Study On The Influence Of Pile Spacing On The Compressive Failure State And Bearing Capacity Of NT-CEP Pile Group

With the increasing development of pile foundation technology,more and more variable section pile types have been introduced one after another,the New Type Concrete Expanded-Plate Pile(hereinafter referred to as NT-CEP pile)is one of the variable cross-section piles widely used in various engineering fields in recent years,compared with the traditional straight hole pile,its own structure has many advantages such as high bearing capacity,flexible design of bearing plate,small and uniform settlement,and good socio-economic benefits.At present,domestic and foreign research on NT-CEP pile single pile and double pile under vertical load tends to be mature,but little research on group pile,because of the interaction between group pile soil body,so the group pile bearing capacity is not exponentially increased with the number of piles.The pile spacing is one of the important factors affecting the load carrying capacity of group pile,and there is a big difference in the load carrying performance under different number of piles and different spacing,how to choose the optimal pile spacing based on the actual engineering conditions,and how the group pile can play the optimal load carrying capacity is very important,so it is necessary to study the influence of pile spacing on the load carrying performance of NT-CEP pile group pile.Based on the existing compression test results of half-section double piles in our research group,this paper uses ANSYS software to analyze the finite element model,and studies the influence of pile spacing on the compressive failure state and bearing capacity of NT-CEP pile group piles.Then,the simulation results are compared with the existing test results,and the law of pile spacing on the compressive failure state of NT-CEP pile group piles is obtained.Finally,the influence of different pile spacing on the compressive bearing capacity and failure state of NT-CEP pile group piles is determined,and the most reasonable arrangement of group piles(four piles,six piles and nine piles)is analyzed.The calculation formula of compressive bearing capacity of NT-CEP pile group based on slip line theory is improved.The results show that under the action of vertical load,increasing the number of piles does not multiply its bearing capacity.It is calculated that the reduction coefficient of bearing capacity of pile groups under different pile numbers and different pile spacing is also different.The bearing capacity of pile group increases with the increase of pile spacing,but the efficiency of bearing capacity improvement is not high when the pile spacing is greater than 4 times the cantilever diameter.Therefore,it is reasonable to control the pile spacing of pile group arrangement in 3 ～ 4 times the cantilever diameter in practical engineering.The calculation formula of compressive bearing capacity of NT-CEP pile group still conforms to the slip line calculation theory,and the reduction coefficient of pile spacing under different pile numbers needs to be considered when calculating the bearing capacity.Based on the results of finite element simulation,this paper systematically analyzes the NT-CEP pile group,improves the research results and theoretical system of NT-CEP pile group under vertical load,and obtains the reduction coefficient of compressive bearing capacity of NT-CEP pile group under different pile numbers and different pile spacing,It provides a meaningful value for the application and technology promotion of NT-CEP pile group in practical engineering.