Widening a Cut; Loading on the Main Track.--The simplest and one of
the most frequent cases for the application of a steam shovel is the
widening of a single track railway cut. The manner of doing this is
shown in Fig. 18. A switch, A B, is put in the main track just beyond
the end of the cut and far enough away to permit the steam shovel (when
standing on the side track) to clear cars on the main track. Cars are
then placed opposite it on the main track and the machine is ready for
excavation.
[Illustration: Fig. 19.]
It very frequently happens that the end of the cut joins directly on
an embankment, as shown in profile, Fig. 19. In cases of this kind it
would be necessary to widen the embankment for the reception of the
side track, near the end of the cut, if the machine were to begin work
at that point, C, Fig. 18. This is very seldom done; the usual method
is to remove the section, A, Figs. 19 and 20, to B by hand labor with
wheelbarrows or with teams and scrapers. The excavated material is
used to widen part of the embankment near the end of the cut for the
reception of the side track. Section A is made barely long enough to
provide a standing place for the steam shovel and clear cars on the
main track; it is seldom over 50 ft. long, and averages about 30 ft.
After placing the machine in this space it is ready for work. Strings
of 10 to 20 cars are then drawn along the main track, and stopped
opposite the machine for loading.
[Illustration: Fig. 20.]
[Illustration: Fig. 21.]
When the machine has reached the end of the switch, it advances on
short sections of track, generally 4 ft. long, which are placed in
front of it, and again taken from its rear when it has moved forward
one section of track more than its own length. When no more cuts are to
be made for still further widening, the switch is taken up again and
the machine advances on its own track sections, Fig. 21. When other
cuts are to follow, however, a loading track is needed for the next
cut; the side track is then extended for this purpose at convenient
intervals, generally about 300 ft. at a time though often after each
space of a rail length (usually 30 ft.) is clear. The latter is by
far the best practice, as it permits the immediate withdrawal of the
machine in case of a threatened cave-in, sidehill slip, or other
unforeseen danger.
After all the cars have been loaded they are taken away for unloading.
Sometimes the steam shovel is left idle until the train returns, which
is a very wasteful method of working, even where the haul to the dump
is short, half a mile to two miles. Two engines and crews should be
furnished for hauls up to ten miles; three engines and crews, or more,
for longer hauls, or where the traffic on the main line is very heavy,
and delays to the work trains are frequent. The material is generally
utilized in filling trestles, widening embankments for side tracks,
double tracks, yards, etc., thereby making two improvements at the same
time.
[Illustration: Fig. 22.]
In widening a cut it is good policy to keep the grade of the pit from 1
to 2 ft. below the surface of the subgrade of the main track, as shown
in Fig. 22, thereby providing for drainage of the ballast and also
providing a receptacle for the spreading of loose material dropping off
the cars and washing in from the surface of the cut; there is nearly
always considerable of this loose material to roll or wash into the pit
after the cut has been completed; and unless room is provided for it,
the accumulation will soon reach the height of the track, washing mud
on it, and choking the drainage, thus injuriously affecting the main
track.
Widening a Cut; Loading on a Side Track Graded by Hand or Steam.--The
delays in loading on the main track of a railway in operation, due to
the clearing of the track for all trains, vary from one to four hours
per day of ten hours, and sometimes amount to as much as seven hours,
depending upon the density of the traffic on the line. The first cut in
a case such as the latter is therefore necessarily an expensive one,
and where the traffic is so heavy it is often cheaper to make a narrow
cut for the side track, on which the steam shovel is to load, either
by wagons and wheel scrapers, Fig. 23, or by hand with wheelbarrows
loading back on cars, Fig. 24.
[Illustration: Fig. 23.]
[Illustration: Fig. 23, a.]
[Illustration: Fig. 24.]
[Illustration: Fig. 24, a.]
The latter plan has the great disadvantage that only one car at a
time can be loaded and only a few men (six to ten) can be employed.
Therefore this plan is never adopted where quick work is required, but
is used only where ample time is available, and mostly as an early
spring preliminary job, preparing the way for the operation of the
steam shovel later in the season. From three to six flat or coal cars
are used, enough to require a whole day for the gang of men employed
to load; the material from the face of the excavation is loaded on
wheelbarrows, and wheeled over the empty cars to the one farthest
from the cut. This car is loaded first, then the one next to it, etc.
