[(22 + 22 + 30
2 × 10) + (22 + 22 + 60
2 × 20) + (22 + 22 + 45
2 × 15 × 4)] × 100./6
EXCAVATION AND EMBANKMENT.
110. Some writers have considered that the grades of a road should be so adjusted as to equalize the cutting and the filling. The total rise and fall might not be much affected by this, but the mechanical effect of grades might. A perfect balance between the cuts and fills is not to be desired. The whole cost of earthwork must be a minimum, and it is often cheaper to waste and borrow, than to make very long hauls, and to form the grade line by interchange of material on the profile only.
111. The transverse slopes depend upon the nature of the soil in which the cut is made. Gravel will stand at a slope of one and a half horizontal to one vertical, and in some cases one and a quarter, or even one to one. Clay stands nearly vertical for some time, but finally assumes a very flat slope, in some cases two, three, and even four horizontal to one vertical. In places where a stratum of clay underlies more reliable earth, to avoid a very long slope, it may be economical to support the clay by a wall, and to slope the earth only.
112. Care should be taken in every case to secure good drainage and to protect the slopes by surface drains at the top. The drains in long cuts should be slightly inclined to insure the running off of the water. A fall of ten feet per mile is enough; five will answer in many cases. On side hill cuts a surface drain along the top of the upper slope will do good service. On many high embankments, catchwater drains, commencing at the road-bed and gradually sloping to the base, will prevent, in a great degree, cutting of the bank.
113. Embankments, when made rapidly, should be finished to the full width, somewhat above true grade, to allow for the after settlement. (See specification.)
114. The following allowances have been made for the shrinkage of material in some parts of America.
| Light, sandy earth | 0.12 |
| Clayey earth | 0.10 |
| Gravelly earth | 0.08 |
| Gravel and sand | 0.09 |
| Loam | 0.12 |
| Clay | 0.10 |
| Clay puddled | 0.25 |
| Wet surface earth | 0.15 |
The bulk of quarried rock on the contrary increases from twenty-five to fifty per cent.
115. When embankments are carried up slowly, in layers of three or four feet at a time, the after settling is very little; when carried up all at once it will be more. The full width must be kept, even above the required height. Fig. 56 shows the forms of a bank both before and after settlement.