The mode of procedure decided upon for r_Tunneling: A Practical Treatise.

open at least one track for the temporary accommodation of traffic; (2)

To remove permanently the causes which had produced the collapse; (3) To

build a new and much stronger lining. Close to the western side wall,

which was still standing, the débris was removed, and the opening

strongly strutted in order to allow the laying of a single track to

reëstablish communication. At the same time a shaft was sunk from the

surface above the caved portion of the tunnel, for the double purpose of

facilitating the removal of the fallen material and of affording

ventilation. The depth of the surface above the tunnel was 41.6 ft.,

which made the construction of the shaft a comparatively easy matter.

The shaft itself was 6¹⁄₂ ft. wide and 18 ft. long, with its longer

dimensions parallel to the tunnel, and it was lined with a rectangular

horizontal frame and vertical-poling board construction. After

temporary communication had been opened on the western track of the

tunnel, the remainder of the fallen earth was removed and the excavation

strutted. The new masonry lining was then built.

To remove permanently the cause of the cave-in, which was the

percolation of water from a close-by stream, this stream was diverted to

a new channel constructed with a concrete bed and side walls.

The failure of the original lining occurred by cracks developing at the

crown, haunches, and springing lines. The new lining was made

considerably thicker than the original lining, and at the points where

failure had first occurred in the original arch cut-stone _voussoirs_

were inserted in the brickwork of the new arch as described in Chapter

XIII.

=Chattanooga Tunnel.=--The Western & Atlantic Ry. passes through the

Chattanooga mountains by means of a single-track tunnel 1,477 ft. long,

constructed in 1848-49. The lining consisted of a brickwork roof arch

and stone masonry side walls. After the tunnel had been opened to

traffic, this lining bulged inward at places, contracting the tunnel

section to such an extent that it was decided to reconstruct the

distorted portions. After careful surveys and calculations had been

made, it was decided to take down and reconstruct about 170 ft. of the

lining.

Owing to contracted space in the tunnel, it was necessary to remove all

men, tools, and material, whenever trains were to pass through; and in

order to do this a work-train of three cars was fitted up with necessary

scaffolds, and supplied with gasoline torches for lighting purposes.

Mortar was mixed on the cars, and all material remained on them until

used. Débris torn out of the old wall was loaded on the cars, and hauled

to the waste dump. A siding was built near the West end of the tunnel

for the use of this train, and a telephone system was installed between

the entrances and the working-train. On account of the contracted

working-space and the greater ease with which brick could be handled,

it was decided to rebuild the walls out of brick instead of stone.

In tearing out the old wall a hole was first cut through the three

bottom courses of the arch and gradually widened. When the opening

became four or five feet long, a small jack was placed near the center

of it and brought to a bearing against the arch to sustain it. After

cutting the opening to a length of from 7 to 10 ft. depending on the

stability of the earth backing, the jack was removed and a piece of 8×16

in. timber placed under the arch and brought up to a bearing with jacks.

One end of the timber rested on the old wall, the other on a seat built

into the adjoining section of new wall. Wedges were then driven under

the ends of timber and the jacks removed. With this timber in place, the

old wall could be taken down with ease, the only trouble being that

small stones and earth fell in from above and behind the arch. This was

obviated by placing a 2 in. plank across the opening and just back of

the 8×16 in. timber. At several points, however, the earth backing was

saturated with water, and it became necessary to put in lagging as the

old wall was removed. This timbering would be taken out as the new work

was built up.

A suitable foundation for the new wall was secured at a depth from 2 to

4 ft., and a concrete footing was used. The section of the new wall was

then built up as near as possible to the 8×16 in. timber; the timber was

then removed and the new wall built up and keyed under the arch.

The new wall had a minimum width of 2¹⁄₂ ft. at the top, and 4 ft. at

the base of rail, and was provided with weep holes at intervals. To

facilitate matters, work was carried on simultaneously at two or three

different places, the intention being to get one place torn out and

ready for the bricklayers by the time they completed a section of the

new wall at another place.

In rebuilding the arch, sections extending from the springing line up as

far as was necessary to obtain the desired clearance, and from 2¹⁄₂ to

4 ft. in length, were removed. Near the sides, the earth above the arch

was a stiff clay, which was self-sustaining; but near the center there

occurred a stratum of gravel and clay saturated with water. This gave

considerable trouble, falling through almost continuously until

timbering could be placed. One end of this timber rested on the old

arch, the other on the adjoining section of the new work. As the new

work was to be set 6 to 13 ins. back from the old, it was necessary to

block up this distance on top of the old arch, to carry the end of the

lagging timber, in order that the timber should be clear of the new

arch.

Owing to the small clearance between the car roof and the arch, a

special form of centering was required, one that would occupy as small

space as possible. Bar iron 1 in. thick, 4 ins. wide, and 20 ft. long

was curved to a radius of 6¹⁄₂ ft., and on the underside of this was

riveted a 6-in. plate ¹⁄₄ in. thick. This plate projected 1 in. on the

sides of the centering, and carried the ends of the 1 in. boards used

for lagging. The rivets were counter-sunk on the outside of the

centering to present a smooth surface next the arch.

In keying up a section of the new work, a space about 18 ins. square had

to be left open for the use of the workmen. As soon as the next section

had been torn out, this space was built up. In building up the last

section, this space had to be filled from below, which proved to be a

tedious undertaking. The opening was gradually reduced to a size of 10 ×

18 in., and the top ring then completed and keyed up, the adhesion of

mortar holding the bricks in place until the key could be driven home.

The next ring was treated in a similar manner, and so on to the face

ring. Altogether 412 lin. ft. of the walls and 178 lin. ft. of the arch

were taken down and rebuilt, amounting in all to 607 cu. yds. of masonry

at the total cost of $7,440, or about $12.25 per cu. yds.

The regular trains arrived so frequently at the tunnel that slightly

over two hours was the longest working-time between any two trains, and

usually less than one hour at a time was all that it could be worked. In

addition to the regular trains, a large number of extra trains, moving

troops, had to be accommodated. Work was in progress eight months, and

during that time there was no delay to a passenger train. The repairs

were completed in August, 1899. The work was under the direction of Mr.

W. H. Whorley, engineer of the Western & Atlantic R. R., and foreman of

construction, A. H. Richards. A recent examination failed to reveal any

sign of settlement cracks at the junction points of the new and old

work.

CHAPTER XXIII.

RELINING TIMBER-LINED TUNNELS WITH MASONRY.

The original construction of many American railway tunnels with a timber

lining to reduce the cost and hasten the work has made it necessary to

reline them, as time has passed, with some more permanent material. In

most cases the work of removing the old lining and replacing it with the

new masonry has had to be done without interfering with the running of

trains, and a number of ingenious methods have been developed by

engineers for accomplishing this task. Three of these methods which have

been employed, respectively, in relining the Boulder tunnel on the

Montana Central Ry., in Montana, the Mullan tunnel on the Northern

Pacific Ry., in Montana, and the Little Tom tunnel on the Norfolk &

Western R. R., in Virginia, have been selected as fairly representative

of this class of tunnel work.

=Boulder Tunnel.=--This tunnel penetrates a spur of the main range of

the Rocky Mountains, at an elevation at the summit of grade of 5,454

ft., and is 6,112 ft. in length. Its alignment is a tangent, with the

exception of 150 ft. of 30′ curve at the north end. The material

penetrated is blue trap-rock with seams for 4,950 ft. from the north

end, and syenitic boulders with the intervening spaces filled with

disintegrated material for the remaining 1,160 ft. The dimensions and

character of the old timber lining and of the new masonry lining

replacing it are shown in Figs. 159 and 160.

The form of masonry adopted consisted of coarse rubble side walls of

granite, 13 ft. 8 ins. high, and generally 20 ins. thick, with a full

center circular arch of four rings of brick laid in rowlock form. When

greater strength was needed the thickness of the side walls was

increased to 30 ins. and that of the arch to six rings of brick.

[Illustration: ~Cross Section.~

~Longitudinal Section.~

~Cross Section.~

FIGS. 159 and 160.--Relining Timber-Lined Tunnel.]

