海原大地震诱发石碑塬黄土滑坡机制探讨

Mechanism of Shibeiyuan Loess Landslide Induced by the Haiyuan Earthquake

1920年海原8.5级大地震诱发的石碑黄土塬滑坡,因其规模大、坡度小、滑距远的特点成为业界关注焦点,目前对该滑坡的物理力学过程仍无统一认识。基于此,文章通过理论分析和数值计算方法研究该滑坡初始状态、地震动力响应和流滑发展过程。为分析震前斜坡初始状态,建立考虑斜坡表面拉裂缝中侧向水压力作用的力学计算模型。结果表明,拉裂缝中侧向水压力削弱了斜坡整体稳定状态;为研究地震时斜坡动力响应过程,建立数值计算模型,获得地震时斜坡饱和土层的孔隙水压力比和斜坡位移的变化特性;为解释远程滑坡,将液化后土层等效为流体,借鉴泥流滑距估算理论,求算石碑塬滑坡的滑距,计算结果与前人现场考察结果吻合。

The Shibeiyuan landslide induced by the Haiyuan MS8.5 earthquake of 1920 has become a research focus because of its large scale,small slope angle,and long sliding distance.At present,there is no unified understanding of the physical and mechanical processes of the landslide.In this study,the initial state,seismic dynamic response,and flow slip development process of the landslide are investigated by theoretical analysis and numerical calculation.To analyze the initial state of the slope before the earthquake,a mechanical model and a slope stability evaluation model considering the action of lateral water pressure in the slope surface tension cracks are established.The results show that the lateral water pressure in the tension fracture weakens the slope overall stability.To study the dynamic response process of the slope under earthquake,a numerical calculation model is established,and the variation characteristics of pore pressure ratio and the slope displacement of saturated soil layer during earthquake are obtained.To explain the long-distance landslide,the liquefied soil layer is made equivalent to a fluid layer,and the slip distance of the Shibeiyuan landslide is calculated using the estimation theory of mudflow slip distance.The calculation results are consistent with previous field investigation results.