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therefore be 2,500 cubic feet per minute. A 70-horsepower
compressor will deliver to the drills about 500 cubic feet of
free air per minute, and there will still be required for ven-
tilation the difference between 2,500 cubic feet and 500
cubic feet, which is 2,000 cubic feet per minute.

Exhaust fans with air pipes leading to the headings
should provide the balance of 2,000 cubic feet per minute.
A 24-inch air pipe, carrying air at a velocity of. about 10 feet
per second, will provide the necessary ventilation. The air
pipe should reach as near to the bench as may be without
injury from blasts. Contractors are invariably negligent in
the matter of ventilation, causing much needless suffering
to their men and much loss to themselves. Men can not
and will not do full work in a tunnel reeking with powder

Exhaust fans give much better results than blowers, as
they remove the foul air and powder smoke direct from the
heading, instead of forcing it out through the shaft or portal,
as in the case with blowers.

1527. Cost of Tunnel Excavation. The cost of
tunnel excavation varies widely, depending principally upon
the character of the material excavated. Firm rock of
moderate hardness can be removed at from $4.50 to $6.50
per cubic yard for the entire tunnel section. The heading
will cost about 40 per cent, more than the balance of the
section, on account of the limited space for working drills
and the greater amount of powder required in blasting.
Where unusual obstacles are met, the cost may increase
200 per cent, or 300 per cent, over the above figures.
Earthy material is easily broken, but the expense and delay
in timbering and lining brings the cost to about the same
figures as for solid rock.

1528. A Day's Work for a Machine Drill. An

average day's work for a machine drill in heading or on
bench is 50 feet of 2-inch to 2^-inch hole. The great records
made on the surface of the ground are not possible in tun-


nels where the accumulated muck from each preceding blast
must be partially removed and the roof trimmed before the
columns can be set up. Before firing, drills, tripods, bench
hose, and scaffolding must be removed to a safe distance,
which requires considerable time.

1529. Average Progress In Driving. Eight sec-
tions of the New York aqueduct tunnel gave an average
monthly progress of 127 feet for full section of about 16 X
16 feet. The average weekly progress in best ten headings,
using Ingersoll drills, was 38.73 feet, an average of 6. 45 feet
per day. Average monthly progress made by Ingersoll
drills at Vosburg tunnel on the Lehigh Valley Railroad was
202 feet, the tunnel section being about 24 X 26 feet. By
hand drills the average monthly progress at the two ends of
the same tunnel was 61 and 73 feet, respectively. Material
was a hard gray sandstone. A monthly average of 150 feet
for a full tunnel section is first-class work. The day is
divided into two shifts of ten hours each. There is an hour's
interval for changing shifts, and a dinner hour at 12 o'clock
noon and 12 o'clock midnight.

1530. Lighting. In modern tunnel work electric
lights are almost exclusively used. Oil lamps are to be
condemned, as they pollute the air. Tallow candles may be
used instead.

1531. Track work in Tunnels. In laying the per-
manent track, only first-class material is admissible. As the
roadbed is free from the action of frost, the track, after two
or three thorough surfacings, should require comparatively
little attention, except that given by the track walker. Rock
ballast is invariably used. Ditches should be large enough
to secure complete drainage. Oak ties are to be preferred,
of uniform dimensions, and spaced 18 inches center to cen-
ter of tie. Tunnel ties should be of the following dimensions :
Length, 8 feet; breadth, 8 inches; thickness, 7 inches.
There should be at least 8 inches of rock ballast between
bottom of tie and tunnel floor, giving a total thickness of



ballast of 15 inches. When the tunnel lining has an invert,
i. e., when the section of .the floor is concave, the drain is
sometimes built under the track, and covered with flags to
prevent clogging with ballast. Side ditches are to be
preferred, as they are always accessible and easily cleared.


1532. Classification. Under this head will be con-
sidered surface ditches, changing channels of streams, crib
work, paving, etc.

