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.

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.

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.

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.

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.