lying at a considerable inclination, the above method of construction will not be sufficiently secure, and recourse must be had to some other means of effecting this.

50. Retaining walls of sufficient thickness, built either dry or with the stones laid in mortar to support the roadway, are constructed for this purpose. These walls may have to be built on either side of the roadway to sustain the embankment on the lower side, and the portion in excavation on the higher part. The wall which sustains the embankment should be built up to the level of the roadway and a parapet or fence wall erected upon it, to protect pedestrian and vehicular traffic against accident. When necessary to erect a wall to form the slope or sustain the ground in excavation, it should be carried up to a height to meet the natural surface of the ground. The arrangement of retaining walls on sidelong cutting is shown. at fig. 16, a b being the natural surface of the ground. Considering the

FIG. 15.-Cross-section of a road showing method of stepping adopted in
sidelong ground.

inclination of the natural surface of the ground a b, it is evident that such a long embankment slope as db would endanger the stability of the roadway. It is necessary, therefore, to secure the solidity of the road in a more permanent manner by the substitution of retaining walls for an embankment on such a slope as that represented in the diagram. Under certain circumstances it might also be advantageous to build a retaining wall at c, to retain the part in excavation, as a long slope exposed to the drainage of the higher ground would in time cause the material composing it to be washed on to the road, and in all probability create a landslip. If a footpath is to be formed alongside of a road in sidelong ground it should be placed on the portion embanked, leaving as much as possible of the solid ground for vehicular traffic.

51. Roads formed over Low-lying or Marshy Ground.-In crossing plains or marshy ground it is necessary to form the surface of the road well above the general level of the surrounding country in order that it may be kept as dry as possible. This is particularly the case where the line of communication traverses a district subject to inundation. The best method

of accomplishing this is to excavate side trenches at sufficient distances apart on either side of the roadway, from 3 to 4 feet deep, 18 inches to 2 feet wide at bottom, and having side slopes 3 to 1. This excavated material is made use of in raising an embankment between the trenches, so as to elevate the road surface above any possible inundation, and the side ditches will serve to collect the surface water and discharge it to the nearest stream or water-course.

Soft or marshy ground is a difficult as well as an expensive obstacle to overcome in the construction of a new road. It must be borne in mind that laying out a road under these conditions is only undertaken when no other reasonable alternative is possible, such as deviating from a direct line by making a detour even of considerable length. The work can only be accoma

FIG. 16.-Cross-section of a road showing arrangement of retaining walls in
sidelong ground.

plished properly by draining the subsoil, so as to consolidate the ground as much as possible, and forming an embankment to carry the roadway. This is effected by excavating a trench in the soft ground to a depth varying with the degree of difficulty to be overcome, and then filling in the trench with stable material. The level part of the excavated portion of the trench is made of a width corresponding to the width of the formation level of the road, while the slopes of the trench should be inclined at the angle of repose of the soft material composing the natural ground. The slope of the stable materials forming the embankment is made to correspond with that of the trench slopes, and as this is much flatter than necessary, a broader foundation and consequently increased stability are secured.

Another method of making soft ground suitable for carrying a roadway is to drive in short piles; this has the effect of consolidating the mass of soft earth. Fascines, hurdles, and dry peat have also been at times employed for a similar purpose with good effect. Should these expedients fail, a bog

or marshy ground may be made secure by tipping sand, gravel, or stones upon it in order to form an embankment which will rest on the hard stratum below the moss, and raising the upper surface to the required level. The slopes of an embankment thus formed assume the same inclination as they would have under ordinary conditions.

52. Half-widths and Extent of Ground required.-When the inclination of the slopes has been determined, the half-widths, or distance on either side of the roadway, may be staked off, and the area of land computed, allowing 6 feet on either side beyond the formation level or the edge of the slope.

53. Finishing Slopes, Drainage. The slopes of cuttings and embankments should be dressed to regular surfaces with soil from 3 to 6 inches. deep and sown with grass seed. This diminishes to a great extent the effect of rain washing or running down the slopes, forming gullies, and helps to prevent any tendency to side-slips. When the slopes are exposed to the action of water they should be covered with dry stone pitching 12 inchesthick and of a height sufficient to protect the material of which the embankment is formed.

54. The numerous and diverse nature of circumstances met with in the laying out and construction of roads are such that no definite rules can be laid down to embrace all cases. The engineer will have to consider which form of construction will best suit the particular piece of work undertaken, with a view to economy in carrying out the operations involved, the stability of the works generally, and the subsequent maintenance of the road. In executing the necessary work in cuttings and embankments, level pegs are fixed indicating the depth or height of formation at convenient points, so that the workmen are enabled, by the use of boning rods or cross heads, to keep the intermediate position of the earthwork at its proper level. Important points, such as where a curve joins a straight line, should be transferred during the progress of the works by means of pilot pegs. This is accomplished by ranging a straight line from the point in question, fixing two pegs clear of the line of works and measuring the distance apart of these; the tangent point can then be readily re-established after the earthwork is completed. A similar operation should be carried out where important structures are to be erected.

