桥基岩溶洞穴顶板稳定性综合评价

以青溪大桥桥基岩溶洞穴围岩工程地质条件定性分析为基础,在岩土自重和桩基的外附荷载作用下,利用定性分析、结构力学的半定量分析方法和三维有限元定量计算手段,对桥墩所在位置的溶洞顶板稳定性进行了综合评价。通过对不同厚度下溶洞顶板的应力和位移的力学响应分析,认为在确保单桩桩端标高选在强岩溶发育带以下的稳定岩层上,且顶板厚度大于8.0m,才能满足溶洞顶板的稳定性要求。考虑到青溪大桥4#桥墩所在承台基坑开挖的爆破震动影响,设计溶洞顶板安全厚度取值为8.5m,并采用钻孔多点位移计对施工荷载施加过程中溶洞及顶板岩体的变形进行了现场监测,结果表明,突破常规设计要求的8.0m溶洞顶板厚度施工是安全稳定的,大大节约了溶洞处理费用,并为类似的岩溶洞穴稳定性施工提供了有力的技术支持。

The Comprehensive Evaluation on Roof Stability of Karst Cave Under Bridge Foundation

Based on qualitative analysis of engineering geology of karst cave-surrounding rock under bridge foundation,with the action of gravity and pile foundation loading,the roof stability of karst cave was comprehensive evaluated with the method of structural mechanics and 3-D finite-element method.The responses of stress and displacement of different thickness karst cave-roof were analyzed,the roof of karst cave is stable if the pile embedded on the stable rock formation,and the thickness of karst cave roof can't less than 8.0m.Considering the effect of blasting vibration when foundation ditch of 4 # pier was excavated,8.5m safety thickness of karst cave roof was determined.And the multiple-point borehole extensometer was inbuilted in Karst rock,so deformation of Karst cave and cave roof rock mass were monitored in-site.The tested results monitoring show that 8.0m thickness of karst cave roof which break through conventional design is safe.It would reduce investment outlay of treating Karst cave,and it supply technic guide for similar stability analysis of Karst cave roof.