不同厚度溶洞顶板与基桩作用机理室内模型试验研究

Laboratory model tests on punching properties of karst cave roof under pile tip considering various thickness-span ratios

根据相似理论,设计了3组不同厚度条件下溶洞顶板破坏模式的大比例模型试验,得到了顶板和基桩的荷载-位移曲线、顶板底部的极限应变曲线和不同厚度条件下溶洞顶板的破坏特性。试验结果表明:当溶洞顶板厚度为1d,2d时,发生冲切破坏,冲切体为圆台;当溶洞顶板厚度为3d时,顶板则以弯拉破坏为主,无冲切体产生。在荷载-位移曲线中,线性阶段转变为非线性阶段的临界点约为极限承载力的一半。最后通过理论计算的方法,获得溶洞顶板最小安全厚度计算公式,分析结果与试验结果吻合较好,能满足工程计算精度要求。本文试验成果是基于工程最不利情况得出的,可供岩溶区基桩初步设计参考。

According to the similarity theory, punching properties of cave roof under pile tip are investigated through three series of large-scale laboratory model tests with different thickness. The load-displacement curves of pile foundation and roof, the ultimate strain curves of roof bottom and the failure charaeteristic of cave roof with different thickness are obtained. The test results show that the punching failure occurs within the circle table punehing body when the thickness of the cave roof equals to ld or 2d; however, the bending failure rather than the punching failure occurs when the thickness of the cave roof equals to 3d. The turning point of the elastic stage is transformed into the plastic stage in half the position of the ultimate bearing capacity according to the load- displacement curves, indicating that the plastic ultimate bearing capacity is two times the elastic ultimate bearing capacity. At last, the calculation formula of the minimum safety thickness is induced based on the theories of bending for thin plates and punching failure. The theoretical calculation results are in good agreement with the test results, which can meet the requirements of engineering calculation accuracy. The test results in this paper are based on critical situation, and they can provide reference for the preliminary design of piles in Karst areas.