At night the loaded cars are taken out of the switch by the first
available freight train and hauled to the nearest yard or side track
where widening of the embankment is wanted, or where the material can
be otherwise used to advantage, and there unloaded by a small gang of
men on the following day; the cars to be returned again the next night.
Other empty cars are placed in the pit track for loading next day, by
a train bound toward the pit the same night the loaded cars were taken
out. The work can be carried on from either one or both ends of the
cut. Coal cars should never be used if flats can possibly be obtained,
as the latter can be unloaded by a gang of men one-third as large as
would be necessary for unloading coal cars.
[Illustration: Fig. 25.]
[Illustration: Fig. 25, a.]
Sometimes small dump cars are used, drawn by horses or mules, and
the material unloaded at the end of the cut, thereby widening the
embankment for a long side track, Fig. 25. The narrow gage track, A,
is laid over the ditch adjoining the main track; the material for any
slight excavation that may be necessary for this track is shoveled on
the slope of the cut, as at C, on the cross section. The material is
then loaded on small dump cars standing on track A, and unloaded at D.
The cars are returned on track B. The cross-overs, E and F, are taken
up occasionally and relaid near the advancing ends of the cut and dump.
In short cuts the narrow excavation necessary for placing a side track
in the cut for the steam shovel to load on is generally taken out by
carts and dumped at the ends of the cut, widening the embankment for a
long side track.
The plan of excavation with wagons or wheel scrapers for this side
track, shown in Fig. 23, is adopted where the traffic is too heavy to
permit loading on the main track; when the side track is wanted at the
earliest possible time; and in cuts not over 40 ft. deep. The material
is dumped at the ends of the cut until the haul becomes too long, then
it is taken to the top of the cut over sidehill driveways excavated for
the purpose, and unloaded at a sufficient distance from the edge of
the new cut to prevent its washing back by rains.
These expedients are necessary only on railways where traffic is very
heavy. On most railways (on all where the total delay does not exceed
five hours per day) it is cheaper to load on the main track until the
first cut has been made. This necessarily involves the delay due to
running to and returning from the nearest side track to get out of the
way of every main line train, until the pit track is long enough to
contain the construction train. This, however, seldom requires more
than two weeks, generally only one; the excavation of all of the first
cut does not often occupy more than a month, and is only a very short
time compared with the whole length of time that the steam shovel is
usually in operation on all but very small jobs.
[Illustration: Fig. 26.]
After a side track has been laid in the first cut made by one of the
methods described above, the steam shovel begins work at A, Fig. 26,
loading cars standing on the side track, and some of them extending out
on the main track. At first not more than ten cars should be coupled to
the engine, so that the train can quickly run into the side track on
the approach of a main line train, and not delay its passage. After the
steam shovel has advanced a train-length, the full number of empty cars
can be coupled to the engine, as they will all be on the side track
while being loaded.
[Illustration: Fig. 27.]
Where the embankment has been previously widened by the excavated
material from the cut, Fig. 27, a sufficient length to permit laying
a side track long enough to hold the construction train, the full
number of cars can be used at once, a great advantage in keeping the
steam shovel at work without interruption by passing trains, which is
unavoidable when some of the cars extend out on the main track.
After the machine has reached the other end of the cut it is either
withdrawn for other work, or placed on the other side of the main track
for widening the cut on that side. The steam shovel begins at A, Fig.
28, loading cars standing on the main track; the main line traffic
being carried over a temporary main track built in the excavation
previously made by the steam shovel on the other side of the main
track. Only a few cars at a time can be used for loading at first,
unless the temporary main track has been extended toward B a sufficient
length to clear the usual string of about 20 cars when the first car is
being loaded.
Grading Wide Areas.--In loading gravel for ballasting, or in widening
a cut for the purpose of grading yard, shop or station grounds, the
usual manner of doing the work is shown in Figs. 29 to 34. After the
first cut has been made by one of the methods already described the
steam shovel is started in at A, Fig. 29, for the second cut. After its
completion the first side track becomes available for the storage of
empty and loaded cars as in Fig. 30, greatly increasing the convenience
of handling the cars and preventing delays by interferences between
the strings of empty and loaded cars, then the latter cannot be taken
away promptly on account of passing or shortly expected trains on the
main line. After the completion of the third cut, another side track
is available for cars, Fig. 31, the loaded cars are then placed on the
first inside track and the empty ones on the second. The former are
taken away by the road crew, and on their return placed on track No. 2.
