考虑土体卸荷力学特性的基坑变形分析

Analysis on Foundation Pit Deformation Considering Soil Unloading Mechanical Properties

基坑开挖过程中侧壁土体和坑底土体受到一定程度的卸载扰动,强度及模量均有一定程度的降低,采用常规三轴试验所确定的土体参数进行基坑变形计算将会产生一定误差。为了寻找在土体开挖卸荷作用下更适合于基坑变形计算的土体参数,对郑州某深基坑工程坑壁主要土层进行了常规三轴试验、轴向应力减小及侧向应力减小的UU-1卸载试验、轴向应力不变及侧向应力减小的IU-1.5卸载试验、轴向应力增大及侧向应力减小的LU-2卸载试验4种不同应力路径试验,得到适用于基坑变形计算的土体参数。通过数值模拟结果与现场监测数据的对比分析,发现不同应力路径对基坑侧壁土体水平位移和土体沉降影响很大,考虑轴向卸荷参数的数值模拟得到的曲线和实际监测得到的曲线比较接近,说明采用轴向卸荷实验参数对工程施工设计更具有参考价值。

During the excavation of foundation pit, the side and the bottom soil are subjected to a certain degree of unloading disturbance, and the strength and modulus are reduced to a certain extent. Using the soil parameters determined by the conventional triaxial test to calculate the deformation of foundation pit will produce certain errors. In order to find soil parameters more suitable for foundation pit deformation calculation. The conventional triaxial test, UU-1 unloading test with axial stress decreasing and lateral stress decreasing, IU-1.5 unloading test with axial stress constant and lateral stress decreasing, LU-2 unloading test with axial stress increasing and lateral stress decreasing were carried out on the main soil of a deep foundation pit in Zhengzhou. By comparing the numerical simulation results with the field monitoring data, the soil parameters were obtained. The results show that different stress paths have great influences on the horizontal displacement and soil settlement of foundation pit. The curves obtained by numerical simulation considering axial unloading parameters are close to the curve obtained by actual monitoring, indicating that the axial unloading experimental parameters are more valuable for engineering construction design.