The first plan adopted in putting in the masonry was to remove all the

timbering; but owing to the large number of falls and slides this was

abandoned, and the plan followed was to leave in the three roof segments

of the timbering with the overlying cord-wood packing and débris. In

carrying on the work the first step was to remove the side timbers. This

was done by supporting the roof timbers, as shown in Fig. 159; that is,

the first and fourth arch rib of an 8-ft. section containing four arch

ribs were supported by temporary posts. The intermediate arch ribs were

supported against the downward pressure by 6 × 6 in. timbers, extending

from the side ribs near the tops of the temporary posts to the opposite

sides of the intermediate roof segments, as shown in the longitudinal

section, Fig. 160. To resist the pressure from the sides, 4 × 6 in.

braces were placed across the tunnel from near the center of the

intermediate segments to the upper ends of the hip segments, as shown in

the cross-section, Fig. 159. The hip segments were then sawed off below

the notch, and the side timbering removed and the masonry built.

The stone was conveyed into the tunnel on flat cars, and laid by means

of small derricks located on the cars. Two derricks were used, one for

each side wall, and the work on both walls was carried on

simultaneously.

The arch was built upon a centering, the ribs of which were 5¹⁄₂ ins.

less in diameter than the distance between the side walls, so as to

permit the use of 2³⁄₄ ins. lagging. Each center had three ribs, made in

1-in. or 2-in. board segments, 10 ins. thick and 14 ins. deep. These

ribs were mounted on frames, which followed the opposite walls, and were

4 ft. apart, making the total length of the center out to out about 9

ft. The frames, upon which the ribs were supported, are shown in Fig.

161. As will be seen, they were mounted on dollys to enable the center

to be moved from one section to another. Jacks were used to raise and

lower the center into its proper position.

[Illustration: ~Cross Section.~

~Longitudinal Section.~

FIG. 161.--Relining Timber-Lined Tunnel, Great Northern Ry.]

The arch was built up from the springing lines on both sides at the same

time, four masons being employed. The rings were built beginning with

the intrados, which was brought up, say, a distance of about 2 ft. from

the springing line. Then the back of the ring was well plastered with

from ³⁄₈ in. to ¹⁄₂ in. of mortar, and the second ring brought up to the

same height and plastered on the back, and so on until the last ring was

laid. After bringing the full width of the arch up some distance, new

laggings were placed on the ribs for an additional height of 2 ft. and

the same process was repeated. All the space between the extrados of the

masonry arch and the old lining was compactly filled with dry rubble.

When high enough so that the hip segments had a foot or more bearing on

the masonry the segments were securely wedged and blocked up against the

brickwork, and the longitudinal 4 × 6 in. timbers removed. The

remaining space was now clear for completion of the arch, and both sides

were brought up until there was not sufficient space for four masons to

work, when the keying was completed by two masons beginning at the

completed and working back toward the toothed end. The brickwork was

built from the top of a staging-car.

[Illustration: ~Cross Section.~

~Longitudinal Section.~

FIG. 162.--Relining Timber-Lined Tunnel, Great Northern Ry.]

In a few instances where slides occurred after the removal of the slide

timbering, the method of re timbering the tunnel shown in Fig. 162 was

adopted. Two side drifts were first run 2¹⁄₂ ft. wide by 4 ft. high, and

the plate timbers placed in position and blocked. Cross drifts were then

run, and the roof segments placed, and the core down to the level of the

bottoms of the side drifts taken out. The lower wall plates were then

placed and the hip segments inserted. The bench was then taken down by

degrees, the side plates being held by jacks, and the posts placed one

at a time. As the masonry at the points where slides occur consists of

30-in. walls and six-ring arch, the timbering was 22 ft. wide in the

clear, with other dimensions as shown in Fig. 162.

Only a single crew of brick and stone masons was employed. In order to

prepare the sections for these masons it was necessary to have timber

and trimming crews at work throughout the whole day of 24 hours, so that

an engine and two train crews were in constant attendance. The single

mason crews were able to complete 8 ft. of side wall and arch in 24

hours. The number of men actually employed at the tunnel was 35. This

included electric-light maintenance, and all other labor pertaining to

the work. The tunnel was lighted by an Edison dynamo of 20 arc light

capacity, one arc light being placed on each side of the tunnel at all

working-places. Each lamp carried a coil of wire 20 or 30 ft. long to

allow it to be shifted from place to place without delay.

=Mullan Tunnel.=--This tunnel is 3,850 ft. long, and crosses the main

range of the Rocky Mountains, about 20 miles west of Helena, Mont. The

tunnel is on a tangent throughout, and has a grade of 20% falling toward

the east. The summit of the grade, west of the tunnel, is 5,548 ft.

above sea level, and the mountain above the line of the tunnel rises to

an elevation of 5,855 ft. Owing to the treacherous nature of the

material through which the tunnel passed, it had been a constant menace

to traffic ever since its construction in 1883, and numerous delays to

trains had been caused by the falls of rock and fires in the timber

lining. For these reasons it was finally decided to build a permanent

masonry lining, and work on this was begun in July, 1892.

[Illustration: ~_With Wall Plates._~

~_Without Wall Plates._~

~Old Timber Sections.~

~_Minimum Section._~

~_Average Section._~

~Permanent Work.~

FIG. 163.--Relining Timber Lined Tunnel, Great Northern Ry.]

The original timbering consisted of sets spaced 4 ft. apart _c._ to

_c._, with 12 × 12 in. posts supporting wall plates, and a five-segment

arch of 12 × 12 in. timbers joined by 1¹⁄₂-in. dowels. The arch was

covered with 4-in. lagging, and the space between this and the roof was

filled with cordwood. Except where the width had been reduced by

timbering placed inside the original timbering to increase the strength,

the clear width was 16 ft., and the clear height 20 ft. above the top of

the rail. Fig. 163 shows the timbering and also the form of masonry

lining adopted. The side walls are of concrete and the arch of brick.

This new masonry, of course, required the removal of all the original

timbering. The manner of doing this work is as follows: A 7-ft. section,

_A B_, Fig. 164, was first prepared by removing one post and supporting

the arch by struts, _S S_. After clearing away any backing, and

excavating for the foundation of the side wall, two temporary posts, _F

F_, were set up, and fastened by hook bolts. Fig. 146, _L_, and a

lagging was built to form a mold for the concrete. Several of these

7-ft. sections were prepared at a time, each two being separated by a

5-ft. section of timbering.

[Illustration: ~Section, with Concrete Car.~

~With Wall Plate.~

~Without Wall Plate.~

~Longitudinal Section.~

FIG. 164.--Construction of Centering Mullan Tunnel.]

The mortar car was then run along, and enough mortar (1 cement to 3

sand) was run by the chute into each section to make an 8-in. layer of

concrete. As the car passed along to each section, broken stone was

shoveled into the last preceding section until all the mortar was taken

up. The walls were thus built up in 8-in. layers, and became hard enough

to support the arches in about 10 to 14 days. The arches were then

allowed to rest on the wall, and the posts of the remaining 5-ft.

sections were removed, and the concrete wall built up in the same way as

before.

The average progress per working-day was 30 ft. of side wall, or about

45 cu. yds.; and the average cost, including all work required in

removing the timber work, train service, lights and tools, engineering

and superintendence, and interest on plant, was $8 per cubic yard.

[Illustration: FIG. 165.--Centering Mullan Tunnel.]

The centering used for putting in the brick arches is shown in Fig. 165.

From 3 ft. to 9 ft. of arch was put in at a time, the length depending

upon the nature of the ground. To remove the old timber arch, one of the

segments was partly sawed through; and then a small charge of giant

powder was exploded in it, the resulting débris, cordwood, rock, etc.,

being caught by a platform car extending underneath. From this car the

débris was removed to another car, which conveyed it out of the tunnel.

The center was then placed and the brickwork begun, the cement car shown

in Fig. 164 being used for mixing the mortar. The size of the bricks

used was 2¹⁄₂ + 2¹⁄₂ + 9 ins., four rings making a 20-in. arch and

giving 1.62 cu. yds. of masonry in the arch per lin. ft. of tunnel. The

bricks were laid in rowlock bond, two gangs, of three bricklayers and

six helpers each, laying about 12 lin. ft. per day. The brickwork cost

about $17 per cu. yd. The total cost of the new lining averaged about

$50 per lin. ft.

[Illustration: ~Cross Section.~

~Longitudinal Section.~

FIG. 166.--Relining Timber-Lined Tunnel, Norfolk and Western Ry.]

