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to see a rock drill pounding away with a bit which has no
edge at all. It then becomes a question of pounding the
rock to pieces instead of cutting it.

A hard blow will do this, while a tappet drill, which has
the force of the blow materially checked by the early admis-
sion of pressure to form a cushion, will run along at a lively
speed, but accomplish very little in proportion to power
consumed. Another quality a rock drill must have is the
power to pull the bit out of the hole as well as to drive it in,
and that when the hole is blocky, crooked, or muddy.


The best rock drills on the market are the Ingersoll-
Sergeant and the Rand drills, operating by steam or com-
pressed air, and the General Electric Co. 's drill, operating
by electricity. Fig. 416 is a sectional view of one form of
a drill using steam or compressed air, without tripod or

The principal parts are as follows: 1 is the cylinder. At
the right hand or " back " end of the cylinder there is a
washer 2, and a buffer 3, to receive the piston when it
strikes at this end. Immediately behind these are the
"rotation washer" 4, an d the "rotating ratchet" 5, both
inside of the back cylinder head 6. To the left, 7 is the
brass "rifle nut," 8 is the "rifle bar," and 9 is the piston.
The rifle nut 7 is secured to the piston 9 and slides back

and forth with it over the rifle bar 8. This compels a
relative rotation between the bar and the piston, but as the
piston is very much the heavier, the tendency is that only
the bar will rotate. It is controlled, however, by the rota-
ting ratchet 5, and allowed to turn only in one direction.
The piston, therefore, must turn on its return stroke, and
in this way it is made to rotate a little at every blow and so
drive the bit to a new place. At the extreme left, 10 is the
piston bushing to take the wear off the bit. The key 11 is
drawn down by the U bolt 12, and so clamps the bit. The
front cylinder head 13 and the gland 14 are both in halves.
The washer 15 and the buffer 16 ease up the blow when the
piston strikes here On top we have the steam chest 17,
the steam chest covers 18, valve 19, valve guide 20, valve
washers 21, and buffers 22. The "goose neck " 23 carries



one end of the feed screw, which is driven by the crank
25 turned by hand.

Fig. 417 represents a drill mounted on a tripod and ready
for work. The feed-screw A is collared at its upper end to
the frame B and is thus prevented
from moving longitudinally when
revolved by the crank fixed to its
top. Its lower end works in a nut
fixed to the cylinder, which last
moves longitudinally backward as
the crank is turned.

The drilling is begun with a short
drill called a starter, the first few
blows being lightly given until the
hole is fairly started, when the full
force of the steajn is turned on.
As the drill penetrates the rock,
the cylinder is fed forward by means
of the feed-screw A as far as the
shell permits. The steam is then
shut off and the drill withdrawn by reversing the movement
of the feed-screw. A longer drill is then substituted and
the drilling continued. The cutting edges of the bits are
necessarily worn by the drilling and constant rotation in the
hole so that the diameter of the bottom of each section of
hole is slightly less than that at the top; accordingly, at each
change of drill, one is selected with a bit from \ to 1 1 g -
inch narrower than the one removed.

In tunnel driving, the drills used in the heading are
usually mounted on columns, similar to that shown in Fig.
418. The column^ is set in an upright position near the
face of the heading, the top B of the column being forced
against the roof of the tunnel by the capstan screws C
which rest in special castings D on the floor of the heading.
It is a common practice to place strong blocks of wood on
the head of the column and under the feet of the capstan
screws, which prevent the rock supports from becoming
loosened by the continued jarring of the column, due to the

FIG. 417.



working of the drills. The arm E at right angles to the
column slides up or down -the column by means of the
collar F, and may be clamped
in any position by the clamp G.
The drill is carried on this arm
and revolves about it as an axis,
thus giving a wide range of
action. Usually two drills are
mounted on each column. In
sinking shafts and driving tun-
nels, as well as in mine work,
compressed air is used instead of
steam, which loses much of its
pressure through condensation.
The use of compressed air greatly
promotes ventilation. Percus-
sion drills are under a pressure
of from 60 to 70 Ib. per square
inch. In one hour one will drill
a hole from 2 to 2 inches in
diameter and from 4 to 10 feet
in depth, depending upon the
character of the rock, the position
of the strata, and the size of the
machine. The cost of drilling
will vary from 8 to 20 cents per
FIG. 418 lineal foot.

