This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Many considerations, seen and unforeseen, enter into the cost of excavations, of which the unforeseen conditions can, at best, be only judged of, making it more important that known circumstances should be carefully considered. Among these may be mentioned the varying kinds of soil and rock, the depth to which the excavation can be carried without shoring, the distance to which the excavated material is to be carried, and whether pumping or bailing will be necessary. Material excavated to a depth of six feet can be thrown on to the surface, but below this depth a stage will be necessary, or else it must be carted or wheeled out.
In taking off quantities for excavation, work in trenches should be kept separate from large areas, as the cost will be greater on account of lack of room for working.
Where the nature of the soil is uncertain, borings should be made or test pits dug, not only to reveal the character of the material, but to determine the depth at which "hard pan" is to be found. This is especially necessary when the specifications call for the foundations of any structure to be carried to hard pan, without reference to the drawings, or when no definite depth of footing is shown.
In the absence of full instructions, it is best to figure to excavate a foot outside of all walls or footings, to give ample working room; and trenches for pipes, etc., should be enough wider than the pipe to allow of working all around. Hollows should be made where hubs rest, so as to give a full bearing for the pipe.
In taking quantities in irregular ground, the plot should be divided into a number of definite squares and the contents of each square taken separately. See Fig. 11.
Cost of Excavating. The cost of excavating varies in different localities and under differing conditions, no two cases agreeing in details or in execution. The governing factors are experience and judgment. Excavating is usually priced by the cubic yard and will average about as follows:
Picking - 12 cu. yds. per day at $2.40
Throwing out - 12 cu. yds. per day at $2.40
Wheeling 50 ft. away
Excavations in clay or very hard soil may cost from $0.50 to $1.00 while rock excavations will cost from $2.00 to $10.00, or more, according to the nature and position of the rock. Re-filling and packing around walls will cost usually from 1/4 to 1/2 of the price of earth excavations. Excavation of sand or loose gravel, which can be done by means of a horse scraper, will cost $0.30 per cu. yd.
Pile Foundations. The cost of piling varies with the nature of the soil and the length of pile necessary. Taking a 30-ft. pile as an average length, then piles 30 ft. long, driven and cut off level to receive footings, will cost $3.50 to $4.00 per pile.