Research On Vertical Load Analysis Method Of Rock-socketed Piles Based On Limit And Its Engineering Application

The rock-socketed piles are widely used in long-span bridges,high-speed railways,highways and high-rise buildings due to their high bearing capacity,good seismic performance,small settlement and effective reduction of uneven settlement.However,for the load transfer mechanism of rock-socketed piles under vertical loads,systematic and mature calculation methods and theories have not yet been given,which will affect the economics of the use of rock-socketed piles to some extent.Numerous studies have shown that the pile-side resistance of the rock-socketed section has a significant impact on the bearing capacity and load-transfer behavior of the rock-socketed pile,and in the early stage of the load,the pile-side resistance accounts for a large proportion of the vertical load.Therefore,based on the theory of limit analysis and considering the roughness of pile-rock interface,the vertical load transfer mechanism of rock-socketed piles is further studied.Firstly,the domestic and foreign analysis of the load transfer mechanism of rock-socketed piles under vertical loads is analyzed.The method of determining the lateral friction of the piles in the rock-socketed section and the factors affecting the lateral friction of the piles are discussed.Furthermore,for the quantification of the interface roughness of piles and rocks,a regular obtuse angle wedge is proposed as the quantitative model of the rock mass of the pile rock interface.On the basis of the model,combined with the mechanism of the pile-rock interface in the process of sliding dilatancy and slip-shearing,the shear function expression corresponding to these two stages is obtained respectively.Then,Based on the limit analysis theory,the upper and lower limit breaking loads of the wedge-shaped rough body are obtained.According to the static equilibrium relationship of the interaction between the rock and rock interface at the critical failure,the upper and lower solutions of the ultimate displacement of the pile-rock interface are obtained respectively.Then,combined wi th the action mechanism of the pile-rock interface in the two stages of slip dilatancy and slip shearing,a shear equation considering the interface roughness of the pile rock is established.Furthermore,the obtained shear equation is combined with the pi le load transfer method to analyze the load transfer behavior of the pile.Finally,the obtained shear function is verified by the indoor model test,and the method is applied to the engineering example.The comparison with the measured results verifies the rationality and applicability of the proposed method.The influence of the quantitative parameters of the interface roughness of the pile rock on the critical displacement of the pile-rock interface and the peak resistance of the pile side is analyzed and discussed.