考虑溶洞顶板自重时桩端持力岩层安全厚度计算方法

A method for calculating the safety rock thickness of pile bearing strata with considering deadweight of karst cave roof

通过对溶洞顶板持力层模型的合理简化,进一步完善了已有研究成果的溶洞顶板持力层抗冲切、抗剪切厚度公式,考虑自重影响因素。提出了可以考虑有效宽度、自重等影响因素的单向板、双向板抗拉弯破坏溶洞顶板持力层厚度公式。该公式力学概念清晰,计算简便。进一步结合工程实际中各种参数的取值范围,按照常规抗冲切、抗剪切和抗拉弯破坏模式,得出一般情况下溶洞持力层顶板抗冲切、抗剪切净厚度大于2.5-3.5倍桩径和抗拉弯破坏顶板总厚度大于5.0-5.5倍桩径即可满足设计要求。该研究可供岩溶区桥梁桩基工程设计和施工参考。

The existing formulae of roof bearing layer thickness for punch damage and shear damage are modified by reasonably simplifying the model for bearing layer of karst cave roof. A formula of roof bearing layer thickness under tensile and bending damage conditions is proposed with considering the deadweight of roof. With clear physical significance, the proposed formula can well address the effects of the effective width and the deadweight in one-way slab and two-way slab models, and it is straightforward to be applied. Based on the observed results in practice, the range of parameter variation is determined for various failure modes such as punching, and it is concluded that the net thickness of roof bearing layer is more than 2.5d-3.5d for punching and shearing（where d is pile diameter）, while the total thickness is more than 5.0d-5.5d for bending, so that the design thickness can meet the design requirements. The results can provide reference for design and construction of bridge piles in karst area.