The pit crew set their loaded cars on track No. 1 for the road crew,
and get their empties from track No. 2. The pit track in the rear of
the steam shovel is used as a repair track for cars.
[Illustration: Fig. 28.]
[Illustration: Fig. 29.]
[Illustration: Fig. 30.]
[Illustration: Fig. 31.]
After the completion of the fourth cut, Fig. 32, track No. 3 is used
for a car repair and extra storage track for loads or empties, for
which there may not be room in tracks 1 or 2. Enough tracks have then
been built for the most efficient and economical handling of the loaded
material, and if the empty cars are promptly returned the steam
shovel can be kept almost constantly at work. Each pit track, on which
the steam shovel advances, becomes a side track on the completion of
that cut, to be used as a loading track for the next cut up to the
fourth cut, after which the loading tracks are taken up on completion
of the cut for which they are used, Fig. 33, and relaid in the pit
of the next cut, to be used, taken up, and relaid as before for the
following cuts. In pits less than one-quarter mile in length, it is
sometimes necessary to retain more of these tracks to provide ample
storage space for all loaded and empty cars.
[Illustration: Fig. 32.]
[Illustration: Fig. 33.]
[Illustration: Fig. 35.]
[Illustration: Fig. 36.]
On all large pieces of work where the main line traffic is heavy it is
important that the first side track from A to B, Fig. 32, shall be of
sufficient length (usually about 700 ft.) to hold the engine and a full
string of cars to avoid going on the main track when switching loads to
C, and obtaining empties from D. If there is an embankment from A to B
it can be widened with material taken from the cut, either by wagon or
cars.
[Illustration: Fig. 34.]
Grading by this method for yard, shop and station grounds occurs mostly
near large cities where better terminal facilities must be provided
for. The width of the area excavated in this manner seldom exceeds 200
ft. (eight cuts) except in old gravel pits used for furnishing material
for ballasting track, which are sometimes 300 ft. (twelve cuts) or more
in width.
Gravel pits and other wide areas excavated are seldom less than
one-quarter mile or more than one mile in length. One-half to
three-fourths of a mile is the most usual length; in exceptional cases
two miles have been reached. Long and narrow pits can be worked more
advantageously than short and wide ones.
Cutting Down Grades.--For cutting down grades on railways where the
traffic is not too heavy to prohibit loading on the main track, the
usual plan of operations is shown in Figs. 35 to 42. The machine begins
work at A, Figs. 35 and 36, the beginning point of the new grade,
loading cars on the main track, cutting to the line of the new grade,
and moving forward on the track on the surface of the pit as long as
the height of the crane permits raising the dipper high enough over the
cars to open the bottom door of the dipper and discharge its contents,
B, Fig. 35. This point is usually about 2 ft. below the main track.
The machine must then be gradually run upward on a cribwork of wooden
blocking, generally pieces of pine 6 by 12 ins. by 4 ft. long, with
some longer track stringers for supporting the sections of track on top
of the blocking, and some thinner pieces for attaining exact heights
of blocking when needed. As the machine moves forward the dipper still
continues cutting to the line of the new grade, while the machine is
gradually run upward on the blocking on a grade parallel to the grade
of the main track, and slightly below it, maintaining a constant height
between the top of the track on the blocking and the highest point to
which the dipper can be raised on the crane to insure discharging its
load on the cars. When the dipper has cut as low as the length of the
dipper handle will permit, C, Fig. 35, the greatest depth to which the
machine will cut below the level of the main track has been reached,
and as the steam shovel advances the surface of the pit will be on a
grade parallel to the grade of the main track, running upward to the
summit, S, then downward, and continue so until it cuts the new grade
line at H, when the dipper is made to cut on this grade, while the
blocking under the machine is gradually lowered as it was previously
raised, until the steam shovel reaches the end of the new grade at I,
when it is again on the surface of the pit.
[Illustration: Fig. 37.]
[Illustration: Fig. 38.]
