基于上限有限元法的下伏溶洞地基极限承载力分析

Analysis of ultimate bearing capacity of foundation above cave based on upper bound finite element method

简要地介绍上限有限元法的基本原理与计算过程,结合岩溶区下伏溶洞地基受力特点,提出合理的计算假定,建立了一个可考虑多种主要因素影响的数值计算模型,利用上限有限元法,计算出了多种工况下的地基极限承载力上限解,并分析溶洞顶板厚度、溶洞宽度和内摩擦角对地基极限承载力的影响规律。最后,在对大量能量耗散图和速度场图分析的基础上,提出三类典型的下伏溶洞地基破坏模式。研究结果表明,地基极限承载力随着内摩擦角和溶洞顶板厚度的增大而增大,随着溶洞宽度的增大而减小;当溶洞顶板厚度较小时,内摩擦角对地基承载力影响较小,当内摩擦角较大时,溶洞宽度和溶洞顶板厚度对地基承载力的影响才显著;岩溶区下伏溶洞地基存在冲切破坏、冲切剪压破坏和Prandtl破坏三类破坏模式。

Research on ultimate bearing capacity of foundation above cave in Karst areas is of great signifi-cance for the design and construction of it,In order to simulate the ultimate failure state of the foundationabove cave,the upper bound finite element method is applied. Firstly,the basic principles and calculationprocess of the upper bound finite element method are briefly introduced. Secondly,according to stress char-acteristics of the foundation above cave,reasonable calculation assumptions are presented,and a numericalmodel considering varied factors of influence n is established. Thirdly,the upper bound solution of ultimatebearing capacity under a variety of conditions is calculated by using upper bound finite element methodand the influence law of the cave roof thickness,width and angle of internal friction on the ultimate bear-ing capacity of foundation above cave is analyzed. Finally,based on large amount of energy dissipation andvelocity field pattern analysis,three typical failure modes for the foundation with karst cave are presented.The analytical results indicate that ultimate bearing capacity(Pu/c) increases with the increase of φ andH B,however,decreases with the increase of L B. When H B is small,φ has little effect on ulti-mate bearing capacity of foundation. When φ is large,the influence of L B and H B on ultimate bear-ing capacity of foundation is significant. Three typical failure mechanisms of foundation above cave in karstarea are presented in this paper:punching failure mode,punching shear press failure mode and Prandtlfailure mode.