基于有限差分法的下伏岩溶对桩基承载特性的影响

为探求下伏岩溶对桩基承载特性的影响规律,基于现场静载荷试验,采用FLAC3D有限差分软件对5种溶洞顶板厚度、5种顶板跨度、5种溶洞高度以及3类顶板围岩类别进行正交数值模拟试验。试验结果表明:其他条件一定时,桩基承载力与岩溶顶板厚度、顶板围岩强度成正比,与岩溶顶板跨度成反比,与溶洞高度无直接影响;溶洞等软弱下卧层对上方桩基的最大影响深度为3倍桩径,继续增大顶板厚度对桩基极限承载力的提高效果不大;溶洞尺寸与桩径相仿(L≤2D)时,对桩基承载力影响不大,溶洞尺寸继续增大则极限承载力有较明显下降;岩体强度在11.5 MPa以下时,承载力随岩体强度的增大有较大的提高,岩体强度达到11.5 MPa以后,继续增大岩体强度,其承载力增幅不明显。研究结果可进一步深化、完善现行的岩溶发育区桩基础的设计并指导施工,具有一定的理论意义及工程应用价值。

Investigation on Influence of Underlying Karst on Bearing Capacity of Pile Foundation by Finite Difference Method

To investigate the influence of underlying karst on pile foundation’s bearing capacity, orthogonal tests were simulated in FLAC3D under different karst conditions—five different thicknesses and widths of karst roof, five different heights of karst cave, and three different types of surrounding rock—based on field static load test. Results demonstrated that given the same other circumstances, the bearing capacity of pile foundation is directly proportional to the thickness of cave roof and strength of surrounding rocks, inversely proportional to the width of cave roof, and has no direct relation with cave height. Karst caves and other weak substratum affects the upper pile foundation within a depth maximum to three times pile diameter. Further increasing the thickness of cave roof has little effect on improving the ultimate bearing capacity of pile foundation. Cave size has little effect on pile’s bearing capacity when cave size is close to pile diameter(L≤2D), but reduces the ultimate bearing capacity evidently when cave size continues to grow. The bearing capacity grows apparently with the increase of rock mass strength when the strength is below 11.5 MPa, but the growth is not obvious when the strength is over 11.5 MPa.