[Illustration: Fig. 39.]
Although the machine is gradually run upward and downward, it is always
blocked level after each forward move before beginning work, to insure
quick and easy swinging of the crane, as previously explained. Most
machines will cut 5 ft. below the main track and load on a flat car
with 18 ins. side boards. Some machines will cut as low as 8 ft., and
they are preferred to others on railways where much work of this kind
is done, as their use often avoids making an extra cut.
[Illustration: Fig. 40.]
[Illustration: Fig. 41.]
[Illustration: Fig. 42.]
After the first cut has been completed, the pit track, A 1, Fig. 36,
becomes the temporary main and loading track; the main track is taken
up from C to H, and the steam shovel run back to C to begin the second
cut, Fig. 42, excavating it in the same way as the first, and loading
on the temporary main track. This track again is taken up after the
second cut, the machine begins at D and ends at G for the third cut
and loads on the pit track in the second cut; the fourth cut is made
in a similar way, the machine beginning at E and ending at F, Fig. 36.
The fifth and last cut is merely a widening cut, made by loading on
the track in the pit of the fourth cut. The material of each cut after
the first is loaded on the track laid in the preceding cut. After the
completion of the last cut, the permanent subgrade having been reached,
the main track is laid on the permanent line, and the small quantity of
material obtained from cutting the ditches loaded on cars by hand and
taken away for unloading. The most frequent depth of cut made at the
summit of grades is about 10 ft. (two cuts), Figs. 38 and 39.
[Illustration: Fig. 42-1/2.]
[Illustration: Fig. 43.]
[Illustration: Fig. 44.]
[Illustration: Fig. 45.]
When the main track is on a curve, as frequently happens, an extra cut
can often be avoided by slightly changing the alinement of the new main
track, and at the same time reducing the degree of curvature, as shown
by Figs. 42-1/2 and 43. This is particularly applicable where an odd
number of cuts must be taken to reach the bottom of the new grades. The
dipper will cut to a slope of about 1 to 1. When greater slopes are
required, it must be done by hand or undercutting resorted to. Sloping
by hand is slow and expensive work, impracticably so in all tenacious
materials; it has therefore become the exception, and undercutting
the rule. Cuts made in the latter manner sometimes present a rather
ragged appearance when just completed, but the irregularities soon
merge into a smooth surface as the action of the elements produces the
natural slope of the material; the smaller cost amply compensates for
the temporary lack of finished appearances. The amount of hand labor
necessary where undercutting is not practiced is shown by the sections
A in Figs. 38 and 41. This can be entirely avoided by undercutting the
slopes, as shown in Figs. 39 and 42; the sections B will slough off
within a year or two and most of the material lodge in the spaces C; a
small part of this material may roll to the bottom of the cut, and can
be removed by loading on cars by hand, or space may be provided for
it by making the cut a few feet wider at the bottom. In most cuts for
reducing grades this extra width must be cut out anyhow to provide room
for both steam shovel and loading track.
[Illustration: Fig. 46.]
[Illustration: Fig. 47.]
[Illustration: Fig. 48.]
In reducing grades on railways with a traffic too heavy to permit
loading on the main track, a temporary main track must first be built
by one of the methods shown in Figs. 23, 24 and 25. The temporary main
track, A, Figs. 44, 45 and 46, is then laid, as shown in Fig. 28, to
carry the traffic of the road unobstructed. The main track then becomes
the loading track for the first cut, and the following cuts are made
as shown in Figs. 44, 45 and 46. The temporary main track, A, is moved
to a second position, B, when the material under it must be cut away.
Great care should be taken to arrange the cuts so that the temporary
main track will have to be moved as few times as possible, and to
attain the lowest level when it is moved. In loose gravel or sandy
materials wider bermes and longer slopes must be allowed for the shelf
on which the temporary main track rests than are shown in the above
figures, but the method of doing the work is essentially the same.
If the depth of the original cut in tenacious materials exceed the
height which the dipper can reach, and break down the material above
it, the cuts are arranged as shown in Figs. 47, 48 and 49. Temporary
loading tracks, L, are built on the side of the slope, and the first
cut on each side made by loading on them; the following cuts are then
made, as shown on the figures. If the main line traffic is very heavy,
it is turned over the temporary main track, A, Fig. 47, until the cut
is completed.
