A laboratory study of the shaft resistance of bored piles

The work presented in this thesis forms a pioneer study for future laboratory investigation into the behaviour of bored piles in clay. The research covered important aspects of installation and the factors affecting the development of pile shaft resistance. Total and effective stress approaches to pile design were examined using the test results.
A series of carefully controlled laboratory scale experiments was conducted on an elemental section of pile installed in a bed of anisotropically consolidated kaolin prepared to a known stress history. The tests were conducted in such a manner that the various stages of field pile construction were simulated as closely as possible.
To monitor the total stresses and pore water pressures in the soil and at the pile-soil interface, small-scale measuring devices were successfully developed.
Test results showed that the shaft resistance of bored piles in clay is primarily a function of the effective horizontal stress acting on the pile shaft and the effective angle of friction between the soil and the pile. For the variables investigated, the development of shaft resistance depended on the degree of moisture migration and soil softening close to the pile, the water-cement ratio of the pile, the time delay between boring and concreting, and the time lapse between casting and load testing.