1533. Surface Ditches. Surface ditches are cut at
the top of slopes, but at sufficient distance from them to
prevent the water from breaking through and washing
down the slope. Where the natural slope of the ground is
towards the center line and of such a degree that a large
proportion of storm water runs off, the surface ditches
should be cut before construction commences. When this
important precaution is neglected, it often occurs that a
great amount of storm water is discharged into open cuts,
effectually stopping all work until the water is drained off

FIG. 455.

and the ground becomes dry enough to handle. The sight
of men and animals floundering in flooded cuttings is too
common in railroad work. Many contractors, and especially
sub-contractors, are of limited experience, financially irre-
sponsible, and generally follow a penny-wise policy. In such
cases, the engineer in charge must insist on such precau-



tions being taken as will insure a vigorous prosecution of
the work. Ditches are usually paid for at the same price
per cubic yard as ordinary excavation.

Fig. 455 shows a section of a surface ditch which will meet
the requirements of most situations. The line A B repre-
sents the natural slope of the ground ; C, the surface ditch ;
B D, the side slope of the cutting, and D E, the half width
of the roadway. The center line of the road is denoted by
E F.

1534. Changing Channels of Streams. It fre-
quently happens when the line of road is parallel to the gen-
eral direction of a stream that the windings of the stream
repeatedly cross the line of the road.

By changing the channel of the stream at favorable points,
a great saving is made in the cost of construction. A situa-

tion which warrants the changing of a channel is shown in
Fig. 456, in which the located line ABC crosses the stream
D G L at F and //, requiring an expensive bridge at each
point. By cutting a channel across the narrow neck , both
bridges are avoided. Such instances are of frequent

1 535. Crib Work. When the foot of an embankment
is subject to the erosion of a current of water, as at L in Fig.
456, a crib work of logs and stones is built into the embank-



ment at the exposed point. Protection cribs are ordinarily
built of round timber, so combined as to form compartments,
which are filled w'th stone to give them stability and with-

stand the action of the current. A general plan of the crib
is given in Fig. 457.

Cribs serve the purpose both of retaining walls and of re-
vetments. Their chief advantage lies in their adaption to
situations where the cost of retaining wall foundations
would be excessive. They can be readily built on wet,
marshy soils or in swift running water. When weighted
with stone, the structure sinks, and additional courses are
added to the top until the required height is attained. The
usual custom is to excavate a pit to a depth of from 12 to
18 inches, the bottom course of rangers, i. e., the logs run-
ning lengthwise in the crib, being laid close together. Where
there is danger of scour from the current, the outside com-
partment is sometimes built with an open bottom. As the
water works under the crib, the stone drops from the com-
partment above, forming a rip rap which prevents further
action of the current. The lower courses of the crib, being
kept constantly moist, are free from decay. The earth and
sand from the sustained embankment are gradually washed
into the cavities in the ballast until the whole forms one
compact mass of great strength and solidity. In Fig. 457
A B is the front elevation, the line A B being parallel to the



direction of the current, C D shows a section of the crib,
and E the foot of the embankment which slopes away at the
natural slope of earth, viz., \\ to 1. A plan of the crib
is shown at F and the foot of the embankment by the broken
line G H. A detail of a joint is shown at K. The log L,
corresponding to r s in the elevation, is called a ranger ;
and the log M, corresponding to C D in the section, is called
a cross-tie or tie. At each joint a drift bolt, usually a
piece of J-inch round iron sharpened at one end, is driven to
fasten the logs together. The bolt should be of sufficient
length to pass through three logs. A hole of slightly
less diameter than the bolt is bored to receive the bolt. A
compartment rilled with stone is shown at O.

1536. Paving. Paving as applied to protection work
consists of a stone covering laid on the surface of embank-
ments where they are exposed to the action of water. The
paving is usually 12 inches in depth and composed of good-


sized stone of fairly regular shape and even beds, the beds
being laid perpendicular to the slope of the embankment,
and when finished the whole to present a fairly uniform sur-
face. The slope of the embankment should be smoothed and
well rammed before the paving is laid. .

A foundation course of heavy stones A, Fig. 458, is laid
at the foot of the embankment in a pit from 12 to 18 inches
in depth, depending upon the nature of the soil. When the
stream has a rocky bed the foundation course is laid


upon the surface. The profile of the surface of the
ground is shown by the irregular line B C; the earth
embankment by D: the bed of the stream by E F\ the sur-
face of low water by G H, and of high water by L M.
The elevation of the protected surface is shown at K, with
the joints of the stones well broken. The grade of the
roadway is indicated by the line N O.


