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软土地区基坑施工通常采用分层降水与开挖,基坑降水开挖应力路径对坑底土体的变形及力学特性产生影响,且坑底不同深度土体所受影响不同。采用SLB—1型应力应变控制式三轴剪切渗透仪模拟基坑分层降水与开挖应力路径对坑底以下不同深度土体进行研究;并在应力路径试验之后进行不排水剪切试验。试验结果表明:基坑降水开挖对土体的影响随土体深度的增加而减小,研究针对的工程案例条件下基坑开挖的影响深度约为坑深2.2倍。对于降水路径,第一个降水步产生沉降随着土体深度的增加而减小,表明随深度增加变形模量逐渐增大;变形模量的增大可能与基坑降水引起的欠固结效应有关。对于开挖路径,总回弹值随着土体深度的增加而减小,表明随深度增加变形模量逐渐增大;随着基坑开挖的进行土体变形模量不断减小;变形模量的变化可能与基坑开挖引起的超固结效应有关。超固结比对变形模量具有一定影响,开挖路径土体变形模量E与1/(OCR-1)之间近似呈线性关系。同时,不排水剪切试验得到的应力-应变关系曲线呈现应变软化特性,也体现了基坑开挖过程中的超固结效应。基于基坑降水开挖对不同深度土体产生的不同效应,在研究基坑土体变形时,需要考虑坑底以下不同深度土体力学性质的差异及其对变形的影响。
In the soft soil area, the dewatering and excavation are usually carried out in the foundation pit construction. The excavation stress path of the foundation pit dewatering has an impact on the deformation and mechanical properties of the soil at the bottom of the pit, and the influence on the soil body at different depths of the pit bottom is different. SLB-1 stress-strain controlled three-axis shear permeameter was used to simulate the stratified dewatering and excavation stress path of foundation pit to study the soil with different depths below the bottom of the pit. Undrained shear tests were conducted after the stress path test. The experimental results show that the influence of foundation pit excavation on soil decreases with the increase of soil depth. The depth of excavation affected by the project case is about 2.2 times that of pit depth. For the precipitation path, the settlement of the first precipitation step decreases with the increase of soil depth, which indicates that the deformation modulus increases with depth; the increase of deformation modulus may be related to the underconsolidation effect caused by the foundation pit precipitation related. For the excavation path, the total rebound value decreases with the increase of soil depth, indicating that the deformation modulus increases with depth; the deformation modulus decreases with the excavation of the foundation pit; Changes in volume may be related to over-consolidation caused by excavation. The overconsolidation ratio has some influence on the deformation modulus, and the linear relationship between the deformation modulus E and 1 / (OCR-1) of the excavation path is approximately linear. At the same time, the stress-strain curve obtained by undrained shear test shows the strain softening characteristic and the overconsolidation effect in excavation of foundation pit. Based on the different effects of foundation pit dewatering on soil with different depths, it is necessary to consider the difference of mechanical properties of soil under different pit depths and its effect on deformation when studying the deformation of foundation soil.