wet were used. The concrete was laid in 8-in. courses and faced with a
1-2 mortar. The forms were 2-in. white pine faced and jack planed on the
edges; upon removal of the forms board marks and other defects were
removed and a wash of neat cement was applied. One contractor used hand
mixing. The sand and gravel were measured in wheelbarrows and wheeled
onto the platform; the sand and cement were spread in thin layers, one
over the other, and thoroughly mixed dry; the gravel was then spread
over the mixture, the whole was shoveled into barrows or the pit again
shoveled into place and rammed. The other contractor used a cubical
mixer. A charging box holding 1¼ cu. yds. and graduated to show the
correct proportions of sand and gravel was filled by shoveling; cement
was placed on top and the box hoisted and dumped into the mixer. A
barrel holding the correct amount of water was emptied into the mixer
which was turned 10 or 15 times and discharged into cars. The costs of
mixing by hand and by machine were as follows:
Hand mixing. Total. Per cu. yd.
½ foreman at $3 $ 1.50 $0.025
3 men wheeling barrows at $1.50 4.50 0.075
10 men wheeling materials at $1.50 15.00 0.250
3 men mixing sand and gravel at $1.50 4.50 0.075
6 men mixing concrete at $1.50 9.00 0.150
1 man sprinkling at $1.50 1.50 0.025
------ ------
Total $36.00 $0.600
The output of the hand mixing gang was 60 cu. yds. per day.
Machine mixing. Total. Per cu. yd.
1 foreman at $3.50 $ 3.50 $0.035
1 stationary engineer at $3 3.00 0.030
½ foreman at $1.75 0.87 0.009
15 men loading charging bucket at $1.50 22.50 0.225
2 men dumping charging bucket at $1.75 3.50 0.035
2 tagmen at $2, ½ time 2.00 0.020
1 man at trap at $2, ½ time 1.00 0.010
------ ------
Total $36.37 $0.364
The output of the cubical mixer was 100 cu. yds. per day.
The costs of placing concrete in the forms above the foundation by hand
below 12 ft., and by cars and derricks any height, were as follows:
By hand (barrows) below 12 ft. Total. Per cu. yd.
4 men loading concrete at $1.50 $ 6.00 $0.100
1 foreman ½ time at $3 1.50 0.025
10 men wheeling at $1.50 15.00 0.250
1 man scraping barrows at $1.50 1.50 0.025
2 men placing concrete at $1.50 3.00 0.050
1 man placing mortar face at $1.50 1.50 0.025
2 men mixing and carrying mortar at $1.50 3.00 0.050
------ ------
Total $31.50 $0.525
By cars and derricks--
1 horse and driver at $3 $ 3.00 $0.030
2 men dumping concrete ½ time at $1.50 1.50 0.015
1 fireman ½ time at $1.75 0.88 0.009
3 tagmen at $1.50 4.50 0.045
8 men placing and ramming conc. at $1.50 12.00 0.120
2 men mixing mortar at $1.50 3.00 0.030
2 men placing mortar at $1.50 3.00 0.030
2 men carrying mortar at $1.50 3.00 0.030
1 foreman at $3 3.00 0.030
1 stationary engineer at $3 3.00 0.030
2 men attending hook at $1.50 3.00 0.030
------ ------
Total $39.88 $0.399
The costs of placing concrete in the foundations were as follows:
By hand-- Total. Per cu. yd.
1 foreman ½ time at $3 $ 1.50 $0.025
4 men shoveling concrete at $1.50 6.00 0.100
1 man placing concrete at $1.50 1.50 0.025
1 man ramming concrete at $1.50 1.50 0.025
------ ------
Total $10.50 $0.175
By machine--
1 horse and driver at $3 $ 3.00 $0.030
3 men pushing and unloading car at $1.50 4.50 0.045
5 men placing and ramming at $1.50 7.50 0.075
1 foreman at $3 3.00 0.030
2 men dumping mixer at $1.50 3.00 0.030
------ ------
Total $21.00 $0.210
~COST OF RETAINING WALL.~--The following figures of the cost of a concrete
retaining wall are given by C. C. Williams:
Cost of Material.
Unit
Kind and amount of material-- Price. Cost.
Stone, 441 tons $ .70 $308.70
Sand, 182.5 yds. .55 100.37
Cement, 536 bbls. .85 453.60
-------
Total $862.67
Lumber ¾ value $205.33
Wheelbarrows, ¾ value, 6 at $3.50 15.75
-------
Total $221.08
Excavation--
Labor, 4,002 hours at 15 cts. $600.30
Carts, 800 hours at 12½ cts. 100.00
Foreman, 460 hours at 35 cts. 171.00
Waterboy, 240 hours at 10 cts. 24.00
-------
Total $895.30
Concrete--
Labor, 2,398 hours at 15 cts. $359.70
Foreman, 224 hours at 35 cts. 77.40
-------
Total $437.10
Handling material--
Unloading cars, 380 hours at 15 cts. $ 57.00
Foreman, 40 hours at 35 cts. 14.00
-------
Total $ 71.00
Forms--
Carpenters, 997 hours at 22½ cts. $224.33
Work to support bridge--
Carpenters, 542 hours at 22½ cts. $121.95
Labor, 458 hours at 15 cts. 68.70
-------
Total $190.65
Superintendence and office--
Superintendent, 30 hours at 50 cts. $15.00
Office 20.00
--------
Total $35.00
--------
Grand total $2,937.13
Proportional costs--
Cost Per Per Cent.
Yard of of Total
Item. Cost. Concrete. Cost.
Concrete materials $ 862.67 $2.02 46.7
Laying concrete 437.10 1.03 23.4
Lumber 205.33 .48 11.3
Building forms 224.33 .53 12.3
Handling material 71.00 .17 03.8
Wheelbarrows 15.75 .04 01.0
Supt., etc. 35.00 .07 01.5
--------- ----- ------
Total $1,851.18 $4.34 100.00
Work on bridge 190.65
Excavation 895.30
---------
$2,937.13
CHAPTER XIV.
METHODS AND COST OF CONSTRUCTING CONCRETE FOUNDATIONS FOR PAVEMENTS.
Contractor's skill or want of skill in systematizing and managing labor
counts as high in street work as in any class of concrete construction.
As previously demonstrated, the cost of mixing is a very small portion
of the labor cost of concrete in place; the costs of getting the
materials to the mixer and the mixed concrete to the work are the big
items, and in street work the opportunity for increasing the cost of
these items through mismanagement is magnified by the large area of
operations involved per cubic yard of concrete placed. One cubic yard of
concrete makes 6 sq. yds. of 6-in. pavement foundations and 100 cu. yds.
of concrete make a 6-in. foundation for 300 ft. of 30-ft. street, while
4 to 5 cu. yds. will build 100 ft. of ordinary curb and gutter. Thus the
haulage per cubic yard is considerable at best, and lack of plan in
distributing stock piles and handling the concrete can easily result in
such increased haulage expenses as to change a possible profit into a
certain loss. A little thought and skill in planning street work pays a
good profit.
~MIXTURES EMPLOYED.~--A comparatively lean concrete will serve for
pavement foundations; mixtures of 1-4-8 Portland cement or 1-2-5 natural
cement are amply good and it is folly, ordinarily, to employ richer
mixtures. Until recently, natural cement has been used almost
exclusively; a 1-2-5 natural cement mixture requires about 1.15 bbls. of
cement per cubic yard of concrete. A 1-4-8 Portland cement mixture
requires about 0.7 bbl. of cement per cubic yard. In the opinion of the
authors a considerably leaner mixture of Portland concrete is
sufficiently good when it is well mixed in machine mixers--for a 6-in.,
foundation 0.5 bbl. per cu. yd. The mixtures actually employed are
proportioned about as stated and their cost, or that of any other common
mixture, may easily be computed from Tables XII and XIII, giving for
different mixtures the quantities of cement, sand and stone per cubic
yard of concrete; the product of these quantities and the local prices
of materials in the stock piles gives the cost. When the concrete is
mixed by hand the ordinary labor cost of foundations is 0.4 to 0.5 of a
10-hour day's wages per cubic yard of concrete; occasionally it may be
as low as 0.3 of a day's wages where two mixing gangs are worked side by
side under different foremen and with an exacting contractor. Data for
machine mixing are too few to permit a similar general statement for
machine work, but in one case coming under the authors' observation, the
cost figured out to a little less than 0.2 of a day's wages per cubic
yard.
~DISTRIBUTION OF STOCK PILES.~--Assuming a 30-ft. street and a 1-3-5
concrete laid 6 ins. thick, the quantities of concrete materials
required per lineal foot of street are: Cement 0.60 bbl., sand 0.27 cu.
yd., stone 0.44 cu. yd. The stock piles should be so distributed that
each supplies enough materials for a section of foundation reaching half
way to the next adjacent stock pile on each side, and they should not
contain more or less material, otherwise a surplus remains to be cleaned
up or a deficiency to be supplied by borrowing from another pile. A
little care will ensure the proper distribution and it is well paid for
in money saved by not rehandling surplus or borrowed materials. For a
given mixture and a given width and thickness of foundation, the sizes
of the stock piles are determined by their distance apart and this will
depend upon whether hand or machine mixing is employed and upon the
means adopted for hauling the raw materials and the mixed concrete. It
is worth while always in stock piles of any size, to lay a flooring of
plank particularly under the stone pile; if dumped directly on the
ground it costs half as much again to handle stone. Current practice
warrants everything from a continuous bank, to piles from 1,000 to 1,500
ft. apart, in the spacing of stock piles.
~HINTS ON HAND MIXING.~--All but a small percentage of the concrete
annually laid in street work is hand mixed. The authors are confident
that this condition will disappear as contractors learn more of the
advantages of machine mixing, but it prevails at present. The general
economics of hand mixing are discussed in Chapter II; in street work as
before stated, the big items of labor cost are the costs of handling
materials and the data in Chapter II on these processes deserve special
attention. It is particularly worth noting that it is seldom economical
to handle materials in shovels where carrying is necessary; it is a
common thing in street work to see an attempt to get the stock piles so
close to the mixing board that the material can be handled with shovels,
and this is nearly always an economic error. Street work is readily
measured; in fact, its progress can be seen at a glance, and advantage
can often be taken of this fact to profit by the rivalry of separate
gangs. The authors have known of the labor costs being reduced as much
as 25 per cent., due to pitting one gang against another where each
could see the progress made by the other.
~METHODS OF MACHINE MIXING.~--Concrete mixers have been slow to replace
handwork in laying pavement foundations. In explanation of this fact it
is asserted: (1) That frequent shifting of the mixer causes too much
lost time, and (2) that the principal item of labor cost in street work
is the conveying of materials to and from the mixer, and this item is
the same whether hand or machine mixing be employed. The records of
machine mixer work given elsewhere in this chapter go far, in the
opinion of the authors, toward disproving the accuracy of both
assertions. If the machine used and the methods of work employed are
adapted to the conditions of street work, machine mixing can be employed
to decided advantage.
A continuous and large output is demanded in a mixer for street work;
the perfection of the mixing is within limits a minor consideration.
This at once admits for consideration types of mixers whose product is
classed as unsuitable for reinforced concrete work, and also admits of
speeding up the output of the better types to a point beyond that at
which they turn out their most perfect product. Keeping these facts in
mind either of the following two systems of work may be employed: (1)
Traction plants which travel with the work and deposit concrete in
place, or so nearly in place that little shoveling is necessary; (2)
portable plants which are set up at wide intervals along the work and
which discharge the concrete into carts or dump wagons which distribute
it to the work.
The secret of economic work with plants of the class cited first is the
distribution of the stock piles so as practically to eliminate haulage
from stock pile to mixer. The mixer backs away from the work, its
discharge end being toward the work and its charging end away from it.
Then deposit the materials so as to form a continuous stock pile along
the center of the street; the mixer moving backward from the completed
foundation keeps close to the materials and if the latter are uniformly
distributed in the pile the great bulk of the charging is done by
shoveling direct into the charging bucket. The point to be watched here
is that the shovelers do not have to carry the materials; separate stock
piles within moderate hauling distance by wheelbarrows are a far more
economic arrangement than a continuous pile so irregularly distributed
that much of the material has to be carried even a few paces in shovels.
Economic work with plants of the second class depends upon efficient and
adequate means of hauling the mixed concrete to the work. The plant
should not be shifted oftener than once in 1,000 to 2,000 ft., or, say,
four city blocks. This does away with the possibility of wheelbarrow
haulage; large capacity hand or horse carts must be employed. With 6 cu.
ft. hand carts, such as the Ransome cart, a haul of 500 ft. each way
from the mixer is possible and with horse carts, such as the Briggs,
this economic distance is increased to 1,000 ft. each way from the
mixer. The mixer must be close to the stock pile and it will pay to make
use of improved charging devices. A 6-in. foundation for 2,000 ft. of
30-ft. street calls for 667 cu. yds. of concrete, and if both sides are
curbed at the same time, 100 cu. yds. more are added, or 767 cu. yds. in
all; where intersecting streets are to be paved in both directions from
the mixer plant these amounts are doubled. A very small saving per cubic
yard due to mechanical handling of the materials to the mixer amounts to
the interest on a considerable investment in such plant. A point that
should not be forgotten is that carts such as those named above spread
the concrete in dumping so that little or no shoveling is required.
~FOUNDATION FOR STONE BLOCK PAVEMENT, NEW YORK, N. Y.~--Mr. G. W. Tillson,
in "Street Pavements and Paving Materials," p. 204, gives the following
data on the cost of granite block pavement in New York City in 1899. The
day was 10 hours long:
Per Per Per
Concrete gang-- day. sq. yd. cu. yd.
