Study On The Influence Of Load-bearing Plate Position On The Uplift Failure State And Bearing Performance Of NT-CEP Pile Group

At present,variable section piles have good market application prospects,and among many variable section pile types,the new concrete expanded-plate pile(NT-CEP pile)is an emerging variable section pile type.NT-CEP pile improves bearing capacity,reduces settlement and material cost by adding load-bearing plates,and reduces mud emissions by drilling and expanding integrated pile forming tools in the construction process,which is now the variable section pile type with international advanced level in the pile foundation market.At present,corresponding theoretical and experimental studies have been carried out on the bearing performance of single piles and double piles,and the soil failure around piles,but the research on NT-CEP pile groups is relatively lacking.Due to the existence of the load-bearing disk,the bearing capacity relationship between NT-CEP pile group piles and single piles and double piles is not simply an integer multiple.At the same time,considering the actual situation of the project,piles are also used more in most civil buildings,transportation and other projects,and even for some large airports,ports and other fields,they are larger pile groups.Due to the lack of pile research,which hinders the promotion and application of NT-CEP piles in engineering,the research on NT-CEP pile piles needs to be carried out urgently.Based on the analysis of the bearing performance of NT-CEP piles monopile and double pile and the failure state of soil around the pile,this paper studies the influence of the key factor of load-bearing disk position on the uplift failure state and bearing performance of NT-CEP pile group pile.At the same time,the 4-pile model,6-pile model and 9-pile model of NT-CEP pile are set up in this paper,and the finite element simulation analysis of NT-CEP pile group piles with different disk positions under three pile numbers is carried out by ANSYS finite element software,and the corresponding displacement,stress and other data are extracted.The displacement cloud,stress cloud,load-displacement curve,pile stress curve and soil stress curve around the pile were compared and analyzed,and the displacement law,stress law and bearing mechanism of NT-CEP pile piles under vertical tension at different disk positions were comparatively analyzed,and the calculation mode of the uplift bearing capacity of NTCEP pile piles was corrected by combining the slip line theory and the calculation formula of the uplift bearing capacity of NT-CEP pile monopiles.The results show that under the vertical tensile force,the soil failure around the pile of NT-CEP pile group is more serious than that of single pile and double pile.During the loading process of NTCEP pile piles with the same number of piles,with the downward movement of the disc position,the bearing capacity of NT-CEP pile piles is significantly improved,but too low arrangement will also reduce the bearing capacity and increase efficiency,and the lower the load-bearing disc,the more serious the damage range when it is completely destroyed,so the distance from the load-bearing plate to the top of the pile is controlled as much as possible at 7R-12 R when arranged in the same disc position,and less than4 R when arranged in the wrong position.Compared with the NT-CEP pile group piles arranged in the same position,the NT-CEP pile group piles arranged in the wrong position are slightly worse in the overall stability,but because the bearing disk has a Ydirection distance,the wrong position arrangement is more suitable for projects with uneven geological conditions and complex drilling conditions.The calculation mode of the uplift bearing capacity of NT-CEP pile group piles still conforms to the slip line theory,but the reduction factor α affected by the position of the bearing disk should be considered when calculating.In this paper,the finite element modeling method of 1:1 equal scale is adopted to realize the working environment of NT-CEP pile group piles under vertical tensile force in actual engineering,which provides strong support for the research of NT-CEP pile piles.At the same time,this paper analyzes the influence of disk position on the uplift failure state and bearing performance of NT-CEP pile group piles for the first time,and puts forward targeted substantive conclusions.This paper improves the design concept of NT-CEP pile group,lays a solid theoretical foundation for the construction site test of NT-CEP pile group pile in the next step,and also provides strong theoretical support for the continuous promotion and application of NT-CEP pile.