15 0.327
Labor cutting wood for fuel 23.80 0.267
Superintendence 42.66 0.480
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Total labor $220.61 $2.478
Total labor and materials $686.19 $7.708
[Illustration: Fig. 79.--Details of Toe Blocks for Footing, Marquette
Breakwater.]
_Molding Concrete Prism in Place._--The concrete prism was molded in
alternate sections 10 ft. long; the form for the isolated sections
consisted of eight pieces so constructed that when assembled in place
and secured with bolts and turnbuckles the form was self-contained as to
strength and required no outside support or bracing. The form once in
place, all that remained to be done was to fill it, the block with the
gallery through it being molded in one operation. The forms for the
connecting blocks consisted of two slope panels, a panel for the harbor
face and the gallery form, the blocks previously molded making the other
sides of the form. The concrete was mixed by hand on shore, conveyed to
the work in 1 cu. yd. cars and shoveled into the forms, where it was
rammed with 35-lb. rammers. The following record covers 1,231 cu. yds.
of concrete prism. In this concrete some 214 cu. yds. of rubble stone
were embedded. The costs given are as follows:
Per
Materials-- Total. cu. yd.
1,780 bbls. natural cement at $1.068 $1,901.04 $1.545
963½ cu. yds. stone at $1.619 1,559.91 1.267
53½ cu. yds. screenings at $0.392 20.97 0.017
485.6 cu. yds. sand at $0.392 190.36 0.154
Miscellaneous materials 78.15 0.063
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Totals $3,750.43 $3.046
Labor Mixing--
254 hrs. master laborer at $0.21-7/8 $ 55.56 $0.045
4,470 hrs. labor at $0.175 782.42 0.635
Superintendence 18.20 0.015
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Total labor mixing $ 856.18 $0.695
Labor Transporting and Placing--
35 days overseer at $2.33-1/3 $ 81.67 $0.066
1,949 hrs. labor at $0.175 342.07 0.277
Superintendence 34.98 0.028
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Total labor transporting and placing $ 458.72 $0.371
Grand total, labor $1,314.90 1.066
Total labor and materials $5,065.33 4.112
No charge is made under materials for rubble stone as the only cost for
this was cost of handling and this is included in transporting and
placing.
~BREAKWATER, BUFFALO, N. Y.~--The following methods and costs of mixing
and placing some 2,561 cu. yds. of concrete are given by Mr. Emile Low,
for 10 parapet wall sections and 17 parapet deck sections for a
breakwater at Buffalo, N. Y.
The concrete used was a 1 cement, 1 gravel, 1 sand grit and 4 unscreened
broken stone. One bag of cement was assumed to measure 0.9 cu. ft. The
voids in the sand grit and gravel were 27 per cent. and in the
unscreened stone 39 per cent. The hardened concrete weighed 152 lbs. per
cu. ft.