Field Test And Numerical Analysis Of Large Diameter Rock-Socketed Piles

With the rapid development of high-rise buildings in China,large diameter rock-socketed piles are widely used because of their high bearing capacity,especially in hilly areas.However,deformation of large diameter rock-socketed piles is small,the relative displacement between pile and soil is not sufficient and the shaft friction of soil does not reach the limit resistance.Therefore,large diameter rock-socketed piles in the design of bearing capacity often do not consider the shaft friction of the soil,resulting in the unreasonable design and improving the project cost.In order to analyze the vertical bearing capacity of large diameter rock-socketed piles in Low hilly areas,the Q-s curve and axial force diagram are obtained by field test to study the situation the shaft friction of the piles.Three-dimensional finite element models of large diameter rock-socketed piles are established by Midas GTS,and the numerical simulation results are compared with the measured data to verify the rationality of the models.On the basis of this,the effects of pile length,pile diameter and depth of rock strata on the shaft friction of large diameter rock-socketed pile are studied respectively.It can be found that the increase of the pile length will promote the shaft friction of the soil,especially when the pile length is 6~9m,but the increase rate will tend to be flat with the increase of pile length.It is considered that using the current technical code for building pile foundations to calculate the shaft friction of soil is larger than the true shaft friction,and It is necessary to introduce the reduction coefficient α to consider the influence of the pile length.The increase of pile diameter weakens the qsik of the soil shaft friction.So it is suggested to multiplie by the reduction factor of 0.9,especially when people use the specification to calculate the soil shaft friction of the large diameter rock-socketed piles and the piles length should be 6~9m and the diameter is more than 1m.The soil shaft friction is enhanced by the increase of the depth of the rock,but the effect is not obvious,and the increased shaft friction can be considered as the safety guarantee.In this paper,the finite element models are established to solve the limitation of the current technical code in the very soft rock’s ζr and the numerical simulation results are combined with the ζr from engineering cases.The value of the very soft rock’s ζr is given in this paper.