Studies On The Foundation Pit And Pile Group Beneath The Basement Under Dewatering And Deep Excavation In Soft Soil

As the extent of exploitation and utilization of underground space rises gradually, excavation of large-scale and large depth is emerging. The engineering of the deep foundation pit in the coastal area construction on the soft soil layer of high compressibility, low bearing capacity, high water content, large void ratio and other characteristics, has the problems of how to effectively control the deformation of the pit and its supporting structure, how to reduce the impact on the surrounding environment due to excavation and dewatering, as well as how to ensure the safety and economic reasonably. Based on actual monitoring data of the deep foundation pit on stage IV of Square Yanlord of Haihe River in Tianjin, this paper established three-dimensional finite element model, and analyzes the entire process of dewatering and excavation of foundation pit and testing pile and cutting pile. In addition, this paper carried out the study of bearing capacity of piles and its settlement characteristics in condition of deep excavation by the geotechnical centrifuge tests.(1) Through the establishment of three-dimensional finite element model, simulate and calculate the dewatering in excavation of the northeast pit of Square Yanlord of Haihe River on stage IV engineering, and compare the results of finite element calculation and field measurement analysis on the internal force and displacement of the enclosure structure and the horizontal strut, on the settlement of soil outside foundation pit.(2) By the calculation and analysis of the results of three-dimensional finite element model of dewatering in excavation of the northeast pit of Square Yanlord of Haihe River on stage IV engineering, compare with field measurement in the respects of soil resilience of pit bottom, piles axial force of pit bottom, side friction of pile, the relative displacement between pile and soil, the uplift of pile and so on.(3)Compare the same length foundation piles at different locations within the pit with the different length foundation piles at the same position near the center of pit, respectively analysis the axial force of pile, the vertical displacement of the pile top, the relative displacement between pile and soil, the degree of side friction, the extent of the losses of contact pressure between pile and soil.(4)This paper introduces the principle of geotechnical centrifuge test, explores the reasons and its control methods in many aspects. And then, three groups of centrifuge test are designed, respectively study on the influence of directly loading on the single pile, on the influence of unloading by liquid drainage on the center piles and corner piles beneath the basement, and on the influence of reloading after unloading on the center piles and corner piles beneath the basement.