The volume or cubical quantity of a piece of earthwork is ascertained by computing the area of a series of cross-sections of known distances apart, and the quantities obtained are stated in cubic yards.

55. Drainage. The drainage of roads is of two kinds, namely, surface and subsoil. It is one of the most important operations in connection with the construction of a road, as on its efficiency the subsequent maintenance of the surface will greatly depend. The slopes in cuttings on sidelong ground are generally the most troublesome, and great pains should

be taken in order to thoroughly intercept, from the rising ground, any flow or filtering of water towards the road bed. This is readily accomplished by forming catch-water ditches or drains on the uphill side of the cutting a few feet back from the crest of the slope or point where the excavation joins the natural surface of the ground, as at e, figs. 15 and 16. These, if possible, should be carried to the most convenient water-courses; but where the surface of the ground is such that a sufficient fall cannot be obtained unless at great expense in cutting and laying drain pipes, the water may be conveyed down the slope to the side channel or covered drain near the formation level as at c, fig. 15. When open conduits are formed for this purpose, the slope should be protected by forming a rough pavement, as the soil cannot withstand the action of the water on the steep slope generally given to cuttings. This object, however, is better attained by laying stoneware drain pipes in the slope 18 inches below the surface. The slopes of cuttings may, when necessary, be further protected by laying drains in a trench 18 inches deep, cut in an oblique direction up the slope, filling the space up to the surface with stones, and connecting them to the drain at the bottom of the cutting. Where springs occur, the water should be carried away by laying the pipes to the side drains, or by some other effective means.

FIG. 17.-Cross-section showing side drains at formation level of road. Drains should also be constructed at the foot of a slope in cuttings, varying in depth from 18 inches to 3 feet, according to circumstances. These may be built with either brick or stone; a less expensive method, however, and much more effective and durable, is made by laying salt-glazed plain pipes in the trench and filling the space up to the surface with broken stones, which must be free from dirt, to a height of 6 inches above the formation level of the road. Fig. 17 shows the two methods of construction, that at A being built of stone, while the drain at B is formed of salt-glazed pipes, the space above, in either case, being filled in with small stones.

56. The lower half of drain pipes may be surrounded with clay to prevent any water lying around them. This precaution should be adopted when the drain has but a small inclination, as the water in the pipe will be discharged more quickly and prevent the lower portion of the ground. becoming waterlogged.

57. In sidelong ground, and on level tracts of country, the side ditches should be formed before the cuttings are excavated and the embankments formed, as greater stability will be ensured by the ground being in a dry state.

58. The drainage of embankments does not require such extensive operations as those necessary in cuttings. The water from the surface of the road should be carried by the water tables or side channels to suitable points where it can be conveyed down the slopes in open troughs. It is usual to form an open ditch on either side, nearly parallel to the axis of the road and at the tail of the embankment, to collect and convey the surface water from the road and slopes of the embankment to the nearest water-course or point of discharge. Where a falling gradient in a cutting adjoins an embankment, a similar course is pursued when such cannot be diverted, great care being exercised to have the conduit of sufficient capacity to convey all the water which will collect in the cutting under the most unfavourable circumstances. On sidelong ground it is seldom necessary to make an opening at the toe of an embankment, the natural slope of the ground being in most cases sufficient to carry away the limited amount of water likely to collect there. All drains and open ditches should have sufficient capacity and acclivity to receive and convey away quickly all the water that may find its way into them; this will also be influenced by the nature of the soil in which they are placed. When a footpath exists at one or both sides of a road, the surface drainage collecting in the side channels is conveyed by pipes laid under them to the ditches, or drains, or on to the surface of the ground on the field side of the footpath.

59. Subsoil Drainage. The drainage of the subsoil provides for the removal of any water found in the soil immediately under the road covering in cuttings and on level tracts of country. This is an essential and important requirement in road construction, and on the efficient state of repair in which the subsoil drainage is maintained, will the cost of keeping the surface of a road in good repair depend.

60. The materials composing a road covering placed on a naturally wet, retentive, or undrained soil, such as clay and kindred earths, will go quickly to pieces by the traffic passing over it or by the action of thaw succeeding frost. The combined effect of these influences, which converting the whole coating material into a disintegrated mass, is simply ruinous.

Soils.-Soils of a siliceous and calcareous nature, and rocks generally, do not present any great difficulty, as their porous nature assists in securing a dry and solid foundation.

61. The side drains in cuttings, and the open ditches on the level portions of a road, will, as a rule, be sufficient for this purpose, even where the roadway is of a great width.

It is the argillaceous and allied soils which require careful treatment, as, being of a retentive nature, they become very unstable when in contact with water and the action of frost. The drainage of such soils may be effected by forming transverse or cross drains in the form of the letter V, as shown at b, a, b, fig. 18.