Construction Effect on Load Transfer along Bored Piles

The load transfer behavior along bored piles is affected by details of pile construction particularly those imposing stress and moisture changes to the surrounding soils. An investigation involving moisture migration tests, in situ horizontal stress measurements, and borehole shear and pressuremeter tests shows clear effects of construction that lead to subsequent changes in soil properties. The construction of bored piles in Singapore and the region often involves casting of concrete either in unsupported “dry” boreholes or in “wet” boreholes filled with water. It is necessary to differentiate these two extreme construction conditions in bored pile design. Based on triaxial compression and pressuremeter tests on the residual soil of the Jurong Formation in Singapore, the variation of soil modulus with shear strain can be described by a hyperbolic function. A procedure is recommended for assessing the combined effect of stress relief and soaking on soil modulus by introducing a modulus reduction factor. Modulus degradation curves from pressuremeter tests with the borehole conditions properly simulated are found capable of producing load transfer curves that are comparable to those deduced in the field.