15O1. Drill-bits are of different shapes, being
varied to suit the work to be done. For uniform hard rock,
the bit is cross-shaped, with the arms of equal length and at
right angles to each other. For seamy rock, the arms of
the bits are of equal length, but cross each other X fashion.
For soft rock, frequently a bit with a Z-shaped cutting edge
is used.

Fig. 419 shows the usual form of drill-bit, and Fig. 420 the
tool for sharpening same. On surface work, a drill is
usually worked by one man; in tunnel work, two men are



commonly employed. The man in charge of the drill is
called the drill runner and his assistant the helper or tailer.
Three or four men are required
in moving and placing the larger

1 5O2. Air Compressors.

As before stated, when percussion
drills are used for surface work,
they are operated by steam which
is usually generated in a portable F io. 420.
boiler and conveyed to the drills through iron
pipes. The direct connection with the drills is
FIG. 4i9. made by means of steam hose. When the work
is of great magnitude and confined to a small area, a sta-
tionary boiler of adequate size is set up.

When compressed air is required for working the drills, as
in mine or tunnel work, air is forced into a receiver by an

air compressor and conveyed thence by iron pipes and steam
hose to the drills. The receiver is a wrought-iron cylinder,
from 2 to 4 feet in diameter and from 5 to 12 feet long. A
cut of a light duplex compressor made by the Rand Drill Co.
is shown in Fig. 421. It is so made that it can readily be


taken apart and transported on mule-back. A and B are
the steam cylinders, and C and D are the air cylinders. E
is the air delivery pipe and /''the steam pipe. Some of the
advantages of the duplex type are the following: Since the
cranks are set at right angles, the engine can not get on a
dead center. One cylinder can be detached when only half
the capacity of the machine is required. The power and
resistance being equalized through opposite cylinders, large
fly-wheels are not necessary.

A horizontal air receiver is shown in Fig. 422. The
air enters the receiver at A, flows through a series of pipe
coils, and discharges through B. Cold water constantly cir-



FIG. 422.

culates about these coils, cooling the air and drying it at the
same time, the moisture dropping to the bottom of the coils.
The glass gauge E indicates the amount of moisture de-
posited. When the gauge indicates too great an accumu-
lation of water, it is drained off. The cooling water enters
the receiver at C and is discharged at D. The gauge F
shows the pressure of the air, and //is a safety valve which
regulates the pressure.




1503. Tunnels. The location and construction of
tunnels are so intimately connected that it has seemed best
to consider them under the head of construction alone.

When grading requires a cutting to exceed 60 feet, it be-
comes expedient to drive a tunnel. Tunnels should, when
possible, be driven on straight lines, especially for single-
track roads, in order to reduce the danger of collisions.

1504. Laying Out the Surface Line. The first
work of the engineer in preparing for tunnel work is to lay
out the tunnel line on the surface of the ground. If the
tunnel line is a tangent, it should be run in by foresights, so
far as possible, in order to obviate those errors due to defects
in the adjustment of the transit, and the work repeated a
sufficient number of times to insure a true line. As a per-
fect line is of the utmost importance, great pains should be
taken, and considerable expense may be incurred in securing
long sights. Special transits, called /w;/w^/transits, of double
the weight and power of ordinary instruments, are used in
running the lines. Frequently, platforms of either timber
or masonry, several feet in height, are erected at the suc-
cessive points on the line, their elevation admitting of much
longer and clearer sights. The hours of the early morning
are the most favorable time for running the test line. v The
air is then of uniform temperature, and the rays of the sun so
low as not to interfere with sights. It is useless to attempt
work of this kind when the wind is blowing. A cool, cloudy
morning is the best time, and in most situations it may be



had by watching one's chances.
Some engineers prefer to run
the surface line (if it is one con-
tinuous tangent) at night, using
plummet lamps for sights. The
center line of the Cascade tun-
nel, on the Northern Pacific
Railroad, was run in this way.
The laying out of the surface
line is illustrated in Fig. 423,

