Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/310

 22 THE BUILDING NEWS. Aprit 12, 1872. a the edge of the slope for the use of the | the foot of the slope of an embankment, and workmen. If the ground is level across the line the half-widths will be equal on the two sides, and are calculated simply by adding to the half-width at the formation level, the width of the slope, and the width of the cess; these three widths being added together, and laid off at right angles to the centre line, will mark the line of the post and rail fenc- ing; but when the ground slopes across the line—which is called sidelong ground—the two half-widths will be unequal, and there are various ways of setting them out. The formation level at any point of a rail- way is the level to which the ground is formed to receive the ballasting, and is generally 2ft. below the level of the rails. Tn Fig. 4, let F be the width at formation level, H the height of the surface above that level, m to 1 the slope of the ground, and nto 1 the slope of the cutting or em- bankment, S the width of the slope on the upper side, and s that on the lower side, then sS= aur x (a4 3 m—n m and mn 3+F ay en
 * wan ( —)

Adding together the half width at the forma- tion level, the width of either slope found as above, and the prescribed width of the cess, the full half-widths on the respective sides of the centre line will be ascertained. Thus, if the width F be 30ft., the height H 20ft, the slope of the ground across the line 12 to 1, and the slope of the cutting 2 to 1, then 12 X2 15 = 20 — = . s 3X ( +5 51ft and — 12% 2 15 — 2 OD OOTe., 242 * ( 12 pale and if the width of cess be taken at %ft., the half-widths will be On the upper side .... 15 -+ 51 +9 = 75ft. On the lower side .... 15-4 32 +9 = 56ft. Another method of finding the position of the top of the slope of the cutting, or foot of the embankment, on sidelong ground, is the following (see Fig. 5):—Find the hori- zontal distance A B by multiplying the height H into the ratio of the slope (m), and adding to the product half the width F. Lay off on the ground the distance so ob- tained, and set up a theodolite over the point B. Using the instrument as a level, read off the staff at C. Set the telescope of the theodolite to the angle of the slope of the cutting (m to 1). Let the staff-holder advance or recede, keeping the staff as near the ground as possible, until the cross hair of the instrument cuts the same reading on the staff at D as had been read off at C. The point E so found will be at the top of the slope on the upper side. To find the top of the slope on the lower side fix a movable slide or arm on the staff, set to the required slope. Plant the staff at the horizontal dis- tance A G=A Bas before found. Fix the top of the arm of the slide at the level of the centre stake A, and observe where the line of it cuts the ground. That point will be at the top of the slope of the cutting. The width of cess being added, the line of fencing will be found. It may here be said of the “cess” that it is sometimes called the bench, and sometimes the berm; but bench ought to be reserved to designate a set-off in the slope, made when the cutting is very deep, to contain a drain, so as to break the fall of water from the top of the slope. Berm, if we mistake not, is a part of a fortification. Cess seems to be the most proper word, as well as, in our experience, the most usual, for the space left for fencing and other uses be- tween the top of the slope of a cutting, or the boundary. In a similar manner the foot of the slope of an embankment may be found on sidelong ground as follows :—Knowing the height of the formation level above the surface on the centre line, calculate the width of slope due to that height according to the prescribed slope (m to 1), and add to it half the forma- tion width ($F). Lay off that width on the ground at right angles to the central line, as from A to B, Fig. 6, and over the point B set up a theodolite. Using the instrument as a level read off the staff at C. Set the tele- scope to the angle of the slope (m to 1), and move the staff until the line of sight cuts the same reading at D as had been read off at C. The point EK will be at the foot of the em- bankment. For the lower side measure out the distance A G=A B, fix the top of the slide level with the centre stake at A, and observe where the line of it cuts the ground. That point will be at the foot of the embank- ment. The width of cess being added on each side, the line of fencing will be found. FIG.F —a---—-— S>,. FILE After the lines of the post and rail fencing have been set out, and nicked out on the ground, the first proceeding is to strip off the top soil between them and wheel it out- side the fences, the erection of the post and rail fences proceeding at the same time. We have already said that stripping the soil and wheeling it to a distance not exceeding 20 yards is worth $d. per square yard in ordi- nary