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采用双向循环恒刚度剪切试验对预制桩的侧阻退化效应进行试验研究。研究显示,剪切应力(摩阻力)随剪切循环数的增加呈指数型衰减,衰减主要发生在开始的部分循环内,约25个循环后基本达到稳定。剪切过程中剪切带发生明显的剪缩,导致法向应力释放,此为摩阻力退化的原因之一。随剪切循环数的增加界面摩擦角发生指数型退化直至达到残余值,此为摩阻力退化的另一原因。法向刚度的大小决定剪切应力、法向应力和界面摩擦角衰减的速度和幅度,法向刚度越大,衰减越快且残余值越小。恒刚度剪切试验说明桩土界面摩擦力的退化与桩周土的坚硬程度密切相关,土体越硬则侧阻退化现象越明显。
The two-way cyclic constant stiffness shear test was used to study the degeneration effect of precast piles. The study shows that the shear stress (friction) decreases exponentially with the increase of the number of shear cycles. The decay mainly occurs in the initial part of the cycle and reaches a steady state after about 25 cycles. Shear shear band during the significant shear contraction, resulting in normal stress release, which is one of the reasons for the friction resistance degradation. As the number of shear cycles increases, the interface friction angle degenerates exponentially until the residual value is reached, which is another reason for the degradation of friction resistance. The normal stiffness determines the speed and amplitude of shear stress, normal stress and interfacial friction angle attenuation. The larger the normal stiffness, the faster the attenuation and the smaller the residual value. The constant stiffness shear test shows that the degradation of the friction force at the pile-soil interface is closely related to the hardness of the soil around the pile. The harder the soil resistance, the more obvious the degradation of the lateral resistance is.