旁孔透射波法确定桩底深度方法的有限元分析

目前国内外利用旁孔透射波检测桩底深度的方法有多种,其理论依据尚须论证。应用轴对称有限元模型,对顶面激振的完整桩用旁孔透射波法检测进行了模拟。结果表明,首至P波时深关系图形中的下段直线须基于一定深度范围内的数据进行拟合,由其与上段直线的交点确定的桩底深度误差较大,须进行修正。验证了旁孔透射波法首至P波的时深关系基本遵从陈龙珠等提出的简化理论模型,所提出的两直线交点深度修正公式可给出合理的桩底深度,经现场试验进一步检验后值得予以推广应用。

Determination of Pile Length Using Parallel Seismic Testing with FEM Simulation

Methods for determining the depth of a pile tip with parallel seismic testing(PST) have not be demonstrated with both theory and experiment.An axisymmetric finite element model was herein deve-loped to simulate the time-versus-depth patterns of the first arrival P wave in PST for an intact pile impacted on its top.The results show that the time-versus-depth plot of P wave consists of three parts: an upper straight section,a curved section and a lower straight section.The lower straight section should be fitted with data at depth greater than 5 times of the pile-borehole spacing under the pile tip.It was proved that the formulation of time-versus-depth in the PST with the simplified ray theory proposed by the second author of this paper and Zhao could agree well with the finite element analysis and then could give a reasonable depth for the involved pile tip,which is worth of application after further verification by field tests.