1537. Routine Work of the Engineer Corps.

The initial work of the construction corps, viz., the checking
and betterment of the alinement, the referencing of transit
points and cross-sectioning, together with the location and
conduct of tunnel work, have already been described. The
routine work which occupies the engineers' time from the
commencement of the construction to its completion will be
considered under one head.

1538. To Lay Out a Culvert at Right Angles to
the Center Line, Which is a Tangent: The rule for
laying out box culverts was given in Art. 1462. The
stakes for pit excavations and for neat lines of masonry are
arranged as shown in Fig. 459.

The broken lines show the outlines of the foundation pit,
which extends from six to twelve inches outside the neat
lines of the masonry, depending upon the depth of the
foundation. Ordinarily six inches is sufficient. The pit
should be large enough to permit a thorough inspection of
the masonry. The face lines of the masonry are located with
the transit. The center line X Fof the culvert being at
right angles to the center line P Q of the road, a plug is set
at A", Fig. 459, at the intersection of the center line of the
road and the center line of the culvert. The instrument is
then set up at K and a right angle turned in the line X Y
for locating face lines. The height of the embankment at
this point is nine feet ; the culvert opening two feet wide and
two feet high ; the covering flags are one foot thick, and the
parapet one foot high. Then, according to the rule for find-



ing the dimensions of a box culvert, given in Art. 1462,
we have 9 feet 4 feet = 5 feet; 1| X 5 feet = 7. 5 feet; 7.5
feet + 1.5 feet = 9.0 feet ; 9 feet + 8 feet, the half -width of the
roadway =17 feet, the distance from center line of road to
the end of the culvert. We then measure on the line X Y the
distance K L = 17 feet, setting a plug at L. On the same
line six or eight feet from L set a temporary point M. Then,
set large stakes at A and C, twelve inches from M, in lines
at right angles to L M, estimating the angles by the eye.
Measure accurately the distances MA and MC, each twelve
inches, and drive a lath nail in both stakes, checking the
distance^ C = 24 inches. Then, reverse the instrument,
setting a plug at A 7 , 17 feet from K, and a point at O for
locating the stakes at B and D, checking the measurements







t- - S





/ o


FIG. 459.

as at A and C. Next, set the instrument at A" and turn the
angle K N H= 90. Applying the rule given in Art. 1462,
for finding the length of wing walls, we have 2 feet, the
height of abutments-)- 1 foot, thickness of flags = 3 feet;
1 X 3 feet = 4. 5 feet ; 4. 5 feet + 2 feet = G. 5 feet, the dis-
tance from the face of the opening to the end of wing wall.
On the line N //"set a stake at H, ten or twelve feet from A 7 ,
and drive a lath nail in the stake on line. Reverse the
instrument, and at the same distance from N set a stake at
G, with a tack on line. Next move the instrument to Z, and
turning a right angle to X Y, set stakes at E and F. With
these stakes for a guide, the engineer can locate the pit





corners with the tape alone. A stake is driven at each
corner of the pit, and after the excavation is made and the
paving is laid, cord is stretched from
the tacks in the stakes from A to B, C
to D, E to F, and G to //, marking the
face lines. All other needed lines the
mason can lay out for himself.

1539. When the Center Line
of the Road Is a Curve. On

curves, as on tangents, wherever pos-
sible, the center line of the culvert is
placed at right angles to the center
line C L on the road, i. e., at right
FIG. 460. angles to the tangent D E of the

curve at the center D of the culvert (see Fig. 460). The wing
walls F and G are parallel to this tangent. The dimensions
of a culvert on a curve are the same as those on a straight
line, with the same height of embankment.

154O. When the Center Line of the Culvert
Makes an Oblique Angle with the Center Line of
the Road, i. e., When the Culvert is Askew. First
find what the length of the culvert would be if it were at
right angles to the center line of the road. This will give
the base of a right-angled triangle, one of whose angles is the
angle of skew. The other is easily found by subtracting
the angle of skew from 90. The hypotenuse will be the
required side distance. The wing walls must, in all cases,
be parallel to the center line of the road.

