METHODS OF HAULING IN TUNNELS.
The transportation from one point to another within the tunnel and its
shafts of any material, whether it is excavated spoil or construction
material, is defined as hauling. In all engineering construction, the
transportation of excavated materials, and materials for construction,
constitutes a very important part of the expense of the work; but
hauling in tunnels where the room is very limited, and where work is
constantly in progress over and at the sides of the track, is a
particularly expensive process. Hauling in tunnels may be done either by
way of the entrances, or by way of the shafts, or by way of both the
entrances and shafts.
[Illustration: FIG. 33.--Platform Car for Tunnel Work.]
=Hauling by Way of Entrances.=--When the hauling is done by the way of
the entrances, the materials to be hauled are taken directly from the
point of construction to the entrances, or in the opposite direction,
by means of special cars of different patterns. For general purposes,
these different patterns of cars may be grouped into three
classes,--platform-cars, dump-cars, and box-cars. Representative
examples of these several classes of cars are shown in Figs. 33 to 36[6]
inclusive, but it will be readily understood that there are many other
forms.
[6] Reproduced from catalogue of Arthur Koppel, New York.
Briefly described, platform-cars (Fig. 33) consist of a wooden platform
mounted on tracks, and they are usually employed for the transportation
of timber, ties, etc. Dump-cars are used in greater numbers in tunnel
work than any other form. Fig. 34 shows a dump-car of metal
construction, and Fig. 35 one constructed with a metal under-frame and
wooden box. These cars are made to run on narrow-gauge tracks, and
usually have a capacity of about one to one and one-half cubic yards.
Box-cars are more extensively employed in Europe for tunnel work than in
America. Fig. 36 shows a typical European box-car for tunnel work. It is
made either to run on narrow-gauge or standard-gauge tracks.
[Illustration: FIG. 34.--Iron Dump-Car for Tunnel Work.]
[Illustration: FIG. 35.--Wooden Dump-Car for Tunnel Work.]
[Illustration: FIG. 36.--Box-Car for Tunnel Work.]
It is usually desirable in tunnel work to employ cars of different forms
for different parts of the work. In rock tunnels it is a common practice
to use narrow-gauge cars of small size in the headings, and larger,
broad-gauge cars for the enlargement of the profile. Where narrow-gauge
cars are employed for all purposes, it will also be found more
convenient to use platform-cars for handling the construction material,
and dump-cars for removing the spoil. The extent to which it is
desirable to use cars of different forms will depend upon the character
and conditions of the work, and particularly upon how far it is possible
to install the permanent track.
As a general ride, it is considered preferable to lay the permanent
tracks at once, and do all the hauling upon them, so that as soon as the
tunnel is completed, trains may pass through without delay. To what
extent this may be done, or whether it can be done at all or not,
depends upon the method of excavation and other local conditions. In
soft-ground tunnels excavated by the English or Austrian methods, it is
quite possible to lay the permanent tracks at first, since the whole
section is excavated at once, and the excavation is kept but a little
ahead of the completed tunnel. In rock tunnels, where the heading is
driven far ahead of the completed section, it is, of course, impossible
to keep the permanent track close to the advance work, and narrow-gauge
tracks must be laid in the heading. The same thing is true in
soft-ground tunnels driven by successive headings and drifts. In these
cases, therefore, where narrow-gauge tracks have to be used for some
portions of the work anyway, the question comes up whether it is
preferable to use temporary narrow-gauge tracks throughout, or to lay
the permanent track as far ahead as possible, and then extend
narrow-gauge tracks to the advance excavation. In the latter case it
will, of course, be necessary to trans-ship each load from the
narrow-gauge to the standard-gauge cars, or _vice versa_, which means
extra cost and trouble. To avoid this, the method is sometimes adopted
of laying a third rail between the standard-gauge rails, so that either
standard- or narrow-gauge cars may be transported over the line.
Whatever form the local conditions may require the system of
construction tracks to assume, it may be set down as a general rule that
the permanent tracks should be kept as far advanced as possible, and
temporary tracks employed only where the permanent tracks are
impracticable.
The motive power employed for hauling in tunnels may be furnished by
animals or by mechanical motors. Animal power is generally employed in
short tunnels and in the advance headings and galleries. In long
tunnels, or where the excavated material has to be transported some
distance away from the tunnel, mechanical power is preferable, for
obvious reasons. The motors most used are small steam locomotives,
special compressed-air locomotives, and electric motors. Compressed air
and electric locomotives are built in various forms, and are
particularly well adapted for tunnel work because of their small
dimensions, and freedom from smoke and heat.
=Hauling by Way of Shafts.=--When the excavated material and materials
of construction are handled through shafts, the operation of hauling may
be divided into three processes: the transportation of the materials
along the floor of the tunnel, the hoisting of them through the shaft,
and the surface transportation from and to the mouth of the shaft. These
three operations should be arranged to work in harmony with each other,
so as to avoid waste of time and unnecessary handling of the materials.
