Study On Vertical Bearing Mechanism And Failure Mode Of Drilling With Cased Of Pipe Pile

Drilling with pipe pile is a new type of large diameter non-compaction PHC pipe pile,which is proposed to overcome the shortcomings of traditional PHC pipe pile.Through the development of complete sets of equipment and construction technology,the drilling,pile sinking and soil drainage of large diameter PHC pipe pile can be realized simultaneously.It has been preliminarily applied in the pearl river delta region of China.At present,there are few researches on the vertical bearing capacity of pipe pile with drilling heel.This paper conducts a systematic analysis and research on the vertical bearing mechanism and failure mode of pipe pile with drilling heel through model test and numerical simulation.The main research contents and research results are as follows:1.Through the model test study on the bearing capacity of pipe pile foundation with different pile forming processes,the differences in the bearing characteristics and load transfer law between pipe pile and other pipe piles with drilling are compared and analyzed,and the influence of the filling depth on the bearing capacity of pipe pile with drilling is discussed.The results show that the ultimate bearing capacity of different pile types is significantly different due to different pile forming processes.The ultimate bearing capacity of pipe pile with drilling is the largest in the homogeneous sand stratum,and it is more than 19% higher than that of the middle excavation method,while that of the hammer strike method is the smallest.Under the same grouting condition,the filling of pile core is helpful to improve the ultimate bearing capacity and lateral friction resistance of pipe pile.2.Through the model test study on the vertical bearing capacity of the pipe pile with drilling considering the sediment at the bottom of the pile,the stress characteristics of the pipe pile with drilling without sediment were compared and analyzed,and the influence of the enlarged head at the bottom of the pile on the bearing capacity of the pipe pile with drilling was discussed.The results show that the existence of sediment has a great influence on the compressive bearing capacity of pipe pile with drilling,but the ultimate bearing capacity can be increased by about 20% after the sediment is removed.The pile foundation load with bottom sediment is basically borne by pile lateral friction,and the axial force near the pile end is reduced,and the thicker the sediment is,the more obvious the reduction is.Through the construction of cement-soil extension head at pile end,the compressive bearing capacity of pipe pile with drilling can be improved.3.Based on the drilling pipe pile with pile grouting body-interface shearing test of soil,pile in different soil,different pile type size of the contact surface friction properties are studied,before and after the analysis of the grouting pile-soil interface shear characteristics and the failure of interface failure mode,and reveal the grouting reinforcement mechanism of the influence law of pile side friction.The results show that the failure mode of the contact surface of the pipe pile with drilling is the shear failure of the contact surface of the grouting body and the soil around the pile.The lateral resistance of pipe pile-grouting and soil interface is mainly controlled by the physical properties of cement slurry.After pile side grouting,the strength of cement slurry stone body is far greater than that of the soil around the pile,so it can be considered that during the load transfer process,there will be no damage between the pipe pile and the grouting body,and the pipe pile and the grouting body are always a whole.4.Based on 3 d scanning technology,while drilling and pipe pile reconstruct 3 d scanning of fine geometric model,using the finite element software to while drilling with compressive strength,pull out bearing properties of pile calculation of three-dimensional model on the basis of verifying the rationality of the established model for drilling and pipe pile compressive strength,pull out the influence factors of the bearing performance is analyzed.According to the results of finite element calculation,the physical properties of grouting have little influence on the vertical bearing capacity of pipe pile with drilling.The property of soil around pile is one of the main factors to control the bearing capacity of pipe pile with drilling.Under the action of uplift load,the enlarged head of the pile end of the pipe pile with drilling can bear a large proportion of load,which can effectively improve its uplift bearing capacity.5.By conducting a large-scale grouting liquidity test on the flow and diffusion rules of grouting slurry on the side of piles with drilling and pipe piles,the flow and diffusion rules of grouting slurry in the pile-soil gap with drilling and pipe piles under different grouting materials on the side of piles and under grouting pressure were directly observed.The test results show that the diffusion of slurry at the pile-soil grouting interface after grouting with pipe piles is mainly divided into upper boundary diffusion stage and lateral boundary diffusion stage.The grouting pressure and the ratio of cement slurry to cement have great influence on the grouting fluidity of pile side with drilling and pipe pile.