1 foreman $ 3.00 $0.0125 $0.075
8 mixers on two boards, at $1.25 10.00 0.0416 0.250
4 wheeling stone and sand, at $1.25. 5.00 0.0208 0.125
1 carrying cement and supplying
water, at $1.25 1.25 0.0051 0.031
1 ramming, at $1.25 1.25 0.0051 0.031
------ ------- ------
Total, 240 sq. yds. (40 cu. yds.). $20.50 $0.0851 $0.512
The concrete was shoveled direct from the mixing boards to place.
Cost 1-2-4 concrete-- Per cu. yd.
1-1/3 bbls. natural cement, at $0.90 $1.20
0.95 cu. yd. stone, at $1.25 1.19
0.37 cu. yd. sand, at $1.00 0.37
Labor 0.51
-----
$3.27
In laying 5,167 sq. yds. of granite block pavement on one job in New
York City in 1905, the authors' records show that one laborer mixed and
laid 1.3 cu. yds. of concrete per day in a 6-in. foundation; this is a
very small output. The work was done by contract and the labor cost was
as follows:
Per Per
Item. Total. sq. yd. cu. yd.
28½ days foreman at $3.50 $ 99.75 $0.0193 $0.118
399 days laborers at $1.75 698.25 0.1351 0.826
------- ------- ------
$798.00 $0.1544 $0.944
The average day's wages was $1.86, so that the labor cost was about 0.5
of a day's wages per cubic yard of concrete.
~FOUNDATION FOR PAVEMENT, NEW ORLEANS. LA.~--Mr. Alfred E. Harley states
that in laying concrete foundations for street pavement in New Orleans,
a day's work, in running three mixing boards, covering the full width
of the street, averaged 900 sq. yds., 6 ins. thick, or 150 cu. yds.,
with a gang of 40 men. With wages assumed to be 15 cts. per hour the
labor cost was:
Cts. per cu. yd.
6 men wheeling broken stone 6
3 men wheeling sand 3
1 man wheeling cement 1
2 men opening cement 2
7 men dry mixing 7
8 men taking concrete off 8
3 men tamping 3
3 men grading concrete 3
1 man attending run planks 1
3 water boys 1
2 extra men and 1 foreman 4
--
Total labor cost 39 cts.
~FOUNDATIONS FOR STREET PAVEMENT, TORONTO, CANADA.~--The following cost of
a concrete base for pavements at Toronto has been abstracted from a
report (1892) of the City Engineer, Mr. Granville C. Cunningham. The
concrete was 1-2½-7½ Portland; 2,430 cu. yds. were laid, the thickness
being 6 ins., at the following cost per cubic yard:
0.77 bbl. cement, at $2.78 $2.14
0.76 cu. yd. stone, at $1.91 1.45
0.27 cu. yd. sand and gravel, at $0.80 0.22
Labor (15 cts. per hr) 1.03
-----
Total $4.84
Judging by the low percentage of stone in so lean a mixture as the
above, the concrete was not fully 6 ins. thick as assumed by Mr.
Cunningham. Note that the labor cost was 1½ to 2 times what it would
have been under a good contractor.
~MISCELLANEOUS EXAMPLES OF PAVEMENT FOUNDATION WORK.~--The following
records of pavement foundation work are taken from the note and time
books of one of the authors:
_Case 1._--Laying 6-in. pavement foundation; stone delivered and dumped
upon 2-in. plank laid to receive it. Sand and stone were dumped along
the street, so that the haul in wheelbarrows to mixing board Was about
40 ft. Two gangs of men worked under separate foremen, and each gang
averaged 4.5 cu. yds. concrete per hour. The labor cost was as follows
for 45 cu. yds. per gang:
Per day. Per cu. yd.
4 men filling barrows with stone and sand
ready for the mixers, wages 15 cts.
per hour $6.00 $0.13
10 men, wheeling, mixing and shoveling to
place (3 or 4 steps), wages 15 cts. per
hour 15.00 0.33
2 men ramming, wages 15 cts. per hour 3.00 0.07
1 foreman at 30 cts. per hour and 1 water
boy, 5 cts 3.50 0.08
----- -----
Total $27.50 $0.61
_Case II._--Sometimes it is desirable to know every minute detail cost,
for which purpose the following is given:
----Per cu. yd.----
Day's labor. Cost.
3 men loading stones into barrows $0.06 $0.09
1 man loading sand into barrows 0.02 0.03
2 men ramming 0.04 0.06
1 foreman and 1 water boy equivalent to 0.035 0.05
Wheeling sand and cement to mixing board 0.02 0.03
Wheeling stone to mixing board 0.026 0.04
9 men mixing mortar 0.013 0.02
Mixing stone and mortar 0.049 0.07
Placing concrete (walking 15 ft.) 0.072 0.11
------ -----
Total $0.335 $0.50
In one respect this is not a perfectly fair example (although it
represents ordinary practice), for the mortar was only turned over once
in mixing instead of three times, and the stone was turned only twice
instead of three or four times. Water was used in great abundance, and
by its puddling action probably secured a very fair mixture of cement
and sand, and in that way secured a better mixture than would be
expected from the small amount of labor expended in actual mixing.
About 9 cts. more per cu. yd. spent in mixing would have secured a
perfect concrete without trusting to the water.
_Case III._--Two gangs (34 men) working under separate foremen averaged
600 sq. yds., or 100 cu. yds. of concrete per 10-hour day for a season.
This is equivalent to 3 cu. yds. per man per day. The stone and sand
were wheeled to the mixing board in barrows, mixed and shoveled to
place. Each gang was organized as follows:
Per day. Per cu. yd.
4 men loading barrows $ 6.00 $0.12
9 men mixing and placing 13.50 0.27
2 men tamping 3.00 0.06
1 foreman 2.50 0.05
------ -----
Total $25.00 $0.50
These men worked with great rapidity. The above cost of 50 cts. per cu.
yd. is about as low as any contractor can reasonably expect to mix and
place concrete by hand in pavement work.
_Case IV._--Two gangs of men, 34 in all, working side by side on
separate mixing boards, averaged 720 sq. yds., or 120 cu. yds., per
10-hour day. Each gang was organized as follows:
Per day. Per cu. yd.
6 men loading and wheeling $ 9.00 $0.15
8 men mixing and placing 12.00 0.20
2 men tamping 3.00 0.05
1 foreman 3.00 0.05
------ -----
Total $27.00 $0.45
Instead of shoveling the concrete from the mixing board into place, the
mixers loaded it into barrows and wheeled it to place. The men worked
with great rapidity.
Mr. Irving E. Howe gives the cost of a 6-in. foundation of 1-3-5 natural
cement at Minneapolis, Minn., in 1897, as $2.80 per cu. yd., or $0.467
per sq. yd. Cement cost 76 cts. per barrel and stone and sand cost
delivered $1.15 and 30 cts. respectively. Mixers received $1.75 per
day.
Mr. Niles Meriwether gives the cost of materials and labor for an 8-in.
foundation constructed by day labor (probably colored) at Memphis,
Tenn., in 1893, as follows:
Per sq. yd.
Natural cement at $0.74 per bbl $0.195
Sand at $1.25 per cu. yd 0.075
Stone at $1.87 per cu. yd 0.355
Labor mixing and placing 0.155
-----
Total $0.780
Labor was paid $1.25 to $1.50 per 8-hour day and 1.16 bbls. of cement
were used per cubic yard of concrete. The cost of materials, as will be
noted, was high and the labor seems to have been inefficient.
~FOUNDATIONS FOR BRICK PAVEMENT, CHAMPAIGN, ILL.~--The concrete foundation
for a brick pavement constructed in 1903 was 6 ins. thick; the concrete
used was composed of 1 part natural cement, 3 parts of sand and gravel,
and 3 parts of broken stone. All the materials were mixed with shovels,
and were thrown into place from the board upon which the mixing was
done. The material was brought to the steel mixing board in wheelbarrows
from piles where it had been placed in the middle of the street, the
length of haul being usually from 30 to 60 ft. The foundation was 6 ins.
thick and it cost as follows for materials and labor:
Cost per
cu. yd.
1.2 bbls. cement, at $0.50 $0.600
0.6 cu. yd. sand and gravel, at $1 0.600
0.6 cu. yd. broken stone, at $1.40 0.840
6 men turning with shovels, at $2 0.080
4 men throwing into place, at $2 0.053
2 men handling cement, at $1.75 0.023
1 man wetting with hose, at $1.75 0.012
2 men tamping, at $1.75 0.023
1 man leveling, at $1.75 0.012
6 men wheeling stone, at $1.75 0.070
4 men wheeling gravel, at $1.75 0.047
1 foreman, at $4 0.027
------
$2.387
This is practically 40 cts. per sq. yd., or $2.40 per cu. yd. of
concrete for materials and labor. It is evident from the above
quantities that a cement barrel was assumed to hold about 4.5 cu. ft.,
hence the cement was measured loose in making the 1-3-3 concrete. The
accuracy of the quantities given is open to serious doubt. It will also
be noted that the labor cost of making and placing the concrete was only
35 cts. per cu. yd., wages being nearly $1.85 per day. This is so
remarkably low that some mistake would seem to have been made in the
measurement of the work. The authors do not hesitate to say that no gang
of men ever made any considerable amount of concrete by hand at the rate
of 5.75 cu. yds. per man per day.
[Illustration: Fig. 112.--Foote Continuous Mixer Arranged for Pavement
Foundation Work.]
~FOUNDATION CONSTRUCTION USING CONTINUOUS MIXERS.~--The following are
records of two jobs of pavement foundation work using continuous mixers
with one-horse concrete carts in one instance and wheelbarrows in the
other instance. The mixer used was the Foote mixer, as arranged for the
work being described it is shown by Fig. 112. One particular advantage
of this and similar mixers for street work is that no proportioning or
measuring of the materials is required of the men. The mixers are
provided with an automatic measuring device, by means of which any
desired proportion of cement, sand and stone is delivered to the mixing
trough. The mixer is mounted on trucks, and the hoppers that receive
the sand and stone are comparatively low down. The sand can be wheeled
in barrows up a run plank and dumped into a hopper on one side of the
mixer, and in like manner the gravel or broken stone can be delivered
into a hopper on the other side. The cement is delivered in bags or
buckets to a man who dumps it into a cement hopper directly over the
mixer. All that the operator needs to attend to is to see that the men
keep the hoppers comparatively full. The records of work on the two jobs
mentioned are as follows:
[Illustration: Fig: 113.--Briggs Cart Distributing Concrete for Pavement
Foundation.]
_Job I._--The sand was delivered from the stock pile by a team hitched
to a drag scraper, and was dumped alongside the mixer where two men
shoveled it into the hopper. On the same job the concrete was hauled
away from the mixer in Briggs' concrete carts. With a gang of 30 men and
2 to 4 horses hauling concrete in Briggs' carts, the contractor averaged
1,200 sq. yds., or 200 cu. yds., per day of 10 hours. With wages of
laborers at 15 cts. per hour, and a single horse at the same rate, the
cost of labor was 26 cts. per cu. yd., or less than 4½ cts. per sq. yd.
of concrete base 6 ins. thick. The coal was a nominal item, and did not
add 1 ct. per cu. yd. to the cost. In this case the mixer was set up on
a side street and the concrete was hauled in the carts for a distance of
a block each way from the mixer. At first four carts were used, but as
the concreting approached the mixer, less hauling was required, and
finally only two carts were used. An illustration of a Briggs cart is
given by Fig. 113; it is hauled by one horse, which the driver leads,
and is dumped by an ingenious device operated from the horse's head. The
cart dumps from the bottom and spreads the load in a layer about 8 or 9
ins. thick, so that no greater amount of shoveling is necessary than
when barrows are used. It took about 20 seconds for the cart to back up
and get its load and about 5 seconds to dump and spread the load.
_Job II._--In this job the mixer was charged with wheelbarrows and
wheelbarrows were also employed to take the mixed concrete to the work,
the mixer being moved forward at frequent intervals. The stock piles
were continuous, sand on one side of the street and stone on the other
side. A 1-3-6 Portland cement concrete was used, a very rich mixture for
a 6-in. foundation. The organization of the working gang was as follows:
Men loading and wheeling gravel 8
Men assisting in loading gravel 2
Man dumping barrows into hopper 1
Men loading and wheeling sand 3
Man dumping barrows into hopper 1
Men wheeling concrete in barrows 7
Men spreading concrete 3
Men tamping concrete 2
Man pouring cement into hopper 1
Man operating mixer 1
Man shoveling spilled concrete 1
Man opening cement bags 1
Engineer 1
--
Total men in gang 32
The average day's output of this gang was 150 cu. yds., or 900 sq. yds.
in 8 hours; but on the best day's work the output was 200 cu. yds., or
1,200 sq. yds. in 8 hours, which is a remarkable record for 32 men and a
mixer working only 8 hours.
The following is the labor cost of 8,896 sq. yds. of 4½-in. concrete
foundation for an asphalt pavement constructed in New York City in 1904:
Item. Per sq yd.
Foreman at $3.75 $0.030
Laborers at $1.50 0.242
Teams at $5 0.040
Steam engine at $3.50 0.028
------
Total $0.340
The concrete was a 1-3-6 mixture and was mixed in a Foote mixer. These
costs are compiled from data collected by the authors.
~FOUNDATION CONSTRUCTION FOR STREET RAILWAY TRACK USING CONTINUOUS
MIXERS.~--The following account of the methods and cost of constructing a
concrete foundation for street railway track at St. Louis, Mo., is
compiled from information published by Mr. Richard McCulloch. The work
was done by day labor by the United Railways Co., in 1906. Figure 114
shows the concrete construction. A 1-2½-6½ Portland cement, broken stone
concrete mixed by machine was used.
[Illustration: Fig. 114.--Concrete Foundation for Street Railway Track.]
