Fig. 56.
The best method of forming a bank of bad material is to ram the layers as in fig. 57; thus the tendency is to consolidate by settling, and not to destroy the work by sliding.
Fig. 57.
TRANSPORT OF MATERIAL.
116. In the formation of embankments it is not always advisable to make the whole bank from an adjoining cut or cuts. The length of haul may be too long. In this case it is customary to waste a part of the cut and to borrow earth from some nearer point for the bank. That the transport shall be effected in the most economical manner, the product of the cube of earth, by the mean distance, (the distance between the centres of gravity, of excavation and embankment) must be a minimum. To determine the theoretical minimum expense, the problem becomes very complicated on account of the great number of variable elements entering therein; and the result obtained is applicable only to a particular case. Local circumstances more than any other thing, determine the position of a borrow pit, and the path over which the material is to be transported.
OF THE AVERAGE HAUL.
117. To find the cost of the movement of earth on any section, we must have, the total amount of earth to be moved, and the average haul; the latter being the distance through which, if the whole amount were moved, the cost would be the same as the sum of the costs of moving the partial amounts their respective distances. To find the average haul proceed as follows: First, find the distance between the centres of gravity of each mass both before and after moving, which may be done with sufficient accuracy for practice by inspection of the profile. Next,
118. Divide the sum of the products of the partial amounts by their respective hauls, by the total amount; the result is the average haul in feet. Or algebraically, representing the partial amounts by m, m′, m″, m‴, the respective hauls by d, d′, d″, d‴, the total amount by S, and the average haul by D, we have