BEARING CAPACITY BASED ON SPT-COMPUTER INTERPOLATION

Abstract

Any structural design must be accompanied with sound analysis referring to the foundation design. The columns carrying the total load of the building may be in very high stress. The actual stress that exists in columns may reach in actual cases to half f'c or more. On the other hand, the maximum carrying stress of soil is very much small compared with that for reinforced concrete, the situation that necessitate the enlargement of column end to have "a footing". While the compressive strength of concrete is easy to measure, the bearing stress of soil is not. Methods of evaluating the soil bearing capacity are numerous and consist of field and laboratory. The SPT is one of these field methods. Scientists tried to relate the SPT-N value with the soil strength properties resulting in large number of tables, charts, and graphs. This research considers the most famous methods to evaluate the bearing capacity from the SPT. A BASIC computer program is written to aid in using these formulas. In going to this step all tables, curves, and graphs must be converted to numerical equations. This is done by using the usual FD technique of interpolation. The authors feel that this program must be used with caution since it is not a replacement of sound hand calculations associated with engineering judgment and experience. This is because the very SPT is used only as a guide and never as a replacement of laboratory testing program except for sands since it is very difficult to get undisturbed samples.