The material for the concrete was distributed on the street beside the
tracks in advance of the machine, the sand being first deposited, then
the crushed rock piled on that, and finally the cement sacks emptied on
top of this pile. The materials were shoveled from this pile into the
concrete mixing machine without any attempt at hand mixing on the
street. Great care was taken in the delivery of materials on the street
to have exactly the proper quantity of sand, rock and cement, so that
there would be enough for the ballasting of the track to the proper
height and that none would be left over. Each car was marked with its
capacity in cubic feet, and each receiver was furnished with a table by
which he could easily estimate the number of lineal feet of track over
which the load should be distributed.
The concrete mixing machines were designed and built in the shops of the
United Railways Co. Three machines were used in this work, one for each
gang. The machine is composed of a Drake continuous worm mixer, fed by a
chain dragging in a cast-iron trough. The trough is 36 ft. long, so that
there is room for 14 men to shovel into it. Water is sprayed into the
worm after the materials are mixed dry. This water was obtained from the
fire plugs along the route. In the first machine built, the Drake mixer
was 8 ft. long. In the two newer machines the mixer was 10 ft. long.
Both the conveyor and the mixer were motor driven, current being
obtained for this purpose from the trolley wire overhead. Two types of
machines were used, one in which the conveyor trough was straight and 45
in. above the rail, and the other in which the conveyor trough was
lowered back of the mixer, being 25 in. above the rail. The latter type
had the advantage of not requiring such a lift in shoveling, but the
trough is so low that a motor truck cannot be placed underneath it. In
the high machine the mixer is moved forward by a standard motor truck
under the conveyor. In the low machine the mixer is moved by a ratchet
and gear on the truck underneath the mixer. A crew of 27 men is required
to work each machine, and under average conditions concrete for 80 lin.
ft. of single track, amounting to 22 cu. yds., can be discharged per
hour.
The costs of the concrete materials delivered per cubic yard of concrete
were: Cement, per barrel, $1.70; sand, per cu. yd., $0.675, and stone,
per cu. yd., $0.425. The cost of the concrete work per cubic yard and
per lineal foot of track was as follows:
Item. Per lin. ft. Per cu. yd.
Concrete materials $0.791 $2.92
Labor mixing and placing 0.071 0.26
------ -----
Total labor and materials $0.862 $3.18
~FOUNDATION CONSTRUCTION USING BATCH MIXERS AND WAGON HAULAGE, ST. LOUIS,
MO.~--The following record of the method and cost of laying a concrete
foundation for street pavement using machine mixing and wagon haulage is
given by Mr. D. A. Fisher. The foundation was 6 ins. thick. The gravel
was dumped from wagons into a large hopper, raised by a bucket elevator
into bins, and drawn off through gates into receiving hoppers on the
charging platform where the cement was added. The receiving hoppers
discharged into the mixers, which discharged the mixed concrete into a
loading car that dumped into wagons, which delivered it on the street
where wanted. The longest haul in wagons was 30 mins., but careful tests
showed that the concrete had hardened well. The wagons were patent dump
wagons of the drop-bottom type. Mr. Fisher says:
"You may consider the following figures a fair average of the plant
referred to, working to its capacity. To these amounts, however, must be
added the interest on the investment, the cost of wrecking the plant and
the depreciation of the same, superintendence, and the pay roll that
must be maintained in wet weather. I am assuming the street as already
brought to grade and rolled.
"With labor at $1.75 per day of 10 hours, teams at $4, engineer and
foremen at $3, and engine at $5 per day, concrete mixed and put in place
by the above method costs:
Per cu. yd.
To mix $0.12 to $0.15
To deliver to street 0.10 to 0.14
To spread and tamp in place 0.08 to 0.11
--------------
Total $0.30 to $0.40
"The mixers are No. 2½ Smith, sold by the Contractors' Supply Co.,
Chicago, Ill., and a ½ yd. cube, sold by Municipal Engineering &
Contracting Co., Chicago.
"The above figures are on the basis of a batch every 2 minutes, which is
easily maintained by using the loading car, as by this means there will
be no delay in the operation of the plant owing to the irregularity of
the arrival of the teams.
"My experience leads me to believe that a better efficiency can be
obtained by using mixers of 1 cu. yd. capacity, and that the batch
mixer is the only type of machine where any certainty of the proportion
of the mixture is realized."
[Illustration: Fig. 115.--Chicago Improved Cube Traction Mixer for
Pavement Foundation.]
~FOUNDATION CONSTRUCTION USING A TRACTION MIXER.~--In laying a 6-in.
foundation for an asphalt pavement in Buffalo, N. Y., an average of 100
sq. yds., or 16.6 cu. yds., of concrete in place was made per hour using
the traction mixer shown by Fig. 115. This mixer was made by the
Municipal Engineering & Contracting Co., of Chicago, Ill., and consisted
of one of that company's improved cube mixers operated by a gasoline
engine and equipped with the regulation mechanical charging device and
also with a swinging conveyor to deliver the mixed concrete to the work.
The feature of the apparatus in its application to paving work is the
conveyor. This was 25 ft. long and pivoted at the mixer end so as to
swing through an arc of 170°. The mixer discharged into a skip or bucket
traveling on the conveyor frame and discharging over the end spreading
its load anywhere within a radius of 25 ft. In operation the mixer
traveled along the center of the street, backing away from the finished
foundation and toward the stock pile, which was continuous and was
deposited along the center of the street. The bulk of the sand and stone
was thus shoveled direct into the charging bucket and the remainder was
wheeled to the bucket in barrows. As the charging bucket is only 14 ins.
high the barrows could be dumped directly into it from the ground. The
gang worked was 17 including a foreman and one boy, and with this gang
100 sq. yds. of 6-in. foundation was laid per hour. Assuming an average
wage of 20 cts. an hour the cost of mixing and placing the foundation
concrete was 3.4 cts. per sq. yd. or 20.4 cts. per cu. yd. for labor
alone.
~FOUNDATION CONSTRUCTION USING CONTINUOUS MIXER.~--The foundation was 6
ins. thick for an asphalt pavement and was laid in Chicago, Ill. The
concrete used was exceptionally rich for pavement foundation work, it
being a 1-3-6 Lehigh Portland cement, broken stone mixture. The mixing
was done by machine, a mixer made by the Buffalo Concrete Mixer Co.,
Buffalo, N. Y., being used. This mixer was equipped with an elevating
charging hopper and was operated as a continuous mixer. The mixer was
mounted on wheels and was pulled along the center of the street ahead of
the work with its discharge end toward the work. Moves of about 25 to 30
ft. were made, the mixer being pulled ahead for this distance each time
that the concrete came up to its discharge end. The stock piles were
continuous, sand on one side and stone on the other side of the street.
Cement was stored in a pile at each end of the block. All materials were
wheeled from stock piles to mixer in wheelbarrows. The men wheeling sand
and stone loaded their own barrows, wheeled them to the mixer and
discharged them directly into the elevating hopper. No runways were
used, the barrows being wheeled directly on the ground. The cement was
brought in barrows, two or three bags being a load, and dumped alongside
a cement box which was located close to and at one side of the elevating
hopper. A man untied the bags and emptied them into the cement box and
another man scooped the cement out of the box in bucketfuls and emptied
it over the sand and stone in the elevating hopper. The mixer discharged
onto a sheet iron shoveling board, and the concrete was carried in
shovels from shoveling board to place, the length of carry being a
maximum of 25 to 30 ft. Two men were required to pull down the cone of
concrete at the discharge end of the mixer and to keep the stone from
separating and rolling down the sides. The gang was organized as
follows:
No. Men.
Loading and wheeling stone 10
Loading and wheeling sand 3 to 4
Loading and wheeling cement 2
Untieing and emptying cement bags 1
Charging cement to hopper 1
Operating mixer and hopper 1
Pulling down and tending discharge 2
Carrying concrete in shovels 8
Spreading concrete 2
Tamping concrete 2
Sweeping concrete 1
General laborers 3
Foreman 1
Watchman 1
Timekeeper 1
--
Total gang 40
This gang averaged 1,000 sq. yds. of 6-in. foundation per 10-hour day; a
maximum of 1,400 sq. yds. was laid in a day. We have thus an average of
167 cu. yds. and a maximum of 234 cu. yds. of concrete foundation mixed
and placed per 10-hour day. At an average wage of $2 per day the average
labor cost of mixing and placing concrete was 48 cts. per cu. yd. or 8
cts. per sq. yd. of 6-in. foundation. It was stated that the gang was
larger by three men than was ordinarily used owing to certain extra work
being done at the time that the above figures were collected. Taking out
three extra men and the timekeeper and watchman we get 34 men actually
working in mixing and placing concrete. This reduced gang gives us a
labor cost for mixing and placing of about 41 cts. per cu. yd. or 6.8
cts. per sq. yd. of 6-in. foundation.
~FOUNDATION CONSTRUCTION USING A BATCH MIXER.~--The following figures are
an average of several jobs using a Ransome ½-cu. yd. mixer for
constructing 6-in. foundations. The mixer was moved 1,000 ft. at a time
and the work conducted 500 ft. in each direction from each station. The
concrete materials were delivered from stock pile to mixer in
wheelbarrows and the mixed concrete was hauled to the work in
two-wheeled Ransome carts. Run planks were laid for the carts and one
man readily pushed a cart holding 6 cu. ft. The men had to work fast on
the long haul but had an easy time when the haul was short. The
organization of the gang was as follows, wages being $1.50 per day:
10 men loading and wheeling stone $15.00
4 men loading and wheeling sand 6.00
2 men handling cement 3.00
1 fireman 2.00
1 man dumping mixer 1.50
5 men wheeling carts 7.50
3 men spreading and ramming 4.50
1 foreman 3.50
------
Total wages per day $43.00
This gang averaged 1,080 sq. yds. of 6-in. foundation or 180 cu. yds. of
concrete in place per day which gives a labor cost of 24 cts per cu. yd.
or 4 cts. per sq. yd. for mixing and placing.
CHAPTER XV.
METHODS AND COST OF CONSTRUCTING SIDEWALKS, PAVEMENTS AND CURB AND
GUTTER.
Next to pavement foundations the most extensive use of concrete in
street work is for cement walks and concrete curb and gutter. Usually
the mixing and placing of the concrete is hand work, practically the
only exceptions being where pavement base, curbing and sidewalks are
built all at once, using machine mixers. The same objections that have
been raised to machine mixers in laying pavement foundation are raised
against them for curb and walk construction, and owing to the much
smaller yardage per lineal foot of street in walk and curb work these
objections carry more force than they do in case of paving work. Another
argument against the use of mixers is that both walk and curb and gutter
work involve the use of forms and the application of mortar finish, the
placing of which are really the limiting factors in the rate of progress
permissible, and this rate is too slow to consume an output necessary to
make a mixer plant economical as compared with hand mixing where so much
transportation is involved. Concrete sidewalk and curb work are
essentially hand mixing work; they, therefore, involve a careful study
of the economies of hand mixing and wheelbarrow haulage which are fully
discussed in Chapter II.
CEMENT SIDEWALKS.
Sidewalk construction consists in molding on a suitably prepared
sub-base a concrete slab from 3½ to 7½ ins. thick, depending on
practice, and finishing its top surface with a ½ to 1½-in. wearing
surface of cement mortar.
~GENERAL METHOD OF CONSTRUCTION.~--The excavation and preparation of the
sub-grade call for little notice beyond the warning that they should
never be neglected. The authors have seen many thousands of feet of
cement walk laid in the middle West in which the sub-base was placed
directly on the natural sod, often covered with grass and weeds a foot
high. Such practice is wholly vicious. The sod should always be removed
and the surface soil excavated to a depth depending upon the climate and
nature of the ground and the foundation bed well tamped. From 4 to 6
ins. depth of excavation will serve where the soil is reasonably hard
and there are no heavy frosts; with opposite conditions a 12-in.
excavation is none too deep. The thickness of the broken stone, gravel,
cinder or sand sub-base should likewise be varied with the character of
the soil, the conditions of natural drainage and the prevalence of
frost. In well drained sandy soils 6 to 8 ins. of sub-base are
sufficient, but in clayey soils with poor natural drainage the sub-base
should be from 10 to 12 ins. thick at least; the local conditions will
determine the thickness of sub-base necessary and in places it may be
desirable to provide by artificial drainage against the accumulation of
water under the concrete. Tile drains are better and cheaper than
excessively deep foundations. The thorough tamping of the sub-base is
essential to avoid settling and subsequent cracking of the concrete
slab. This is a part of sidewalk work which is often neglected.
Portland cement concrete, sand and broken stone or gravel mixtures in
the proportions of 1-3-5 and 1-3-6 are used for base slabs. For walks up
to 7 ft. wide the slab is made 3½ ins. thick for residence streets and
4½ to 5 ins. thick for business streets; for wider walks the thickness
is increased to 7 ins. for 8-ft. width and 7½ ins. for 9 to 10-ft.
width. Roughly the thickness of the walk in inches (base and top
together) is made about equal to its width in feet. The concrete is
deposited in a single layer and tamped thoroughly, either in separate
blocks behind suitable forms or in a continuous slab which is while
fresh cut through to make separate blocks. For walks up to 8 ft. wide
the slab is divided by transverse joints spaced about the width of the
walk apart, but for the wider walks the safety of this division depends
upon the thickness of the base; an 8-ft. walk with a 5-in. base can
safely be laid with joints 8 ft. apart, but if the slab is only 4 ins.
thick it had better be laid in 4×4-ft. squares. The mode of procedure in
base construction is as follows:
The sub-base being laid, side forms held by stakes are placed as shown
by Fig. 116, with the top edges of the boards exactly to the grade of
the top surface of the finished walk. The concrete is then deposited
between these side forms and tamped until it is brought up to the level
marked by the templet A. If the plan is to deposit the base in
sections transverse plates of 3/8 to ¼ in. steel are set across the walk
between the side boards at proper intervals and the concrete tamped
behind them; sometimes the concreting is done in alternate blocks. When
the steel plate is withdrawn an open joint is left for expansion and
contraction. Where the plan is to lay the base in one piece which is
afterwards cut into blocks, the cutting is done with a spade or cleaver.
