降雨诱发采动滑坡物理模拟试验研究

采动滑坡是岩土工程中极具挑战性的问题之一,采动滑坡为矿区地质灾害的主要类型,其危害性相较于其他类地质灾害更加严重。采煤会诱发平缓结构斜坡发生强烈的地面变形,研究结果表明天然状况下采煤结束后一定时间内地面变形将趋于稳定,采动滑坡的发生受降雨影响显著。以贵州马达岭滑坡为地质原型,马达岭斜坡为平缓倾内的层状结构斜坡,具有上硬下软和上陡下缓结构特征,是受采矿和降雨影响诱发的滑坡。采用物理模拟方法,应用模型箱和相似材料根据相似比建立滑坡模型,采用土压力监测计、孔压力监测计和三维激光扫描仪对模型进行监测,研究了模型在开采与降雨两类工况下变形及内部应力的变化情况和在开采与降雨共同作用下斜坡变形破坏过程,再现了滑坡从孕育到发生的全过程,分析强降雨诱发采动滑坡形成的机制。研究表明:采空区形成后,坡内原有的应力平衡被打破,发生应力重分布,采空区顶板应力卸荷,边界部位应力集中,顶板位置首先发生弯曲沉陷,产生大量离层裂缝,裂缝不断向四周扩展,逐渐形成大量竖向拉张裂缝,采空区的边界部位出现多条斜向裂隙;同时采动的影响不断向上传播,采空区顶板处产生裂缝多与上覆岩体中发育的裂缝贯通形成大型裂缝;降雨作用下,坡内裂缝持续发展,降雨导致采空区及上覆岩体中形成稳定水位,增大坡后的静水压力,使裂缝不断增大,推动斜坡向临空面发生变形,雨水下渗作用下,逐渐沿下部"阶梯状"裂缝、采空区、竖向拉张裂缝形成基本贯通的潜在滑动面,最终在水压作用下,剪断锁固段形成贯通的滑面,发生整体滑动。马达岭滑坡其演化过程可分为3个阶段:①采空区覆岩-斜坡变形阶段:由于开采使上覆岩层产生变形破坏,模型坡表及内部发育大量裂隙,为雨水的入渗提供有利条件;②降雨诱发斜坡整体变形演化阶段:雨水入渗模型,加剧裂缝发育,使模型向临空向发生变形,坡内裂隙已基本贯通,模型到达失稳的临界点;③滑面扩展-滑坡发生:降雨作用下,岩体不断被软化,同时,模型内裂缝充水,使裂缝不断发育直至贯通,导致滑坡发生。因此其变形破坏机制可总结为采空区覆岩-斜坡变形→降雨诱发斜坡整体变形演化→滑面扩展-滑坡发生。

Experimental study on failure process of mining landslide induced by rainfall

Mining landslide is one of the most challenging problems in geotechnical engineering.Mining landslide is a main type of geological disasters in mining areas,and its hazards are more serious than other types of geological disasters.Coal mining will induce strong ground deformation of gentle structural slope,and the ground deformation will tend to be stable within a certain period after coal mining under natural conditions.The occurrence of mining-induced landslide is significantly affected by rainfall,so it is of significance to study the influence of rainfall on mining-induced landslide.The Madaling landslide in Guizhou was used as a geological prototype.The Madaling landslide is a layered structure slope with gentle dip,which has the structural characteristics of upper hard and lower soft,upper steep and lower gentle,and was induced by mining and rainfall.Using the physical simulation method,the model box and similar materials were used to establish the landslide model according to the similarity ratio.The model was monitored by soil pressure monitor,pore pressure monitor and 3 D laser scanner.The model was studied under mining and rainfall conditions.The deformation and internal stress changes and the slope deformation and failure process under the joint action of mining and rainfall reproduce the whole process of landslide from generation to occurrence,and analyze the mechanism of heavy rainfall induced mining landslide formation.After the formation of the goaf,the original stress balance in the slope is broken,the stress redistribution occurs,the stress in the goaf roof is unloaded,the stress at the boundary is concentrated,and the top position of the roof is first bent and then subsided,resulting in a large number of cracks.Continuously expanding to the surrounding area,a large number of vertical tensile cracks are gradually formed,and a number of oblique cracks appear at the boundary of the goaf.At the same time,the influence of mining continues to propagate upwards,and cracks occur in the goaf roof and in the overlying rock mass.The developed cracks penetrate to form large cracks.Under the action of rainfall,the cracks in the slope continue to develop,and the rainfall leads to the formation of a stable water level in the goaf and overlying rock mass,increasing the hydrostatic pressure behind the slope,increasing the crack and pushing the slope.The deformation of the air-front surface,under the action of rain and water,gradually forms a basic sliding surface along the lower "stepped" crack,goaf,and vertical tensile crack,and finally cuts the locking segment under water pressure.The sliding surface that penetrates has an overall sliding.The evolution process of the Madaling landslide can be divided into three stages including ① the overburden-slope deformation stage of the goaf:due to the deformation and failure of the overburden strata caused by mining,a large number of fissures are developed on the slope and the interior of the model,which provide favorable rainfall infiltration condition;② the rainfall induced slope overall deformation evolution stage:rainwater infiltration aggravates the development of cracks,causing the model to deform toward the vacant direction.The crack in the slope basically penetrates,and the model reaches the critical point of instability;③ the slip surface expansion-landslide occurrence:under the action of rainfall,the rock mass is continuously softened.At the same time,the crack in the model is filled with water,so that the crack continues to develop until it penetrates,resulting in landslide.Therefore,its deformation and failure mechanism can be summarized as the overburden-slope deformation of the goaf,the overall deformation evolution of the rainfall-induced slope,and the slip surface expansion-slope occurrence.