=Little Tom Tunnel.=--The tunnel has a total length of 1,902 ft., but

only 1,410 ft. of it were originally lined with timber. This old timber

lining consists of bents spaced 3 ft. apart, and located as shown by the

dotted lines in the cross-section, Fig. 166. Instead of renewing this

timber, it was decided to replace it with a brick lining. Although the

tunnel was constructed through rock, this rock is of a seamy

character, and in some portions of the tunnel it disintegrates on

exposure to the air. In removing the timber to make place for the new

lining some of the roof was found close to the lagging, but often also

considerable sections showed breakages in the roof extending to a height

varying from 1 ft. to 12 ft. above the upper side of the timbering. This

dangerous condition of the roof made it necessary that only a small

section of the timber lining should be removed at one time. It made it

necessary, also, that the brick arch should be built quickly to close

this opening, and finally that all details of centers, etc., should be

arranged so as to furnish ample clearance to trains. The accompanying

illustrations show the solution of the problem which was arrived at.

[Illustration: FIG. 167.--Relining Timber-Lined Tunnel, Norfolk and

Western Ry.]

Referring to the transverse and longitudinal sections shown by Fig.

166, it will be seen that two side trestles were built to carry an

adjustable centering for the roof arch. Two sections of these trestles

and centerings were used alternately, one being carried ahead and set up

to remove the timbering while the masons were at work on the other. The

manner of setting up and adjusting the trestles and centerings is shown

by Fig. 166 and also by Fig. 167, which is an enlarged detail drawing of

the set screw and rollers for the centering ribs. The following is the

bill of material required for one set of trestles and one center:

Trestles:

Caps and sills 8 pieces 8 × 8 ins. × 20 ft.

Posts 18 „ 8 × 8 „ × 11 „

Braces 16 „ 6 × 4 „ × 7 „

Centerings:

Ribs 27 „ 2 × 18 „ × 7 „

Bracing 12 „ 2 × 8 „ × 7 „

Support to crown lagging 2 „ 6 × 6 „ × 10 „

Crown lagging 20 „ 3 × 6 „ × 2 „

Side lagging 30 „ 3 × 6 „ × 10 „

Side strips 2 „ 2 × 12 „ × 9 „

Blocking for rollers 1 „ 5 × 8 „ × 12 „

6 screw and roller castings complete with bolts and lever; 114 bolts

³⁄₄-ins. in diameter; 7¹⁄₂ U. H. hexagonal nut and 2 cast washers

each.

With this arrangement the progress made per day varied from 2 lin. ft.

to 3 lin. ft. of lining complete. By work complete is meant the entire

lining, including stone packing between the brickwork and the rock. On

Feb. 23, 1900, 363 ft. of lining had been completed, at a cost of $33.50

per lin. ft. This cost includes the cost of removing the old timber, the

loose rock above it, and all other work whatsoever.

CHAPTER XXIV.

THE VENTILATION AND LIGHTING OF TUNNELS DURING CONSTRUCTION.

VENTILATION.

In long tunnels, especially when excavated in hard rock, proper

ventilation is of great importance, because the air cannot be easily

renewed, and the amount of oxygen consumed by miners horses and lamps

during construction is very large. The gases produced by blasting also

tend to fill the head of excavation with foul air. Pure atmospheric air

contains about 21% of oxygen and only 0.04% of carbonic acid; when the

latter gas reaches 0.1% the fact is indicated by the bad odor; at 0.3%

the air is considered foul, and when it reaches 0.5% it is dangerous. It

is generally admitted that the standard of purity of the air is when it

contains 0.08% of carbonic acid.

A large quantity of carbonic acid in the air is easily detected by

observing the lamps, which then give out a dim red light and smoke

perceptibly; the workmen also suffer from headache and pains in the

eyes, and breathe with difficulty. Naturally, miners cannot easily work

in foul air and, therefore, make very slow progress. It is, therefore,

to the interest of the engineer to afford good ventilation, not only

because of his duty to care for the safety and health of his men, but

also for reasons of economy, so that the men may work with the greatest

possible ease, thus assuring the rapid progress of the work.

It would be impossible to change completely the atmosphere inside a

tunnel, as the gases developed from blasting will penetrate into all the

cavities and gather there, but the fresh air carried inside by

ventilation has a very small percentage of carbonic acid, mixes with

that which contains a greater quantity, and dilutes it until the air

reaches the standard of purity. We have not here considered the gases

developed from the decomposition of carboniferous and sulphuric rocks,

which may be met with in some tunnels, and which render ventilation

still more necessary. Tunnels may be ventilated either by natural or

artificial means.

=Natural Ventilation.=--It is well known that if two rooms of different

temperatures are put in communication with each other, e.g., by opening

a door, a draft from the colder room will enter the other from the

bottom, and a similar draft at the top, but with a contrary direction,

will carry the hot air into the colder room, thus producing perfect

ventilation, until the two rooms have the same temperature. Now, during

the construction of tunnels the temperature inside may be considered as

constant, or independent of the outside atmospheric variations; hence

during summer and winter, there will always be a draft affording

ventilation, owing to the difference of temperature inside and outside

the tunnel. In winter time the cold air outside will enter at the bottom

of the entrances and headings, or along the sides of the shafts, and the

hot air will pass out near the top of the headings or entrances or the

center of the shafts; in summer the air currents will take the contrary

direction.

Natural ventilation in tunnels is improved when the excavation of the

heading reaches a shaft, because the interior air can then communicate

with the exterior at two points, at different levels. In such cases a

force equal to the difference in weight between a column of air in the

shaft and a similar one of different density at the entrance of the

tunnel, will act upon the mass of air in the tunnel and keep it in

movement, thus producing ventilation. Consequently, during winter, when

the outside air has greater weight than that inside, the air will come

in by the headings and go out by the shaft, and in the summer it will

enter at the shaft and pass out at the entrance. Sometimes to afford

better ventilation shafts 8 or 12 in. in diameter are sunk exclusively

for the purpose of changing the air. When the inside temperature is

equal to that outside, as often happens during the spring and autumn,

there are no drafts, and consequently the air in the excavation is not

renewed and becomes foul; then fires are lighted under the shaft and a

draft is artificially produced. The hot air going out through the shaft,

as through a chimney, allows the fresh air to come in as in ordinary

ventilation.

When the head of the excavation is very far from the entrances, or when

the mountain is too high to allow excavation by shafts, it is quite

impossible to secure good natural ventilation, especially during the

spring and autumn months, and the engineer has to resort to some

artificial means by which to supply fresh air to the workmen.

=Artificial Ventilation.=--Artificial ventilation in tunnels may be

obtained in two different ways, known as the vacuum and plenum methods.

Their characteristic difference consists in this, that in the vacuum

method the air is drawn from the inside and the vacuum thus produced

causes the fresh air from the outside to rush in, while the plenum

method consists in forcing in the fresh air which dilutes the carbonic

air produced inside the tunnel by workingmen and explosives. In the

vacuum method the pressure of the atmosphere inside the tunnel is always

less than the pressure outside, while in the plenum method the pressure

within is always greater than that outside. Ventilation is the result of

this difference of pressure, as the tendency of the air toward

equilibrium produces continuous drafts. Both these methods have their

advantages and disadvantages; but in the presence of hard rock, when

explosives are continually required, the vacuum method is considered the

best, because the gases attracted to the exhaust pipes are expelled

without passing through the whole length of the tunnel, thus avoiding

the trouble that a draft of foul air will give to the workmen who are

within the tunnel. In both these methods it is necessary to separate

the fresh air from the foul one; and this is done by means of pipes

which will exhaust and expel the foul air in the vacuum method, or force

to the front a current of fresh air when the plenum method is used.

Artificial ventilation may also be obtained by compressed air which is

set free after it has driven the machines, especially in tunnels

excavated through rock, when rock drilling machines moved by compressed

air are employed.

=Vacuum Method Contrivances.=--The most common of the vacuum appliances

consists in the simple arrangement of a pipe leading from the head of

the tunnel out through the fire of a furnace. The air in the pipe is

rarefied by the heat of the furnace and then set free from the other end

of the pipe, thus creating a partial vacuum in the pipe, into which the

foul air of the head rushes, the fresh air from the entrance taking its

place, and thus ventilating the tunnel. A similar arrangement may be

used with shafts, and the foul air may be driven out by a furnace which

is placed either at the top or bottom of the shaft. Such furnaces act

the same as those commonly used for heating purposes in the houses, with

this difference, that, instead of fresh air being forced in, foul air is

expelled. Another simple arrangement for producing a vacuum is by means

of a steam jet which is thrown into the pipe, and which helps the

expulsion of the air by heating it, thus producing a different density

which originates a draft besides that mechanically originated by the

force of the steam jet, which tends to carry out the foul air of the

pipes.