[Illustration: Fig. 49.]
The original cuts are not often more than 10 ft. deep, and the section
shown in Fig. 45 covers the majority of cases.
On double-track railways the traffic in both directions is generally
turned over one track for the length of the new cut, thereby avoiding
considerable expense in providing two temporary main tracks.
Each different piece of work presents different conditions; and
while the same general principles apply to all, every case requires
disposition according to its own special circumstances. Great care and
study should be exercised in arranging the cuts, to reduce them to the
fewest possible number, and avoid shifting, taking up and relaying
tracks oftener than absolutely necessary.
[Illustration: Fig. 50.]
[Illustration: Fig. 51.]
Construction Work.--On railways the steam shovel is used mostly in
connection with maintenance of way work: loading gravel for ballasting
the track, widening cuts, filling trestles, etc., but it is also
largely used for various construction work, particularly re-alinements
of the main track for reducing grades and curvature. In excavation of
this class, thorough cutting should be avoided if possible, for reasons
which will be subsequently explained. The work is begun by laying a
temporary track, A, Figs. 50, 51 and 52, over the surface of the ground
if its natural grade is not too steep to permit operating construction
trains over it. Grades up to 6 per cent. (316.8 ft. per mile) can be
used. A mogul engine will draw six empty flats over such a grade, a
sufficient number of cars to start the work for the short cuts near the
summit. The cuts are then made as indicated in Fig. 52.
[Illustration: Fig. 52.]
[Illustration: Fig. 53.]
[Illustration: Fig. 54.]
If the grade of the ground is too steep to operate a track laid on it,
one of the three methods may be adopted to obtain a grade for this
track:
1. The steam shovel is made to cut a trench between the points A and B,
Fig. 53, where the slope of the ground is too steep to permit operating
a track laid on its surface, and varying in depth from 5 to 10 ft. as
may be necessary to attain the desired grade. The excavated material
is dumped at D, Fig. 54, to be removed with the next cut. The length
of the crane will not permit dumping at E a sufficient distance (20
ft. or more) to obtain a berme and prevent the material washing back
into the new cut in the course of time; it must, therefore, be dumped
at D and removed as described, unless the slope of the ground is away
from the cut, as indicated by the line D F, Fig. 54; in such a case the
excavated material can be dumped at F.
2. By excavating the trench with teams and scrapers.
3. By through-cutting a trench with the steam shovel, loading the
material on small dump cars or wagons, and wasting it at the nearest
available place.
[Illustration: Fig. 55.]
[Illustration: Fig. 56.]
[Illustration: Fig. 57.]
After the first loading track has been laid in this trench, the cuts
are made as indicated in Fig. 54.
When the slope of the ground is too steep to permit a track to be laid
on it which can be operated, or to cut a trench for it, as frequently
occurs when the excavation passes through a high spur or knoll, Figs.
55, 56 and 57, the steam shovel mounted on standard gage railway tracks
cannot be used, and a machine independent of a railway track for
transportation must be employed. It is started at A, Figs. 56 and 57,
loading small dump cars drawn by horses, and dumping at the nearest
available place outside of the lines of the new cut, as at D, Figs. 56
and 57. Sometimes wagons are used if the cuts near the top are short
and not very deep, so that a temporary standard gage track can soon
be run through the cut, and the material loaded on cars. The dumping
track at D is changed to E F, etc., Fig. 57, as the machine cuts lower,
maintaining a descending grade from the steam shovel.
[Illustration: Fig. 58.]
[Illustration: Fig. 59.]
[Illustration: Fig. 60.]
In cases of this kind it is often necessary to run the steam shovel up
a very steep grade to reach the point where it is to begin work. This
can readily be done by attaching one end of a one and a half inch rope
to a strong tree and winding the other end around the driving axle.
Then starting the running gear the machine can be drawn up grades where
it could not otherwise propel itself. As a precautionary measure, it is
advisable to use at least two ropes.
A combination of all these methods sometimes becomes necessary, as
shown in Figs. 58 and 59. The material in the knoll, K, Fig. 58, is
loaded on small dump cars and unloaded at the nearest available place.
