Study On The Influence Of Pile Spacing On The Uplift Bearing Capacity Of NT-CEP Pile Group Pile

The new type of concrete expanded plate pile(hereinafter referred to as NT-CEP pile)is a new type of multi-section drilled and expansion cast-in-place pile in recent years.When this kind of pile is under uplift load,the interaction between pile and soil not only has the friction resistance of the pile side,but also has the uplift resistance of the bearing plate.As the construction machine is updated,the construction process is also more economical,green,energy saving,and environmentally friendly.In practical engineering,especially in high-rise buildings,NT-CEP piles are more common in the form of pile group.Pile group foundation is a foundation form composed of multiple piles and cap.When pile group foundation is subjected to vertical load,considering the interaction between piles and other factors,in many cases,The tensile bearing performance of pile group in pile group foundation is different from that of single NT-CEP pile under the same conditions..However,at present,domestic and foreign scholars’ research on the performance of concrete expanded plate pile group is still in the preliminary development stage,and there are no relatively mature theoretical research results,which cannot fully meet the needs of practical engineering.Therefore,it is necessary to conduct in-depth research on the concrete reaming pile group foundation.In this paper,the influence of pile spacing on the uplift bearing performance of NT-CEP pile groups is studied.Using ANSYS finite element simulation software,On the basis of single and double pile studies,select the appropriate plate position,plate spacing,plate slope Angle,plate form,plate overhang diameter and plate number of expanded plate pile,and establish the pile and soil model of NT-CEP pile group withdifferent pile spacing for theoretical analysis.This paper studies the failure state of soil around pile group foundation under vertical tension and the change law of failure state of soil around pile with the change of pile spacing,determines the main influence range of soil in bearing plate between pile group foundation when the soil reaches the limit state,and then determines the reasonable pile spacing,and deduces the calculation model of uplift capacity of pile group foundation.The results show that the group pile effect of the new type of concrete extendedplate pile is affected by the pile spacing.When the overhanging diameter of the bearing plate(the horizontal distance between the end of the bearing plate and the pile surface)is fixed,the distance between the piles can be expressed by the distance between the end of the bearing plate(the horizontal distance between the inner ends of the two bearing plates).When the distance between disc ends is less than twice the cantilever diameter of the plate,the compressed soil on the disc will slip and damage,forming an arc-shaped sliding area.In the test,there is water in the curve range,and the watermark is analyzed to form a watermark,and the watermark has an overlapping part.In the displacement cloud diagram of theoretical analysis,the area with large soil displacement also has an overlapping part,and the shape is similar to the watermark,which indicates that the soil in the overlapping part is affected by the joint action of two bearing discs;When the disc spacing reaches two times or more of the disc cantilever diameter,most of the watermark and displacement formed on the two bearing discs are not superimposed.In the stress nephogram and shear stress curve diagram,the XY shear stress of soil around the pile reaches its maximum value near the bearing disk.The smaller the pile spacing is,the more obvious the pile group effect is,the faster the soil between the piles is destroyed under the action of bearing disk,and the lower the uplift bearing capacity of pile groups.Therefore,inthe actual engineering design,the pile spacing shall try to ensure that the disc end spacing is greater than twice the disc cantilever diameter.By comparing the bearing capacity of group pile and single pile of the concrete extended-plate pile,the expansion times of bearing capacity of group pile of the concrete extended-plate pile with different pile spacing compared with single pile under the action of vertical tension are calculated,and the correction coefficient of the influence of pile spacing on bearing capacity is introduced,and the calculation formula of uplift bearing capacity of group pile of the new type of concrete extended-plate pile is put forward.In this paper,the influence of pile spacing on the uplift bearing capacity of NTCEP pile group is studied,and the theoretical system of NT-CEP pile is further improved,which lays a foundation for the study of NT-CEP pile group foundation.It provides a theoretical basis for the popularization and application of NT-CEP pile in practical engineering field.