白鹤滩水电站左岸坝肩开挖边坡稳定性分析

Stability analysis of left bank abutment slope at Baihetan hydropower station subjected to excavation

白鹤滩水电站左岸坝基边坡地质构造错综复杂,坡内多条陡倾断层和顺坡向错动带是控制边坡稳定性的主要因素。结合现场地质资料、监测数据及勘察认识,利用通用离散元软件UDEC建立左岸边坡开挖变形分析模型。首先在无支护开挖工况下研究主要结构面F_(17)、LS_(331)、LS_(3319)上下盘岩体关键点应力及位移变化,并指出潜在失稳破坏区;同时采用预应力锚索单元在不同施工时序下对潜在不稳定块体进行加固计算,对比研究了不同方案下左岸边坡的变形破坏机制和整体稳定性。计算结果和现场监测表明:左岸边坡变形破坏与结构面密切相关,在开挖卸荷作用下主要表现为沿错动带的压剪破坏和陡倾断层的张拉破坏,采用预应力锚索加固处理能够有效提高边坡稳定性,并且在开挖后及时跟进支护可以有效抑制边坡剪切变形。研究结果对白鹤滩左岸坝基边坡后续工程加固和施工工序具有一定的参考价值。

The geological structures of the left bank slope at Baihetan hydropower station are extremely complicated. Many steep faults and interlayer staggered zones are the most significant risks which influence the stability of the left bank slope. Based on the analysis of the survey and field monitoring data, a numerical software UDEC was then adopted to build the numerical model for deformation analysis of the left bank slope. Under the condition of unsupported excavation, the stress and displacement changes of the key points of F17, LS331 and LS3319 at hanging wall and footwall rock masses were analysed to identify the potential instability failure areas. Meanwhile, the behaviours of potentially unstable block reinforced using pre-stressed anchorage cables were simulated at different construction procedures. The deformation characteristics, failure mechanisms and overall stability of the left bank slope were comparatively analysed using different models. Numerical modelling and field observation both show that the slope stability is strongly related to rock mass structural planes. Moreover, the deformation and damage of the left bank slope are mainly induced by the shear failure of interlayer staggered zones and tensile fracture of faults under unloading conditions. Pre-stressed anchorage cables can efficiently improve the stability and reduce the deformation of the rock slope. To efficiently control the shear deformation of rock slope, the excavation and support should be carried out simultaneously. The obtained results have particular significance to the design of reinforcement and construction process.