基于相似理论设计并完成了下伏溶洞嵌岩桩承载力破坏模型试验,研究了顶板厚度对下伏溶洞嵌岩桩极限承载力的影响.结果表明:下伏溶洞嵌岩桩在加载过程中呈脆性破坏,荷载位移曲线有明显陡降点;下伏溶洞的存在会明显降低嵌岩桩极限承载力,且主要发生冲切破坏,冲切破坏体近似圆锥台;桩端荷载分担比随溶洞顶板厚度增大而增大;采用S型生长曲线能较好地拟合不同溶洞顶板厚度时桩端极限承载力变化规律.顶板厚度为1~4倍桩径时,桩端承载力随溶洞顶板厚度增加呈线性增长,顶板厚度为5倍桩径时桩端承载力基本趋于稳定值.最后结合规范给出了不同溶洞顶板厚度时的安全系数.%A failure model for bearing capacity of rock-socketed pile over karst cave was designed based on the similarity theory and tested, and influence of roof thickness on the ultimate bearing capacity of the rock-socketed pile over karst cave was studied. Results show that, the rock-socketed pile over caves occurs with brittle failure during the loading and there′s an obvious steep drop point on the load displacement curve. The presence of underlying caves can significantly reduce the ultimate bearing capacity of rock-socketed pile. A punching shear failure will be predominantly occurred, resulting in a punching cone. The load-sharing ratio between pile-ends will increase with an increase in the cave roof thickness. A S-shaped growth curve can fit the variation rule of the ultimate bearing capacity of cave roof with different thickness. The pile-end bearing capacity grows linearly with the increasing of cave roof thickness when being 1~4 times of pile diameter and it tends to be stable when thickness is 5 times of pile diameter. Finally, the safety coefficient for roofs with different thickness was given based on the standards.
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