EXAMPLE. A railroad embankment is 12 feet in height. A box
culvert with opening 3 feet wide and 3 feet high must be built askew
at an angle of 70 with the center line. What is the distance from the
center line of the road to the center of the opening at the face of the
culvert ?

SOLUTION. Let A B, Fig. 461, be the center line of the road, and
C D the center line of the culvert, A K C 70 being the angle of skew.
At A' draw fat right angles to A B. From the given dimensions of
culvert and height of embankment, we have for a right-angled culvert,
side distances as follows: 12 5 = 7, H X 7 = 10.5, 10.5 + 1.5 = 12,


12 + 8 = 20 feet, the side distance. Lay off on KE the distance KG =
20 feet. Draw G H perpendicular to KG, forming the right-angled
triangle K G H, of which the angle G KH=W and the side K G =

FIG. 461.
20 feet. The side length, which is the hypotenuse K H, is found by

the formula cos 20 = '.^ r^fr or hypotenuse KH= '

hypotenuse K H 1 ~ cos 20 ~

21.28 feet = the side distance. Ans.

The wing walls for a right-angled culvert of the given
dimensions would have a length of, 1 X 4 = 6 ; 6 + 2 = 8
feet. Their length L M for the given culvert is found by
the following proportion:

20ft. : 21.28 ft. ::8 ft. : L M,

21 2*3 v 9
whence the length of skewed wing wall LM=

8.51 feet.

Side and wing walls are 2^ feet thick and covering stones
1 foot thick. The dimensions of the foundation pit are pro-
portionately the same as in Fig. 459. The stakes for the
neat lines of the masonry are located as in that figure.

Skewed culverts are of greater length and contain more
material than those at right angles to center line of road,
and, when arched, they are much more costly to build.
Considerable expense may, therefore, be properly incurred
in altering a channel so as to obtain a right-angled crossing.


1541.' Borrow Pits. Borrow pits are excavations
made for the purpose of obtaining additional material for
embankments when the regular excavation does not furnish
an adequate supply. The simplest form of borrow pit is a
trench dug parallel to the center line, a space of suitable
width being left between the slope stakes and the edge of
the pit. This space, or berme, as it is called, should be
six feet in width. Formerly, much of the material taken
from such borrow pits was handled with wheelbarrows. In
modern practice, where the material admits of it, the
wheeled scraper is invariably used. The amount of ma-
terial needed for the embankment in excess of that fur-
nished by the adjacent cuts is readily calculated. This
excess is first excavated from side borrow pits and deposited
in place, after which the material from the adjacent cuttings
is added.

Another means of borrowing material, and one which is
always adopted where the haul is not too great, is by widen-
ing the cuts. In proportion as the cut is widened, the
danger of the ditches being filled up by caving embankments
or snow is removed.

Where embankment is made from material cast from the
sides of the road, the berme is rarely more than four feet in
width. When the building of a road is only possible
through the exercise of the greatest economy, a berme of
four feet is admissible, even though it may involve increased
expense at some future time. Side work of this kind has
been let on some of the cheap Dakota lines at a price as low
as 12 cents per cubic yard, with an average height of em-
bankment of 2 feet. These lines were built through an
unsettled country, and carried the settlers who were to fur-
nish the future business for the road. As the country set-
tled up and traffic increased, these roads were practically
rebuilt. The original grade lines, whenever practicable,
followed the undulations of the prairie. In rebuilding,
these grades were greatly improved by filling up the sags.
On many sections the amount of material added was double
that put in the original work.



1542. Calculating the Contents of Borrow
Pits. Where the entire embankment is made from side
borrow pits, the contents of the embankment with an allow-
ance for shrinkage is taken as the contents of the pits.
This process of measurement saves work and is more
accurate than measuring the dimensions of the several pits,
especially when they are made with wheeled scrapers which
leave the pits in irregular shape.

