顺坡陡-中倾角裂隙组合结构边坡稳定性分析

Stability Analysis of Slope with Alongslope Steep-gentle-dipped Fractures

顺坡向倾外裂隙易与开挖坡面组合形成不利块体,严重威胁边坡稳定。以雅砻江中游某电站石料场顺坡向(后缘)陡倾裂隙-(中下部)中倾外裂隙组合结构边坡为例,通过勘探查明边坡长大结构面的延伸及组合,陡-中倾坡外裂隙的存在使可能的失稳模式为沿后缘陡裂张开的底面单面滑动。为评价边坡稳定性,针对Ⅱ区边坡进行了定性和定量分析,通过判断底滑面中岩桥的抗剪强度较大,定性分析认为边坡处于稳定状态;采用极限平衡法求出不同工况下开挖边坡安全系数,结果表明:开挖至高程2 165 m时,在天然、暴雨及地震工况下,边坡整体均处于稳定状态,开挖至高程2 110 m时,天然、暴雨工况下稳定,但安全浴度不足,而地震工况下处于临界稳定状态,同时分析了底滑面裂隙连通率对边坡稳定性的影响;采用三维离散元程序分别计算天然工况下边坡开挖至高程2 165 m和2 110 m时的力学响应特征。结果表明:边坡开挖至高程2 165 m时,沿顺坡裂隙发生侧向位移,开挖至2 210 m,位移增大,位移变形受后缘陡倾裂隙与坡体中下部顺坡向节理控制。研究成果可为边坡后续支护设计提供建议。

Co-working of alongslope fractures and excavation surface could easily result in unstable blocks, which could seriously threaten the slope stability. A quarry of a hydropower station in the middle stream of Yalong River was taken as the study case. The quarry featured composite-structured slope of steep-dip fracture(rear edge) and gentle-dip fracture(middle and lower part). Exploration on long fractures was done for revealing the continuity and combination, and suggested that the possible mode of instability could be single-sided sliding along the bottom face with the steep fracture at the rear edge. To evaluate the slope stability, qualitative and quantitative analyses were carried out in Area 2, in which the slope was judged stable for having strong shear strength of rock bridge. Calculation of slope safety factor using the limit equilibrium showed that when slope was excavated to the elevation of 2 165 m, the slope was stable in the natural, stormy, and earthquake conditions. When slope was excavated to the elevation of 2 110 m, the slope remained stable in natural and storm conditions, but in critical stable state in earthquake condition. Meanwhile, the influence of connectivity rate of bottom sliding base on slope stability was analyzed. The discrete element 3 DEC method was used to calculate the mechanical response of slope excavation. Results show that when the slope was excavated to the elevation of 2 165 m, lateral displacement occurred along the fracture alongslope. When the slope was excavated to the elevation of 2 210 m, the displacement increased. The displacement was controlled by the steep-dip fracture at the rear edge and developed in the alongslope joints. This study provides a fine reference to the slope follow-up support design.