深厚淤泥质土中基坑开挖对基桩影响的离心模型试验研究

Impacts of pit excavation on foundation piles in deep silty soil by centrifugal model tests

为研究深厚淤泥质软土地基中开挖基坑时桩土间的作用机制,以江苏省长江沿岸某电厂锅炉房基坑开挖为背景,按1:50的相似比设计了室内离心模型试验,从桩身应变、桩身位移、桩顶位移、地表沉降、土体变形影响范围、桩身弯矩和孔隙水压力等方面,分析了基坑开挖对坑内已有基桩和周围土体的影响,并与现场基坑开挖出现的问题进行了对比分析。结果表明:对上部为淤泥质土,下伏较好土层的地基,当淤泥质土的抗剪强度相对较高时,开挖时基桩受力较大,容易出现断桩事故;开挖过程中基桩应变出现两处极值,深度分别在开挖深度附近和淤泥质土与下伏土层交界面附近;由于基桩的存在,靠近开挖面一侧的土体孔隙水压力变化平稳,而桩后土体孔隙水压力随着开挖的进行变化剧烈;基坑开挖后桩土之间的相互作用主要发生在开挖后48h内,之后趋于稳定。试验结果与现场实测数据基本吻合,为深厚软土内基坑设计和施工过程提供了可借鉴的依据。

The foundation pit excavation of a power plant located along the Yangtze River in Jiangsu province is selected to study the interaction mechanism between piles and soils during excavation of foundation pits in deep silty soft soil.Thus an indoor centrifugal model test with the similarity ratio of 1:50 is designed.The influence of foundation pit excavation on existing pile and surrounding soil in deep silty soft soil are analyzed from different aspects including the pile strain,pile displacement,pile top displacement,surface settlement and soil deformation influence range,pile bending moment and pore water pressure.Results from the centrifugal test and the excavation of the foundation pit in situ are compared and analyzed.It shows that when the shear strength of silty soft soil in the upper part of the layered foundation is relatively high,the pile foundation is subjected to a large force and it is prone to the breakage accident during the excavation process.Two extreme values of pile strain occur near the excavation depth and the interface between the silty soil and the underlying soil layer.Due to the influence of the pile,the pore water pressure of the soil near the excavation face changes smoothly,but the pore water pressure of the soil after the pile changes drastically with the excavation.The interaction between piles and soils mainly lasts 48 hours after excavation before the restoration of stability.The test results match with the field measured data,which can provide a reference for the design and construction process of the foundation pit in deep and thick soft soil.