When the cuts are widened for borrowed material, the
surface cross-sections are extended far enough to include the
additional excavation. After
the work is completed, the
cross-sections are again
taken. Both cross-sections
are platted on the same sheet,
which, at once, shows the
amount of the excavation.

Frequently the embank-
ment is many times greater
in volume than the tributary
cuttings, involving an ex-
tended borrow pit. In such
cases the cross-sections some-
times extend several hun-
dred feet from the center
line. Fig. 462 shows a bor-
row pit of this character with
the usual form of cross-

In this figure the proposed
borrow pit is situated on the
left of the center line, and
the cross-sections include an
area extending in length
from station 100 to station FIG. 462.

106, and in width 250 feet from the center line. A bench
mark is established at a convenient distance from the bor-
row pit, to be used in taking cross-sections for monthly









estimates and final cross-sections. The surface levels are
taken as follows: Stakes are driven on the center line
25 feet apart, commencing at station 100, and an equal
number at corresponding points on a line 250 feet from and
parallel to the center line. A rope 250 feet in length, with
tags tied at intervals of 25 feet, is stretched from station
100 to the stake at A, 250 feet distant. A rod reading is
then taken at each 25-foot tag and recorded. The line is
then moved forward 25 feet, one end being held at station
100-}- 25, and the other at B, and the levels on this line
taken. In the same way the entire surface is covered.
This arrangement divides the surface into squares of 25 feet
on a side. For monthly and final estimates the cross-
sections are taken at the same points, which insures accuracy
and greatly simplifies calculation.

The surface sections are platted on cross-section paper,
and placed far enough apart on the sheet to avoid over-
lapping when the monthly and final sections are platted.
The cross-sections for each monthly estimate are platted in
a different color, excepting the surface and final sections,
which are in black. Cross-section books, the leaves of
which are ruled like standard cross-section paper, are very
convenient for platting sections of borrow pits and special
excavations. They may be used in the field, like ordinary
note-books, the notes being recorded in pencil, and inked
in at the office when leisure time permits. For platting
work of this kind, cross-section books are far prefer-
able to loose sheets, which are sure to become soiled from
repeated use, and, in spite of the greatest care, some are

1543. Checking the Center Line. During con-
struction, and especially on embankments, the center line
should be frequently checked, i. e., run in on the incom-
pleted embankment. All materials will not at once take
the natural slope of 1 horizontal to 1 vertical. Frequently
the embankment becomes one-sided, and a line of centers
reveals at once any irregularity. Contractors of ten sustain


a loss on account of material being wasted. It is the duty
of the engineer to restore centers whenever they are needed,
whether asked for or not.

1544. Grade Stakes. When the roadway, either in
cutting or on embankment, is brought approximately to
grade, a grade stake is set at intervals of 100 feet. On
embankments the stake is driven on the center line, with
its top at grade. In cuttings the stake is driven at the side
of the roadway, and a peg is driven near the foot of the
stake. The elevation of the top of the peg is taken, and
the amount of cutting which must be made below the top
of the peg to reach the grade line is written upon the

1545. Care of Stakes. The destruction of stakes
by contractors' workmen, and the disregard of them by
contractors themselves and their foremen, is about universal.
There is no regularly prescribed penalty for such criminal
carelessness. The cost of restoring stakes should be charged
to the contractor at double price. A literal enforcement of
specifications in minor details, where they might be relaxed
to the advantage of the contractor and with no detriment
to the railroad company, has caused many a contractor to
regret his carelessness in this matter. A trick of dishonest
contractors is to move slope stakes nearer to the center line,
and so reduce the quantity of excavation or of embank-
ment. An alert engineer will soon get the true measure
of the contractors under him, and detect deceit of this

1546. Provision for Settling. Embankments are
raised from 5 to 10 per cent, above the established grade to
provide for the shrinkage which invariably takes place in all
earth embankments. The amount of this percentage is/
fixed by the engineer in charge, and depends upon ^he
nature of the material composing the embankment. Com-
pact clay or gravel will not settle or shrink more than half
as much as soft alluvial soils.


Online LibraryInternational Correspondence SchoolsThe elements of railroad engineering (Volume 2) → online text (page 25 of 35)