cases, but more when it is very dry or very wet; if it is required to be wheeled to a greater distance add 4d. per square yard for every stage of 20 yards beyond the first. This soil is to be brought back after the cutting and embankment have been made, and spread over the slopes. Soiling the slepes is worth 14d. per square yard in cuttings and 2d, on embankments, the depth of cutting or height of embankment not being excessive. The slopes of the cuttings and embank- ments of the railways of England, if culti- vated, would produce a large amount of vegetation, but the chief object in soiling them and sowing them with a mixture of rye- grass and clover seeds in about equal propor- tions is to produce a grass surface that will shed the rainwater and help to prevent slips. Slips of the slopes of cuttings and embank- ments are most difficult to guard against, and every possible precaution is taken to prevent them, one of which is to cut a drain along the top of the slope on the upper side of cuttings in sidelong ground, as well as to protect the slopes themselves. But even where no question of a slip need be enter- tained, as on that side of a cutting which is in the direction of the dip of the strata, a protection from the weather is necessary to prevent the slope being gradually worn away by the rainfall, the debris lodging in the side drains of the cutting and requiring constant remoyal. All stratified rocks—and they form nearly the whole of those cut through in engineering works, taking the term ‘‘rocks” to mean not only stone but all deposits—were originally deposited at the bottom of seas and lakes in a nearly horizontal position. The study of geology tells us that the action of the acid gases of the atmosphere upon the original rocks—plutonie rocks, granite, and the metamorphic rocks—loosened the exposed surfaces, the particles of which were carried away by rainwater into the rivers, and on- wards to the sea or into lakes. When the current necessary to keep these particles suspended in the water ceased in the expanse of sea or lake, and the water became quies- cent, or nearly so, the particles of earth settled, by their own gravity, to the bottom, stratum upon stratum. When, after the lapse of time, these deposits became covered by others of different materials—mineral, vegetable, or animal, the internal motions of the earth fixed them in the positions in which we now find them, inclined at all angles to the horizon—fixed, that is to say, at least for us so far that if we would re- move them we have to labour to doit. But the weather still continues to act upon them, and the rain to carry their particles down to the rivers. However hard we find it to separate some of the rocks now, they were at one time, it is reasonable to suppose, from the evidence presented to us, in a minute state of subdivision, and have become hard and compressed, as we find them, by the enormous weight of superincumbent strata. A stone put into a building should always be set upon its natural bed, for then the edges only of the lamin are exposed to the perishing action of the atmosphere ; while, if set in the contrary way, the weather peels off thin layers from time to time until the face of the stone becomes eaten away. ‘This natural bed is not horizontal in the quarry from which the stone is got, or very rarely so, but it was so originally, and quarrymen know when they are getting the stone which is its natural bed, however much inclined to the horizon now. Perhaps the shale of the coal measures shows this lamination more plainly than other strata do. Shale has every appearance that one would expect a thick bed of mud to have in which fern-like leaves and stalks of plants had been imbedded, and which afterwards had been subjected to enormous pressure. ‘This is a treacherous material to deal with; in making a cutting along the line of strike of this kind of ground, in which case the dip of the strata lies on one hand and the rise on the other, slips are very likely to occur on the upper side ; and this is the more likely when a thick bed of clay is passed through, the inclination of which has been thrown up conformably with the harder strata. The post and rail fencing is usually of larch, the posts not less than 6ft. long, set 2ft. into the ground. The posts are got by taking round sticks of not less that 7in. in diameter, cutting them down the middle, and afterwards squaring them to a dimension of 6in. by 8in. ‘Chey should be morticed for four rails and set 9ft. apart, and if of oak the tops should be bound round with hoop iron to prevent splitting by the weather. The mortices should be at the following distances : The upper mortice din. from the top, the - second lft. 5in. from the top, the third 2ft. 5in., and the bottom mortice 3ft. 2in. from the top. The rails should be 3Jin. by 1}in., 10ft. long, scarfed in the mortices of the posts. In the middle of each length a prick- post din. by 2in. should be driven into the