降雨作用下青石镇政府后山堆积层滑坡渗流与稳定性

以黄冈地区青石镇政府后山堆积层滑坡为例,在分析了其工程地质特征及地质结构特征的基础上,采用有限元法研究了非饱和土瞬态体积含水量及孔隙水压力的分布,采用考虑孔隙水压力的Janbu法分析计算了降雨对堆积层滑坡安全系数的影响。研究结果表明:①降雨入渗导致坡体孔隙水压力升高,滑面抗剪强度降低,安全系数也随之逐渐降低,其中在降雨前期,两侧的抗剪强度下降速率比中部快,而到了后期中部的抗剪强度下降速率明显快于两侧;②安全系数变化表现为前19 d以0.008/d的速率缓慢下降,19~30 d以0.03/d的速率缓慢下降,30 d以后下降速度降低,至36 d之后不再发生变化,其中在0~11 d两侧抗剪强度变化对滑坡整体稳定性变化的贡献比中部大,19~36 d中部抗剪强度变化对滑坡整体稳定性变化的贡献要比两侧大;③降雨入渗过程中,地下水从坡体表层和两侧流向坡体中部,负孔压区面积向中部不断压缩,中部地下水变化受到两侧及上层的制约,体积含水量及孔隙水压力变化相对滞后;④该滑坡的防治重点是做好降雨前期坡体后缘地下水截流以及前缘地下水排泄工作,同时,做好地表排水,减少降雨入渗。

Seepage and stability of the colluvial landslide on the back hill of Qingshi Town Government under rainfall

Taking the colluvial landslide of the back hill of Qingshi Town Government in Huanggang area as an example, this paper used finite element method to study the transient volumetric water content and pore water pressure of unsaturated soil based on the analysis of its engineering geological characteristics and geological structure characteristics.The Janbu method considering pore water pressure was used to calculate the effect of rainfall on the safety factor of the colluvial landslide. The results show that:①Rainfall infiltration leads to the increase of pore water pressure in the slope, and then the shear strength of the sliding surface to decrease, and so the safety factor decreases gradually. In the early stage of rainfall, the shear strength on both sides decreases faster than that in the central part. At the end of the period, the rate of decline in shear strength is significantly faster than that on both sides.②The change in safety factor shows a slow decline at the rate of 0.008/d for the first 19 d and a slow decrease at the rate of 0.03/d for 19-30 d. After 30 d, the descending speed decreases, and no change occurres after 36 d. Among them, the change of shear strength on both sides of 0-11 d contributes more to the change of overall stability than that of the central part. The contribution of shear strength change to the overall stability of 19-36 d is greater than that of the central part.③During the rainfall infiltration, groundwater flows from the surface and sides of the slope to the middle of the slope, and the negative pore water pressure area is continuously compressed to the central part. The groundwater changes in the central area are restricted by the two sides and the upper layer. The volumetric water content and the pore water pressure change are relatively lagging.④The prevention and control of the landslide is focused on the groundwater interception at the trailing edge of the slope and the groundwater discharge at the leading edge. At the same time, a good surface drainage may reduce rainfall infiltration.