Study On The Influence Of Bearing Plate Position On The Compressive Failurestate And Bearing Capacityof NT-CEP Pile Group Piles

With the diversified development of pile foundation,more and more new variable cross-section piles stand out.New Type Concrete Expanded-Plate Pile(NT-CEP Pile)is a new variable cross-section pile.In recent years,it has become a research hotspot of many scholars because of its good bearing performance,flexible pile design,economic and environmental protection,and wide application range.Through the continuous research of our research group in the past ten years,it is concluded that the factors affecting the bearing capacity and failure state of NT-CEP single pile mainly include the position of bearing plate(referred to as plate position),pile spacing,plate cantilever diameter,plate slope angle and so on.At present,the research of NT-CEP single pile has been basically perfect,but there are often pile groups in practical engineering,so it is necessary to systematically study NT-CEP pile groups.In this paper,NT-CEP pile group compressive piles(4 piles,6 piles,9 piles)are the main research objects.Based on the research of single pile and double piles,ANSYS simulation analysis is applied to the pile body and soil.The method of mapping is innovatively used for meshing.Aiming at the main influencing factor of disc position,ANSYS finite element is used for simulation analysis to determine the influence of disc position on the bearing performance of NT-CEP pile group compressive piles.The failure state and bearing capacity of NT-CEP single pile,double pile and pile group under vertical pressure are studied.Through the vertical displacement of the pile body and the soil around the pile,the stress of the pile body,the slip area of the soil around the pile,the shear stress of the soil around the pile and other nephograms,data and curves,the settlement of the pile body and the failure state of the soil around the pile under the limit state during the loading process when the flat plate arrangement and the staggered plate arrangement are studied respectively.Through the simulation data analysis of 6 piles and 9 piles,the influence of different plate positions on the bearing capacity and failure state of NT-CEP piles in different positions of 6 piles and 9 piles is studied.The design principle of NT-CEP pile group is put forward and the calculation model of bearing capacity is improved.Impact;put forward the design principle of NT-CEP pile group and improve the bearing capacity calculation model.The results show that the failure process of NT-CEP pile group is basically similar to that of single pile and double pile when it is subjected to vertical pressure.In the initial stage of loading,pile-soil separation occurs on the disk.As the load gradually increases,the soil under the disk compresses and slips until it reaches failure,which conforms to the slip line failure theory.Through the comparison of the displacement of the top of the four piles and the double piles and the single pile,the bearing capacity reduction coefficient of the four single piles is 0.88;the reduction coefficient of bearing capacity of single pile is0.96.When the flat plate is arranged,the closer the plate position is to the pile top,the higher the bearing capacity of the pile group is.However,attention should be paid to the actual engineering situation.The plate position should not be too close to the soil surface and should be set at 1 / 4 of the upper part of the pile body as far as possible.When the staggered plate is arranged,as the vertical spacing of the plate gradually expands,the position of the plate gradually approaches the top of the pile,and the soil between adjacent piles has little interaction,and the bearing capacity of the NT-CEP pile group becomes better and better.The simulation data of 6 piles and9 piles are compared and analyzed.Under the ultimate load state,the bearing capacity of side piles,corner piles and middle piles at the same plate is different.By comparing and analyzing the load displacement curve of pile top and the displacement curve of soil around piles,it is concluded that the middle pile bears the largest external force when resisting vertical load,followed by side piles and corner piles.By comparing the load displacement nephograms of side piles,corner piles and middle piles at different disk positions,it is concluded that the bearing capacity of NT-CEP piles at different positions increases with the disk position gradually approaching the pile top.Combined with the slip line theory and the simulation analysis conclusion,the reasonable setting position of the bearing plate is put forward,the influence coefficient of the plate position is determined,and the bearing capacity calculation formula of NT-CEP pile group is included.In this paper,the innovative simulation method is adopted,and good research conclusions are obtained.The design and calculation theory of NT-CEP pile group is improved,which provides theoretical support for the application of NT-CEP pile group in practical engineering in the future.