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supported by a wall raised two or three feet high at the bottom of them. These walls prevent the earth from falling from the slopes into the side channels of the road, and add
very much to the finished and workmanlike appearance of a road.
In many cases it may be advisable, particularly if an additional quantity of earth be wanted for an embankment, to make the slopes through the cuttings on the south side of a road of an inclination of three horizontal to one perpendicular, in order to secure the great advantage of allowing the sun and wind to reach more freely the surface of the road.
In districts of country where stones abound, expense in moving earth and purchasing land may be avoided, by building retaining walls, and filling between them with earth. In rocky and rugged countries this is generally the best way
of obtaining the prescribed inclinations.
In forming a road along the face of a precipice, a wall must be built to support it. The difficulty of forming a road in such a place is not so great as is imagined, for the face of a precipice is seldom perpendicular, and if the inclination should be half a foot perpendicular to one foot horizontal, this will admit of a retaining wall being built.
By building such a wall, say thirty feet high, and cutting ten feet at that height into the rock, and filling up the space within the wall, a road of sufficient breadth will be obtained, as shown in Plate II, fig. 1.
In forming a road along the face of a hill that is indented with ravines, in place of carrying the road over the natural surface of the land, the projecting points should be cut through and the earth laid across the hollows so as to straighten the line, as shown in Plate II. fig. 2., where the road, instead of following the sinuosities of the hill, as represented by the dotted line a a a, takes the line bbb.
In forming the bed for the road materials care should be taken, except where cutting into the surface is wholly unavoidable in order to obtain the proper longitudinal inclinations, to elevate the bed with earth, two feet at least, above the natural surface of the adjoining ground: by following this course the road will not be affected by water running under or soaking into it from the adjoining land. In arranging the inclinations, they should be obtained by embanking, when that is practicable, in preference to cutting.
Almost all old roads across flat and wet land are sunk below the adjacent fields: this has arisen
from the continued wearing of them, and carrying away the mud. No improvement is more generally wanting than new forming these roads so as to raise their surfaces above the level of the adjoining land. This would greatly contribute to the hardness of them, to economy in keeping them in repair, and to enabling horses to work with the advantage of having sufficient air for respiration.
Great care is necessary to be taken in making high embankments. No person should be intrusted with these works who has not had considerable experience as a canal or road maker; for, if the base of an embankment be not formed at first to its full breadth, and if the earth be not laid on in regular layers or courses of not exceeding four feet in thickness, it is almost certain to slip. In forming high embankments the earth should be laid on in concave courses, as represented in Plate II. fig. 3., in order to give firmness and stability to the work. It is not at all uncommon in many parts of the country to see embankments formed convexly, as represented in Plate II. fig. 4., the consequence of which is, that they are for ever slipping.
There have been but few attempts to make embankments by turnpike trustees that do not afford illustrations of this defect, and of a want of knowledge of the proper rules by which these works should be managed. No doubt, a chief reason for making cuttings and embankments, as is frequently the case, with slopes of one to one, has been, to save expense
in the purchase of land, and moving earth. But the consequence of making such slopes, is that the earth is constantly slipping ; so that, in the end, the expense is always greater in correcting the original error, than it would have been if proper slopes had been made in the first instance.
In forming embankments along the sides of hills, or what is called side-forming, the rule that should be followed, is that the slope to be covered should be cut into level steps to receive the earth, otherwise it will be very
liable to slip down the hill: in such cases, the earth should be well compressed, and great care should be taken to intercept all the land springs about it by proper drainage. For this purpose, a drain should be cut on the upper side of the road, and open drains should be made on the side of the hill above the road, to catch the surface water of the hill.
The figure 5. in Plate II. explains the manner in which the ground should be formed for side embankments, by cutting the level steps a a a, and shows where the drains should be made.
The slopes at which cuttings and embankments can be safely made entirely depend upon the nature of the soil. In the London and plastic clay formations, it will not be safe to make the slopes of embankments or cuttings, that exceed four feet high, with a steeper slope than three feet hörizontal for one foot perpendicular. In cuttings in chalk or chalk marl, the slopes will stand at one to one. In sandstone, if it be solid, hard,
. and uniform, the slopes will stand at a quarter to one, or nearly perpendicular.
If a sandstone stratum alternate with one of clay or marl, as represented in Plate II. fig. 6., it is difficult to say at what rate of inclination the slopes will stand; this will, in fact, depend upon the inclination of the strata. If the line of the road is parallel to the line of the bearing of the strata *, in such cases, large masses of the
* The line of intersection of any inclined stratum with the horizontal plane, is called the line of bearing of that stratum, or the drift-line. The dip, or inclination, of the stratum is the angle formed between a horizontal plane and a line drawn at right angles to the drift-line on the bed of the stratum.