Bearing Capacity of Shallow Foundations
3.4.1 Background and History of Bearing Capacity
In the era before Karl Terzaghi's bearing capacity equation was introduced in the United States, engineers went to their local building codes to determine what the allowable bearing pressure was for design of their foundations. If they were working outside of a major metropolitan area, where no local experience or building codes existed, they had to refer to general texts on “foundation soils.”
In my library, I have a textbook, Foundation Soils, published by the International Textbook Company in 1909 with no author noted, which I find to be weird. This 1909 engineering text suggests that foundation soils should first be examined to determine their character, be it rock, gravel, sand, or clay.
They go on to say, “Where no test of the sustaining power of the soil is made, different soils, excluding mud, at the bottom of the footings shall be deemed to sustain safely the following loads to the superficial foot: soft clay – 1 ton per square foot; ordinary clay and sand together in layers, wet and springy – 2 tons per square foot; loam, clay or fine sand, firm and dry, 3 tons per square foot; very firm, coarse sand, stiff gravel or hard clay – 4 tons per square foot.” They strongly suggest performing a full-scale footing load test. They state that a large building or important structure where the designer wants a greater bearing capacity than given in the list above, a load test is to be performed. ...