考虑裂隙影响的桩端岩溶顶板破坏形态与安全厚度

Failure Form and Safe Thickness of Pile Karst Roof Considering the Influence of Cracks

为了研究桩端岩溶顶板破坏形态和安全厚度受岩体质量的影响,借助离散元软件,建立含节理裂隙的岩溶顶板承载计算模型,揭示顶板损伤断裂破坏细观机制,明确含裂隙顶板破坏形态,以此为基础提出考虑裂隙影响的顶板安全厚度修正计算法。研究表明:完整岩体岩溶顶板表征出典型的脆性破坏,破坏临界位移仅为较破碎岩体的60%,对应的破坏荷载则大了67.5%,岩体裂隙会明显影响桩基安全冗余度的判断,实际工程应充分考虑;桩基荷载作用下含裂隙岩溶顶板发生渐进破坏,主要经历局部压缩、微裂隙闭合→新裂隙萌生、旧裂隙扩展→形成宏观裂纹并张开→生成贯通破坏面与断口,岩体割裂成块→破坏面发展,岩体割裂加剧→形成滑动带,顶板整体破坏;岩溶顶板因错综复杂分布的节理裂隙,其空间破坏形态并非遵循规则的椎台,也非以特定曲线为母线的旋转体,而是源于裂隙的空间不规则破坏体;提出了考虑岩体节理裂隙和桩基荷载作用的岩溶顶板安全厚度修正分析方法,与模型试验结果对比表明,修正计算具备合理性。

In order to study the influence of rock quality on failure form and safe thickness of karst roof,the bearing calculation model of karst roof with rock fracture is established by discrete element software.The mesoscopic mechanism of roof damage fracture failure was revealed and the failure form of karst roof with fractures was clarified.Based on the above,the correction calculation method of safe thickness of karst roof coupling fractures was proposed.The results show that the karst roof of intact rock characterizes typical brittle failure,in which critical displacement for failure is only 60% of more broken rock,and the corresponding failure load is increasing at 67.5% larger.Rock fractures can obviously affect the judgment of the safety redundancy of pile foundations,so the actual project should be fully considered.The karst roof with fracture occurs progressive failure under the pile foundation load and mainly undergoes local compression,micro-fracture closure→new fracture initiation,old fracture expansion→formation of macro-cracks and opening→formation of penetrating failure surface and breaks,rock fragmentation into blocks→development of failure surface,rock fragmentation intensifies→formation of sliding zone,roof overall failure.Because of the complex distribution of rock fracture in karst roof,its spatial failure form is not a regular vertebral platform,nor a rotating body with a specific curve as the busbar,but a spatial irregular failure body derived from fracture.The correction calculation method of roof safe thickness coupling rock fracture and pile load is proposed.Its comparison with the model test results indicates that the correction calculation is reasonable.