An endeavor should be made to avoid, if possible, breaking or
trans-shipping the load from the time it starts at the heading until it
is dumped at the spoil bank. This can be accomplished in two ways. One
way is to hoist the boxes of the cars from their trucks at the bottom of
the shaft, and place them on similar trucks running on the surface
tracks. The other way is to run the loaded cars on to the elevator
platform at the bottom, hoist them, and then run them on to the surface
tracks. If the first method is employed, the car box is usually made of
metal, and is provided at its top edges with hooks or ears to which to
attach the hoisting cables. When the second method is used, the elevator
platform has tracks laid on it which connect with the tracks on the
tunnel floor, and also with those on the surface.
=Hoisting Machinery.=--The machines most commonly employed for hoisting
purposes in tunnel shafts are steam hoisting engines, horse gins, and
windlasses operated by hand. Windlasses and horse gins are rather crude
machines for hoisting loads, and are used only in special
circumstances, where the shaft is of small depth, when the amount of
material to be hoisted is small, or where for any reason the use of
hoisting engines is precluded. The steam hoisting engine is the standard
machine for the rapid lifting of heavy vertical loads. Recently oil
engines and electric hoists have also come to be used to some extent,
and under certain conditions these machines possess notable advantages.
The construction of hand windlasses is familiar to every one. In tunnel
work this device is located directly over the shaft, with its axis a
little more than half a man’s height, so that the crank handle does not
rise above the shoulder line. To develop its greatest efficiency the
hoisting rope is passed around the windlass drum so that the two ends
hang down the shaft, and as one end descends the other ascends. A skip,
or bucket, is attached to each of the rope ends; and by loading the
descending skip with construction materials and the ascending skip with
spoil, the two skip loads tend to balance each other, thus increasing
the capacity of the windlass, and decreasing the manual labor required
to operate it. Skips varying from 0.3 cu. yd. to 0.5 cu. yd. are used.
The horse gin consists of a vertical cylinder or drum provided with
radial arms to which the horses are hitched, which revolve the cylinder
by walking around it in a circle. The hoisting rope is rove around the
drum so that the two ends extend down the shaft with skips attached, as
described in speaking of the hand windlass. The power of the horse gin
is, of course, much greater than that of a windlass operated by hand,
skips of 1 cu. yd. capacity being commonly used. Horse gins are no
longer economical hoisting machines, according to one prominent
authority, when V(H + 20) > 5000, where V equals the volume of material
to be hoisted, and H equals the height of the hoist, the weight of the
excavated material being 2100 lbs. per cu. yd. As a general rule,
however, it is assumed that it is not economical to employ horse gins
with a depth of shaft exceeding 150 ft.
As already stated, the most efficient and most commonly used device for
hoisting at tunnel shafts is the steam hoisting engine. There are
numerous builders of hoisting engines, each of which manufactures
several patterns and sizes of engines. In each case, however, the
apparatus consists of a boiler supplying steam to a horizontal engine
which operates one or more rope drums. The engines are always
reversible. They may be employed to hoist the skips directly, or to
operate elevators upon which the skips or cars are loaded. In either
case the hoisting ropes pass from the engine drum to and around vertical
sheaves situated directly over the shaft so as to secure the necessary
vertical travel of the ropes down the shaft. Where the shaft is divided
into two compartments, each having an elevator or hoist, double-drum
engines are employed, one drum being used for the operations in one
compartment, and the other for the operations in the other compartment.
Where the work is to be of considerable duration, or when it is done in
cold weather, more or less elaborate shelters or engine houses are built
to cover and protect the machinery.
Choice between the method of hoisting the skips directly, and the method
of using elevators, depends upon the extent and character of the work.
Where large quantities of material are to be hoisted rapidly, it is
generally considered preferable to employ elevators instead of hoisting
the skips directly. In direct hoisting at high speed, oscillations are
likely to be produced which may dash the skips against the sides of the
shaft and cause accidents. The loads which can be carried in single
skips are also smaller than those possible where elevators are used; and
this, combined with the slower hoisting speed required, reduces the
capacity of this method, as compared with the use of elevators. Where
elevators are employed, however, the plant required is much more
extensive and costly; it comprising not only the elevator cars with
their safety devices, etc., but the construction of a guiding framework
for these cars in the tunnel shaft. For these various reasons the
elevator becomes the preferable hoisting device where the quantity of
material to be handled is large, where the shafts are deep, and where
the work will extend over a long period of time; but when the contrary
conditions are the case, direct hoisting of the skips is generally the
cheaper. The engineer has to integrate the various factors in each
individual case, and determine which method will best fulfill his
purpose, which is to handle the material at the least cost within the
given time and conditions.
[Illustration: FIG. 37.--Elevator Car for Tunnel Shafts.]
The construction of elevators for tunnel work is simple. The elevator
car consists usually of an open framework box of timber and iron, having
a plank floor on which car tracks are laid, and its roof arranged for
connecting the hoisting cable (Fig. 37[7]). Rigid construction is
necessary to resist the hoisting strains. The sides of the car are
usually designed to slide against timber guides on the shaft walls. Some
form of safety device, of which there are several kinds, should be
employed to prevent the fall of the elevator, in case the hoisting rope
breaks, or some mishap occurs to the hoisting machinery, which endangers
the fall of the car. Speaking tubes and electric-bell signals should
also be provided to secure communication between the top and bottom of
the shaft.
[7] Reproduced from the catalogue of the Ledgerwood Manufacturing
Company, New York.