[Illustration: Fig. 116.--Sketch Showing Method of Constructing Cement
Walks.]
[Illustration: Fig. 117.--"Jointer" for Cement Sidewalk Work.]
Portland cement mortar mixed 1 to 1½ to 1 to 2 is used for the wearing
surface, and is laid from ½ in. to 1½ ins. thick, depending upon the
width of the walk and the thickness of the base. As a rule the mortar is
mixed rather stiff; it is placed with trowels in one coat usually, but
sometimes in two coats, and less often by tamping. The mortar coat is
brought up flush with the top edges of the side forms by means of the
templet B, and the top finished by floating and troweling. The
wearing coat is next divided into sections corresponding with the
sections into which the base is divided, by cutting through it with a
trowel guided by a straight edge and then rounding the edges of the cut
with a special tool called a jointer and shown by Fig. 117. An edger,
Fig. 118, is then run around the outside edges of the block to round
them. The laying of the mortar surface must always follow closely the
laying of the base so that the two will set together.
[Illustration: Fig. 118.--"Edger" for Cement Sidewalk Work.]
~BONDING OF WEARING SURFACE AND BASE.~--Trouble in securing a perfect bond
between the wearing surface and the base usually comes from one or more
of the following causes: (1) Applying the surface after the base
concrete has set. While several means are available for bonding fresh to
old concrete as described in Chapter XXIV, the better practice is not to
resort to them except in case of necessity but to follow so close with
the surfacing that the base will not have had time to take initial set.
(2) Poor mixing and tamping of this base concrete. (3) Use of clayey
gravel or an accumulation of dirt on the surface. In tamping clayey
gravel the water flushes the clay to the surface and prevents the best
bond. (4) Poor troweling, that is failure to press and work the mortar
coat into the base concrete. Some contractors advocate tamping the
mortar coat to obviate this danger. Conversely, to make the surface coat
adhere firmly to the base it must be placed before the base concrete has
set; the base concrete must be thoroughly cleaned or kept clean from
surface dirt; the surface coat must be tamped or troweled forcibly into
the base concrete so as to press out all air and the film of water which
collects on top of the concrete base.
~PROTECTION OF WORK FROM SUN AND FROST.~--Sun and frost cause scaling and
hair cracks. For work in freezing weather the water, sand and gravel
should be heated or salt used to retard freezing until the walk can be
finished; it may then be protected from further action of the frost by
covering it first with paper and then with a mattress of sawdust,
shavings or sand and covering the whole with a tarpaulin. Methods of
heating concrete materials and rules for compounding salt solutions are
given in Chapter VII. The danger from sun arises from the too rapid
drying out of the surface coating; the task then is to hold the moisture
in the work until the mixture has completely hardened. Portable frames
composed of tarpaulin stretched over 2×4-in. strips may be laid over the
finished walk to protect it from the direct rays of the sun; these
frames can be readily removed to permit sprinkling. Practice varies in
the matter of sprinkling, but it is the safe practice in hot weather to
sprinkle frequently for several days. Moisture is absolutely necessary
to the perfect hardening of cement work and a surplus is always better
than a scarcity. In California the common practise is to cover the
cement walk, as soon as it has hardened, with earth which is left on for
several days.
~CAUSE AND PREVENTION OF CRACKS.~--Cracks in cement walks are of two
kinds, fractures caused by any one of several construction faults and
which reach through the surface coating or through both surface and
base, and hair cracks which are simply skin fractures. Large cracks are
the result of constructive faults and one of the most common of these is
poor foundation construction; other causes are poor mixing and tamping
of the base, too large blocks for thickness of the work, failure to cut
joints through work. Hair cracks are the result of flushing the neat
cement to the surface by excessive troweling or the use of too wet a
mixture. The prevention of cracks obviously lies in seeing that the
construction faults cited do not exist. If expansion joints are not
provided, a long stretch of cement walk will expand on a hot day and
bulge up at some point of weakness breaking the walk.
~COST OF CEMENT WALKS.~--The cost of cement walks is commonly estimated in
cents per square foot, including the necessary excavation and the cinder
or gravel foundation. The excavation usually costs about 13 cts. per
cu. yd., and if the earth is loaded into wagons the loading costs
another 10 cts. per cu. yd., wages being 15 cts. per hr. The cost of
carting depends upon the length of haul, and may be estimated from data
given in Chapter III. If the total cost of excavation is 27 cts. per cu.
yd., and if the excavation is 12 ins. deep, we have a cost of 1 ct. per
sq. ft. for excavation alone. Usually the excavation is not so deep, and
often the earth from the excavation can be sold for filling lots.
In estimating the quantity of cement required for walks, it is well to
remember that 100 sq. ft. of walk 1 in. thick require practically 0.3
cu. yd. concrete. If the concrete base is 3 ins. thick, we have 0.3 × 3,
or 0.9 cu. yd. per 100 sq. ft. of walk. And by using the tables in
Chapter II we can estimate the quantity of cement required for any given
mixture. In cement walk work the cement is commonly measured loose, so
that a barrel can be assumed to hold 4.5 cu. ft. of cement. If the
barrel is assumed to hold 4.5 cu. ft., it will take less than 1 bbl. of
cement to make 1 cu. yd. of 1-3-6 concrete; hence it will not require
more than 0.9 bbl. cement, 0.9 cu. yd. stone, and 0.45 cu. yd. sand per
100 sq. ft. of 3-in. concrete base. The 1-in. wearing coat made of 1-1½
mortar requires about 3 bbls. of cement per cu. yd., if the barrel is
assumed to hold 4.5 cu. ft., and since it takes 0.3 cu. yd. per 100 sq.
ft., 1 in. thick, we have 0.3 × 3, or 0.9 bbl. cement per 100 sq. ft.
for the top coat. This makes a total of 1.8 bbls. per 100 sq. ft., or 1
bbl. makes 55 sq. ft. of 4-in. walk.
As the average of a number of small jobs, the authors' records show the
following costs per sq. ft. of 4-in. walk such as just described:
Cts. per sq. ft.
Excavating 8 ins. deep 0.65
Gravel for 4-in. foundation, at $1.00 per cu. yd. 1.20
0.018 bbl. cement, at $2.00 3.60
0.009 cu. yd. broken stone, at $1.50 1.35
0.006 cu. yd. sand, at $1.00 0.60
Labor making walk 1.60
----
Total cents 9.00
This is 9 cts. per sq. ft. of finished walk. The gangs that built the
walk were usually two masons at $2.50 each per 10-hr. day with two
laborers at $1.50 each. Such a gang averaged 500 sq. ft. of walk per
day.
~Cost at Toronto, Ont.~--Mr. C. H. Rust, City Engineer, Toronto, Ont.,
gives the following costs of constructing concrete sidewalks by day
labor. The sidewalks have a 4-in. foundation of coarse gravel or soft
coal cinders, thoroughly consolidated by tamping or rolling, upon which
is placed a 3½-in. layer of concrete composed of 1 part Portland cement,
2 parts clean, sharp, coarse sand, and 5 parts of approved furnace slag,
broken stone or screened gravel. The wearing surface is 1 in. thick, or
1 part Portland cement, 1 part clean, sharp, coarse sand, and 3 parts
screened pea gravel, crushed granite, quartzite or hard limestone. Costs
are given of a 6-ft. and a 4-ft. walk as follows:
COST OF 6 FT. SIDEWALK.
Per 100
Item. sq. ft.
Labor $ 5.59
Cement, 1.66 bbls., at $1.54 2.49
Gravel, 2.7 cu. yds., at $0.80 2.21
Sand, 0.46 cu. yd., at $0.80 0.37
Water 0.05
----
Total $10.71
COST OF 4 FT. SIDEWALK.
Per 100
Item. sq. ft.
Labor $ 6.73
Cement, 2.04 bbls., at $1.54 3.15
Gravel, 2.06 cu. yds., at $0.80 1.65
Sand, 0.49 cu. yd., at $0.80 0.39
Water 0.07
----
Total $11.99
The rates of wages and the number of men employed were as follows: 1
foreman, at $3.50 per day; 1 finisher, at 30 cts. per hour; 1 helper, at
22 cts. per hour; 15 laborers, at 20 cts. per hour.
~Cost at Quincy, Mass.~--The following costs are given by Mr. C. M.
Saville for constructing 695 sq. yds. of granolithic walk around the top
of the Forbes Hill Reservoir embankment at Quincy, Mass. This walk was
laid on a broken stone foundation 12 ins. thick; the concrete base was 4
ins. thick at the sides and 5 ins. thick at the center; the granolithic
finish was 1 in. thick. The walk was 6 ft. wide and was laid in 6-ft.
sections, a steel plate being used to keep adjacent sections entirely
separate. The average gang was 6 men and a team on the base and 2 masons
and 1 tender on the finish. The average length of walk finished per day
was 60 ft. The cost was as follows:
Stone Foundation: Per cu. yd. Per sq. ft.
Broken stone for 12-in. foundation $ 0.40 $0.015
Labor placing at 15 cts. per hour 1.50 0.056
----- ------
Totals $ 1.90 $0.071
Concrete Base 4½ ins. Thick:
1.22 bbls. cement per cu. yd. at $1.53 $ 1.87 $0.026
0.50 cu. yd. sand per cu. yd. at $1.02 0.51 0.007
0.84 cu. yd. stone per cu. yd. at $1.57 1.32 0.019
Labor (6 laborers, 1 team) 3.48 0.050
---- -----
Total for 90 cu. yds. $ 7.18 $0.102
Granolithic Finish 1 in. Thick:
4 bbls. cement per cu. yd. at $1.53 $ 6.12 $0.019
0.8 cu. yd. sand at $1 0.80 0.002
Lampblack 0.29 0.001
Labor (2 masons, 1 helper) 6.36 0.016
---- -----
Totals $13.57 $0.038
The two masons received $2.25 per day each and their helper $1.50 per
day, and they averaged 360 sq. ft. per day, which made the cost 1-2/3
cts. per sq. ft. for labor laying granolithic finish. The cost of
placing the foundation stone is very high and the cost of concrete base
also runs unusually high, the reasons for these high costs are not
evident.
~Cost at San Francisco.~--Mr. George P. Wetmore, of the contracting firm
of Cushing & Wetmore, San Francisco, gives the following figures
relating to sidewalk work in that city. The foundations of cement walks
in the residence district of San Francisco are 2½ ins. thick, made of
1-2-6 concrete, the stone not exceeding 1 in. in size. The wearing coat
is ½ in. thick, made of 1 part cement to 1 part screened beach gravel.
The cement is measured loose, 4.7 cu. ft. per barrel. The foundation is
usually laid in sections 10 ft. long; the width of sidewalks is usually
15 ft. The top coat is placed immediately, leveled with a straight edge
and gone over with trowels till fairly smooth. After the initial set and
first troweling, it is left until quite stiff, when it is troweled again
and polished--a process called "hard finishing." The hard finish makes
the surface less slippery. The surface is then covered with sand, and
watered each day for 8 or 10 days. The contract price is 9 to 10 cts.
per sq. ft. for a 3-in. walk; 12 to 14 cts. for a 4-in. walk having a
wearing coat ¾ to 1-in. thick. A gang of 3 or 4 men averages 150 to 175
sq. ft. per man per day of 9 hrs. Prices and wages are as follows:
Cement, per bbl. $2.50
Crushed rock, per cu. yd. 1.75
Gravel and sand for foundation, per cu. yd. 1.40
Gravel for top finish, per cu. yd. 1.75
Finisher wages, best, per hr. 0.40
Finisher helper, best, per hr. 0.25
Laborer, best, per hr. 0.20
~Cost in Iowa.~--Mr. L. L. Bingham sent out letters to a large number of
sidewalk contractors in Iowa asking for data of cost. The following was
the average cost per square foot as given in the replies:
Cts. per sq. ft.
Cement, at $2 per bbl. 3.6
Sand and gravel 1.5
Labor, at $2.30 per day (average) 2.2
Incidentals, estimated 0.7
---
Total per sq. ft 8.0
This applies to a walk 4 ins. thick, and includes grading in some cases,
while in other cases it does not. Mr. Bingham writes that in this
respect the replies were unsatisfactory. He also says that the average
wages paid were $2.30 per man per day. It will be noted that a barrel of
cement makes 55½ sq. ft. of walk, or it takes 1.8 bbls. per 100 sq. ft.
The average contract price for a 4-in. walk was 11½ cts. per sq. ft.
CONCRETE PAVEMENT.
Concrete pavement is constructed in all essential respects like cement
sidewalk. The sub-soil is crowned and rolled hard, then drains are
placed under the curbs; if necessary to secure good drainage a sub-base
of gravel, cinders or broken stone 4 to 8 ins. thick is laid and
compacted by rolling. The foundation being thus prepared a base of
concrete 4 to 5 ins. thick is laid and on this a wearing surface 2 to 3
ins. thick. As showing specific practice we give the construction in two
cities which have used concrete pavement extensively.
~Windsor, Ontario.~--The street is first excavated to the proper grade and
crown and rolled with a 15-ton roller. Tile drains are then placed
directly under the curb line and a 6×16-in. curb is constructed, vising
1-2-4 concrete faced with 1-2 mortar. Including the 3-in. tile drain
this curb costs the city by contract 38 cts. per lin. ft. The pavement
is then constructed between finished curbs, as shown by Fig. 119.
[Illustration: Fig. 119.--Concrete Pavement. Windsor, Canada.]
The fine profile of the sub-grade is obtained by stretching strings from
curb to curb, measuring down the required depth and trimming off the
excess material. The concrete base is then laid 4 ins. thick. A 1-3-7
Portland cement concrete is used, the broken stone ranging from ¼ in. to
3 ins. in size, and it is well tamped. This concrete is mixed by hand
and as each batch is placed the wearing surface is put on and finished.
