单桩残余应力实测分析

Field Measurement and Analysis of Residual Stress in a Bored Pile

在桩顶荷载施加之前,桩身往往已经存在残余应力。分析了卸载后桩身残余应力产生的机理、残余应力的分布规律及影响因素,并与负摩阻力桩基进行了对比分析。跟踪测试了一根单桩在竖向抗压静载试验卸载之后桩身应力和变形的分布情况。结果表明:卸载后,残余应力在桩身的分布类似负摩阻力作用的桩基,是桩周土体约束桩体充分回弹的结果,相当于桩周土体对桩施加了预应力;残余应力引起的侧摩阻力比负摩阻力小,残余应力不会引起桩基沉降发生变化。残余应力跟桩的尺寸、桩土接触面刚度及桩周土体的性质密切相关。

Residual stress exists in piles before the load from upper structure is applied on pile head. The generating mechanism distribution of residual stress in piles after unloading as well as the influencing factors are analysed and compared with those of the pile foundation with negative skin friction on piles. An instrumented bored pile is measured after vertical compressive static loading test to obtain the distribution of residual stress and deformation. The result indicates that （ 1 ） the distribution of residual stress in the pile is similar to that in the pile foundation with negative skin friction on piles due to the soil constraints piles fully spring back, which is equivalent to a 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 cannot affect the settlement of pile foundation; （3） the magnitude of residual stress is closely related to pile size, the property of soil and the stiffness of the contact surface between pile and soil.