Foul air may also be expelled by means of exhaust fans which are

connected with pipes near the entrance of the tunnel. The fan consists

of a box containing a kind of a paddle wheel turned by steam or water

power and arranged so as to revolve at a high speed. The air inside the

pipe is forced out by blades attached to the wheel, and thus the foul

air of the front is driven away and fresh air from the entrance rushes

in to take its place, and perfect ventilation is obtained.

The best manner of expelling foul air from tunnels, according to the

vacuum method, is by means of bell exhausters. This consists of two sets

of bells connected by an oscillating beam and balancing each other. Each

set consists of a movable bell, which covers and surrounds a fixed bell

with a water joint. In the central part of the fixed bell there are

valves which open upwards, and on the bottom of each movable bell there

are valves which open from the outside. When one bell ascends, the

valves at the bottom are closed, the air beneath is then rarefied, and a

vacuum is produced; the valves in the central part of the fixed bell

filled with water are opened, and there is an aspiratory action from the

pipe leading to the headings, and the foul air is thus carried away. The

apparatus makes about ten oscillations per minute, and the dimensions of

the bells depend upon the quantity of air to be exhausted in a minute.

In the St. Gothard tunnel, where these bell exhausters were used, they

exhausted 16,500 cu. ft. of air per minute.

=Plenum Method Contrivances.=--Fresh air may be driven into tunnels to

dilute the carbonic acid by two different ways, viz., by water blast and

by fans. Water when running at a great velocity produces a movement in

the air which may be sometimes usefully and economically employed for

ventilating tunnels. Water falling vertically is let run into a large

horizontal zinc pipe having a funnel at the outer end; into this the air

attracted by the velocity of the water is forced. By an opening at the

bottom the water is afterward withdrawn from the pipe, and there remains

only the air which is pushed forward by the air which is being

continually sucked in by the velocity of the water.

The best and most common means of ventilation by the plenum method is by

fans. There are numerous varieties of these fans in the market, but they

all consist of a kind of fan wheel which by rapid revolution forces the

fresh air into the pipe leading to the headings of the tunnel or to the

working places. Instead of a large single fan, such as is used for

mining purposes, it is better to have a number of small fans acting

independently of each other, conveying the fresh air where it is needed

through independent pipes.

=Saccardo’s System.=--A new method of ventilating tunnels was devised by

Mr. Saccardo for the ventilation of the Pracchia tunnel along the

Bologna and Lucca Railway in Italy. At the highest end of the tunnel the

mouth was contracted inward in a funnel shaped form so as to just admit

a train. Immediately at this contraction, a lateral tunnel, 50 feet

long, branched off from one side of the main tunnel. At the mouth of

this lateral tunnel was installed a fan which forced air into the tunnel

and with 70 revolutions per minute delivered 3.532 cu. ft. of air per

second at a water pressure of 1 in. This air current was directed inward

through a second contraction or funnel, parallel to the one at the

entrance and 23 ft. beyond it. In operation the action of the artificial

air current was to suck in a considerable volume of outside air, while

the air pressure was sufficient to counterbalance the movement of air

produced by a train moving at a velocity of 16.1 ft. per second. Mr.

Saccardo’s method was employed in ventilating a tunnel on the Norfolk

and Western Railway with satisfactory results.

=Compressed Air.=--In the excavation of tunnels in hard rock a number of

rock drilling machines are employed which are moved by compressed air at

a pressure of not less than five atmospheres. At each stroke about 100

cu. ins. of compressed air are set free, and at an average of 10 strokes

per minute there would be 5000 cu. ins. of air at five atmospheres or

25,000 cu. ins., or a little more than 175 cu. ft. of fresh air at

normal pressure set free every minute by each of the machines employed.

But the air exhausted from the drilling machine is foul.

Regarding ventilation by compressed air, Mr. Adolph Sutro, in a lecture

delivered to the mining students of the University of California, said:

“I will note a curious fact which I have never seen explained, and

which is worthy of close investigation by means of experiments. In the

Sutro tunnel we found that the compressed air used for driving the

machine drills, after having been compressed and expanded and

discharged from the drills, was not wholesome to breathe, and the men

and mules would all crowd around the end of the blower pipe to get

fresh air. Whether the air in being compressed has parted with some of

its oxygen or because vitiated from some other cause, I do not know,

and I hope that this subject will at some future day be carefully

examined into.”

In the December, 1901, number of “_Compressed Air_,” a magazine

especially devoted to the useful application of compressed air, is read:

Compressed air wasted from power drills is so contaminated with oil

from the cylinders that it cannot be taken into consideration as

ventilation. It is as important to displace it with pure air as it is

to drive out or draw off other vitiated air. The ventilation should be

an independent supply provided by fan or blower, delivering by pipe at

the point where miners are working.

=Quantity of Air.=--The quantity of air to be introduced into tunnels

must be in proportion to the oxygen consumed by the men, the animals,

and the explosions. It is allowed that the quantity of air required for

breathing purpose and explosions is as follows:

1 workman with lamp needs 240 cu. yds. of fresh air in 24 hours.

1 horse „ 850 „ „ „ „

1 lb. gunpowder 100 „ „ „

1 lb. dynamite 150 „ „ „

In a long tunnel excavated through hard rock the number of workmen all

together may be assumed at 400 at each end, and each workman is supposed

to be furnished with a lamp. No less than ten horses are employed, and

the average quantity of dynamite consumed is 600 lbs. per day. From the

data given the consumption of air by workmen and lamps would be: 240 ×

400 = 96,000 cu. yds.; the consumption of air by horses would be 850 ×

10 = 8500 cu. yds.; the consumption of air by dynamite would be 150 ×

600 = 90,000 cu. yds.; making a total consumption of air per day of

194,500 cu. yds., or about 8000 cu. yds. per hour.

To obtain good ventilation, then, it will be necessary to furnish every

hour a quantity of fresh air amounting to not less than 8000 cu. yds.

Since, however, a large quantity of pure air is expelled with the foul

air, it is necessary greatly to increase this quantity.

It may be observed, in closing, that the water having its particles

divided, as in a fog or mist, rapidly precipitates the gases produced by

explosions. Now, when hydraulic machines are used, there is a hollow

ball pierced by holes that are almost imperceptible, from which the

compressed water spreads in very subtile particles, and this causes the

fall of the gases from explosions. Such a method of precipitating gases

is very good, but does not have the advantage of supplying new oxygen to

replace that consumed by the men, animals, lamps, and explosions;

besides, it has the defect of increasing the quantity of water to be

removed. In tunnels the pipes used either for conveying the fresh air or

for carrying away the foul air, are of iron, having a diameter of about

8 in.; they are fixed along the side walls about 3 ft. above the

inverted arch.

LIGHTING.

The object and necessity of a perfect lighting of the tunnel-workings

during construction are so obvious that they need not be enlarged upon.

Comparatively few tunnels require lighting after completion; and these

are generally tunnels for passenger traffic under city streets, of which

the Boston Subway is a representative American example. Considering the

methods of lighting tunnels during construction, we may, for sake of

convenience, chiefly, divide the means of supplying light into (1) lamps

and lanterns usually burning oil; (2) coal-gas lighting; (3) acetylene

gas lighting; and (4) electric lighting.

=Lamps and Lanterns.=--Lamps and lanterns are commonly employed by

engineers for making surveys inside the tunnel, and to light the

instrument. For ranging in the center line, a convenient form of lamp

consists of an oil light inclosed in glass chimney covered with sheet

metal, except for a slit at the front and back through which the light

shines, and on which the observer sights his instrument. To direct the

operations of his rodmen the engineer usually employs a lantern, either

with white or colored glass, much like the ordinary railway trainman’s

lantern, which he swings according to some prearranged code of signals.

Lamps and lanterns are used by the workmen both for signaling and for

lighting the workings. For signaling purposes red lanterns are usually

placed to denote the presence of unexploded blasts or other points of

possible danger; and colored or white lights are usually placed on the

front and rear of spoil and material trains. For lighting purposes, two

forms of lamps are employed, which may be somewhat crudely designated as

lamps for individual use and lamps for general lighting. Individual

lamps are usually of small size, and burn oil; they may be carried in

front of the miner’s helmet, or be fixed to standards, which can be set

up close to the work being done by each man. Miners’ safety lamps should

be employed where there is danger from gas. A great variety of lamps for

mining and tunneling purposes are on the market, for descriptions of

which the reader is referred to the catalogues of their manufacturers.