The two layers are placed within 10 minutes of each other, the purpose
being to secure a monolithic or one-piece slab. The top layer consists
of 2 ins. of 1-2-4 Portland cement and screened gravel, ¼ in. to 1 in.,
concrete. This layer is put on rather wet, floated with a wooden float
and troweled with a steel trowel while still wet. Some 20,500 sq. yds.
of this construction have been used and cost the city by contract:
Per sq. yd.
Bottom 4-in. layer 1-3-7 concrete $0.57
Top 2-in. layer 1-2-4 concrete 0.32
Excavation 0.10
-----
Total $0.99
This construction was varied on other streets for the purpose of
experiment. In one case a 4-in. base of 1-3-7 stone concrete was covered
with 2 ins. of 1-2-2 gravel concrete. In other cases the construction
was: 4-in. base of 1-3-7 stone concrete; 1½-in. middle layer of 1-2-4
gravel concrete, and ½-in. top layer of 1-2 sand mortar. All these
constructions have been satisfactory; the pavement is not slippery. The
cost to the city by contract for the three-layer construction has in two
cases been as follows:
Church St., 8,000 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.57
1½-in. 1-2-4 and ½-in 1-2 mixture 0.32
Excavation 0.10
-----
Total $0.99
Albert and Wyandotte Sts., 400 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.66
1½-in. 1-2-4 and ½-in. 1-2 mixture 0.39
Excavation 0.10
-----
Total $1.15
The cost of materials and rates of wages were about as follows:
Portland cement f. o. b. cars Windsor, per bbl. $2.05
River sand, per cu. yd. 1.15
River gravel, screened, per cu. yd. 1.25
Crushed limestone, ¼ to 3 ins., per ton 1.15
Labor, per day 1.75 to 2.00
At these prevailing prices the contractor got a fair profit at the
contract price of $1.15; at 99 cts., any profit is questionable,
according to City Engineer George S. Hanes, who gives us the above
records. Expansion joints are located from 20 to 80 ft. apart and are
filled with tar.
~Richmond, Ind.~--The first concrete pavement was built in 1896 and since
then it has been used extensively, especially for wide alleys and narrow
streets where traffic is heavy and concentrated in small space. The
method of construction has varied from time to time but the construction
shown by Fig. 120 is fairly representative. Usually a 1-3-5 concrete is
used for the base, 5 ins. thick, and a 1-2 mortar for the top coat, 1½
ins. thick. In 1904 this pavement cost the city by contract 16 cts. per
sq. ft. or $1.54 per sq. yd, with wages and prices as follows: Stone on
the work, $1.25 per cu. yd.; gravel and sand, $0.75 per cu. yd.; cement,
$2.25 per barrel; common laborers, 16½ cts. per hour, and cement
finishers, 40 cts. per hour.
[Illustration: Fig. 120.--Concrete Pavement, Richmond, Ind.]
~CONCRETE CURB AND GUTTER.~
Current practice varies materially in constructing concrete curb and
gutter. The more common practice is to lay the curb and water table in
one piece, or as a monolith, but this is by no means universal practice.
In much work the curb wall and the water table slab are constructed
separately, the construction joint being sometimes horizontal where the
curb wall sits on the slab and sometimes vertical where the water table
butts against the wall. Again it is the common practice to construct
curb and gutter in sections, laid either alternately or in succession,
separated by sand joints to provide for expansion and contraction, but
this is not universal practice, much of such work being constructed as a
continuous wall with no provision for temperature movements except the
natural breaks at driveways. All of these types of construction appear
to have given reasonable satisfaction, but exact data for a final
comparison are not available, so that we are forced to reason on general
principles. Such a course of reasoning indicates that the best results
should be expected where the curb and water table are built in one
piece and in sections of reasonable length separated by expansion
joints.
[Illustration: Fig. 121.--Box Form for Concrete Curb.]
[Illustration: Fig. 122.--Continuous Form for Concrete Curb.]
~FORM CONSTRUCTION.~--The form construction for curb and gutter work is
determined by the general plan of construction followed,--whether
monolithic or two-piece construction. In monolithic construction two
types of forms are employed, sectional or box forms and continuous
forms. A good example of box form is shown by Fig. 121. This form was
designed for a curb 14 ins. high at the back, 6 ins. high in front and
24 ins. from face of curb to outer edge of gutter, constructed in
sections 7 ft. long. The form, it will be observed, is a complete box,
in which alternate sections of curb are molded and after having set are
filled between using the same form but dispensing with the end boards
which are replaced by the completed sections of curb. A fairly
representative example of continuous form is shown by Fig. 122; in this
construction a continuous line of plank is set to form the back of the
curb and another line to form the face of the gutter slab, both lines
being held in place by stakes. When the gutter slab concrete has been
placed and surfaced the form for the front of the curb is set as shown
and the upper portion of the curb wall concreted behind it. The method
in detail of constructing curb and gutter, with this type of form, at
Ottawa, Ont., is described in a succeeding section. Here the joints
were formed by inserting a partition of 3/8-in. boiler plate every 12
ft., which was withdrawn just previous to finishing up the surface; the
sections between partitions were concreted continuously. Another method
is to make the partitions of plank, concrete every other section, then
remove the partition plank and concrete the remaining spaces against the
previously finished work. A different method of supporting the plank
forming the face of the curb wall, is to clamp it to the back form (Fig.
123), spacers being inserted to keep the two their proper distances
apart. The forms shown by Figs. 121 to 123 are for monolithic curb and
gutter. In two-piece construction where the curb wall is constructed on
the finished gutter slab practically the same method of construction is
employed as is illustrated by Fig. 122 except that no attempt is made to
concrete the curb wall before the slab concrete has begun to set. The
more common and the preferable method of two-piece construction is
illustrated by Fig. 124; the curb proper is built first using the simple
box form shown at the right hand, then the water table is built using
the completed curb as the form for the back and a board held by stakes
as a form for the front. This board is set with its top edge exactly to
the grade of the finished water table so as to serve as a guide for one
end of the template, the other end of which rides on the top of the
finished curb wall. Forms for curves at street intersections are best
constructed by driving stakes to the exact arc of the curve and bending
a 3/8-in. steel plate around them or bending and nailing 7/8×1¼-in.
strips. Soaking the wood strips thoroughly will make them bend easily.
The cost of form work in constructing curb and gutter is chiefly labor
cost in erecting and taking down the forms.
[Illustration: Fig. 123.--Continuous Form for Concrete Curb.]
[Illustration: Fig. 124.--Form for Two-Piece Curb Construction.]
~CONCRETE MIXTURES AND CONCRETING.~--The curb body is usually made of a
1-3-5 or 6 concrete and the curb finish of a 1-2 mortar. Portland cement
is employed almost exclusively. The concrete mixture commonly used is of
such consistency that thorough ramming is necessary to flush the cement
to the surface. The cubical contents of combined curb and gutter of the
forms illustrated will run from 3 to 5 cu. yds. per 100 ft., and about
one-eighth of this will be facing mortar 1 in. thick; thus a curb
running 5 cu. yds. per 100 ft. will contain per 100 ft. about 0.83 cu.
yd. of mortar and 4.17 cu. yds. of concrete. The usual method of
concreting is to erect the forms for the back of the curb wall and the
front of the gutter slab and concrete to the height of the water table
clear across; then shape the exposed top of the water table to section
and place the mortar finish, and then erect the face form for the gutter
wall, bring the concrete backing and vertical face finish up together
and, finally, finish the top. The finish coat is placed by troweling on
the horizontal surfaces; on the vertical face of the curb wall it may be
placed in any one of several ways. Frequently the mortar coat is simply
plastered against the face board and filled behind with concrete.
Another method is to lay a 1-in. board against the inside of the form,
concrete behind it, then withdraw the board, fill the space with mortar
and tamp concrete and mortar to a thorough bond. The special face forms
shown in Chapter VIII may be used in place of the board. The securing of
a good bond between the backing concrete and the mortar facing is
governed by the same conditions that govern sidewalk work.
~COST OF CURB AND GUTTER.~--The cost of concrete curb and gutter is
commonly estimated in cents per lineal foot. The cost of excavating,
loading and carting will run about the same per cubic yard as for
sidewalks. Excavating the trench and preparing the sub-grade usually
runs from ½ ct. to 2 cts. per foot of curb, but sometimes it amounts to
3 cts. Placing the sub-base will cost for placing and tamping 1 ct. per
ft., to which is to be added the cost of materials; a 6-in. sub-base 30
ins. wide contains 4.7 cu. yds., tamped measure, of materials per 100
ft. The amount of materials per foot depends upon the cross-section of
the curb; it equals in cubic yards the area of cross-section in square
feet divided by 27, and of this volume about one-eighth will be 1-2
mortar and seven-eighths 1-3-6 concrete. The tables in Chapter II give
the amounts of materials per cubic yard of these mixtures; the product
of these quantities and the cost of the materials on the ground gives
the cost. The labor cost of mixing and placing, including the form work,
will run from 10 to 14 cts. per foot. In round figures curb and gutter
of the section shown in the accompanying illustrations may be estimated
to cost in the neighborhood of 40 cts. per lineal foot. The following
sections give records of cost of individual jobs of curb and gutter
construction.
~Cost at Ottawa, Canada.~--The method and cost of constructing 1,326 ft.
of concrete curb and gutter at Ottawa, Ont., are given in some detail by
Mr. G. H. Richardson, Assistant City Engineer, in the annual report of
the City Engineer for 1905. We have remodeled the description and
rearranged the figures of cost in the following paragraphs.
The concrete curb was built before doing any work on the roadway, and
the first task was the excavation of a trench 2½ ft. wide and averaging
1 ft. 8 ins. in depth through light red sand. On the bottom of this
trench there was placed a foundation of stone spalls 8 ins. thick; in
width this foundation reached from 3 ins. back of the curb to 6 ins.
beyond the front of the water table. The curb was made 5 ins. thick and
ran from 10 ins. to 5½ ins. in height, and the water table was 14 ins.
wide and 4 ins. thick, with a fall of 1¼ ins. from front to back. The
concrete used was a mixture of 1 Portland cement, 3 sand, 3 5/8-in.
screened limestone, and 4 2-in. stone. It was deposited in forms and
tamped to bring the water to the face and then smoothed with a light
troweling of stiff mortar.
The forms were constructed by first setting pickets and nailing to them
a back board 2 ins. thick and 12 ins. wide and a front board 2 ins.
thick and 6 ins. wide. The concrete for the water table was deposited in
this form in sections and brought to surface by straight edge riding on
wooden strips nailed across the form and properly set to slope, etc.
After the water table had been troweled down and brushed a 1×10-in.
board was set to mold the front face of the curb. This board was
sustained by small "knee frames" made of three pieces of 1×2-in. stuff,
one conforming to the slope of the water table and long enough to extend
beyond the front of the 2×6-in. front board, a second standing plumb and
bearing against the 1×10-in. face board, and the third forming a small
corner brace between the two former to hold them in their proper
relative positions. The 1×10-in. face board, etc., was separated from
the 2×12-in. back board by a 5-in. block at each end, and then braced by
the knee frames every 3 or 4 ft. In this way it was possible to bring
this 1×10-in. board into perfect line by moving the knee braces in or
out, and when correct nailing them to the 2×6-in. front board. The
1×10-in. face board being in position and braced and lined, the curb
material was thoroughly tamped in, and when ready was troweled and
brushed on the top, a small round being worked onto the top front corner
with the trowel.
Expansion joints were provided for by building into the curb every 12
ft., a piece of 3/8-in. boiler plate, which was afterward withdrawn and
the joint filled with sand and faced over. As soon as the concrete had
set sufficiently the face board was taken down and face of curb finished
and brushed, the fillet between curb and water table being finished to
2½ ins. radius. Circular curb and gutter of same construction was built
at each corner, ½-in. basswood being used for forms, instead of 2×1-in.
lumber.
In addition to the actual construction of curb and gutter the cost given
below includes the cleaning up of the street, spreading or removal of
all surplus material from excavation, and the extension of all sidewalks
out to the curbs at the corners. It was also necessary to maintain a
watchman on this work, which duty, under ordinary circumstances, would
be done by the general watchman. The total length built was 1,326 ft.,
of which 1,209 ft. is straight and 117 ft. curved to a 12-ft. radius.
The rates of wages paid were $2 for horse and cart, $1.65 for watchman,
and an average of $1.90 per day for labor, including foreman; all for
nine hours' work per day. The working force consisted of foreman,
finisher, handy man. four concrete men, and three laborers.
The labor cost of the work was as follows:
Per ft. P. C. of
Item. Total. cts. total.
Excavation and setting boards $ 88.90 6.7 30
Laying stone foundation 43.30 3.3 14
Concreting 61.30 4.6 20
Finishing 45.15 3.4 15
Carting 9.85 0.76 3
Watchman 25.00 1.89 8
Clearing up 13.60 1.04 4
Extras (sidewalk extensions) 17.23 1.31 6
------- ----- --
Total $304.33 23.00 100
The cost of materials for curb and foundation were as follows:
Per lin. ft.
Total. cts.
171.112 tons spalls $102.93 7.76
42 tons 2-in. stone 41.16 3.09
30.8 tons 5/8-in. stone 42.57 3.21
33,000 lbs. cement 161.70 12.19
24 cu. yds. sand 19.20 1.45
------- -----
Total $367.56 27.70
The cost of supplies and tools was as follows:
1,000 ft. B. M. 2×12 boards charged off $ 9.25
500 ft. B. M. 2×6 boards charged off 4.12
1,000 ft. B. M. 1×10 boards charged off 14.25
½-in. basswood 4.30
½ keg 3-in. nails 1.42
½ keg 4-in. nails 1.43
Pickets 3.25
Tools charged off 3.15
------
Total $41.17
This total, when divided by 1,326 lin. ft. of curb, gives the cost per
lineal foot as about 3 cts. We can now summarize as follows:
Per lin. P. C. of
Item. Total. ft. total.
