广清高速改扩建工程桩基溶洞顶板稳定性研究

针对广清高速公路改扩建工程,选取两个典型桥梁桩基存在下伏溶洞工点,构建溶洞地质概化模型。采用理论分析和数值模拟方法研究桩基溶洞顶板的稳定性,以便为岩溶区桩基设计、施工提供依据。通过规范方法确定桩底作用在溶洞顶板上的荷载,通过成层地基和地应力计算方法计算上覆岩土层作用在顶板上的自重应力。对溶洞顶板分别进行抗冲切、抗剪切、抗弯验算,分别求出稳定系数和桩底竖向极限荷载。运用ANSYS数值模拟方法,对顶板位移、第一主应力和塑性应变进行分析,计算得出桩底竖向极限荷载。理论分析与数值模拟结果对比表明桩基溶洞顶板处于稳定状态,抗剪切、抗弯验算是桩基下溶洞顶板稳定性分析的主要验算指标。

Study on the Roof Stability of Karst Cave under Pile Foundation in Guangzhou-Qingyuan Highway Reorganization and Expansion Project

Aiming at Gugangzhou-Qingyuan highway reorganization and expansion project, this paper selects two typical karst caves under the bottom of pile foundations and structures geological models of karst caves. By theoretical analysis and numerical simulation it studies the stability of karst cave roof under the pile foundation, in order to provide the basis for pile foundation design and construction in karst area. Firstly, it calculates the load on karst cave roof applied by the pile according to code, and calculates gravitational stress on top of karst cave applied by the weight of soil and rock formations above the karst cave by using the way of calculating ground stress in rock or soil mechanics. Secondly, the cave roofs capacity of punching, shearing and bending are checked respectively, the stability factors and vertical ultimate loads applying on the bottom of pile foundation are calculated. Thirdly, using ANSYS numerical simulation, the paper analyzes displacement, first principal stress and plastic strain of the cave roofs, and calculates the vertical ultimate load applying on the bottom of pile foundation. Comparing the theoretical analysis result with numerical simulation, it indicates that the karst cave roofs are both in stable state, and the anti-shear and anti-bend checking calculation are the main checking targets for the stability analysis of cave roofs under pile foundations.