Let E D C G represent the
profile of the hill or mountain
to be tunneled. Setting up the
instrument at A and foresight-
ing to , a point is set at >,
the highest point on the surface
line which can be seen from A.
Intermediate points //, P, and

1 K are also set from A. Moving

2 the instrument to B, a backsight
is taken to A and a second
principal point set at C, an in-
termediate point being at L.
Removing the instrument to C,
a backsight is taken to B, an
intermediate point set at Q, and
a fourth principal point set at
D in the opposite tunnel ap-
proach. Intermediate points
M, N, and O are also set from
C. This surface line may be
from 2,000 to 10,000 feet in
length, and yet not have more
than half a dozen intermediate
points. Frequently the surface
is so broken as to require more.
The instruments require the
most careful and repeated ad-



justments. Mountainous country is especially favorable for
making careful adjustments, on account of the long sights
which are easily obtained in such localities. Substantial
monuments should be set at each of the principal points. A
short section of log, cut off square, or a section of Sawed tim-
ber of equal length, set on end in a pit and bedded in cement
mortar rubble, answers this purpose well. The timber should
extend three inches above the surface of the ground.

On each monument two points are set about four inches
apart. At one of these points a vertical hole one inch in
diameter by six inches in depth is bored to hold the per-


FIG. 424.

FIG. 425.

manent target, which is set up at each of the principal points.
A monument corresponding with the above description is
shown in Fig. 424, and target in Fig. 425.

The target is made of pine or spruce. The shank which
fits the hole in the monument and the target are of one
piece. The surface of the target is divided as shown in Fig.
425, the inner figures painted eather red or black and the
outer figures white. The target is set up plumb, the points
of the squares of different colors uniting in a vertical line
which coincides with the established center line denoted* in
both figures by the letters C L. Such a target can be readily
distinguished with a good instrument at a distance of one
mile, and is easily and cheaply made.


1 5O5. Measuring the Line. After the line is estab-
lished, it is measured, a work requiring great care and re-
peated checking. Either of the following methods may be
used to obtain horizontal or true measurement: The first
method is by the use of a steel tape, plumb-bobs, and spring
balance, in which the tape is held in a horizontal position
and strained to the same tension at each measurement, the
strain being measured by a spring balance. There will be,
of course, no uniformity in the length of the sections of line
measured, the varying lengths depending mainly upon the
degree of, the slope. Before the measuring is commenced,
stakes are firmly set on line at such distances apart as will
permit easy plumbing. A 100-foot standard tape is used,
unless the sections are very short, when a 50-foot tape is
used. Tacks with small heads are set on line in each stake.
In measuring, an allowance of .0000066 part of the length
per degree is made for expansion or contraction, according as
the temperature at the time of measurement is above or
below the normal temperature, which will of course vary
in different latitudes.

EXAMPLE. If a temperature of 50 is assumed as normal and at a
temperature of 90 a line measures 72.421 feet, what is its normal
length ?

SOLUTION. 90 - 50 = 40. 40 X .0000066 (the rate of expansion
per degree) = .000264, the amount of expansion for each unit of length
of line. The line measures 72.421 feet. The total expansion will,
therefore, be .000264 X 72.421 - .019 ft. 72.421 ft. +.019 ft. = 72.440, tbe
normal length of the line.

For measurements of 100 feet or less a tension of 16 pounds
is sufficient. This process of measuring is illustrated in
Fig. 426.

The head tapeman holds the zero end of the tape with the
spring balance attached at B.

The hind tapeman, standing at A, holds the tape above
the stake until it is in a horizontal position. The tape
carries a rider containing a spirit level and a small eye
through which the plumb-bob cord is passed. There are
two rear tapemen. One holds the tape and gives it the



requisite tension, which is reported by the head tapeman at
B; the other directs the raising or lowering of the tape while
bringing it into a horizontal position, adjusts the plumb-

bob, and reads the tape. The reading is then recorded.
The rear tapemen then change places and repeat the work
and record the measurements. Each man must read and

FIG. 427.

record his measurements independently of the other, in order
that they may the better check each other's work. Accord-
ingly they do not call out the measurements, but after each


has read and recorded his measurements, they compare
results, and if there is any considerable discrepancy, the work
must be repeated.

