Experimental Study And Numerical Simulation Analysis On Rebounding Of Foundation Pit Under Deep Excavation

The excavation of foundation pit is an unloading process. The excavation of upper soil and the release of self-gravity will result in swelling of soil under the foundation pit bottom, and then the resilience happened. The resilience of the soil is the main reason of the swelling on the central foundation pit bottom, exactly calculating the resilience of the foundation pit is one of the most important factors that can judge the stability of the foundation pit and calculate the settlement of the building, and is very useful to the design and construction of the piles and the quantificational evaluation of the environmental influence due to the excavation of foundation pit. So studying the resilience and calculating the quantity of the resilience is one of the effective means to guarantee the stability of foundation pit and decrease the hazard of settlement.In this thesis, firstly, experimental studies on the influence depth due to excavation were introduced. Some stress path and numerical simulation methods used to study foundation pit excavation were also concluded.Secondly, experimental studies on influence depth due to excavation were carried out. Through some consolidation-rebound tests, deformation characteristics of soil samples under unloading are studied. The critical unloading ratio and the ultimate ratio were confirmed after analyzing the relationships of resilience ratio, resilience strain and resilience modulus to unloading ratio. Through some consolidation-direct shear tests, the relationship between shear residual ratio and unloading ration was analyzed. The critical unloading ratio and the ultimate ratio were gained. These two ratios can be used to estimate the depth of unloading influence area and strong rebound area.Thirdly, comparing and analyzing altered triaxial test system and other stress path triaxial test system, the GDS triaxial test system has some advantages on K0 consolidation test and stress path test. It can well meet the needs of the unloading test.Fourthly, The K0 of the test samples was calculated through K0 consolidation test on GDS triaxial test system. Then different stress path tests were carried out to simulate different stress condition of passive soil of foundation pit during the excavation. The critical unloading ratio and the ultimate ratio were confirmed after analyzing the relationships between resilience strains and unloading ratio. After analyzing the relationship curves between resilience stress and strain, initial unloading deformation modulus was calculated and the deformation modulus formula under unloading was deduced.Lastly, two-dimensional plain model was founded by the PLAXIS finite element program. The depth of the total resilience area and strong rebounding area were calculated under different excavation depth. They were similar to the test results, so the test methods and results were right.