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桩基支撑于溶洞顶板的情况时有发生,研究地震作用下桩端溶洞顶板的稳定性具有重要意义。根据相似定理和分离相似设计方法,基于振动台模型试验对顶板厚度及溶洞直径变化下桩端顶板的动力响应特征进行了研究。结果表明,桩端溶洞顶板在地震作用下的破坏模式与顶板厚度及溶洞尺寸大小密切相关,一定顶板厚度情况下溶洞尺寸较小时(洞径l≤2d,d为桩径)表现为剪切破坏,而洞径较大时(如l≥4d)为显著的冲剪破坏,洞径越大,冲切块体积所占比例越大;基于振动台试验得到的岩溶顶板破坏模式,结合拟静力法构建了可考虑岩体特性、地震烈度及桩径大小影响的最小顶板安全厚度理论计算模型。通过算例分析表明,最小安全厚度相比静力条件下要大,且随地震烈度的增强而增大,相同条件下冲-剪破坏的计算值均大于剪切破坏情况,说明地震环境下溶洞尺寸越大,所需顶板厚度越大。其成果可为实际工程中岩溶顶板安全厚度的计算提供理论基础。
It is very important to study the stability of pile roof under the action of earthquake. According to the similarity theorem and the similar separation design method, the dynamic response characteristics of the roof at the top of the pile under the variation of roof thickness and cave diameter were studied based on the shaking table model test. The results show that the failure mode of roof caverns under earthquake is closely related to the thickness of roof and the size of caverns. When the caverns size is small (the hole diameter is l≤2d and d is the diameter of pile), the shear failure , While the larger the hole diameter (eg, l≥4d) is the obvious punching failure. The larger the diameter of the hole is, the larger the proportion of the punched block volume is. Based on the karst roof failure model obtained from shaking table test, Method is used to establish the theoretical calculation model of the minimum roof safety thickness considering the characteristics of rock mass, seismic intensity and pile diameter. The results of numerical examples show that the minimum safety thickness is larger than that under static conditions and increases with the increase of earthquake intensity. The calculated values of erosion-shear failure under the same conditions are all greater than those under shear failure. The larger the size, the larger the required roof thickness. The results provide a theoretical basis for the calculation of the safe thickness of karst roof in practical engineering.