Finite Element Analysis Of Retaining Structure With Double-row Piles In Foundation Pit

Increase of high-rise buildings and multilayer underground buildings required thefoundation pit stability more strictly. Scholars and technicians have done many works toresearch how to make the retaining structure control deformation and decrease innerforces effectively.Retaining structure with double-row piles was a new style. It had strongerdeformation control force and lower cost than single-row piles. So it was wildly used inBeijing and Shanghai. Based on Duncan-Chang soil constitutive model, this paper set aproject in Shanghai as background, and studied the deformation and inner forcecharacters of retaining structure with double-row piles using finite element numericalanalysis method. The main contents were displayed as follow:（1） To simulate the soil deformation and resilience nonlinear character in theprocess of foundation excavation unloading, Duncan-Chang soil constitutive model waschosen to simulate the soil deformation law. The determination method of modelparameters was discussed by stress-strain curve. The model parameters contained thetangential elastic modulus E_t, tangential Poisson’s ratio μ_t, and unloading modulus E_ur.Tangential Poisson’s ratio μ_t couldn’t be got easily, so tangential Poisson’s ratio μ_t wasreplaced with tangential volumetric deformation modulus K_t, which could be gotexactly from conventional tri-axial test.（2） The finite element model of retraining structure of double row piles wasestablished. The piles were regarded as flat shell structure with the bottom clampedsupport, and the ring beam was regarded as flat shell structure consolidated with piles.According to the principle of deformation coordination, no thickness interface structure（elements） was set between soil and structure. The numerical analysis method of retraining structure of double row piles was established using finite elements method,elastic mechanics and variation method.（3） Based on the finite element model above, regarding a project in Shanghai asbackground, the deformation and inner forces effect of pile character and soil characterwere numerically analyzed:①The variations of retraining structure with double-rowpiles with excavation depth;②The comparison of single-row piles and double-rowpiles;③The effect of row distance and pile stiffness on the deformation and innerforces;④The effect of soil cohesion, internal friction angle ψ, soil strengthening atthe bottom of pit on the retraining structure.（4） The influence of the space effect was analyzed from two aspects:①the beamstiffness effect,②the corner effect. The calculation results considering the space effecttallied well with project measured dates. That meant the influence of space effectshouldn’t be ignored.（5） The effect on environment around the foundation pit was discussed bynumerical simulation. And the ground settlement scope causing by excavation, thedistribution law of ground settlement, the maximum position were studied. Setting thesilt for example, the ground settlement variation law with excavation was analyzed.This paper analyzes the variation law of the retraining structure deformation andinner forces. Several reasonable suggestions are provided for the design andconstruction of foundation pit engineering. These research achievements supply usefulreference for similar projects.