Lamps for general lighting are always of larger size than lamps for

individual use. A common form consists of a cylinder ten or twelve

inches in diameter, provided with a hook or bail for suspension, and

filled with benzine, gasolene, or other similar oil. Connected with this

cylinder is a pipe of considerable length and small diameter through

which the benzine or gasolene vapor runs, and burns when lighted with a

brilliant flame. Lamps of this type burning gasolene were extensively

employed in building the Croton Aqueduct tunnel. Various patented forms

of lamps for burning coal-oil products are on the market, for

descriptions of which the manufacturers’ catalogues may be consulted.

=Coal-gas Lighting.=--A common method of lighting tunnel workings is by

piping coal-gas into the headings and drifts from some nearby permanent

gas plant, or from a special gas works constructed especially for the

work. Gas lighting has the great advantage over lamps and lanterns of

giving a light which is more brilliant and steady. Its great objection

is the danger of explosion caused by leaks in the pipes, by breaks

caused by flying fragments of rock, and by the carelessness of workmen

who neglect to turn off completely the burners when they extinguish the

lights. In nearly every tunnel where gas has been used for lighting, the

records of the work show the occurrence of accidents which have

sometimes been very serious, particularly when fire has been

communicated to the tunnel timbering.

=Acetylene Gas Lighting.=--The comparatively recent development of

acetylene gas manufactured from carbide of calcium has given little

opportunity for its use in tunnel lighting, and the only instance of its

use in the United States, so far as the author knows, is the water-works

tunnel conduit for the city of Washington, D. C. Col. A. M. Miller, U.

S. Engineer Corps, who is in charge of this work, describes the method

adopted in his annual report for 1899 as follows:--

“It had been the practice to do all work underground by the light of

miners’ lamps and torches. This means of illumination is very poor for

mechanical work. The fumes and smoke from blasting, added to the smoke

from torches and lamps, render the atmosphere underground, especially

when the barometer conditions were unfavorable to ventilation, very

offensive and discomforting to the workmen. An investigation of the

subject of lighting the tunnel by other means, more especially at the

locality where the mechanics were at work,--brick and stone masons,

and the workmen on the iron lining,--resulted in the selection of

acetylene gas as the most available and economical in this special

emergency. Accordingly, an acetylene gas plant for 300 burners was

erected at Champlain-Avenue shaft, and one for 60 lights at Foundry

Branch. The engine-houses at the shafts, the head-houses, and

localities in the tunnel, when required, are lighted by these plants.

“Gas pipes were carried down the Champlain-Avenue shaft and along the

tunnel both in an easterly and westerly direction, with cocks for

burners at proper intervals every 30 feet; and this system sufficed

for illumination from Hock Creek to Harvard University, a distance of

over two miles. The plant erected at Foundry Branch was in like manner

utilized for the illumination from that point in both directions.

“By connecting with the stopcocks by means of a rubber hose, a

movable light, chandelier, or ‘Christmas-tree’ of any required number

of burners is used, thus concentrating the light in the immediate

vicinity of the work, and also enabling the illumination to be carried

into the cavities or ‘crow-nests,’ so called, behind the defective old

lining.

“This method of illuminating has proved very satisfactory and quite

economical. It is especially valuable as enabling good work to be

done, and facilitating a thorough inspection of the same.”

=Electric Lighting.=--By far the most perfect, and at present the most

commonly employed means for lighting tunnel workings, is electricity.

The light furnished by electric lamps is steady and brilliant, and does

not consume oxygen or give off offensive gases. The wires are easily

removed and extended, and the lamps are easily put in place and removed.

About the only objection to the method is the fragility of the lamps,

which are easily broken by the flying stones and the concussion produced

by blasting.

CHAPTER XXV.

THE COST OF TUNNEL EXCAVATION AND THE TIME REQUIRED FOR THE WORK.

=Cost.=--The cost of a tunnel will depend upon the cost of the two

principal operations required in its construction, viz., the excavation

of the cross section and the lining of the excavation with masonry,

metal, or timber. These two operations may in turn be subdivided, in

respect to expense, into cost of labor and cost of materials. It is a

comparatively simple matter to calculate the cost of the building

materials required to construct a tunnel; but it is very difficult to

estimate with accuracy what the cost of labor will be. The reason for

this is that it is impossible to foresee exactly what the conditions

will be; the character of the material may change greatly as the work

proceeds, increasing or decreasing the cost of excavation; water may be

encountered in quantities which will materially increase the

difficulties of the work, etc. Nevertheless, while accurate preliminary

estimates of cost are not practicable, it is always desirable to attempt

to obtain some idea of the probable expense of the work before beginning

it, and the more usual means of getting at this point will be discussed

here.

Two methods of estimating the cost of tunnel work are employed. The

first is to calculate the probable expense of the various items of work,

based upon the available data, per unit of length, and then add to this

a margin of at least 10% to allow for contingencies; the second is to

apply to the new work the unit cost of some previous tunnel built under

substantially the same conditions. In the first method it is usual to

consider the strutting and hauling as constituting a part of the work

of excavation. To estimate the cost of excavation involves the

consideration of three general items, viz., the excavation proper, the

strutting of the walls of the excavation, and the hauling of the

excavated materials and the materials of construction.

The cost of excavating the preliminary headings or drifts is greater per

unit of material removed than that of excavating the enlargement of the

section. The cost of bottom drifts is also always greater than that of

top headings, the material penetrated remaining the same. Mr. Rziha

gives the comparative unit costs of excavating drifts, headings, and

enlargement of the profile as follows:--

Bottom drifts $9.20 per cu. yd.

Top headings 4.80 „ „ „

Enlargement of profile 2.84 „ „ „

The cost of hauling increases with the length of the tunnel. This fact

and amount of this increase are indicated by the following actual prices

for the Arlberg tunnel:--

Top heading $6.76 per cu. yd., increasing 37 cts. per mile

Bottom drift 7.40 „ „ „ „ 26 „ „ „

Enlargement of profile 2.70 „ „ „ „ 10 „ „ „

In all the prices given above, the cost of strutting and hauling is

included in the cost of excavation.

The cost of excavation is not always the same for the same character of

materials in different tunnels. The following figures show the prices

paid for the excavation of calcareous rock in four different German

tunnels:--

Berliner Nordhausen Wetzler R.R. $1.24 per cu. yd.

Ofen 1.30 „ „ „

Stafflach 2.76 „ „ „

Gries 1.92 „ „ „

The method of tunneling has little influence upon the cost of the work,

as shown by the following figures from tunnels excavated through

calcareous rock by different methods:--

Ofen tunnel Austrian method $93.19 per lin. ft.

Dorremberg tunnel Belgian method 86.08 „ „ „

Stafflach tunnel English method 91.69 „ „ „

The Martha and Merten tunnels, excavated through soft ground by the

Austrian and German methods respectively, cost $87.95 and $87.55 per

lin. ft. respectively. In the excavation of the various sections of the

tunnel for the new Croton Aqueduct in America, the following prices were

paid:--

Excavation of heading $8 to $10.00 per cu. yd.

Tunnel in soft ground 8 to 9.00 „ „ „

Tunnel in rock 7 to 8.50 „ „ „

Brick masonry 10.00 „ „ „

Timber in place $40 per M. ft. B. M.

It is the practice in America to include the work of hauling under

excavation, but not to include the strutting, which is paid for

separately. In some cases only the market price of the timber is paid

for separately, the cost of setting up being included in the price of

excavation. The writer prefers the European practice of including the

total cost of timbering under excavation, since the two operations are

so closely connected, and since the contractor employs the same timber

over and over again. Knowing the dimensions of the several members of

the strutting, it is a simple, although somewhat tedious,

process to calculate the total quantity required. An idea of the

quantity of timber required for strutting in soft ground may be had from

the data given on page 55. The quantity will decrease as the cohesion of

the material penetrated increases, until it becomes so small in hard

rock-tunnels as to cut very little figure in the total cost.

