Experimental Investigation And Numerical Simulation Of Stability Of Foundation Pit Supported By Steel Pipe Pile

Based on the 1-1 support section of a foundation excavation engineering in Beijing,this paper investigates the displacement,stress and deformation of steel pipe pile foundation pit support through the theoretical calcaulation,scale model test and numerical simulation.Besides,the feasibility of steel pipe pile instead of bored pile is studied.There are 6 kinds of steel pipe piles with different diameters and thickness using to replace bored piles,which are designed by theoretical calculation.The steel pipe piles with maximum and minimum diameters are chosen for scale model test.The results show that the horizontal and vertical displacements of soil and the influence range caused by a single pipe pile construction with a large diameter are larger than that of a single pipe pile with a small diameter,but the cumulative horizontal displacement has little difference within the same supporting area.The results of stress show that,the soil stress increase caused by pipe pile construction mainly occurred in the lower part of the pipe pile,the amplification of the stress increase in a smaller diameter pile construction is greater than that of a larger one.According to the analysis of blow counts,with the increasing depth into the soil,the blow counts of a large diameter pipe pile are greater than those of the small one.However,the squeezing soil effect caused by a smaller diameter pipe pile is more obvious.The result of scale meodel test for pit excavation shows that the maximum horizontal displacement appears at the edge of the pit,the maximum horizontal displacement values in the excavation simulation of both large and small piles are 3.23 mm,10.16 mm,respectively.The maximum measured value is about 4 mm.After the excavation,small parts of the soil collapse at the edge of the model box in the case of pipe pile supporting with a small diameter.However,large-scope collapse occurred when using pipe pile with a large diameter.The steel pipe pile with a small diameter is more effective in keeping the entirety of soil,but the ability to control the horizontal displacement is poor.While the steel pipe pile with a large diameter needs to be used with other supporting structures.In the model test of the settlement trends of soil shows similarity to the measured value,and the final settlements of the steel pipe piles with large and small diameters are-2 mm,and-3.48 mm,respectively.The maximum measured value is-2.04 mm.According to the simulation and measured values,the settlement trends of soil can be divided into 3 stages:the development stage,the transition stage and the stability stage.In the scale model test,the duration of transition stage was short.The numerical simulation results show that with the diameter of the steel pipe pile increases,the stiffness of the pile increases,and the soil displacement and the stress of pile becomes smaller,but the steel pipe pile diameter has little influence on the base uplift.The simulation values,model test results and measured values of soil displacement are less than the alarm values.The stresses of steel pipe pile are far less than the steel strength design values,which means that the steel pipe pile is designed meeting the requirements of controlling the soil displacement and also keeps safety and stability.At last,taking the steel pipe pile with diameter of 1.0 m as an example,this paper also analyzes the influence of pile arrangement distance on the foundation pit.It is proposed that in actual project the arrangement distance of steel pipe pile is better chosen to be 2.0D.