Fig. 427 shows form of tape rider for plumbing tape. It
consists of a piece of sheet brass A B, 6 inches in length, an
end view being shown at C. It is bent so as to fit closely
to the sides and top of the tape when stretched, and slides
along the tape. An open slot a , 2 inches in length, in the
side of the rider shows the graduations on the tape. A spirit
level D E is attached to the under side of the rider. To
the under side of the bubble tube at its middle point an eye
c is attached, from which the plumb-bob F is suspended.
Directly over this eye and fastened to the rider is a fine
point d, which indicates to the tapemen the precise reading
of the tape.

The second method of measuring is as follows: The
stakes are driven as in the first method, and the slope meas-
urements .from center of tack to center of tack are taken,
the spring balance used, and allowance for expansion or
contraction made as in the first method. The levels are
then taken between the different stakes, the tack in the top of
each stake being taken instead of the surface of the ground,
and the slope distances are then reduced to horizontal dis-
tances. This method is illustrated in Fig. 428.

The distance a b measured on the slope is 68.10 feet,
<r=75.111 feet, ^=57.166 feet. The difference in ele-
vation between a and b is a a' = 16.811 ; between If and c is
' = 20.42 feet; between c and d is c <:' = 20.752 feet.
a a' b forms a right-angled triangle, right angled at a', in
which the hypotenuse is the slope distance, 68.10 feet, and
the altitude a a' is the difference in elevation between a
and =16.811 feet. From the trigonometrical formula

side opposite , , 16.811

sin = -j- , we have sin a b a = = .24686,

hypotenuse 68.1

whence angle aba' 14 17'. The base a' , which is the
horizontal distance between a and , is obtained by apply-

side opposite

ing the formula tan aba' -^ . Substituting

side adjacent



have tan 14

quantities, we

whence a' b = ^ =

a' b

66. 032 feet. By a similar
process we determine the
length of b c, and find
that it equals 72.242 feet,
and that c' d = 53.272
feet. The total horizon-
tal distance between a
and d is the sum of
a' b _|_ b' c + c' d = 191. 546
feet. This method of
measurement is possible
where the slopes are so
abrupt as to render the
use of the plumb-bob
practically impossible.

1506. Stationing.

Stations are e s t a b -
lished at each 50 feet, and
if the surface be very
rough, at each 25 feet, in
order that a correct pro-
file of the surface may be

1507. Curved Tun-
nel Lines. When the
tunnel line is curved, the
tangents are made to
intersect, if possible, and
the angle of intersection
is measured with the



transit. The tangent distances are calculated and the P. C.
and P. T. located by direct measurement. The work and
calculations are repeated many times, and every possible
precaution taken to secure perfect accuracy of results.

The sketch given in Fig. 429 shows the difficulties attending
the laying out of the Rockport tunnel on the Lehigh Valley

The original line A B C D followed the course of the
Lehigh river, which hugs the bluff E. The tunnel line
A F G H would have been adopted and the tunnel driven
when the road was first constructed, but a rival line was
building on the opposite side of the river, and there was a


race to .reach the Wyoming Valley coal fields and command
the coal traffic. The tunnel line was accordingly postponed
and the river line adopted. After a lapse of twenty years
the tunnel was driven in 1882-3. The neck F G through
which the tunnel passes (a profile of which is shown in Fig.
430) reached a height of more than 300 feet. The hillsides
were so steep that in places a man could hardly stand. The
tangent K F is the prolongation of the original tangent A K.
The grade of the original line was about 20 feet per mile,
and as there was a gain in distance of nearly 1 miles, there
resulted a discrepancy in grades at L of about 30 feet. In
order to dispose of this difference, the grade on the old
tangent A K and on the tunnel curve was increased to
40 feet per mile. In place of the original tangent L D, the
tangent G H was substituted, and as G H has a grade of
40 feet per mile against L D of 20 feet, it will be seen that
the two grade lines constantly approach each other. The
difference in grade being 30 feet, it required, at a gain in
grade of 20 feet per mile, a distance of 1^- miles for the two
grades to meet. The tangents A K and G H being estab-
lished, they were produced intersecting at M. The inter-
section angle G M N measured 57. A 5 18' curve was
decided upon, and the tangent distances M F and M G
measured by direct measurement, and the P. C. and P. T.

