基坑降水对坑底土体回弹影响的试验研究

Effect of dewatering of foundation pits on soil heave

采用逆作法时,深基坑开挖引起的坑底隆起对于地下工程结构会产生显著影响。目前对于深基坑的回弹量计算,都是以基坑开挖卸荷为基本应力路径获取变形模量,并未考虑降水的影响。软土地区深基坑的开挖,特别是深度达20～30 m甚至更深的超深基坑工程,均要涉及到大幅度降低坑内地下水位的问题。应用三轴试验对基坑工程开挖与降水交替作用下开挖区土体的强度与变形性状进行模拟,并与仅考虑基坑开挖作用下被动区土体的强度与变形性状进行比较。结果表明:对超深基坑,降水作用可改善土体的力学性状;大深度降水对基坑总的回弹量有较大影响,能显著减小回弹总量。基于降水对基坑被动区土体强度及变形性状的显著影响,在深基坑工程设计中应考虑实际的应力路径,即进行考虑降水与开挖综合影响的分析。

For deep excavation using the top-down method, the soil heave may produce significant effect on the underground structure. In the calculation of soil heave, the deformation modulus is obtained by taking the unloading path as the basic stress path and the effect of dewatering is not taken into account. However, for deep excavations in soft soil deposits, especially for excavation depth more than 20-30 m, large depth of water table lowering within the excavation has to be faced. The strength and deformation properties of the soil within the diaphragm walls under the alternate effect of excavation and dewatering are studied using wiaxial tests. The test results show that compared with the test results obtained by only considering the effect of excavation, the dewatering in pit excavation can improve the strength properties of the soil. Large depth dewatering can also remarkably reduce the total soil heave due to excavation. Due to the remarkable influence of large depth dewatering on the strength and deformation properties of the soil in the passive region, the effect of dewatering on the soil heave must be taken into account.