高频次微小地震下顺倾软硬互层边坡动力稳定性研究

Dynamic stability of slopes with interbeddings of soft and hard layers under high-frequency microseims

三峡库区(TGR)自蓄水以来微震活动加剧、强度增大,频发微震会对库区边坡产生一定影响。采用振动台模型试验和UDEC数值模拟方法,对库区顺倾软硬互层边坡在不断微、小地震作用下的破坏失稳演化过程及动力稳定性进行了研究。研究成果如下:在不断地震作用后,边坡自振频率下降、阻尼比上升,自振频率下降的速度随加载次数和加载幅值的增加而增大;在不同加载阶段,边坡坡面PGA放大系数不断降低,动力响应呈现减弱趋势;弱层成为顺倾软硬互层边坡变形破坏的优势区域;边坡的破坏失稳演化过程为分段式的滑移破坏过程,上部软、硬层滑落后,剩余滑体沿着由上部弱层剪切裂缝、中部硬层次级节理拉裂缝和下部弱层剪切裂缝贯通形成的滑移面滑移破坏;UDEC数值模拟表明顺倾软硬互层边坡的累积永久位移随微震作用次数的增加而增加,稳定性系数则呈现递减趋势。研究成果对库区滑坡形成机制的认识和减灾、防灾有一定的价值。

Since the impounding of Three Gorges Reservoir(TGR), the microseismic activity is intensified and the earthquake intensity is increased. The high-frequency microseisms induced by TGR will have some influence on the slopes. The evolution process of failure and dynamic stability are studied based on the shaking table tests and UDEC numerical analysis method. The results are as follows: the natural frequencies decrease with the loading times, while the damping ratios increase. The descending rate of the frequencies increases with the loading times and earthquake amplitude. The PGA magnification factors decrease at different loading stages, showing that the dynamic response becomes weaker. The soft layers tend to be the dominant areas where shear failure occurs in the slopes. The whole model slope eventually presents a segmented failure process,whose upper part of soft and hard layers slides and then the slope slides along the transfixion surface forming with the shear fracture in the upper soft layer, tension fracture of secondary joint in the intermediate hard layer and shear fracture in the lower soft layer. UDEC numerical simulation shows that the permanent displacement increases with the loading times, while the stability coefficient decreases. The research results are of some value to the understanding of the formation mechanism of reservoir landslides and the prevention of disasters.