.Excavaiing-inachincs, or steam-shovels for excavating and loading the material of a cutting, have been devised, and where large amounts of work are to be done they may be used to advantage. Figure 6 (pl. 27) very clearly exhibits the construction and method of operation of a machine of this description. The application of such machines is limited, of course, to the excavating- and removing of sand, gravel, clay, aud the like. Traut wine does not recommend their use where the depth of the cutting is less than m feet, for the reason that moving- them from place to place involves too great a loss of time. The following statements respecting the service ability of the steam-excavator are given upon this authority. In stiff soils cuttings may be made about 17 to 2o feet deep without changing the level of the machine. For greater depths, in such soils, the work must be done in two levels, since the bucket or dipper cannot reach so high. But in sand or gravel much deeper cuts may be made from a single level. In appearance and mode of operation the excavator resembles a dredging machine. A large plate-steel bucket, like a dredging-bucket, with a flat hinged bottom and provided with steel cutting-teeth, is forced into and dragged through the soil by steam-power. It dumps its load by means of the hinged bottom, either into cars for transportation or upon the waste bank. Each machine is mounted upon a locomotive-car, so that it can be moved from point to point as the work progresses, and carries its own water-tank to supply its boiler.
the construction of embankments two modes of procedure may be distinguished. In one, the embankment is built up from the base in successive thin layers. This method affords the best re sults in respect of the solidity of the structure, but, as it can be carried out conveniently only by hand-labor, it is not generally applicable. In the other method the embankment is extended forward by material dumped or poured upon it from the top. This is the method commonly adopted, as it permits of more rapid construction. If the embankment is advanced full width by this mode of construction, the successive increments form layers extending across the embankment, and a sliding or lateral giving wav of the structure need not be feared. Where, however, a narrower embankment is first constructed and this is widened by dumping on the sides, crevices which will endanger its stability may form lengthwise of the structure, and these may become the predisposing cause of its lateral displacement by sliding-. In this latter mode of embanking- the dumping of the material may often be facilitated by the employment of a crude species of trestle, which is covered up with the earth thrown down, and extended as the work advances. Fig-ure ro (pl. 24) exhibits a simple form of portable bridge supported on scaffolding, which may be shifted along- in advance of the embankment as this progresses. Figure 7 shows a burden car designed to tip forward, which may be used advantageously for this kind of work without the aid of trestles.
The of the roadway for a double-track road of normal gauge may be taken at about 22 feet. The intermediate distance between two lines of track is 6 feet, which allows sufficient free space for the engines of two trains to pass each other.
Slopes of are made as deep as from 5o to ED° feet below the surface, and embankments as high above the surface. The slopes for cuttings and embankments will be determined by a variety of circumstances, such as the nature of the material in respect of stratifica tion, coherence, and capability of resisting- weathering, by the height of the walls or banks, and by the presence or absence of springs. As a gen eral rule, the slopes of cuttings may be steeper than those of embankments, but in sand or earth a rise of one foot for to 1;4 or 2 feet is the common practice. In cuttings through solid rock the slopes may be nearly ver tical.
Stability of stability of the slopes is sometimes increased by planting them with grasses, by sodding, etc. Withes interlaced with stakes form an excellent means of conferring stability, and are occasionally used with good results. The most secure—and generally, also, the most costly—expedient is the walling up of the slopes. Sometimes, as where the line is contig-uous to water, protecting-walls of stonework become necessary, as in the case exhibited in Figure 4. In similar situations, where a portion of the slope is under water, piles, cribs of timber, fas eines, and the like, may be employed. The materials best adapted for embankments, as well as for cuttings, are sharp sand, gravel, or rubble, as these, while sufficiently insoluble, yet permit free drainage. To insure thorough drainage, lateral ditches are provided, as shown in Figure 3.
embankments are built of rock the stones adjoining and forming the face of the slopes should be regularly disposed in courses. Should the rock be readily decomposable, the surface of the slopes should receive a protective covering of soil. Sometimes only the lower portion of the embankment is formed of stone. Again, the configu ration of the ground may compel the use of rock embankments with steep slopes. Where these are confined to moderate heights, slopes of 2, 3, or even 4, feet rise to one foot of base may be admissible. Whether the face of the wall with the steeper inclines above named should be laid up in mor tar, or whether it will be sufficiently substantial without it, will depend upon whether the rock employed can be laid solidly in layers or not. Where, however, the question relates to the construction of a steep em bankment of considerable height, to be filled in with loose materials, re taining-walls solidly laid up in mortar are necessary. Figure 6 (j5/. 26) exhibits the construction of the retaining-walls of the Kulinbach inclined plane. This is over Too feet high, with concave slopes.