膨胀性顺(互)层边坡崩塌机制研究

Study on collapse mechanism of expansive bedding layered slope

研究在干湿循环和集中降水条件下甘肃古浪砂岩泥岩互层顺层边坡的崩塌机制,对于砂岩此类边坡的崩塌治理具有重要意义。崩塌机制可概括为在干湿循环作用下软层泥岩反复胀缩,致硬层砂岩产生节理并贯通;在集中降雨影响下泥岩崩解致砂岩悬空,极限平衡打破则形成倾覆崩塌或滑动崩塌。基于室内侧限膨胀试验和直剪试验,考虑泥岩遇水膨胀和软化共同作用,建立膨胀性顺层边坡的砂岩抗裂、倾覆和滑动稳定力学模型,推导相应的抗裂系数、倾覆和滑动稳定系数计算公式,并在实际工程中进行了应用与验证。研究表明:(1)在含水率阈值范围内,泥岩的抗剪强度随着含水率的增加而增大,吸水膨胀所产生的膨胀力对抗剪强度起主要作用;当含水率超过阈值,则抗剪强度随着含水率的增加而减小,此时泥岩吸水致抗剪强度参数c,φ值降低对抗剪强度起主要作用。(2)悬空砂岩抗裂系数与砂岩岩层厚度的平方成正比,与下层泥岩的膨胀力成反比,与下层泥岩风化深度的平方成反比。(3)悬空砂岩的滑动稳定系数与岩层厚度成反比,与w d w(d-d)/d成正比,砂岩岩层倾角呈负相关关系,与抗剪强度参数c,φ呈正相关关系。

The collapse mechanism of the sandstone and mudstone bedding slope under the condition of drying-watering cycles and concentrated precipitation in Gulang,Gansu,was studied,which has great significance to the treatment of this kind of collapse. The collapse mechanism can be summarized as follows. The formation and connection of joints in the hard sandstone layer is caused by the repeated expansion and contraction of soft mudstone under drying-watering cycles. Under the influence of concentrated precipitation, the suspended sandstone is formed by the mudstone collapse. The overturning or sliding sandstone collapse appears when the limit equilibrium is broken. Considering the mudstone＇s swelling and softening mechanisms,the mechanical models of crack,overturning and sliding stabilities for expansive sandstone and mustone bedding slope were established based on the confined swelling tests and direct shear tests in laboratory. The formula of anti cracking coefficient,overturning stability coefficient and sliding stability coefficient were deduced. These formula have been applied and verified in the practical project. The results show that,when the water content is less than its threshold,the shear strength of mudstone increases with the increasing of water content,and the swelling force caused by the water absorption expansion play a major role in the shear strength. When the water content exceeds the threshold,the shear strength decreases with the increasing of water content,and the decreases of c,φ of the mudstone caused by the water absorption play a major role. The anti cracking coefficient of the suspended sandstone is proportional to the square of the thickness of the sandstone,inversely proportional to the swelling force of the lower mudstone and the square of the weathering depth of the lower mudstone. The sliding stability coefficient of the suspended sandstone is inversely proportional to its thickness. The sliding stability coefficient is proportional tow d w（d-d） / d,it is negatively correlated with the dip of the sandstone and it is positive correlated with c and φ.