The estimator will first ascertain from a comparison of specifications whether the digging of pipe trenches is to be part of the plumbing contract. In case it is, he must next determine the length, depth and materials through which the trench must be cut. The length and depth will give him the breadth, which in turn will give the cubical contents of the earth to be removed. The material to be cut through is important, because the cost per cubic yard of excavating varies with the different materials. If a trench is carried to a depth of over six feet the earth must be handled twice and a scaffold must be built in the trench to hold the earth thrown up while at the same time affording space for the workmen to stand. Further, the trench will have to be made wider to afford room for the men. In loose or sandy soil, wet clay, or any kind of earth which is liable to cave, sheet piling will be necessary to protect the trench from caving in, and to safeguard the workmen. The . cost of sheet piling can be ascertained by figuring the length of trench which will require protection at one time then finding the number of two-inch planks of the required length that will cover the surface on both sides and adding four beams the length of the trench. Having the amount of lumber required the cost can be easily ascertained. It is assumed that the contractor has suitable adjustable trench braces for holding the piling in place. An allowance of time must, of course, be made to cover the labor of setting the sheet piling in place and removing it after the trench is partly filled. When the trench is a long one it may be opened in sections and the sheet piling used over and over again. It is a question which must be decided according to the circumstances of the case whether the lumber for sheet piling is a legitimate item of cost or should be supplied like tools and apparatus. Usually the sheet piling can be removed and used over again. When such is the case and the contractor has plenty of use for the lumber it should be considered as tools or machinery and as belonging to his plant. The only loss is the wear and tear on the lumber which would be allowed for in his general expenses. If, however, the work is to be done at a distance from home where the material would not repay the cost of transportation to the shop, should the use of sheet piling be an exceptional requirement, made necessary by the particular conditions of that one installation, and the lumber be of no further use to the contractor in his business; or if once the sheet-piling is in place it cannot be economically removed then the lumber should be entered on the estimating blank as a legitimate item of cost.

The soils differ so in different localities that the cost of digging trenches in one locality cannot be accepted as a base for estimating the cost of trenching through a different kind of soil in another locality. The contractor must familiarize himself with the substrata in his city and post himself as to the cost per lineal foot for digging trenches of various depths in the different soils. The presence of water in soil will complicate matters to such an extent that less earth can be thrown out of a trench per day by a man, and, in addition, pumps must be employed for keeping the trench dry. The cost of pumping will depend greatly on the amount of ground-water seeping into the trench. If but slight, a couple of hours per day for one man might suffice, while with an extremely wet ditch a man may be required steadily at the pump. In very long trenches, such as street sewer work, power pumps may be required, All of these various phases of excavating must be considered in connection with each operation, and the cost carefully worked out from the data at hand. However, until such data is available, the information contained in Table I will serve as a guide, and at all times as a check on the cost of handling water in trenches. Table I was compiled by Mr. Eliot C. Clarke, C. E. in 1885 for use during surveys made for the Massachusetts Drainage Commission.

Table I. Cost Of Handling Water Per 100 Linear Feet Of Trench

The removal of rock, particularly when the plumbing contractor is inexperienced in blasting, had better be sublet to a quarryman. This will prove less expensive to the plumber in the long run, besides relieving him of the responsibility. Until such time as the beginner can learn the exact cost of rock excavation for trenches in his locality, he can figure that it will not be less than $3.50 per cubic yard, and not over $5.50 per yard, provided the quantity to be removed is over ten cubic yards.