The cost of hoisting excavated materials through shafts depends upon the

depth from which it is hoisted, and upon the character of hoisting

apparatus employed. The following table, showing the cost of hoisting

for different lifts and by different methods, is given by Rziha, the

cost being in francs per cubic meter:--

+-------+----------+----------------------+-------------+

| IN +----------+----------+-----------+-------------+

+-------+----------+----------+-----------+-------------+

| 15 | 0.172 | 0.077 | 0.062 | 0.035 |

| 30 | 0.212 | 0.087 | 0.070 | 0.045 |

| 45 | 0.257 | 0.100 | 0.080 | 0.050 |

| 60 | 0.305 | 0.112 | 0.092 | 0.082 |

| 90 | 0.410 | 0.152 | 0.110 | 0.087 |

| 120 | 0.535 | 0.195 | 0.135 | 0.092 |

| 150 | 0.722 | 0.240 | 0.157 | 0.112 |

+-------+----------+----------+-----------+-------------+

Mr. Séjourné, a French engineer, who has been connected with the

construction of numerous tunnels by the Belgian method where he was in

position to secure comparative figures, has given the following rules

for calculating the cost of tunnels. Assuming _A_ to represent the cost

of excavating a cu. yd. in the open air, the cost of excavating the same

quantity underground in driving headings will be from 9 _A_ to 11 _A_,

and in enlarging the profile it will be about 5 _A_. The cost of

constructing single-track tunnels varies with the thickness of the

lining, and may be calculated by the following formulas:

Without lining, _C_ = 5.5 _A_.

With roof arch only, _C_ = 6.4 + 6.4 _A_.

With lining 18 in. thick, _C_ = 9.4 + 7 _A_.

With lining 2 ft. thick, _C_ = 11 + 8 _A_.

In these formulas _C_ is the cost per cu. yd. of excavation, including

the masonry. For double-track tunnels the amounts given by the above

formulas may be used by reducing them about 7¹⁄₂% or 8%.

The second method of estimating the cost of tunnel work consists in

assuming as a unit the unit cost of tunnels previously excavated under

similar conditions. Mr. La Dame gives the following unit prices for a

number of tunnels driven through different materials:

+-------------------+--------+-------------+--------+----------------+

+-------------------+--------+-------------+--------+----------------+

|Granite-gneiss | 56 |$3.07 @ $3.85| $100. |$61.46 @ $190.40|

|Schist | 39 | 1.38 @ 1.53| 75.42| 43.11 @ 70.68|

|Triassic | 3 | ... | 90.85| 84.75 @ 93.33|

|Jurassic | 69 | 1.23 @ 1.38| 77.86| 35.24 @ 157.2 |

|Cretaceous | 34 | 0.61 @ 0.77| 59.60| 27.37 @ 92.25|

|Tertiary and modern| 39 | 0.33 @ 0.61| 105.80| 51.52 @ 188.36|

+-------------------+--------+-------------+--------+----------------+

In the following table is given a list of tunnels excavated through

different soils, from the most compact to very loose materials, and

driven according to the various methods which have been illustrated.

DOUBLE-TRACK TUNNELS.

+--------------+-----------------+--------+-------------+

+--------------+-----------------+--------+-------------+

|St. Gothard |... | 193.63 |Heading. |

|Church-Hill |Clay with shells,| 178.0 |... |

|Bergen No. 1 |Trap rock, | 182.31 |... |

+--------------+-----------------+--------+-------------+

SINGLE-TRACK TUNNELS.

+--------------+--------------------+----------+-------------+

+--------------+--------------------+----------+-------------+

|Burk |... | 83.90 |Wide heading.|

|Brafford Ridge|... | 85.33 |Wide heading.|

+--------------+--------------------+----------+-------------+

[16] Are unlined.

[17] Lined with timber.

The Habas tunnel through quicksand, between Dax and Ramoux, France,

cost $118.50 per lin. ft. The cost of the Boston subway was $342.40 per

lin. ft. The Severn and Mersey tunnels, constructed through rock under

water, cost respectively $208.38 and $263 per lin. ft. The First Thames

Tunnel, driven by Brunel’s shield, cost $1661.66 per lin. ft. The Hudson

River and St. Clair River tunnels, excavated through soft ground by

means of shields and compressed air, cost respectively $305 and $315 per

lin. ft. The Blackwall double-track tunnel under the River Thames, which

is the largest tunnel ever built by the shield system, cost $600 per

lin. ft.

In making estimates of the cost of projected tunnel work based on the

cost of tunnels previously constructed through similar materials, it is

important to keep in mind the date and location of the work used as the

basis for calculations. For example, a tunnel excavated in Italy, where

labor is very cheap, will cost less than one excavated in America, where

labor is dear, all other conditions being the same. Other reasons for

variation in cost due to difference of date and location of construction

will suggest themselves, and should be taken into full consideration in

estimating the cost of the new work.

=Time.=--The time required to excavate a tunnel depends upon the

character of the material penetrated and upon the method of work

adopted. Tunnels driven through soft ground by hand require about the

same time to construct as tunnels driven through hard rock by the aid of

machinery. Tunnels can be driven through hard rock at about as great a

speed as through soft or fissured rock, chiefly because the work of

blasting is more efficient in hard rock, and because no time is required

in timbering. The following table shows the average rate of progress in

different parts of the tunnel excavation through both hard and soft

materials in feet per month:--

+---------------+--------------------+--------------------+-----------+

| +----------+---------+---------+----------+-----------+

+---------------+----------+---------+---------+----------+-----------+

|Very loose soil|16.7- 26.8| | 6.6-16.7| | 6.6- 16.7|

|Loose soil |33.4-100 | |16.7-33.4| | 16.7- 33.4|

|Soft rock |66.8 |233.8-334|33.4-66.8|66.8-132.6| 33.4- 50 |

|Hard rock |50 - 66.8|233.8-334|33.4-50 |66.8-132.6| 66.8-100 |

|Very hard rock |33.4 |233.8-334|16.7-33.4|66.8-132.6| 66.8-100 |

+---------------+----------+---------+---------+----------+-----------+

The following tables showing the average rate of progress have been

compiled from the actual records made in the tunnels named:

+-------------+-------------+--------+--------------+-------------+

+-------------+-------------+--------+--------------+-------------+

| Sutro | 6.7 × 5.7 | 70.14 |Quartzose, |... |

| | | | | |

| Mount Cenis |10 × 10 | 188.7 |Calcareous | |

| Sutro | 8.15 × 10 | 227.45 |Quartzose, |... |

| Franklin |15 × 7 | 240 |... |Top heading. |

+-------------+-------------+--------+--------------+-------------+

The following table shows the monthly progress of completed tunnel in

feet excavated through rock:

+---------------+--------+----------+------------+

+---------------+--------+----------+------------+

+---------------+--------+----------+------------+

The average monthly progress in feet of excavating tunnels through

treacherous ground may be quite generally assumed to be for: (1) clay of

the first variety from 43.4 ft. to 60 ft.; for clay of the second

variety from 33.4 ft. to 43.4 ft.; for clay of the third variety from

23.3 ft. to 33.4 ft., and for quicksand from 30 ft. to 50 ft. The

monthly progress in feet made in sinking the shafts of the Hoosac and

Musconetcong tunnels in America was as follows:--

+---------------+------------+---------+--------+------------+

+---------------+------------+---------+--------+------------+

| East shaft |15.4 × 27.7| 1035 | 21.7 |Mica schist.|

| West shaft | 8 × 16 | 267 | 16.7 |Gneiss. |

| Vertical shaft| 8.35 × 16.7| 113.5 | 100 |Loose rock. |

| Inclined shaft| 8.35 × 26 | 304. | 32 |Loose rock. |

+---------------+------------+---------+--------+------------+

The average monthly progress of sinking shafts in treacherous soils may

be assumed to be as follows: clay of first variety, 50 ft. to 75 ft;

clay of second variety, 36.75 to 50 ft; clay of third variety, 23.4 ft.

to 36.75 ft; quicksand, 16.7 ft. to 33.4 ft.

For the reason that the details change with the various conditions

encountered in every work, all the tunnel operations have been treated

in a general way, purposely avoiding to give any detail. Also the rate

of progress and items of cost of tunnels have been given in a broad

manner because they greatly vary in the different works. This

information, however, can be easily obtained by consulting the

Engineering Magazines, where are reported all the tunnel works of

America and Europe, and where are given so many details which are very

valuable to expert engineers in charge of similar works, but not to

students and people who are looking only for general knowledge.