Labor $304.33 23 43
Material 367.56 28 51
Supplies 41.17 3 6
------- ---- ---
Total $713.06 $0.54 100
As indicated above, on more extensive work the costs of carting,
watchman, cleaning up, and extras would be avoided. They cost on this
work 5 cts. and the work could therefore be done for 49 cts. if no such
charges were included. On such work also the charge for supplies would
be lower per foot and on any future work the labor cost could be
materially lowered, this curb having been somewhat of an experiment as
to method of construction. It is thought that with no charges for
carting, cleaning, watchman, and extras, and with the experience
obtained, this curb could be built for about 46 cts. The proportions
adopted and the method of construction followed, produce a very strong,
dense, homogeneous curb and gutter.
[Illustration: Fig. 125.--Concrete Curb and Gutter at Champaign, Ill.]
~Cost at Champaign, Ill.~--The following costs were recorded by Mr.
Charles Apple, and relate to work done at Champaign, Ill., in 1903. The
work was done by contract, at 45 cts. per lin. ft. of the curb and
gutter shown in Fig. 125.
The concrete curb and gutter was built in a trench as shown in the cut.
The earth was removed from this trench with pick and shovel at a rate of
1 cu. yd. per man per hour. The concrete work was built in alternate
sections, 7 ft. in length. A continuous line of planks was set on edge
to form the front and back of the concrete curb and gutter; and wood
partitions staked into place, were used. The cost of the work was as
follows:
No. of Total Cost per
Item. men. wages. 100 ft.
Opening trench, 18×30-in. 2 $3.50 $2.43
Placing and tamping cinders 2 3.50 1.00
Setting forms:
Boss setter 1 3.00 ...
Assistant setter 1 2.00 ...
Laborer 1 1.75 ...
-- ----- -----
3 $6.75 $1.69
Mixing and placing concrete:
Clamp man 1 $1.75 ...
Wheelers 3 5.25 ...
Mixing concrete 4 7.00 ...
Mixing finishing coat 2 3.50 ...
Tampers 1 1.75 ...
Finishing:
Foreman and boss finisher 1 4.00 ...
Assistant finisher 1 3.00 ...
Water boy 1 .50 ...
-- ------ -----
Total making concrete 14 $26.75 $7.64
Total for labor per 100 ft $12.76
Materials for 100 lin. ft.: Quantity. Price.
Portland cement 8-1/3 bbls. $1.85 $15.42
Cinders 7.5 yds. .50 3.75
Gravel 2.5 yds. 1.00 2.50
Broken stone 2.5 yds. 1.40 3.50
Sand 1.0 1.00 1.00
Total for material per 100 ft $26.17
Total for material and labor per 100 ft. $38.93
This is the total cost, exclusive of lumber, tools, interest, profits,
etc., and it is practically 40 cts. per lin. ft.
In 100 lin. ft. of curb and gutter there were 4.6 cu. yds. of concrete
and mortar facing, 4 cu. yds. of which were concrete; hence the 9 men in
the concrete gang laid 14 cu. yds. of concrete per day, whereas the 4
men mixing and placing the mortar finishing laid only 2½ cu. yds. of
mortar per day, assuming that the mortar finishing averaged just 1 in.
thick. Since these 4 men (2 mixers and 2 finishers) received $10.50 a
day, it cost more than $4 per cu. yd. to mix and place the 1-2 mortar,
as compared with $1.41 per cu. yd. for mixing and placing the concrete.
The concrete was built in alternate sections 7 ft. long. The 3 men
placing forms averaged 400 lin. ft. a day, so that the cost of placing
the forms was $1 per cu. yd. of concrete. The 2 men placing and tamping
cinders averaged 16 cu. yds. of cinders per day, or 8 cu. yds. per man.
This curb and gutter was built by contract at 45 cts. per lin. ft.
For several jobs, in which a curb and gutter essentially the same as
shown in Fig. 125 was built, our records show a general correspondence
with the above given data of Mr. Apple. Our work was done with smaller
gangs, 1 mason and 2 laborers being the ordinary gang. Such a gang would
lay 80 to 100 lin. ft. of curb and gutter per 10-hr. day, at the
following cost:
1 mason at $2.50 $2.50
2 laborers at $1.50 3.00
-----
Total $5.50
This made a cost of 5½ to 7 cts. per lin. ft. for labor, and it did not
include the cost of digging a trench to receive the curb and gutter.
CHAPTER XVI.
METHODS AND COST OF LINING TUNNELS AND SUBWAYS.
[Illustration: Fig. 126.--Section Showing Lining for Capitol Hill
Tunnel. Washington, D. C.]
Tunnel lining work is of two distinct classes: Lining work, done during
original construction and relining of tunnels in service. The methods of
work to be adopted and the cost of work will be different in the two
cases. In relining work the costs are increased by the necessity of
providing for the movement of trains and by the delays due to these
movements and also by the labor of removing the old lining and, often,
of enlarging the excavation. Comparatively few published figures are
available on the cost of concrete tunnel lining, and such as exist are
commonly incomplete. The common practice is to record the cost as so
much per lineal foot of tunnel. This should be done, but the record
should also show the cost per cubic yard of concrete in the lining. The
notions of engineers vary as to the proper thickness of lining to use
and this dimension also varies with the character of the ground. One
tunnel lining may easily contain twice as many cubic yards of concrete
per lineal foot of lining as another tunnel contains.
The two problems in form construction for tunnel work are: First, to
construct the form work so that it does not interfere with train
movements, and, second, to construct it so that it can be taken down,
transported and re-erected and thus used over and over. The examples of
practice given in the succeeding sections are the best instructions that
can be laid before the reader in regard to possible ways of solving
these problems and, also, the problem of handling the concrete and other
materials to the work.
[Illustration: Fig. 127.--Traveling Derrick for Constructing Side and
Center Walls, Capitol Hill Tunnel.]
[Illustration: Fig. 128.--Steel Forms for Side Walls for Capitol Hill
Tunnel.]
~METHOD OF LINING CAPITOL HILL TUNNEL, PENNSYLVANIA R. R., WASHINGTON, D.
C.~--The tunnel through Capitol Hill for the Pennsylvania R. R. approach
to its new Union Station at Washington, D. C, is a two-track, double
tube tunnel 4,000 ft. long through earth. Figure 126 shows the lining
construction; it consists of stone masonry center wall, mass concrete
inverts and side walls and a brick roof arch backed with concrete. For
building the center and side walls the traveling derrick shown by Fig.
127 was employed. This traveler moved ahead with the work on a 14-ft.
gage track and it handled the stone and concrete buckets from the
material cars to the workmen on the walls. In connection with the
derrick in the concrete side wall construction use was made of steel
plate forms for the inside faces of the walls. These forms were made of
4×10 ft. sections of steel plate, constructed as shown by Fig. 128, and
connected together by bolting through the flanges. The steel forms were
erected by hand in advance of the derrick, 20 ft. of form on each side
at a time. The concrete buckets were brought into the tunnel on cars
hauled by electric motors from the mixing plant at the portal, and the
buckets were lifted by the derricks and emptied into the forms. The side
walls were concreted to the springing line and then the five-ring brick
roof arches were constructed on traveling centers and in 20-ft.
sections. The remainder of the concrete was then placed over the arches
by means of the special back-filling machine, shown by Fig. 129. This
machine also handled the earth used to fill behind the masonry. It
consisted of a platform mounted on wheels and of the same general
construction as the derrick platform. On the forward end of this
platform a stationary hoist was mounted and behind this a belt conveyor
platform.
[Illustration: Fig. 129.--Device for Placing Concrete Back Filling for
Roof Arch, Capitol Hill Tunnel.]
The latter structure was pivoted near the forward end so that it could
swing right and left on a circular track under its rear end. It carried
a 30-cu. ft. hopper on its forward end, from under which a belt conveyor
ascended an incline toward the rear and was carried back into the space
behind the roof arch on a cantilever arm. In operating the back-filling
machine the material bucket was lifted from the car below, carried back
on the trolley beam until over the hopper and then dumped by hand into
the hopper. From the hopper the material dropped onto the conveyor belt
and was carried back over the arch and dumped in place ready for
tamping. The trolley beam of the hoist was so arranged that the hoisting
movement was vertical until the bucket hit the trolley and was then up
and backward until the stop at the end of the trolley beam was reached.
This point was directly over the hopper. Hoisting was done by a Lambert
engine, driven by a 15 H.P. electric motor. The conveyor belt was 20
ins. wide and was operated at a speed of 180 ft. per minute by a 7½ H.P.
electric motor. The machine required two men to operate and was
considered to save the labor of twelve shovelers.
~METHOD OF CONSTRUCTING SIDE WALLS IN RELINING THE MULLAN TUNNEL.~--The
Mullan Tunnel, 3,850 ft. long, on the Northern Pacific Ry., about 20
miles west of Helena, Mont., had its original timber lining replaced in
1894 with a lining consisting of concrete side walls and a brick roof
arch. The construction of the old and new linings is shown by Fig. 130.
The method of constructing the side walls was as follows:
The original timbering consisted of sets of 12×12-in. posts carrying
five segment arches of 12×12-in. timbers joined by ½-in. dowels. For a
portion of the lining the posts carried plates on which the arches set;
elsewhere the arches rested directly on the post tops. The arches and
posts carried 4-in. lagging filled behind with cordwood. The timber
lining was removed to make place for the new work in the manner shown by
Fig. 130. When there were no plates a 7-ft. section AB was first
prepared by removing one post and supporting the undermined arch ribs by
struts SS. The timbering in this section was cut out and excavation
made for the wall footing. Two temporary posts FF were then set up,
fastened by hook bolts L and lagged behind to make the wall form.
Several of these 7-ft. sections were cut out at once, each two being
separated by a 5-ft. section of timbering. The mortar car shown in Fig.
130 was then run alongside the sections in order and enough 1-3 mortar
was run by chute into each to make an 8-in. layer. As the car moved
ahead to succeeding sections enough broken stone was shoveled into the
last preceding section to take up the mortar. The walls were thus built
in 8-in. layers and became hard enough to support the arches in from 10
to 14 days. The arches were then allowed to take footing on the wall,
and the posts of the remaining 5-ft. sections were removed and the
concrete wall built up as for the 7-ft. sections. Where the posts
carried wall plates the struts SS were not needed, the wall plate
supporting the undermined post as a beam. English Portland cement was
used and the concrete mixture was about 4 parts mortar to 5 parts broken
stone--a very rich mixture. The average progress was about 30 ft., or 45
cu. yds. of side wall per working day; the average cost of the walls,
including everything, was $8 per cu. yd. of concrete. The brick arch
cost $17 per cu. yd. Mr. H. C. Relf is authority for these figures.
[Illustration: Fig. 130.--Sketches Showing Method of Lining Mullan
Tunnel.]
~METHOD AND COST OF LINING A SHORT TUNNEL, PEEKSKILL, N. Y.~--The
following methods and costs of lining a double track railway tunnel 275
ft. long near Peekskill, N.Y., are given by Mr. Geo. W. Lee. In
presenting these data it is important to note that while some of the
methods described are applicable to so short a tunnel they could not be
used on a long tunnel. Figure 131 is a cross-section of the tunnel
showing the lining. The tunnel was through rock, which stood up without
timbering, and the rock section was excavated from 6 ins. to 3 ft.
outside the lining. A 1-2-4 concrete using crusher run stone below 1 in.
in size was used for the lining and portal head wall coping and a 1-3-6
concrete for the portal head walls proper. The cost of the portal head
walls is included in the costs given further on.
[Illustration: Fig. 131.--Cross-Section of Peekskill Tunnel, Showing
Lining.]
The side wall foundation trenches were first excavated from 1 to 3 ft.
deep and footing concreted and leveled up, the back of the footing being
carried up against the rock and the front lined to forms giving a 12-in.
offset to the side wall. The footings contained 200 cu. yds. of
concrete. Platforms 25 ft. square and level with the springing lines
were then erected at each end of the tunnel. A derrick was placed at
each platform to handle skips between it and the material tracks which
ran underneath and through the tunnel with a turnout at each end for
switching back empty cars. A 60 H.P. portable boiler supplied steam for
the derrick engines and a pump. The wall forms were built and erected in
panels 12 ft. long; these panels had 4×6-in. plates and sills, 4×4-in.
studs 3 ft. on centers and 2-in. dressed and matched spruce sheeting.
Four panels were set up, two on each side, midway of the tunnel and
braced to the tunnel track. Wheelbarrow runways carried on bents were
built from the platforms to the forms, one from one platform to one
side, another from the other platform to the opposite side. Temporary
bulkheads were erected to close the ends of the forms and they were
filled. Meanwhile carpenters were setting other panels at each end of
the two first erected on each side. After 24 hours the panels first set
were taken down and moved ahead and the processes described continued
until the full length of side wall was completed. The side walls were
not concreted back to the rock; back forms of 1-in. hemlock were used
and the space remaining was filled with spalls. The side walls contained
692 cu. yds. of concrete.
Arch forms were erected for 96 ft. at the center of the tunnel, using
12-ft. lagging, so that sections of this length could be taken down and
moved ahead, nine at each end. The lagging was first laid to a height of
3 ft. above the springing line on each side and the concrete dumped
directly in place from runways laid on the lower chords of the arch
ribs, which were placed 4 ft. apart. When the concrete reached a height
too great for direct discharge into the forms it was dumped on the
runway and passed over with shovels. On the upper portion of the ring
the concrete was first shoveled to a platform erected on the center
posts of the ribs about 2 ft. below the crown and then passed in on the
lagging which was laid in 4-ft. instead of 12-ft. lengths at this stage
of the work. As soon as each section of arch ring was completed it was
waterproofed with six layers of tar paper laid in hot tar and then
packed behind with spalls. The arch centers were struck in a
comparatively short time; in one instance they were struck 90 hours
after the last concrete was placed and no settlement was apparent. The
arch forms stuck so fast to the concrete, however, that they had to be
jacked down by chiseling out the lagging so as to get a bearing on the
arch concrete and by nailing thrust blocks to the rib posts. The section
was then hauled ahead by passing the main fall of the derrick through a
snatch block on the first rib. When hauled clear of the lining all but
the first 3-ft. of lagging on each side was removed; they were then
jacked into position. The arch ring contained 932 cu. yds. of concrete.
