In-situ Test And Numerical Simulation On Bearing Characters Of Rock-socketed Pile For Medium Weathred Granite

In the construction of various large-scale projects,the requirements for foundation bearing capacity and deformation displacement are increasingly stringent.Because of its high bearing capacity and small settlement deformation,the rock-socketed pile is widely applied in engineering construction.Therefore,it is difficult to obtain the ultimate bearing capacity in static load test;the calculation method of vertical compressive bearing capacity of rock-socketed pile has not yet been unified by various industry standards;and rock-socketed piles are designed as end-bearing piles.Insufficient perception of the bearing behavior of rock-socketed piles;The influence of rock-socketed depth,elastic modulus of bedrock and roughness of hole wall on the bearing characteristics of rock-socketed piles is not fully understood.In this paper,the bearing characteristics and load transfer theory of rock-socketed piles are discussed by combining the vertical compressive static load in-situ test of single pile,mathematical model fitting and numerical simulation of ABAQUS finite element software.(1)Through the in-situ static load test,mathematical model fitting and finite element simulation analysis of 12 rock-socketed piles in moderately weathered granite foundation in Qingdao area,it is found that 12 rock-socketed piles reflect the behavior of friction pile to varying degrees,which is not a complete end-bearing pile.Rock-socketed piles in moderately weathered granite foundation have high vertical ultimate bearing capacity and small settlement deformation,which are suitable for the requirements of foundation engineering.(2)Three large diameter rock-socketed piles in moderately weathered granite are simulated by ABAQUS finite element method.It is shown that the simulated load settlement curve matches well with the measured load settlement curve,and the error of pile top settlement is small.The pile tip resistance accounts for 56.9% of the total load,and the side friction resistance accounts for 43.1% of the total load.The side friction resistance plays a greater role in the load transfer process,and the bearing characteristic is friction end-bearing pile.By comparing the finite element simulation value,the design limit value of vertical compressive bearing capacity,the exponential curve model prediction value,and the calculation result according to the material strength of pile body,it is established that the finite element software numerical simulation method and the exponential curve model prediction method are closer to the actual situation.It can be applied to predict the ultimate bearing capacity of rock-socketed pile and to analyze the bearing characteristic and load transfer theory of rock-socketed pile.(3)Numerical simulations with ABAQUS finite element software were conducted to demonstrate the effects of dimensional ratio,embedded rock depth(embedded rock ratio),bedrock elastic modulus(pile-rock elastic modulus ratio),and hole wall roughness on the vertical bearing characteristics of rock socketed piles.It is found that the lateral friction of the rock-socketed section presents a nonlinear distribution and a bimodal curve distribution with a large upper part and a small lower part.As the dimensional ratio increases,the lateral frictional resistance of the rock socketed pile increases and the pile top settlement grows.Under different rock-socketed ratios,the variation of axial force of pile shaft is basically the same.With the increase of rock-socketed ratio,the proportion of bearing capacity shared by end resistance decreases,and the bearing behavior of rock-socketed pile changes from end-bearing pile to friction pile.It is appropriate to take the rock-socketed ratio between 2 and 3.As the modulus of elasticity of bedrock increases(the pile-rock modulus of elasticity ratio decreases),the pile axial force increases at the same depth of the pile,the average value of side friction of overlying soil decreases,the average value of side friction of rock-socketed section increases,the total side friction decreases,the settlement of pile top reduces,the bearing capacity of single pile increases,and the proportion of tip resistance to total load increases.With the increase of hole wall roughness,the side friction of the overlying soil and rock-socketed section increases significantly,the total side friction increases,the pile tip resistance decreases,the pile top settlement decreases,and the vertical compressive bearing capacity of a single pile increases.