Field Measurement and Analysis of Residual Stress in Bored Piles

Abstract

Residual stress exists in piles before load transferring from the upper structure to the pile head. The resulting mechanism of residual stress distribution in piles after unloading and the influencing factors are analyzed and compared with those of pile foundations with negative skin friction conditions. An instrumented bored pile was measured after a vertical compressive static loading test to obtain the distribution of residual stress and deformation. The results indicate that (1) the distribution of residual stress in the pile is similar to that in a pile foundation with negative skin friction on the piles due to the soil-constrained piles fully springing back, which is equivalent to prestress exerted by the surrounding soil on the pile; (2) compared with negative skin friction, the shaft resistance induced by residual stress is smaller, and the residual stress does not affect the settlement of the pile foundation; (3) the magnitude of residual stress is closely related to the pile size, properties of the soil, and stiffness of contact surface between the pile and the soil.