溶洞特征对地基破坏模式及基桩承载力的作用机理研究

Calculation problems about foundation pile bearing capacity with karst cave roof as bearing layer are very common in karst area and not solved well. The action mechanism of karst cave characteristics aiming at ground failure mode and foundation pile bearing capacity is studied systematically. Calculation method of foundation pile bearing capacity is established considering karst cave effects. According to the theory of thick plate the force models of karst cave roof are constructed with different karst cave characteristics; researching on basic equations with parameters about karst cave characteristics and external loads under different boundary conditions, exploring the influence of single characteristic parameters on the deformation of the roof of karst cave, which is to reveal the mechanism of karst cave characteristics on the foundation failure mode. According to the equations and Hoek-Brown criterion，the functional relation between the thickness of karst cave roof and pile diameter being obtained，then the critical safety thickness is obtained. Weighting the effect of single characteristic parameter to karst cave roof deformation using grey relational theory, based on this the calculation method of bearing capacity of foundation pile is constructed considering the influence of Karst. Constructing many group geo mechanical and numerical model tests with different characteristics, the spatial distribution characteristics of stress and deformation，plastic zone of karst cave roof and the ultimate load characteristics when cave roof damaged are studied, which is to verify theoretical results. The research provides a theoretical basis for pile bearing capacity design in karst area.

岩溶地区普遍存在溶洞上覆岩层作为桩端持力层的基桩承载力计算问题，至今仍未很好的解决。本项目系统研究溶洞特征对地基破坏模式及基桩承载力作用机理，建立含溶洞影响的基桩承载力计算方法。根据厚板理论构建不同溶洞特征的溶洞顶板受力模型，研究不同边界条件下含溶洞特征参数及外荷载的基本方程，探求单一特征参数对溶洞顶板变形的作用规律，揭示溶洞特征对地基破坏模式的作用机理；根据基本方程并结合Hoek-Brown准则，研究不同破坏模式下岩溶顶板厚度与桩径之间的函数关系，得到不同溶洞特征的溶洞顶板临界安全厚度；应用灰色关联理论量化单一特征参数对溶洞顶板承载变形影响的权重，构建考虑溶洞特征影响的基桩承载力计算方法；开展多组不同溶洞特征的地质力学试验及数值模型试验，研究溶洞顶板受力变形、塑性区的空间分布、溶洞顶板产生破坏的极限荷载特征，对理论研究结果进行验证。本研究可为岩溶地区基桩承载力的设计计算提供理论依据。

岩溶地区普遍存在溶洞上覆岩层作为桩端持力层的基桩承载力计算问题，本项目系统研究了不同条件下的岩溶土洞的发育机理，建立了溶洞上覆竖向土压力的计算模型；考虑了溶洞上覆岩层受力成拱效应，按拱中心受荷考虑，分别按无铰拱和三铰拱考虑研究了溶洞上覆岩体作为持力层保持稳定的临界厚度确定方法；根据相似原理，进行了模型试验的相似材料研究及模型试验测试方法研究，设计了模型试验装置，在此基础上，建立了不同溶洞特征的桩基承载力模型试验，研了究不同边界条件下考虑含溶洞特征参数的地基破坏模式及桩基承载力，开展了数值模型试验，研究溶洞顶板受力变形及塑性区的空间分布特征，并对理论研究结果进行验证。