含软弱岩层反倾岩质边坡地震动力响应与破坏模式

Seismic Dynamic Response and Failure Mode of Anti-Dip Rock Slope with Weak Rock Stratum

以鲁甸地震诱发的红石岩崩塌滑坡为研究对象,通过大型振动台模型试验和3DEC数值模拟,研究了含软弱岩层的反倾岩质边坡的动力响应和破坏失稳模式.研究结果表明:水平加载下,随频率增大PGA放大系数先减小后增大,在接近坡体自振频率8 Hz的波形加载下,坡体动力响应最为剧烈,软弱岩层对不同频率的横波具有放大和吸收作用,对5~10 Hz的横波放大效应明显,对15~20 Hz的横波则明显吸收;竖向加载下,随加载正弦波频率的增加,PGA放大系数先增大,25 Hz时PGA放大系数减小,随后又继续增大,在频率为30 Hz时PGA放大系数达到最大,在5~30 Hz范围内软弱岩层对纵波均具有一定的放大效果;双向加载下,坡体水平和竖向PGA放大系数分布与单向加载一致,但双向加载下坡体部分位置动力响应加剧,部分位置动力响应则受到抑制.含软弱岩层的反倾岩质边坡破坏过程可以分为6个阶段:坡体内部轻微损伤-软岩挤出、软硬岩交界上方硬岩拉裂-硬岩裂纹向上延展-软弱岩层挤压滑动-层面和纵向节理贯通形成滑面-边坡破坏.在软弱岩层的反倾岩质边坡中,软弱岩层具有对地震波的放大吸收、折射反射作用,影响着边坡的动力响应特征,软弱岩层的挤出破坏导致上部岩体岩结构面松动开裂,是该类岩质边坡破坏发展的主要原因,对该类边坡需应注意对软弱岩层进行加固防护,减小边坡的动力破坏.

Taking the Hongshiyan collapse and landslide induced by Ludian earthquake as the research object,the dynamic response and failure instability mode of anti-dip rock slope with weak rock stratum are studied through large-scale shaking table model test and 3DEC numerical simulation.The results show that under horizontal loading,the PGA amplification coefficient first decreases and then increases with the increase of frequency,and the dynamic response of the slope is the most intense under the waveform loading close to the natural frequency of 8 Hz.The weak rock stratum can amplify and absorb transverse wave of different frequencies.It has obvious amplification effect on 5-10 Hz waves,obvious absorption on 15-20 Hz waves,and absorption on 25-30 Hz waves,but not obvious in 15-20 Hz frequency.Under vertical loading,with the increase of loading sine wave frequency,the PGA amplification factor first increases,decreases at 25 Hz,and then continues to increase.When the frequency is 30 Hz,the PGA amplification factor reaches the maximum.In the range of 5-30 Hz,the weak rock stratum has a certain amplification effect on the longitudinal wave.Under two direction loadings,the horizontal and vertical PGA amplification factor distributions of the slope are consistent with that under single direction loading.However,two direction loadings,the dynamic response at some positions of the slope is intensified,while the dynamic response at some positions is restrained.The failure process of anti-dip rock slope with weak rock stratum can be divided into six stages:slight damage inside the slope bodyweak rock stratum extrusion and hard rock cracking above the boundary of soft and hard rock-hard rock crack extends upwardsqueezing sliding of weak rock stratum-sliding surface formed by bedding plane and vertical joints-slope failure.In the anti-dip rock slope with weak rock stratum,the weak rock stratum has the amplification and absorption of seismic waves and the refraction and reflection effect,which affects the dynamic response characteristics of the slope.The extrusion failure of weak rock stratum leads to the disintegration and rupture of the structural plane of the upper rock mass,which is the main reason for the failure and development of the rock slope.For this kind of slope,attention should be paid to strengthening the weak rock stratum to reduce the dynamic damage of the slope.