非饱和土刚性挡墙抗倾覆临界嵌固深度研究

CRITICAL EMBEDMENT DEPTH OF RIGID RETAINING WALL IN FOUNDATION PIT OF UNSATURATED SOILS

基坑周围土体实际处于非饱和状态,忽略基质吸力的饱和土挡墙抗倾覆设计不合理。基于非饱和土的平面应变抗剪强度统一解,考虑非饱和土强度的中间主应力效应和非线性,利用力矩相等推导基质吸力均匀和线性2种分布下基坑刚性挡墙的抗倾覆临界嵌固深度方程,给出工程应用步骤,并得到新提出的抗倾覆临界嵌固系数的参数影响特性。所得结果为系列化的有序解答,具有广泛的理论意义和很好的适用性。研究表明:基坑刚性挡墙抗倾覆设计的强度理论效应明显,考虑中间主应力效应可以更加发挥非饱和土体的强度潜能;基质吸力及其分布对抗倾覆临界嵌固系数具有显著影响,应合理假定基质吸力分布并采取工程措施确保其稳定存在;处理非饱和土强度非线性影响有2种方法,采用稳定较小吸力角的方法 1简单偏保守,采用分段双曲线吸力角的方法 2精确稍复杂,应正确认识高基质吸力对非饱和土强度及其结构设计的双重影响。

When the soils around the foundation pit are actually in an unsaturated state,the design of anti-overturning retaining wall based on the saturated soil mechanics neglecting matric suction is unreasonable. Assuming the matric suction with the uniform and linear distributions,equations for critical embedment depths of anti-overturning were obtained on the basis of the unified solution of shear strength for unsaturated soils under the plane strain condition,and the moment equality considering the intermediate principal stress effect and the strength nonlinearity. The procedure of engineering application with the obtained results was given and the parametric analysis about the coefficient of critical embedment for anti-overturning was discussed. The proposed results are orderly solution series. The effect of strength theory on the anti-overturning design for rigid retaining wall of foundation pit led to remarkable difference. The greater strength of unsaturated soils in comparing to the saturated soil could be utilized considering the intermediate principal stress effect. The critical embedment coefficient was significantly influenced by the matric suction and its distributions. Therefore,the distributions of matric suction should be reasonably assumed and some engineering measures should be adopted to ensure its stability. Two methods can deal with the effect of strength nonlinearity of unsaturated soils：the method 1 with a small stable suction angle which is simple but conservative;while the method 2 with piecewise hyperbolic suction angle is precise but slightly complicated. The dual effects of high matric suction on the strength of unsaturated soil and the structural design should be correctly understood.