MATERIALS FOR BALLAST.

71

are pressed down, and the water is squirted up at the sides and ends of the sleepers. In such cases some kinds of ballast under continued attrition gradually become mud, and the sleepers subside more and more as the process goes on This action may at times be seen on railways, where either bad ballast has been employed or where the side drains are inefficient.

Ballast should be composed of a hard and unfriable material, such as gravel, broken stone, broken bricks, hard burnt clay, or slag from blast furnaces, and great care should be taken to exclude from it dirt or soluble substances. If burnt clay is used-as is sometimes the case in localities where the other materials above-mentioned are not easily to be obtained-it should be burnt as hard as possible, so that it may not be crushed or become dusty under the weight of the trains. Hard broken stone or sound broken bricks are often too expensive to be used as ballast, from the first cost of the materials themselves as well as from the cost of the labour required to break them; but occasionally these materials are available, and, if they can be used, answer admirably.

One of the best materials is slag from blast furnaces, which is now extensively used on railways in the iron districts. Slag, when broken or cast in small pieces, is extremely well suited for ballast, and is perhaps the best material to be found. It is, moreover, a great advantage to the ironmaster to find a use and a market for his slag, which until lately was worse than useless, causing him great difficulty and expense in finding places where it could be deposited.

The material, however, most generally used is gravel, which answers its purpose extremely well when it is free from loam or dirt. On coast lines shingle from the beach is often employed, and forms excellent ballast.

Care should, however, be taken that no great quantity of shells is mixed with the shingle, as they will be crushed under heavy weights, and cause the ballast to become dirty.

In many cases materials for ballast can be obtained of uniform quality, and composed of stones, at once suitable for the upper portions of the ballast, which have to be packed round and under the sleeper, and for the lower portions of the ballast, the object of which is to provide efficient drainage. Such a description of material is shown in Figs. 22 and 23 (p. 58), there being no difference in those figures between the upper and the lower ballast. When, however, stone, slag, or bricks have to be broken, or where the gravel in its natural state contains stones which are too large for the upper ballast, the coarse and fine materials are separated the one from the other, the former being put into the lower half of the depth of the ballast used, and the latter into the upper half, as shown in Fig. 26. The upper ballast would in such cases be composed of stones or fragments, each of which would not exceed 3 cubic inches in bulk, and would average about two cubic inches, while the lower ballast would be composed of stones or fragments of from 3 to 30 cubic inches.

The width of the top of the ballast beyond the ends of the cross sleepers is generally about 18 inches. Thus, the width of ballast for a single line of railway is, at the top 12 ft., for a double line 23 ft., for a treble line 34 ft., and for a quadruple line 45 ft. The slopes of the ballast at the sides are usually about 1 to 1, at which inclination good ballast stands well. Occasionally, in expensive cuttings, as has been already referred to, or where natural ballast is scarce, and where, consequently, stone or brick or slag has to be broken for ballasting the line, it is

RAILWAYS WITHOUT BALLAST.

73

desirable to keep the width of ballast as narrow as possible. In such cases the necessity for side slopes is avoided by roughly packing the sides with large stones placed nearly vertically, so as to resemble a dry retaining wall, as shown in Fig. 26.

The width, depth, and slopes of the ballast for a line laid with longitudinal sleepers are usually much the same as those for a line with cross sleepers; but for light

FIG. 26. Rough ballast packed at the side.

railways the ballast might be concentrated under the longitudinals, in order to diminish the amount required.

In this country railways invariably have ballast more or less good; but in some foreign countries, where ballast is not to be procured, railways are laid without any ballast. The sleepers, which in such cases are generally of iron, are usually laid in the best soil that can be found and when the soil procurable affords little or no facility for drainage, the top of the railway is dressed to a curved surface, so as to assist the water to flow off the railway to the sides of the line. I have seen many lines laid entirely without ballast, and was surprised to find in what good order the permanent way was maintained.

LECTURE III.

DIFFERENT DESCRIPTIONS OF PERMANENT WAY-SLEEPERS-LONGITUDINAL COMPARED WITH TRANSVERSE SLEEPERS-CHAIRSSLEEPERS-DOUBLE-HEADED RAIL-VIGNOLES RAIL

IRON

BRIDGE

ON

RAIL-ACTION OF WHEELS ON RAILS-WHEELS CURVES-MANUFACTURE OF RAILS-FISH-PLATES-FASTENINGSKEYS-SUPER-ELEVATION-CURVE OF ADJUSTMENT.

In my last lecture I brought down my description of the railway to the completion of the ballast.

The weights which rest on the small upper surface of the rails have to be distributed over a much larger surface of the ballast, which will be sufficient to bear the weight, just as we make large footings or foundations to distribute the weight of any structure over a large area. This distribution of weight is effected in rare cases by making the lower part of a specially designed rail so broad as to afford sufficient bearing area on the ballast, but ordinarily by introducing between the rail and the ballast intermediate appliances, of which sleepers and chairs are the most important.

6

An example of a rail made with a sufficiently broad base is the saddle-back,' or 'Barlow rail' (Fig. 27), which was designed to dispense with sleepers and chairs altogether. The rail is laid di

FIG. 27. Barlow rail.

rectly on the ballast, and the ballast is intended to completely

fill the inside of the saddle-back. The bearing area on the

PERMANENT WAY-RAILS.

75

ballast can no doubt in this way be made large enough to support the loads coming on the line, but the Barlow rail, unless its two sides be held fast, is vertically weak; while unless the ballast be kept absolutely tightly packed into the rail the wings of the rail spread elastically, and, working in and out, gradually displace the ballast beneath them. The Barlow rail has been largely used at home and abroad, and was thought at one time likely to form a very desirable and efficient description of road, composed of lasting materials with a minimum number of parts and fastenings; but experience has shown that so far at least as it has up to this time been used it leaves much to be desired, and that it is not well fitted for high speed or for heavy traffic.

Of other rails I need only mention three kinds, all of which require the addition of some kind of sleeper to distribute the weight upon the ballast. These are—

(a) The double-headed rail (Fig. 28), which has to

오

FIG. 28. Double-headed rail. FIG. 29. Flat-bottomed rail. FIG. 30. Bridge rail.

have chairs, as they are called, to keep it upright in place on the sleeper; (b) the flat-bottomed or Vignoles rail (Fig. 29), which requires no chair, but rests directly on the sleeper; and (c) the bridge rail (Fig. 30), introduced by the late Mr. Brunel for use with longitudinal sleepers. I will describe the special characteristics of each of the above well-known sections of rails further on, and after I have referred to some of the other parts of permanent way.

Sleepers in the present day are of wood or of