On account of the steepness of the slopes and the height
of the hill, much difficulty was experienced in making a
satisfactory intersection. Within a distance of 500 feet
there was a difference in elevation of more than 300 feet, and,
though taking every precaution, some of the sights contained
a vertical angle of more than 60. The lines were run
principally in the early morning hours, though some of the
best results were obtained on cloudy days. A large tunnel
transit with powerful lenses, and of more than double the
weight of an ordinary transit, was used. Common pins
against a dark background were used for backsights. First
an intersection was made, large plugs (6 inches square)
being used. The tangent KM was then repeatedly run,


and each line marked on the plugs O and P, Fig. 431, with
tacks, each one of which was numbered, as shown in the
figure. The lines varied each time, no two coinciding.
One or two fell wide of the mark and were ignored. Finally
the mean of the lines (as shown by the heavy line in the
figure) was adopted as final. The tangent G M was then

FIG. 431. FIG. 432.

run an equal number of times, and each intersection on the
line O' P' , Fig. 432, marked on the plug Q with a tack and
numbered. The mean of these intersections, as indicated
by the heavy line, was taken as final.

Equally great difficulty was experienced in locating the
P. C. and P. T. The distance was measured many times,
and each distance marked. The mean was then taken as
the correct measurement. The top of the hill had the form
of a plateau, and the center of the curve, O, was located .by
turning a right angle to the tangent K F at /% the P. C. ,
and measuring the radius 1,081.44 feet, locating the center
O. The central angle F O G of 57 was then turned, and
the second radius O G run out and measured. The line and
measurement falling on the plug at the P. T. at G proved
the work correct. The reward for all this care and pains
was in the almost perfect alinement of the tunnel. The
tunnel was driven from both ends, and when the headings
met there was found to be less than a half inch discrepancy
in .the two lines.

15O8. Tunnel Sections. Tunnel sections vary
somewhat, according to the material to be excavated, but
the general form and dimensions are much the same



The general dimensions are as follows : For double track
from 22 to 27 feet wide and from 21 to 24 feet high, and

Section of Single Track Tunnel.

for single track from 14 to 10 feet wide and from 17 to 20
feet high. See Figs. 433 and 434.

In seamy or rotten rock the section is sufficiently enlarged
to receive a lining of substantial rubble or brick masonry
laid in good cement mortar. When the material has not
sufficient consistency to sustain itself until the masonry
lining is built, resort is had to timbering, which furnishes the
necessary support.

1509. Tunnel Driving. Tunnels in rock are driven
either by hand or machine drills. The requirements of
modern railroad construction are such that hand drills play
a very important part in tunnel work. There are many
points in favor of hand drills and hammers, viz., portability,
cheapness, and immunity from the accidents which fre-
quently cause delays where machine drills are used. But
the process is slow, compared with machine work, and time
limitations have made the use of machine drills compulsory.

1510. Plant. The plant for furnishing the com-
pressed air used in working the drills consists of a boiler
house where steam is generated, and an engine house


containing the engines, air compressor, and air receiver. Both
houses are usually under one roof. If the tunnel is short, a
single plant, situated near one of the tunnel portals, furnishes
power for all the machinery used at both working faces.
When the tunnel is of great length, an air compressing plant
is stationed at both ends. About 12 horsepower is required
to run each drill (drill cylinders 3 to 3^ inches in diameter),
and as each tunnel face requires six drills, a 70-horsepower
boiler and engine is required to work each tunnel face.
When the air is conveyed a great distance, there is some
loss of power through friction. A three-inch pipe will carry
sufficient air for six drills. The pipe couplings are well leaded
to prevent waste of air.

1511. Method of Driving. When the material is
rock, the mode of driving is the following : The tunnel sec-
tion is divided into two parts, viz., the heading and the
bench. The heading comprises from one-fifth to one-fourth
of the entire section extending from the roof downward. It
is from 6 to 8 feet in height, and is kept from 50 to 250 feet

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