INDEX

Accidents and Repairs in the Belgian Method, 152

Accidents in Tunnels:

After Construction, 308

Baltimore Belt Line, 165

Chattanooga Tunnel, 311

During Construction, 301

General Discussion, 301

Giovi Tunnel, 309

Repairing of, 304

Acetylene Gas Lighting, 334

Air Compressors, Description of, 87

Air Locks, 264-272

Air Pressure, 268

American Method:

General Description, 172

Excavation, 172

Strutting, 174

Hauling, 175

Arrangement of Drill Holes, 90

Artificial Ventilation, 327

Austrian Method of Tunneling:

Advantages and Disadvantages, 180

Excavation, 176

General Description, 176

Lining, 180

Strutting, 177

Average Progress in Tunnels, 342

Baltimore Belt Line Tunnel, General Description, 160

Barlow’s Shield, 242

Beach’s Shield, 246

Belgian Method:

Accidents and Repairs, 152

Advantages and Disadvantages, 152

Excavation, 145

General Description, 144

Lining, 148

Hauling, 150

Strutting, 146

Bench, 131

Bends, 268

Blackwall’s Tunnel Shield, 248

Blasting-cone, 33

Blickford Match, 31

Boston Subway:

General Descriptions, 203

Roof Shield, 251

Boulder Tunnel Relined, 315

Box-cars, 61

Box Strutting, 51

Brandt Drilling Machine, 28, 112

Brown, W. L., 269

Brunel’s Shield, 240

Caissons, 293

Canals and Pipe Lines, 86

Cascade Tunnel, 98

Center-cut, 91

Center Line:

Curvilinear Tunnels, 14

Determination of, 9

Rectilinear Tunnels, 9

Simplon Tunnel, 106

Submarine Tunnels, 265

Triangulation, 12

Transferred through Center Shafts, 13

Transferred through Side Shafts, 14

Value’s Device, 10

Centers:

For Arches, 68

English Method, 169

Ground Molds, 66

Italian Method, 184

Lagging, 71

Leading Frames, 67

Setting Up, 70

Striking, 71

Chattanooga Tunnel, Accident, 311

City and South London Railway Shield, 250

Classification of Tunnels, 42

Coal-gas Lighting, 333

Cofferdam Method of Tunneling, 281

Van Buren Street Tunnel, Chicago, 282

Collapse of Tunnels, 302

Compressed Air:

For Power, 87

For Ventilation, 330

Concrete Lining, 75

Fort George Tunnel, 139

Murray Hill Tunnel, 126

Cost of:

Double-track Tunnels, 340

Hauling, 338

Headings, 337

Hoisting, 338

Single-track Tunnel, 340

Submarine Tunnels, 341

Subways, 209-217

Tunnels, 336

Craven, Alfred, 39

Craven’s Sunflower, 39

Cross-section:

Dimensions of, 20

Form of, 18

Hudson River Tunnel Pennsylvania Railroad, 277

Crown-bar (see American Method).

Subways, 204-211

Croton Aqueduct Tunnel, 95

Culverts, 80

Detroit River Tunnel, 296

Diamond Drilling Machine, 27

Directing the Shield, 265

Drift, 37

Drift Method:

General Discussion, 102

Murray Hill Tunnel, 123

Simplon Tunnel, 103

Drilling Machines:

Brandt, 112

Ingersoll, 26

Drills:

Diamond, 27

Hand, 23

Mountings for, 25

Percussion, 24

Power, 24

Rotary, 27

Dumping Cars, 60

Electric Firing, 32

Electric Lighting, 335

English Method:

Advantages and Disadvantages, 171

Centers, 169

Excavation, 166

General Discussion, 166

Lining, 170

Strutting, 167

Enlargement of the Profile, 38

Entrances, 81

Erector, 272

Excavation:

American Method, 172

Arrangement of Drill Holes, 90

Austrian Method, 176

Belgian Method, 145

Center-cut, 91

Enlargement of Profile, 38

English Method, 166

Fort George Tunnel, 136

German Method, 155

Headings, 37, 91

Hudson River Tunnel of Pennsylvania Railroad, 273

Italian Method, 182

Murray Hill Tunnel, 124

Quicksand Method, 189

Pilot Method, 193

Shield and Compressed Air Method, 267

Simplon Tunnel, 110

Excavating Machines:

For Earth, 22

For Rock, 23

Explosions, 33

Dynamite, 30

Gunpowder, 28

Nitroglycerine, 29

Quantity of, 34

Storage of, 30

Failure of Tunnel Roof, 305

Forgie, James, 269

Fort George Tunnel, 135

Foundations for Lining, 76

Fox, Charles B., 103

Frame Strutting, 49

Fuses, 31

Geological Survey, 3

German Method:

Advantages and Disadvantages, 159

Excavation, 155

General Description, 155

Hauling, 158

Strutting, 156

Giovi Tunnel Accident, 309

Graveholz Tunnel, 98

Greathead’s Shield, 245

Hand Drills, 23

Harlem River Tunnel, 285

Hauling:

American Method, 175

Belgian Method, 150

Italian Method, 185

German Method, 158

Hudson River Tunnel of Pennsylvania Railroad, 278

Motive Power, 61

By Way of Entrances, 59

Simplon Tunnel, 111

By Way of Shafts, 62

Heading and Bench Method:

Fort George Tunnel, 135

General Discussion, 130

St. Gothard Tunnel, 1

Headings, 37, 91

Hewett, H. B., 269

History of Tunnels, xiii

Hoisting Machines:

General Discussion, 62

Elevators, 64

Horse Gins, 63

Windlass, 63

Hoosac Tunnel, 93

Hopkins, Stephen W., 135

Hudson River Tunnel of Pennsylvania Railroad, 269

Hydraulic Jacks, 260, 271

Hydraulic Rams, 271

Illumination:

Acetylene Gas, 334

Coal-gas, 333

Electric, 335

Hudson River Tunnel of Pennsylvania Railroad, 280

Lamps and Lanterns, 330

Inclination of Strata, 6

Ingersoll Drilling Machine, 26

Inverted Arch Lining, 77

Iron and Masonry Lining, 74

Iron Lining, 73, 261, 276

Iron Strutting, 55

Full Section, 56

Headings, 56

Shafts, 57

Italian Method:

Advantages and Disadvantages, 188

Excavation, 182

General Description, 182

Modifications, 186

Strutting, 183

Jacks, 260, 271

Joining the Caissons, 295

Lagging, 71

Lamps and Lanterns, 330

Lighting (see Illumination).

Lining:

Austrian Method, 180

Belgian Method, 148

Concrete, 126, 139

English Method, 170

Foundations, 76

General Observations, 78

German Method, 158

Hudson River Tunnel Pennsylvania Railroad, 276

Invert, 77

Iron, 73, 261, 276

Iron and Masonry, 74

Italian Method, 185

Masonry, 74

Quicksand Method, 191

Roof Arch, 77

Side Tunnels, 79, 83

Side Walls, 77

Subways, 207-213

Timber, 72

Thickness of Masonry, 78, 83

Little Tom Tunnel Relined, 321

Loose Soil (see Soft Ground).

Masonry (see Centers).

Masonry Culverts, 80

Masonry (see Lining).

Masonry Lining, 74

Masonry Niches, 81

McBean, Daniel, 285

Mechanical Installations for Tunnel Work, 84

Milwaukee Tunnel, 226

Mont Cenis Tunnel, 92

Monthly Progress of Tunnels, 342

Mullan Tunnel Relined, 319

Murray Hill Tunnel, 123

Natural Ventilation, 326

New York Rapid Transit Subway, 209

Niagara Falls Power Tunnel, 97

Niches, 81

Open Cut or Tunnel, 1

Open-cut Tunneling:

General Discussion, 195

Parallel Longitudinal Trenches, 197

Single Trench, 196

Single Narrow Trench, 197

Transverse Trenches, 200

Tunnels on the Surface, 200

Palisade Tunnel, 94

Pennsylvania Railroad Shield, 270

Percussion Drills, 24

Pilot Method of Tunneling, 192

Plank Centers, 69

Platform Cars, 59

Plenum Method of Ventilation, 329

Pneumatic Caissons, 287

Polar Protractor, 39

Portals, 81

Power Drills, 24

Power Plants:

Air Compressors, 87

Canals and Pipe Lines, 86

Cascade Tunnel, 98

Croton Aqueduct Tunnel, 95

General Description, 84

Graveholz Tunnel, 98

Hoosac Tunnel, 93

Hudson River Tunnel Pennsylvania Railroad, 279

Mont Cenis Tunnel, 92

Murray Hill Tunnel, 128

Niagara Falls Power Tunnel, 97

Palisades Tunnel, 94

Receivers, 89

Reservoirs, 86

Simplon Tunnel, 117

Sonnstein Tunnel, 99

St. Clair River Tunnel, 99

St. Gothard Tunnel, 133

Steam, 85

Strickler Tunnel, 96

Turbines, 86

Prelini’s Shield, 251

Presence of Water, 7

Prevention of Collapse, 303

Progress in Sinking Shafts, 343

Progress of Excavation, 342

Progress of the Work, 342

Progress in Simplon Tunnel, 122

Quantity of Air for Ventilation, 331

Quicksand Tunneling:

General Discussion, 188

Removing the Seepage Water, 191

Quantity of Timber in Strutting, 54

Receivers, 89

Relining Tunnels, 315

Boulder Tunnel, 315

Little Tom Tunnel, 321

Mullan Tunnel, 319

Repairing of Accidents in Tunnels, 308

Reservoirs, 86

Roof Arch Lining, 77

Roof Shield for Boston Subway, 251

Roof of Caissons, 287-291

Rotary Drills, 27

Ryder, B. H., 296

Saccardo System of Ventilation, 330

Saunders, W. L., 88

Seepage Water, 191

Seine River Tunnel, 293

Setting up Centers, 70

Severn Tunnel, 221

Shafts, Description of, 40

Shaler, Ira A., 142

Shield and Compressed Air Method, 263

Shield Construction:

Diaphragm, 256

Cellular Division, 255

Dimensions of Shields, 259

Front End, 254

General Form, 252

Rear End, 257

Shell, 253

Shield Method:

Barlow Shield, 242

Beach’s Shield, 245

Blackwall Tunnel Shield, 248

Brunel Shield, 240

City and South London Railway Shield, 250

Greathead’s Shield, 245

History, 238

Prelini’s Shield, 251

St. Clair River Tunnel Shield, 247

Side Shafts, 41

Side Tunnels Lining, 79

Side Walls Lining, 77

Simplon Tunnel, 103

Soils Encountered in Tunnels, 3

Sonnstein Tunnel, 99

Stations of Subways, 207-216

St. Clair River Tunnel Shield, 247

St. Gothard Tunnel, 132

Steam Power Plant, 85

Stratification of the Soils, 6

Strickler Tunnel, 96

Striking the Centers, 71

Strutting:

American Method, 174

Austrian Method, 177

Belgian Method, 146

Dimensions of Timber, 54

English Method, 167

Fort George Tunnel, 137

Full Section, 51

German Method, 156

Headings, 48

Italian Method, 183

Murray Hill Tunnel, 125

Pilot Method, 193

Quantity of Timber, 54

Shafts, 52

Iron: Full Section, 56

Headings, 56

Shafts, 57

Submarine Tunneling:

Cofferdam Method, 281

Compressed Air Method, 225

Detroit River Tunnel, 296

General Discussion, 218

Harlem River Tunnel, 285

Hudson River Tunnel Pennsylvania Railroad, 269

Lining, 261

Milwaukee Water-Works Tunnel, 226

Pneumatic Caisson Method, 284

Seine River Tunnel, 293

Severn Tunnel, 221

Shield and Compressed Air Method, 263

Shield System, 238

Sinking and Joining Sections Built on Land, 293

Van Buren Street Tunnel, 282

Subways:

Boston, 203

Cost of, 209-217

Cross-sections, 204-211

General Discussion, 195-202

Lining, 207-213

New York Rapid Transit Railway, 209

Stations, 207-216

Sutro, Adolph, 330

Tamping, 32

Thickness of Lining Masonry, 78, 83

Thomson Excavating Machine, 22

Timber Lining, 72

Timbering (see Strutting).

Tremies, 299

Trussed Centers, 70

Tunnel or Open Cut, 1

Tunnels:

Baltimore Belt Line, 160

Classification of, 42

Fort George, 135

Murray Hill, 123

Simplon, 103

St. Gothard, 132

Hard Rock, 84

Drift Method, 102

Comparison of Methods, 141

Heading and Bench Method, 152

Heading Method, 130

Soft Ground:

American Method, 172

Austrian Method, 176

Belgian Method, 144

English Method, 166

German Method, 155

Italian Method, 182

Pilot Method, 192

Quicksand Method, 188

Submarine:

Detroit River Tunnel, 296

Harlem River Tunnel, 285

Hudson River Tunnel of Pennsylvania Railroad, 269

Milwaukee Tunnel, 226

Seine River Tunnel, 293

Severn Tunnel, 221

Van Buren Street Tunnel, Chicago, 282

Under City Streets:

General Description, 201

Boston Subway, 203

Turbines, 86

Vacuum Method of Ventilation, 328

Value, Beverley R., 10

Van Buren Street Tunnel, 282

Ventilation, 325

Artificial, 327

Compressed Air, 330

Natural, 326

Plenum Method, 329

Quantity of Air, 331

Saccardo’s System, 330

Simplon Tunnel, 120

Vacuum Method, 328

Vernon-Harcourt, L. F., 221

Working Platforms, 286

Wyman, Erastus, 293

Transcriber’s Notes

Inconsistencies in spelling and hyphenation have been retained except

as mentioned below; non-English words and phrases have not been

corrected except as listed below. The (minor) differences between the

Table of Contents and the chapter headings have not been rectified.

Page 36/132: Figs. 14 and 61 are identical.

Page 92/93, Sommeilier: possibly an error for Sommeiller.

Page 134, Soummelier: possibly an error for Sommeiller.

Page 174, Footnote 11: presumably Fig. 92, indicating the planes of

the sections, is from the same publication.

Page 176, Austrian method: Dresden and Leipsic, and the Oberau Tunnel,

are (and were in 1837) in Saxony, Germany (or Prussia).

Page 179, The short transverse beam _c_, Fig. 90: there is no short

transverse beam visible in Fig. 90, nor is it clear which other figure

might be intended; there is therefore no hyperlink to the

illustration.

Page 279, Stirtling boiler: possibly an error for Stirling boiler.

Pages 337 and 342, Arlberg: possibly an error for Aarlberg.

Page 340, Wartha: possibly an error for Martha; Mertin: possibly an

error for Merten.

Changes made

Footnotes, tables and illustrations have been moved out of text

paragraphs; some table data have been re-arranged for better

legibility. In some of the formulas brackets have been added for

clarity.

Several obvious minor typographical and punctuation errors have been

corrected silently.

Page 12, footnote 3: Chapter IX. changed to Chapter X.

Page 35: on page 155 changed to on page 135

Page 36: on page 34 changed to on page 35

Page 53: The lagging plank may be ... changed to The lagging planks

may be ...

Page 113: (1) changed to (_I_) (2×)

Page 117: ... and it in this clearing ... changed to ... and it is in

this clearing ...

Page 130: as indicated by Fig. 58 changed to as indicated by Fig. 61

Page 136: as indicated in the Fig. 63 changed to as indicated in the

Fig. 65

Page 146: as shown by Fig. 63 changed to as shown by Fig. 69

Page 149: underpining changed to underpinning

Page 150: Since the roof arch rests for some time ... changed to Since

the roof arch rests are for some time ...; as shown by Fig. 66 changed

to as shown by Fig. 72

Page 172: illustrated in Fig. 12 changed to illustrated in Fig. 11

Page 175: page 127 changed to page 123

Page 179: as at _b_, Fig. 90 changed to as at _b_, Fig. 97

Page 204: The third type of section is shown by Fig. 116 changed to

The third type of section is shown by Fig. 117

Page 218: Malinö changed to Malmö

Page 261: Fig. 118 shows the hydraulic jacks changed to Fig. 136 shows

the hydraulic jacks

Page 282: shown by Fig. 119 changed to shown by Fig. 141

Page 297: towed down to the tunnel side changed to towed down to the

tunnel site

Page 315: shown in Figs. 141 and 142 changed to shown in Figs. 159 and

160

Page 324: shown by Fig. 148 changed to shown by Fig. 166

Page 338: given on page 50 changed to given on page 55

Page 340: Scloss Matrei changed to Schloss Matrei

Page 341: _Time._ changed to =Time.=

Page 348, entry Ryder: page number 296 added; Sounstein changed to

Sonnstein (2×).

The mode of procedure decided upon for repairing the damage was: (1) To