Experimental Study On Working Behavior Of Composite Foundation Of Pipe-pile Groups With Holes & Cap

Nowadays,for the highways,high-speed railway and other projects of deep soft ground,many researchers at home and abroad are working incessantly for the use of appropriate vertical reinforcement to form a composite foundation for foundation treatment,in order to reduce the settlement of buildings and improve the bearing capacity of the foundation.The composite foundation of pipe-pile with cap is suitable for the treatment of relatively deep soft soil foundation,but the squeezing effect caused by the static pressure piling process of the pipe-pile will cause the pile to be displaced,floating,tilted and even broken adverse consequences.For this reason,the research group put forward the technology of composite foundation of pipe-pile with holes & cap.At present,the research on the composite foundation technology of pipe-pile with holes& cap is mainly focused on the bearing behavior of single pile of pipe-pile with holes.It is still blank in the study of the working traits of pipe-pile groups with holes,but group piles are more used in actual engineering.Therefore,it is of great necessity and practical significance to study the working behavior of composite foundation of pipe-pile groups with holes & cap.In this paper,through two methods of the indoor model test and numerical simulation,pipe-pile groups with holes & cap composite foundation of the working traits were studied and discussed.The main research contents and achievements are as follows:(1)The indoor model test was carried out on the excess pore water pressure caused by driving pipe-pile groups with holes.The results showed that the excess pore water pressure produced by driving pipe-pile groups with holes is not simple addition by superposition of the excess pore water pressure,but the cumulative result of the mutual accumulation and dissipation of the single pile.The excess pore water pressure generated by the measuring point was related to the direction of the pile sinking.Whereas the excess pore water pressure caused by the pile-sinking increased when the pile direction tends to the measuring point,and the excess pore water pressure decreases when it is facing the measuring point.In addition,the pipe-pile groups penetrated in a radial way has the least peak of excess pore water pressure,and the dissipation rate is the fastest,which is the most favorable for reducing the squeezing effect of the sinking piles,and pile sinking effect is the best.Pile wall opening method provides a new way to reduce the squeezing effect of pile.(2)The indoor model test was carried out on the working characteristics of composite foundation of pipe-pile groups with holes & cap under vertical load.The results show that the settlement of composite foundation of pipe-pile groups with holes& cap is less than that of composite foundation of pipe-pile groups without holes & cap,that is,the compressive capacity of composite foundation of pipe-pile groups with holes& cap is much stronger.The axial force of pile groups decreases with the increase of depth,and the decrease rate of axial force increases with the increase of vertical load.At the beginning of loading,the load is mainly borne by the pile,with the load continued to increase,the load borne by the pile and soil together until the pile and soil to work together to achieve a stable state.in addition,with the loading level increased,the pile-soil stress ratio of composite foundation of pipe-pile groups with holes & cap is always less than that of composite foundation of pipe-pile groups without holes & cap,which further illustrates the opening of pile body to enhance soil bearing capacity of composite foundation pile groups.(3)ABAQUS software was used to simulate the working traits of composite foundation of pipe-pile groups with holes & cap and compared with the indoor test results.The results confirmed that the indoor model test results were correct.