Including the portal head walls 1,948 cu. yds. of concrete were laid at
the following costs for labor and materials:
Item. Total. Per cu. yd.
Cement at $1.63 per bbl. $ 5,755.50 $2.951
Sand at $0.75 per cu. yd. 662.94 0.339
Stone at $0.80 per cu. yd. 1,303.20 0.668
Lumber--
Mixing platforms and runways 336.89 0.174
Ribs, including hand sawing 234.10 0.120
Backing boards 134.44 0.069
Lagging 341.04 0.176
Sheathing 268.49 0.137
Plates, sills, studs, braces 182.75 0.093
Coal 118.73 0.061
Oil 16.12 0.008
Hardware, nails, spikes, etc. 224.39 0.118
Tools 181.10 0.093
Freight on stone, cement, etc. 3,089.86 1.584
Labor of all kinds 8,036.31 4.121
---------- -------
Total $20,885.86 $10.712
~METHOD OF LINING CASCADE TUNNEL, GREAT NORTHERN RY.~--The Cascade Tunnel,
13,813 ft. long, built in 1897-1900, was lined throughout with concrete
from 24 ins. to 3½ ft. thick, mixed and placed in the following manner:
It was necessary to place the lining without interfering with the
transportation of materials and excavated material to and from the work
ahead. The arrangement adopted to secure this end is shown by Fig. 132.
A platform 500 ft. long was constructed at the elevation of the wall
plates; the rear end of this platform was reached by an incline, up
which the cars loaded with concrete were hauled by an air hoist and
cable and delivered to any point on this platform. While each 500 ft. of
tunnel was being concreted, the next 500 ft. of platform in advance was
being built, with its approach incline, so that there was no delay in
the work.
Complete concrete plants were installed at each portal, advantage being
taken of the side hills of the approach into the mountain to handle as
much material as possible by gravity. Each plant was equipped with a No.
6 Gates crusher, 40-in.×8-ft. rock screens, and 16-in.×16-ft. screw
concrete mixers. Large storage bins for the cement, sand and stone were
built adjacent to the mixer plant. A 1-3-5 concrete was used. The stone
was crushed from the best rock obtained in the tunnel excavation. This
rock was loaded into the regular muck cars, taken to the portal by
electric motors, and then dumped into other cars below the level of the
muck cars. These cars were hauled by hoisting engine and cable to the
crusher floor and then dumped and sorted to avoid danger from pieces of
unexploded dynamite. It was then run through the crushers, washers and
screens to the stone bin and thence to the mixers. The mixed concrete
was discharged into cars on the level of the muck car tracks and these
cars were taken by motor into the tunnel to the incline, up which they
were hauled by cable and dumped on the platform. From the platform the
concrete was shoveled into the wall forms or onto the centers as
desired.
[Illustration: Fig. 132.--Traveling Platform Used in Lining Cascade
Tunnel.]
The walls were concreted in alternate 12-ft. sections, the weight on the
timber arch thus being gradually transferred from the plumb posts to the
walls. The roof arch was also built in 12-ft. sections, the centers
being in sections of corresponding length which were moved forward on
dollies and jacked up as the work advanced. Ten sections of centering
were used at each end. An average of 7 bbls. of cement were used per
lineal foot of lining. The average monthly progress of lining was about
600 ft. at each end. The concrete lining cost $44 per lin. ft. of
tunnel, done by company forces.
~METHOD OF RELINING HODGES PASS TUNNEL, OREGON SHORT LINE RY.~--The
centers and side wall forms and the methods of work adopted in relining
the Hodges Pass tunnel on the Oregon Short Line Ry. are explained in the
accompanying illustrations. This tunnel is 1,425.8 ft. long and when
constructed in 1882 was lined with timber. The new lining consists of
concrete side walls carrying a brick roof arch. Both the old and the new
linings are shown in the drawings. The tunnel is through a variety of
rock and clay strata, and through the soft strata an invert was
required. Altogether about one-third of the length of the tunnel was
provided with an invert. It will be noted also that the new lining
occupies materially more space than the old; this made necessary
considerable excavation in enlarging the section.
[Illustration: Fig. 133.--Method of Placing Invert Concrete, Hodges'
Pass Tunnel.]
The work of relining consisted of three operations, viz., the invert
construction, the construction of the side walls and the arch
construction.
[Illustration: Fig. 134.--Method of Constructing Concrete Side Walls,
Hodges' Pass Tunnel.]
The form of the invert is shown in Fig. 136. It, of course, had to be
constructed without entailing a break in the track, and the method
adopted was as follows: The ties and ballast were removed from a section
of track about 12 ft. long and in their place was substituted the timber
frame shown in Fig. 133. Under the middle portion of this frame a trench
reaching clear across the tunnel and having a width of 6 to 7 ft. in the
direction of the track was excavated to sub-grade of the invert. The
concrete was filled into this trench, formed to shape on top, and
allowed to harden. The bridging frame was then taken out and the ties
and ballast were replaced. Another section of track was then bridged,
trenched and concreted and so on until the length of invert required was
constructed.
[Illustration: Fig. 135.--Side Wall Forms for Plans A and B, Fig. 134.]
The side wall construction was a more complex operation. It comprised
first the removal of the old lining, the enlarging excavation and the
form erection and concreting. Two methods of performing this task were
employed. Both are illustrated in Fig. 134. By the first method,
designated as Plan A, the concreting was done continuously in sections
of considerable length. The forms used are shown in detail by Fig. 135.
By the second method, the concreting was done in alternate short panels.
This method is designated Plan B on the drawings, Fig. 134. The forms
used are shown in detail by Fig. 135. The only difference in the form
construction for the two plans is in the connection of the posts at the
top.
[Illustration: Fig. 136.--General Plan of Centers for Roof Arch, Hodges'
Pass Tunnel.]
The construction of the centering for the roof arch is shown by Figs.
136 and 137, Fig. 137 giving detail dimensions of the ribs and lagging.
The center, as shown by Fig. 136, consisted of four ribs spaced 3 ft. on
centers. Each rib consists of two side posts and an arch piece. The side
posts on each side are connected at the bottoms by a sill and at the top
by a cap. Jacks between the sill and a mud sill laid on the concrete
invert or in the ditch held the center in place during arch
construction. Lowering these jacks dropped the center onto trucks
traveling on the mud sills. Thus the center was moved along as the work
progressed. As will be noted from Figs. 134 and 135, the side wall forms
carried the work only to the bottoms of the old caps. The arch center
completed the concrete wall work and the roof arch. Only about one-third
of the new lining had the brick arch, as shown by the drawings; in the
remaining two-thirds the concrete was carried up much further on each
side; in fact, the brickwork constituted only the top third of the arch.
[Illustration: Fig. 137.--Details of Centers for Roof Arch, Hodges' Pass
Tunnel.]
In describing the forms and centers we have left much of the explanation
to the drawings. These show all dimensions and details, and indicate in
a measure the mode of procedure. The work done consisted of excavation
enlarging the section, of removing the old timber lining and of the form
work, concreting and bricklaying for the new lining. All of it above
convenient reach from the ground was done from a movable staging formed
by a deck fixed on a flat car so as to be adjustable in height. The
concrete was mixed by hand on this car platform and shoveled directly
into the forms, the platform being raised as the work increased in
height. The concrete used was a 1-3-5 mixture of 2½-in. broken stone.
The organization of the working force is not easily stated since the
work was done as the traffic permitted and varied with the conditions.
Generally from 12 to 16 men were all that could be employed to
advantage. Complete records of cost were kept, but they were destroyed
by fire, so that the only figures available on this point are the
totals. These are as follows:
Item. Totals. Per lin. ft.
Labor $21,129 $14.81
Materials 13,939 9.77
------- -------
Total $35,068 $24.58
These amounts average the cost of the invert, which was required for
about one-third of the length, over the whole tunnel.
~RELINING A SHORT TUNNEL.~--The following figures show the cost of
relining with concrete a timber lined railway tunnel. The concrete side
walls were 14 ft. high and had an average thickness of 2½ ft. Therefore
each side wall averaged nearly 1.3 cu. yds. per lin. ft., and the two
walls averaged 2.59 cu. yds. per lin. ft. of tunnel. The concrete was
mixed 1-3-5, being, we believe, unnecessarily rich in cement. The
average amount of concrete placed in the walls per day was 50 cu. yds.
Cost of Side Walls.
Materials-- Per cu. yd.
1.33 bbl. cement at $2.00 $2.66
0.5 cu. yd. sand at 0.18 0.09
0.75 cu. yd. stone at 0.55 0.41
-------
Total $3.16
Labor on concrete--
0.01 day foreman at $5.00 $0.05
0.03 day foreman at $3.00 0.09
0.03 day engineman at $3.00 0.09
0.35 day laborer at $1.75 0.61
------- -------
0.42 Total $0.84
Labor, removing timber, building forms, excavating, etc.--
0.02 day foreman at $5.00 $0.10
0.05 day foreman at $3.00 0.15
0.40 day laborer at $1.75 0.70
------- -------
0.47 Total $0.95
Miscellaneous--
0.02 day engineer and superintendent at $5.00 $0.10
Falsework and forms, timber and iron 0.07
Tools, light, etc. 0.10
Interest and depreciation of $1,800 plant at 20% per annum 0.09
Train service, 0.03 day work train at $25 0.75
Summary concrete side walls-- Per cu. yd.
Materials $3.16
Labor on concrete 0.84
Labor removing timber, etc. 0.95
Train service 0.75
Miscellaneous 0.34
-------
Total $6.04
In the two side walls there were 2.59 cu. yds. of concrete per lin. ft.
of tunnel, hence the cost of the side walls was $6.04 × $2.59 = $15.64
per lin. ft. of tunnel. The concrete arch varied in thickness,
averaging from 14 to 20 ins. at the springing line to 8 to 14 ins. at
the crown. The arch averaged 1.2 cu. yds. per lin. ft. of tunnel. About
20 cu. yds. of arch were placed per day. The arch concrete was mixed
1-3-5 and the cost was as follows:
Cost of Concrete Arch.
Materials-- Per cu. yd.
1.36 bbls. cement, $2.00 $2.72
0.05 cu. yd. sand, 0.18 0.09
0.75 cu. yd. stone, 0.55 0.41
-------
Total $3.22
1.8 cu. yds. dry rock backing at 0.55 $0.99
Labor on concrete--
0.02 day foreman at $5.00 $0.10
0.12 day foreman at 3.00 0.36
0.88 day laborer at 1.75 1.54
------- ------- ------
1.02 Total $1.96 $2.00
Labor placing 1.08 cu. yds. rock backing--
0.01 day foreman at $5.00 $0.05
0.51 day foreman at 3.00 0.15
0.55 day laborer at 1.75 0.96
------- ------- -------
0.61 Total $1.90 $1.16
Labor removing timbers, forms, excavations, etc.--
0.02 day foreman at $5.00 $0.10
0.04 day foreman at 3.00 0.12
0.06 day carpenter at 2.50 0.15
0.40 day laborer at 1.75 0.70
------- ------- -------
0.52 Total $2.06 $1.07
Train service--
0.06 day at $25 $1.50
Miscellaneous--
Engineering and superintendence. .07
Falsework, timber and iron .13
Tools, light, etc .12
Interest and depreciation, $1,800 plant, 20% per annum 0.09
Summary concrete arch--
Concrete materials $3.22
Dry rock backing (1.8 c. y.) 0.99
Labor and concrete 2.00
Labor placing 1.8 cu. yds. rock backing 1.16
Labor removing timber, etc 1.07
Train service hauling materials 1.50
Engineering and superintendence 0.07
Falsework, timber and iron 0.13
Tools, light, etc. 0.12
Interest and depreciation plant 0.09
------
Grand total $10.35
It will be noted that the "train service" is an item that really should
be considered as a part of the cost of the materials, for the cost of
the sand and stone is the cost f. o. b. cars at the sand pit and at the
quarry, to which should be added the cost of hauling them to the
tunnel--to-wit, the "train service."
Summing up, we have the following as the cost per lineal foot for lining
this single-track tunnel with concrete: Per lin. ft.
2.59 cu. yds. side walls at $6.04 $15.64
1.20 cu. yds. arch at 10.33 12.40
------- ------ -------
3.79 cu. yds. Total $9.38 $28.04
It should be remembered that the higher cost of the arch concrete is due
in large measure to the fact that 1.8 cu. yds. of dry rock packing above
the arch are included in the cost of the concrete. Strictly speaking,
this dry rock packing should not be charged against the arch concrete,
and, segregating it, we have the following:
Per lin. ft.
2.59 cu. yds. concrete side walls at $6.04 $15.64
1.20 cu. yds. concrete arch at 8.18 9.82
2.16 cu. yds. dry rock at 0.55 1.19
Labor placing 2.16 cu. yds. at 0.64 1.39
------
Total $28.04
This is a much more rational analysis of the cost and a still further
reduction in the cost of the arch concrete might be made by prorating
the train service item ($1.50 per cu. yd. concrete). At least half of
this train service should be charged to the dry rock backing, for there
are 1.25 cu. yds. of sand and broken stone to 1.80 cu. yds. of dry rock
backing.