When this knoll has been cut down sufficiently, and trenches cut
between A B and C D, the track A B C D is built, and the excavation
proceeded with, as heretofore described. The high points B, K and C
are cut down first until the grade of the loading track between B
and C is parallel to the grade of the proposed new main track. Cuts
nearly 100 ft. in depth and a mile in length have been excavated in
this manner. Two and often three steam shovels are employed at the
same time, working near the ends of the cut until the through track
has been laid, and then following each other, as shown in Fig. 60. As
soon as possible, a through track should always be laid, as it greatly
increases the capacity for the prompt and efficient handling of the
cars.
[Illustration: Fig. 61.]
[Illustration: Fig. 62.]
Enough side tracks for storing both empty and loaded cars should be
built close to the work, where they can be reached without going out on
the main track. Sometimes the pit tracks behind the steam shovels are
utilized for this purpose, but these tracks are taken up too often, and
should not be depended upon for side tracks, though they may be used as
such occasionally.
In through-cutting the material is loaded on small dump cars running
on tracks of about 3 ft. gage, drawn by horses, and wasted on some
side hill or other nearest available place; this haul seldom exceeds a
quarter of a mile in length. In Fig. 61, the empty dump cars standing
at A are drawn over the cross-over C by a horse, to be loaded at B;
then run to D, and when from four to six cars have been loaded they are
taken to the dumping place and unloaded; then returned to A.
In loose materials considerable time is lost in waiting from the time
the loaded car is run to D and the next empty brought from A to B. In
tenacious materials not nearly so much time is lost, as the dipper
cannot be filled so rapidly. This loss of time is largely avoided by
arranging double loading tracks, Fig. 62, one on each side of the steam
shovel, and connected to a central track for empties by the cross-over
C and C´ and switches S and S´. Two horses are used, one on each side
of the central track, to bring forward the empty cars from A to B, and
A to B´, and return them to D and D´; these operations are alternately
performed, each empty car on one loading track being brought forward
while the other is being loaded. The cross-overs C and C´ should be
kept close to the rear of the steam shovel, and as it advances they
must be taken up and relaid; this becomes necessary about once in three
days in soft materials and about once a week in hard stuff.
Portable sections of tracks, switches and cross-overs are generally
used between the points A and B, and can be relaid very quickly.
Standard gage railway cars cannot be used in thorough cutting, as the
track cannot be laid in front of a point at right angles to the post of
the steam shovel, and when the track ends there the crane cannot swing
back far enough to load the car. Thorough cutting should be avoided if
possible, the cost due to the loss of time in switching cars, relaying
tracks, extra horses and men, etc., makes it more expensive than
excavating from a side cut.
In excavating canals, harbor and dockwork, stripping coalfields, stone
quarries, grading for new city additions, and other work not connected
with a railway, as well as railway construction and re-alinement work
which is inaccessible to a railway track in its early stages, the
general manner of using the steam shovel is the same as for railway
work; varying only in details, depending upon the means of disposing
of the loaded material, by wagons, carts or dump cars, and the use or
waste of this material.
Although the steam shovel is employed mostly on railway work, it is
not exclusively a railway machine. It is already largely used on other
work, and its use in this direction is rapidly extending, especially
on the increasing number of extensive public works in the vicinity of
large cities.
The most economical height of cut varies greatly with the nature of
the material. In dry clay, loam and other dry materials which can be
broken down readily with a bar or iron pointed pole (Fig. 17), cuts of
25 to 30 ft. in height are usually taken. In harder and more tenacious
materials it should not exceed the height to which the dipper can be
raised, 14 to 20 ft., varying with the size of the machine. In sand
and loose gravel which easily falls down to the machine heights up to
60 ft. are common, and sidehill cuts in loose gravel up to 300 ft.
in height have been taken. In such cases, and also in the removal of
landslides, great care must be taken to avoid an avalanche of the
material burying the machine when the toe of the slope is cut away. The
pit track should always be kept close up to the sections of track under
the steam shovel, so that it can be quickly withdrawn when necessary.
As a general rule, the higher the cut the better, as the machine can
then load the greatest amount of material between each advance, and
lose the least possible amount of time. Each forward move of the
machine requires from three to ten minutes, depending upon the height
of blocking, if any, it is working on; this is a dead loss, as no cars
or wagons can be loaded during that interval.
