不同毛细阻滞覆盖层处治膨胀土边坡的渗流及稳定性研究

Study on seepage and stability of expansive soil slope treated by different capillary barrier cover layers

为探究采用不同结构毛细阻滞覆盖层处治的膨胀土边坡的防渗能力,基于非饱和渗流理论并运用Geo Studio有限元软件,开展持续大雨作用下“细-粗”型(Ⅰ型)、“细-导排层-粗”型(Ⅱ型)、“细-粗-细”型(Ⅲ型)和“细-粗-细-粗”型(Ⅳ型)这4种毛细阻滞覆盖层(厚度均为5 m)处治膨胀土边坡的渗流及稳定性数值分析,研究不同降雨历时下各覆盖层内部体积含水率的分布特性、膨胀土边坡的体积含水率变化规律及其对边坡安全系数的影响。研究结果表明:在持续大雨作用下,不同结构覆盖层均能在一定程度上减少降雨渗入边坡内部膨胀土;雨水入渗突破不同结构覆盖层所需的时间不同,覆盖层按防渗性能由强至弱顺序排列依次为Ⅱ型、Ⅳ型、Ⅰ型和Ⅲ型;未经处治边坡的安全系数急剧降低,易发生破坏;4种覆盖层处治边坡的安全系数均在降雨前期稍降低;在长期降雨条件下,Ⅰ型和Ⅲ型覆盖层处治边坡的安全系数降幅大,而Ⅱ型和Ⅳ型覆盖层处治边坡的安全系数降幅较小,且各方案处治的边坡稳定性较好。因此,建议在实际工程采用Ⅱ型和Ⅳ型毛细阻滞覆盖层处治膨胀土边坡。

In order to explore the anti-seepage ability of expansive soil slope treated by capillary barrier cover with different structures,based on the unsaturated seepage theory,Geo Studio finite element software was used to carry out the numerical simulation of the seepage and stability analysis of expansive soil slope treated by four kinds of capillary barrier cover layers with thickness of 0.5 m with continuous heavy rain,namely,"fine−coarse"(type I),"fine−drainage layer−coarse"(typeⅡ),"fine−coarse−fine"(typeⅢ)and"fine−coarse−fine−coarse"(typeⅣ).The distribution characteristics of volume moisture content in each cover layer during different rainfall periods were studied.The variation law of volume moisture content of expansive soil on the treated slope and its influence on slope safety factor were investigated.The results show that during continuous heavy rain,the time required for rainfall to break through the different cover layer is different.The existence of different cover layer can reduce the infiltration of rainfall into expansive soil slope to a certain extent,among which typeⅡcover layers has the best anti-seepage performance,followed by typeⅣ,type I and typeⅢcover layers.With the sustained rainfall,the safety factors of untreated slopes decrease sharply,which is easy to be destroyed.The safety factors of the slopes treated by the four kinds of cover systems all decrease slightly in the early stage of rainfall.Under long-term rainfall condition,the safety factors of the slopes treated by type I andⅢcover layers decrease greatly,while the safety factors of the slopes treated by typeⅡandⅣcover layers decrease slightly.The slope treated by each cover layer is still stable.Therefore,in practical engineering,it is suggested to use typeⅡorⅣcapillary barrier cover to treat expansive soil slope in the condition of long-term rainfall.