Methods for obtaining more information from pile load tests were determined. To assist in the interpretation of test results it is useful to consider the pile as a spring. In the lower ranges of load application the elastic compression of the pile is resisted by the friction or adhesion of the soil around the shaft. Consequently only part of the load applied at the top reaches the pile tip. By mathematical examination and by the results of an instrumented pile it is shown that compressive stress just reaches the tip of the pile when the slope of the load settlement curve becomes parallel to the elastic compression line for the pile. With this knowledge it is possible to make realistic estimates of the mobilized shaft friction, of the maximum load at the pile tip and of the elastic and plastic strain of the soil below the pile tip. Examples of analyzed results for seven piles have been given. The ultimate or long term capacity of a pile may be more reliably estimated by an effective stress analysis. Measurements are given of the effective or drained friction angle generated along the shaft of a model steel pile embedded both in clay and silt. Direct shear tests for smooth steel and wood in contact with remoulded clay and silt also are given. It was found that the friction angle is almost equal to the effective angle of shearing resistance of these two soils. /author/.
Abstract