The foundation pit for the south anchorage of 4th Nanjing Yangtze River Bridge is protected with concrete diaphragm wall. The wall will be embedded in the medium-weathered layer with 3 meters. Because the dredging layer at the wall bottom and the strongly weathered rock are more permeable than the wall, under-ground water may flow through the dredging layer to the foundation pit. On the basis of numerical simulation with 3D seepage field model, the permeability sensitivity is analyzed and the seepage control efficiency is compared among different designs. The results indicate that the thickness and permeability of medium-weathered layer influence the discharge and seepage stability of the pit significantly, that under cases without curtain grouting in the bed-rock, the seepage gradient in the dredging layer is high and seepage deformation might occur, and that under cases with curtain grouting , the discharge would be much lower and the stability of foundation pit would be ensured.%南京长江第四大桥南锚碇基础采用井筒式地连墙结构形式,地连墙嵌入中风化层约3m,下部可能形成沉渣层,且强风化层裂隙较多,局部透水性较好,地下水可能通过沉渣层及裂隙绕渗进入基坑.建立三维模型模拟基坑渗流场,通过参数敏感性分析和方案对比表明:中风化层厚度及渗透性对基坑的渗流量及渗透稳定性有明显影响;基岩无灌浆帷幕条件下,地连墙底面沉渣层渗透比降过大,可能引发渗透变形问题;对基岩进行帷幕灌浆后,可有效减小基坑渗流量,使基坑渗透稳定性得到保障.
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