The amount of this dry rock backing, or packing, varies greatly in
different parts of a tunnel. In the first half of this tunnel it
averaged 1.8 cu. yds. per lin. ft., while in the second half it averaged
nearly 2.4 cu. yds. per lin. ft.
~METHOD OF MIXING AND PLACING CONCRETE FOR A TUNNEL LINING.~--The tunnel
known as the Burton tunnel is located on the Jasper-French Lick
extension of the Southern Ry., and about 4 miles from French Lick, Ind.
It is a single track tunnel 2,200 ft. long with 300 ft. at one end on a
4°-30' curve and 1,900 ft. on tangent. The material penetrated was slate
and loose rock, requiring solid timbering throughout. This timbering is
shown by Fig. 138, which also shows the concrete lining; the timbering
was embedded in the concrete lining.
[Illustration: Fig. 138.--Sections Showing Concrete Lining for Burton
Tunnel.]
The original timber lining was composed as follows: Posts 10×12 ins. and
spaced 3 ft. apart were set on 3×12-in. sills and carried 10×12-in.
wall plates which supported 10×12-in. segmental arch ribs spaced 3 ft.
apart. The lagging behind the posts was 3×6-in. stuff and the lagging
over the arch ribs was 4×6-in. stuff. The section of the concrete lining
is shown by Fig. 138, it required 4,132 cu. yds. of concrete and 161.43
lbs. of reinforcement per lin. ft. The concrete was a 1-2½-5 crushed
stone--between 2 in. and ¼ in. size--mixture; it required 1.16 bbls. of
cement, 0.52 cu. yds. sand and 0.92 cu. yds. of stone per cubic yard of
concrete. The amount of reinforcement per cubic yard of concrete was
39.1 lbs.
[Illustration: Fig. 139.--View of Mixer Plant Showing Car Tracks, Burton
Tunnel.]
[Illustration: Fig. 140.--View of Mixer Plant Showing Method of
Unloading Materials, Burton Tunnel.]
All the concrete was mixed and handled from one end of the tunnel. The
mixing plant was located in the approach cut at one end. A standard gage
main track ran through the cut. About 20 ft. in the clear to one side of
this track a trestle 500 ft. long was built, carrying an 18-ft. gage
derrick track and a narrow gage 3-cu. yd. dump car track. A stiff leg
derrick operating a 1 cu. yd. orange peel or a 1½ cu. yd. clam-shell
Hayward bucket was mounted on a carriage traveling on the 18-ft. gage
track. The side of the trestle nearest the railway track was sheeted
vertically and the space between this sheeting and the track was floored
over at track level for stock piles. Near the end of the trestle toward
the tunnel and on the same side of the track was the mixer plant. This
consisted of two 85 cu. yd. bins, one for sand and one for stone,
carried by a tower so that their bottoms were 25 ft. above track level.
Below the bins was a charging platform pierced by a measuring hopper.
Below the measuring hopper was a 1½ cu. yd. cubical mixer and below the
mixer was a 3-ft. gage track for 1½ cu. yd. Koppel side dump cars. To
the rear of the tower at ground level there was a 20-cu. yd. sand bin
and a 20-cu. yd. stone bin set side by side with a continuous bucket
elevator leading from each to the corresponding bin on the tower. The
cement house was located directly across the railway track from the
tower. At the side of the cement house nearest the track there was an
inclined bag elevator leading up to a bridge spanning the railway track
at the level of the charging floor of the mixer plant. On this bridge
ran a car for carrying bags of cement. The plant as described is shown
by Figs. 139 and 140.
In operation the derrick unloaded the stone and sand cars by means of
the Hayward buckets either into the bins at the feet of the bucket
elevators or onto stock piles on the flooring beside the trestle. When
put into stock piles the materials had to be reloaded by derrick into
the 3 cu. yd. cars on the trestle narrow gage track and carried by these
cars to the elevator boots. The sand and stone were chuted from the
tower bins directly into the charging hopper below. Here the cement
bags, brought across the bridge on the car into which they were loaded
directly by the bag elevator, were opened and the cement added to the
sand and stone. The charge was then dropped into the mixer and from the
mixer the batch dropped into the Koppel concrete cars.
In the tunnel a traveling platform was constructed on two standard gage
flat cars so coupled that a platform 100 ft. long and slightly narrower
than the clear space between side wall forms was obtained. Connecting
the end of the platform toward the mixing plant was a rampe or inclined
platform mounted on wheels. The Koppel car tracks from the mixer were
carried up the incline and the full length of the level platform. The
cars were hauled to the foot of the incline by a light locomotive. A
cable was then hooked to them; this cable was run through a block on the
level platform, its free end coming back to the locomotive, which thus
pulled the cars up the incline by moving back toward the mixer. On the
level platform the cars were pushed by hand and dumped on the floor,
whence the concrete was shoveled into the forms.
The platform construction deserves mention in the particular that it
provided for adjusting the platform vertically. At each corner of the
car a vertical post some 7 or 8 ft. high was set up. The side stringers
of the platform carried two vertical posts at each end; these two posts
were spaced just far enough apart to slide over the corner post, one on
each side of it. A block at the top of the corner posts with the hoist
line connected to the bottoms of the platform posts and the lead line
going to a winch head, thus made it possible to lift the platform any
distance within the height of the vertical post guide and hold it there
by blocking under the posts. The arrangement is shown roughly by the
sketch, Fig. 141. There was block and tackle for each corner post and a
winch at each end of the car. The vertical movement of the platform was
between 6 and 7 ft.
The floor was cemented first, then the side walls and finally the roof
arch. Floor construction was begun at the portal farthest from the
mixing plant. Koppel car tracks were laid through the tunnel and the
concrete was dumped from them directly on the ground. The cars were
hauled by a light locomotive. As the concreting advanced the dump car
track was raised and suspended from timbers across tunnel so that the
concrete could be placed under it. As fast as the floor hardened the
permanent standard gage track was laid and a temporary third rail placed
to give also a dump car track.
[Illustration: Fig. 141.--Sketch Showing Telescopic Support for
Concreting Platform, Burton Tunnel.]
When the floor had been finished the side walls were constructed, using
the traveling platform and beginning at the far portal. The wall forms
consisted of 4×6-in. studs, spaced 3 ft. apart and carrying 2×12-in.
lagging. A 6×6-in. waling outside the studs at about mid-height held the
studs to the timbering by lag bolts reaching through the wall to the
10×12-in. posts. A strip of plank nailed across wall between stud and
post held the form at the top. Wall forms were erected for 100 ft. of
wall at a time. These forms required about 45 ft. B. M. lumber per
lineal foot of form on one side or 90 ft. B. M. for both sides. Two sets
of side wall forms or 200 ft. of wall forming were built, and used over
and over again. The concrete was shoveled into the wall forms from the
traveling platform, the lagging being placed a board at a time as the
work progressed upward and the platform being elevated as required, its
final position being at about springing line level. When 100 ft. of side
walls had been completed the traveling platform was moved ahead for
another 100-ft. section.
[Illustration: Fig. 142.--Sketch Showing Device for Removing Centering
Ribs, Burton Tunnel.]
The centers consisted of 6×12-in. ribs, made up of 3×12-in. plank. The
feet of the ribs rested on folding wedges on 6×12-in. wall plates,
supported by 6×6-in. posts setting close against the finished wall.
The ends of the ribs were held from closing in by 6×6-in. walings, one
on each side, lag-bolted through the lining to the timbering. The
centering required about 315 ft. B. M. of lumber per lineal foot of
center. The method of removing the centers was novel. A flat car had
erected on it a narrow working platform high enough to reach well up
into the arch. Along this platform at the center was erected a sort of
"horse," which could be elevated and lowered by jacks. The sketch, Fig.
142, shows the arrangement. At each end and at the middle of the
platform two guide posts a a were erected and braced upright. Between
these guide posts set plunger posts which were raised and lowered by
screw jacks. The three plunger posts carried a longitudinal timber c.
The car was run under the ribs of centering to be removed and the timber
c raised by working the jacks until it came to close bearing under the
ribs d. The railings and the wedges at the foot of the ribs were then
removed, leaving the ribs hanging on the timber c. This timber was
then jacked down to clear the lining and the ribs rotated horizontally
on the point of suspension as a pivot until their ends swung in over the
platform. The car was then moved ahead to where the centers were to be
used again; the ribs were rotated back to their normal position across
tunnel; the timber c was jacked up, and the wedges and railings placed
at the first of the ribs.
The concreting on the roof arch was begun at the portal. Two shifts were
worked and 42 ft. of arch were concreted each shift.
~METHOD AND COST OF LINING GUNNISON TUNNEL.~--The costs are for concrete
in place in the side walls and the arch of the tunnel, for a length of
440 lin. ft. The quantity of concrete considered in estimating the cost
per cubic yard was 616 cu. yds. The material was mixed and placed in ½
cu. yd. batches, the proportion of the mixtures being 1-2.2-4.4. The
final cost includes the labor of excavating and screening gravel and
sand, the hauling of the same from the bins at the pit to the storage
bins at the main shaft, the care of the chutes in the shaft and the
mixing of the concrete in the tunnel at the bottom of the shaft, the
transportation of the concrete from the mixer to the traveler, the
deposition of the concrete, the setting up and taking down of forms and
the cost of the cement. It does not include the construction of the
gravel pit chutes that hold the screens, the building of the road from
the gravel pit to the storage bins at the shaft, the concrete mixer and
its installation, the traveler and its installation, the cost of
material and labor in the construction of the concrete forms, the
requisite power to run the machinery and other expenses of a similar
nature.
The gravel used for the concrete was obtained from a pit situated on top
of a hill not far from the main shaft leading down to the tunnel. This
gravel bed contains very closely the proper proportions of sand and
gravel for the concrete aggregates. The gravel was excavated and loaded
by hand into side dump cars of 35 cu. ft. capacity. These cars were run
to the edge of the hill where the gravel was dumped upon a screen from
which it ran by gravity, passing thence into storage bins. From the
storage bins the sand and gravel were drawn off into dump wagons having
a capacity of 2 cu. yds. and hauled a distance of one-half mile to a
second set of storage bins located at the top of the shaft leading into
the tunnel. The road from the storage bins at the gravel pit to the
storage bins at the head of the shaft was down grade. A two-horse team
could readily haul 2 cu. yds. of gravel over this road. The storage bins
at the top of the shaft leading into the tunnel communicated with the
measuring boxes at the bottom of the shaft by means of chutes. The
measuring boxes discharged directly into tram cars. The average length
of haul from the mixer to the place of deposition of concrete was about
4,500 ft.
The concrete was placed in the side walls by means of a traveler, which
was so operated in the tunnel as to allow the passage of the concrete
trains beneath it. The traveler was 64 ft. long and was provided with a
slow motion electric hoist, by which the cars containing the concrete
were elevated to the top of the traveler and thence transferred to any
desired position. The concrete was dumped from these cars into boxes
where any remixing or tempering that was required was done, after which
the concrete was shoveled directly into the forms. The entire operation
of handling the materials of the concrete, it will be seen, utilized
gravity to the greatest possible degree.
In order to get a good average cost per cubic yard for handling gravel
and sand, this analysis has been based on five months' operation, from
November, 1906, to March, 1907. In these five months there were 4,123
cu. yds. of sand and gravel handled. The concrete considered was placed
during the month of March. Below is given the distribution of the cost
of the concrete as to the specified divisions of the work and as to the
class of work involved in each division. Measurements taken at the mixer
show that each cubic yard of concrete contained 0.74 cu. yds. of gravel,
0.445 cu yds. of sand and 5.6 sacks of Portland cement. The total of the
aggregates is, therefore, 1.185 cu. yds. per cubic yard of concrete. The
cement costs $0.62 per sack on the work, making a cost of $3.472 per
cubic yard of concrete.
Excavating and screening 4,123 cu. yds. gravel--
Total Per cu. yd.
cost. gravel.
Foreman, 66-7/8 days at $3.04 $ 203.30 $0.049
Labor, 397½ days at $2.56 1,017.60 0.247
Labor, 116¼ days at $2.08 241.80 0.059
-------- ------
Total $1,462.70 $0.355
Hauling 4,123 cu. yds. gravel and sand--
2-horse team and driver, 210 days at
$3.60 $756.00 $0.183
2-horse team and driver, 4½ days at $4 18.00 0.005
------- ------
Total $774.00 $0.188
As there were 1.185 cu. yds. of gravel per cubic yard of concrete the
cost of gravel per cubic yard of concrete was for--
Excavating and screening (1.185 × $0.355) $0.421
Hauling (1.185 × $0.188) 0.223
------
Total $0.644
Adding to this the cost of cement $0.62 × 5.6 = $3.472, we have $0.644 +
$3.472 = $4.116, as the cost of concrete materials per cubic yard of
concrete. The cost of labor, mixing and placing was as follows for 616
cu. yds.:
Total Per cu. yd.
Mixing 616 cu. yds. concrete-- cost. concrete.
Superintendent, 2 days at $5.83-1/3 $ 11.67 $0.020
Foreman, 1 day at $4.50 4.50 0.007
Labor, 45 days at $3.04 130.72 0.215
Labor, 93 days at $2.56 238.08 0.381
Hoist engineer, 34 days at $3.52 119.68 0.196
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Total $504.65 $0.819
Transporting 616 cu. yds. concrete--
Superintendent, 1 day at $5.83-1/3 $ 5.83 $0.009
Foreman, 1 day at $4.50 4.50 0.007
Motorman, 34 days at $3.04 103.36 0.175
Brakeman, 34 days at $2.56 87.04 0.135
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Total $200.73 $0.326
Depositing 616 cu. yds. concrete--
Superintendent, 4 days at $5.83-1/3 $ 23.33 $0.038
Foreman, 4 days at $4.50 18.00 0.029
Foreman, 68 days at $3.04 200.72 0.326
Labor, 238½ days at $2.56 610.56 0.991
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Total $852.61 $1.384
Setting and moving forms--