Powder and dynamite are frequently used to good advantage to shatter
the harder materials before excavating. When thus broken up about
twice the amount of these materials can be loaded in a day. Great care
must be exercised in the quantity of the explosive used, and in the
location of the drill holes to prevent injury to the steam shovel. The
explosives should be stored in a safe place, preferably in a vault at
some distance from the place where they are to be used.
The use of dynamite is confined mostly to bowlders, ledges of rock
and stumps of trees, while powder is generally used for hardpan,
shale, slate, cemented gravel and hard clays. For the latter materials
dynamite is usually too powerful, as instead of merely lifting and
loosening them, as desired, it shatters shale and slate into fragments,
and compresses the other materials about it, forming a "cistern" from 3
to 5 ft. in diameter, as shown in Fig. 63. Sometimes small quantities
of it are used specially for this purpose to make room for a large
charge of powder at the bottom of the drill hole, where its explosion
will have the most effect in loosening the superincumbent material. A
charge of one-quarter to one-half of an ordinary dynamite cartridge
will usually blow out a "cistern" large enough to contain from one-half
to one keg of powder, Fig. 64.
The depths of the drill holes in these materials vary from 4 to 20
ft.; they are made with a drill, or, in the softer materials, with an
auger similar to a plank auger, generally about 2 ins. diameter, with
extension pieces for deep holes, as shown in Fig. 65. Crowbars and
wooden and iron wedges are also often used in breaking down overhanging
material when it cannot quite be reached by the dipper.
The excavation of materials for which powder or dynamite are used to
loosen them requires a powerful machine, with a strongly built, medium
size dipper. A small or lightly built machine giving good satisfaction
in soft materials would prove an utter failure here.
[Illustration: Fig. 63.]
[Illustration: Fig. 64.]
[Illustration: Fig. 65.]
Assuming good management and a competent crew, the daily output of a
steam shovel depends mostly upon the nature of the material excavated;
it is also somewhat dependent upon the height and width of the face
of the cutting, and largely upon the facilities for disposing of the
loaded material, and keeping the machine almost constantly at work
by an ample supply of empty cars and wagons. Although these varying
conditions differ on each piece of work, the probable output of a
machine for a given excavation can be closely estimated by good
judgment based on previous experience with similar work. The average
daily output in different kinds of materials, and under average,
favorable and unfavorable conditions, as described above, is shown in
Table II.:
TABLE II.
Loose Damp
Capacity Delay. Sand. gravel. Dry loam. Dry clay. clay.
of dipper. hours.[2] Cu. yds. Cu. yds. Cu. yds. Cu. yds. Cu.yds.
2-1/2 cu. yds. 1 Good 2,400 2,400 2,000 1,800 1,200
" 5 Poor 1,200 1,200 1,000 900 600
" 2-1/2 Avg. 1,800 1,800 1,500 1,350 900
1-3/4 cu. yds. 1 Good 1,600 1,600 1,200 1,000 800
" 5 Poor 800 800 600 500 400
" 2-1/2 Avg. 1,200 1,200 900 750 600
1 cu. yd. 1 Good 1,000 1,000 800 700 500
" 5 Poor 500 500 400 350 250
" 2-1/2 Avg. 750 750 600 525 375
[Footnote 2: The delay in hours is the time lost in moving forward and
waiting for empty cars.]
TABLE II.--Continued.
+----- Loosened by explosives.---+
| Mixed |
Stiff Hard clay and Loose Cemented
Capacity Delay. blue clay. pan. boulders. rock. gravel.
of dipper. hours.[3] Cu.yds. Cu.yds. Cu.yds. Cu.yds. Cu.yds.
2-1/2 cu. yds. 1 Good 800 600 600 600 600
" 5 Poor 400 300 300 300 300
" 2-1/2 Avg. 600 450 450 450 450
1-3/4 cu. yds. 1 Good 600 400 400 400 400
" 5 Poor 300 200 200 200 200
" 2-1/2 Avg. 450 300 300 300 300
1 cu. yd. 1 Good 400 300 300 300 300
" 5 Poor 200 150 150 150 150
" 2-1/2 Avg. 300 225 225 225 225
[Footnote 3: The delay in hours is the time lost in moving forward and
waiting for empty cars.]