Research On Bearing Characteristics Of Rock Socketed Pile In Mudstone Bearing Layer

Rock-socketed piles are commonly used in low mountain and hilly areas,and have the advantages of large single bearing capacity,good seismic performance,and small settlement.Mudstones are widely distributed in low mountain and hilly areas,have lower strength and are easier to be compressed than hard rocks,and often show different bearing characteristics than traditional rock-socketed piles.Based on the actual engineering in the low mountain and hilly area of Tai'an,this paper uses GTS NX finite element analysis software to carry out numerical simulation on the static load test of the rock-socketed pile,and analyzes the load transfer and displacement development law during the loading process.On this basis,by establishing a variety of The finite element model studies the influence of the physical and mechanical properties of mudstone,pile bottom sediment,pile diameter,and thickness of the overlying soil layer on the bearing properties under this geological condition.The specific work is as follows:(1)The Q-s curve is obtained through the field static load test,and the finite element simulation of the loading process is carried out.Through simulation,it is concluded that the pile end resistance ratio in the normal working state is very small,and the load is mainly borne by the pile side resistance;loading During the process,the side resistance of the pile is not synchronized.The side resistance of the overlying soil layer reaches the limit before the side resistance of the rock-socketed section.After the side resistance of the pile reaches the limit,the resistance at the pile end increases significantly.(2)Continue to load the rock-socketed piles through GTS NX.It is concluded that the Qs curve of mudstone-socketed piles before the limit state can be divided into three stages: in the first stage,the contact surface of the pile side is in an elastic state,and the displacement of the pile top increases linearly with the load;In the second stage,the pile-side contact surface gradually enters a plastic state from top to bottom.The pile-end resistance increases with the increase of the load,and the displacement of the pile top increases with the increase of the load.The third-stage pile-side resistance has reached its limit.The resistance of the pile end bears,due to the mudstone compression,the displacement of the pile end increases rapidly,and the displacement of the pile top also increases rapidly.(3)By setting different mudstone physical and mechanical parameters in the finite element model,it is concluded that when the pile top load is constant,the mudstone elastic modulus has a greater effect on the displacement of the pile top,and the cohesion and internal friction angle have relatively small effects;The larger the modulus,the smaller the displacement of the pile top under the same load,and the smoother the Q-s curve;the larger the elastic modulus,the higher the pile top load required for the pile side resistance to reach the limit during loading,and the degree of side resistance under the same load.The lower the load,the higher the load transferred to the end of the pile.(4)Settlement of pile end sediments with different thicknesses through solid elements,it is concluded that the sediment will greatly increase the displacement of the pile top,resulting in a reduction in ultimate bearing capacity.For this rock-socketed pile,the bearing capacity cannot meet the design requirements when the sediment is 200mm;during the loading process,the sediment will delay the exertion of end resistance.(5)Through the establishment of finite element models of different pile diameters,it is found that the pile diameter compression and pile end displacement of a large diameter pile under the same load are reduced,making the Q-s curve smoother;at the maximum loading value,the pile side resistance varies with The increase of pile diameter increases first and then decreases.(6)By establishing a finite element model of different overlying soil layer thicknesses,it is found that when the pile top load is constant,the thickness of the overlying soil layer within a certain range will reduce the displacement of the pile top,and it will affect the displacement of the pile top after a certain value.very small.The above analysis of the rock-socketed cast-in-place pile in the mudstone bearing layer can provide reference for the design and static load test of the pile foundation under the same or similar geological conditions.