花岗岩残积土遇水软化崩解不仅造成施工困难,也给基坑自身安全及周边环境保护带来极大风险。为了研究坑底被动区花岗岩残积土遇水软化崩解对基坑的影响,以花岗岩残积土地区某地铁车站深基坑为对象,运用PLAXIS有限元软件,系统地开展了土体弱化及弱化深度对基坑变形受力影响的有限元计算。结果表明:围护结构水平位移最大值、踢脚变形、地表沉降最大值均随着坑底土体弱化深度的增加而增大,当弱化深度较小时,上述值增长幅度较小,当弱化深度较大时,上述值急剧增大;此外,围护结构水平位移最大值位置及最大弯矩会随着土体弱化深度的增加而增大,临近坑底支撑会随土体弱化深度的增加而承担较大的转移压力。因此,在花岗岩残积土地区基坑工程施工过程中,需减少坑底土体弱化深度,避免土体大范围弱化。研究结果可为其他类似工程施工决策提供参考。

The softening and then disintegration of granite residual soil encountering water often pose great difficulties to construction and security threats to foundation pit and surrounding environment. With the deep excavation of a metro station in granite residual soil zone as case study, we probed into the influence of granite residual soil softening at the bottom of excavation encountering water through PLAXIS finite element simulation. Results illustrated that the maximum horizontal displacement of support structure, the deformation of skirting, and the maximum ground settlement all raised with the deepening of softened soil. When the depth of softened soil was small, the above deformations were small too; when the depth of softened soil was large, the above values surged correspondingly. Moreover, the location of maximum horizontal displacement and the maximum bending moment also increased with the deepening of softened soil. The inner bracing around excavation face undertook more shift pressure as the depth of softened soil increased. Therefore, the depth of softened soil in passive zone should be reduced in the deep excavation in granite residual soil zone. The research finding serves as an experience for similar construction.