考虑砂土地基预制桩侧向挤土影响的单桩承载力分析研究

Load bearing capacity analysis of single jacked pile considering lateral squeezing effect in sand ground

预制桩的沉桩过程产生了对桩周土体的挤密作用,桩周土体的力学特性发生了相应的改变,这种改变会直接影响预制桩桩基础的承载力。利用有限元计算分析方法对砂性土地基预制桩沉桩过程进行了数值求解,得到了桩周土体的位移和应力变化规律;在应力路径控制的三轴试验中,模拟土体在受到预制桩沉桩影响的应力状态,试验研究了标准砂在再受荷载作用时的力学特性;在荷载传递法中,运用桩周土体性质的变化试验结果,进行了有限差分数值分析,得到了考虑和不考虑挤土作用的单桩P-S曲线。研究结果表明:预制桩的沉桩过程对桩周土中的径向和轴向应力都有明显的影响,对径向应力的影响大于对轴向应力的影响;挤土效应提高了桩周土的剪切模量值和强度,影响范围大致相当;考虑沉桩侧向挤土影响单桩承载特性有明显的提高,现行的预制桩设计偏于安全。

The squeezing effect can be caused by the construction of jacked piles. The behavior of soils surrounding a jacked pile is changed; and it has an influence on the load bearing capacity of the pile. The jacked-in process of a single pile is simulated by FEM. The displacement and stress of the soils surrounding the pile are calculated. In addition, stress path controlled triaxial tests were carried out to simulate the stress state of the soils after the construction of a jacked pile; and the mechanical characteristics of standard sand under subsequent loading were studied. Furthermore load transfer method based on finite difference calculation is used to predict the load-settlement curve of single pile with and without consideration of the squeezing effect. It is shown that the axial and radial stresses bo^h are affected significantly; and the radial effect is more obvious than the axial effect. The shear modulus and strength of the soil surrounding the pile increase; and the influence zone is essentially the same. The load bearing capacity of a single jacked pile increases in consideration of lateral squeezing effect. The design method of jacked piles is conservative.