香溪长江公路大桥桥头边坡顺层发育f1、f2断层,且多面临空,工程地质问题较为突出。基于勘察资料分析、现场调查充分掌握地质背景,通过开挖平洞开展现场力学试验对控制性结构面参数进行精细评价,在此基础上,采用Sarma法计算分析不同层位结构面以及不同滑面长度下边坡安全系数,建立潜在不稳定滑体安全系数与支护力、滑块平均厚度的关系曲线。结果表明:对于结构面贯通至地表的顺层边坡,结构面上滑体的安全系数与滑块平均厚度呈负相关,而与滑面长度的相关关系较弱。坡体可按地形划分为3段,即坡脚锁固段、主滑段、坡顶牵拉段。f1断层上滑体因岩层厚、滑面强度低(抗剪断峰值摩擦角27.0°,抗剪断峰值黏聚力0.07 MPa,残余摩擦角25.2°,残余黏聚力为0.05 MPa)导致安全储备不足,加之主滑段长,为满足稳定标准下限需增加4 283 kN/m支护力或卸载32.6%方量,工程量巨大,建议结合工程挖方进行抗滑桩设计。研究成果可供类似含断层多面临空顺层高边坡稳定性分析作参考。

The Xiangxi Highway Bridge in the Three Gorges Reservoir Area is faced with prominent engineering geological problems as f1 and f2 faults and multiple free faces developed in the high bedding slope. On the basis of survey data and field investigation, we analyzed the geological background, and finely evaluated the parameters of dominant structural planes of the slope via site mechanical test. Moreover, we calculated the safety factor of the slope in different structural planes in different layers and slip surfaces with different lengths via the Sarma method. We further established the relations of support force and average thickness of sliding body against safety factor. Results demonstrated that for bedding slope with structural plane penetrating through to ground surface, the safety factor of sliding body on the structural plane is in a negative correlation with the average thickness of the sliding body, and in a weak correlation with the length of the sliding surface. The slope body can be divided into three sections according to the terrain: the locking section at slope foot, the main sliding section, and the pulling section at slope top. The sliding body on the f1 fault has insufficient safety reserve because of large thickness of rock layer and low strength of the sliding surface: the shear-off peak friction angle is 27.0°, the cohesive force is 0.07 MPa, the residual friction angle is 25.2°, and the residual cohesion is 0.05 MPa. An additional support force of 4 283 kN/m or unloading 32.6% of the slope volume is needed to meet the lower limit of stability standard. Due to huge work quantity, we recommend anti-slide pile design in combination with engineering excavation.