多溶洞地层桩端极限承载力下限有限元法分析

为计算多溶洞地层桩基的极限承载力,通过MatLab平台编制了用于分析多溶洞地层桩端极限承载力下限的有限元法计算程序。采用平面应变模型,并假定材料符合Mohr-Coulomb准则和塑性关联流动法则。定义无量纲参数N来衡量各参数对桩端极限承载力的影响。根据桩与溶洞间的相对位置关系,详细探讨了6种工况下桩端极限承载力的变化规律,并分析了嵌岩深度h_r、上覆土层自重q_s和溶洞直径D的影响程度。分析结果表明:桩端极限承载力随h_r的增大而增大,随D的增大而减小,而q_s的影响基本可忽略不计。此外,还对不同工况下桩端的极限破坏模式进行了分析。最后,通过考虑无溶洞、有溶洞下的2种桩基算例,验证了本文方法的正确性。

Lower Bound Limit Element Analysis on Bearing Capacity of Pile Foundation above Karst Caves

The procedures of calculating the limit bearing capacity of pile foundation above karst caves are provided in this paper based on MatLab using the theorem of the lower bound solution with finite element method. A plain strain model in no consideration of 3D space effect is built with the rock mass material assumed to obeying the Mohr-Coulomb criterion with plastic associated flow rule. A dimensionless parameter N is defined to describe the effect of different parameters on the bearing capacity of pile foundation. According to the position relation between piles and karst caves, the variation of limit bearing capacity of pile foundation in six different cases are examined in detail. The influences of rock-socketed pile depth h_r, self-weight q_s of overlying soil, and diameter D of karst caves on the bearing capacity of pile foundation are also investigated. Results reveal that the limit bearing capacity of pile foundation increases with the increase of h_r, but decreases with increasing of D, while the influence of q_s is negligible. In addition, the failure modes of pile foundation in different cases are also analyzed. The computation method in this paper is verified correct through two examples in the presence and in the absence of karst caves.