Simulationalanalysis Of Interaction Between The Superstructure And The Pile-group Foundation With Variable Stiffness Caused By Adjusting The Pile Spacing

As the main form of modern high-rise building foundation,the design and construction of pile-group foundation occupies a pivotal position in the whole project.The current mainstream design methods in the engineering field usually do not consider the interaction between the superstructure and the foundation.The two are separated and calculated separately,most of them adopt the method of the same stiffness and uniform pile laying.This design method will lead to disc-shaped differential settlement and saddle-shaped reaction force distribution that occurs in the foundation,then the secondary stress will be produced in the cap and superstructure,which not only causes great waste,but may even affect the use function and longevity of the building.In order to solve these problems,experts and scholars put forward the concept of optimized design of pile foundation stiffness to reduce differential settlement,which means“suppressing the strong and complement the weak”.However,there is still much room for research on the specific methods of implementation.Pile spacing is the main influencing factor of pile group effect,adjusting the pile spacing not only has the ability to change the basic stiffness and reduce the differential settlement,but also has the advantages of more flexibility and variability.Therefore,through the reasonable adjustment of the pile spacing,the optimized design of pile foundation stiffness to reduce differential settlement can be realized.For achieving the purpose,this paper intends to use the numerical simulation method to study the basic performance of the interaction of the superstructure and the pile-group foundation with variable stiffness caused by adjusting the pile spacing.The research contents and achievements are roughly divided into the following five aspects:(1)The finite element models were established based on the relevant data of model test,and the feasibility of the numerical simulation method was verified by comparing the results of finite element calculation and model test.(2)Six finite element models of low-cap pile-group foundation with different pile spacing were established,and two different methods of variable pile spacing were considered.Through comparison,the rule of influence of pile spacing on the working performance of pile-group foundation was obtained.(3)Combined with an engineering example,a three-dimensional finite element model of the frame core tube structure-pile raft foundation with equal pile spacing-soil working system was established.Systematic research was carried out from six aspects:internal force of superstructure,settlement characteristics of pile-raft foundation,internal force of raft,distribution of soil reaction at raft bottom,distribution of reaction force at pile top,load sharing between raft and piles.The differences in the performance of the system considering the interaction or not were compared and analyzed.(4)According to the different ways of load exertion and stiffness formation of superstructure,three different construction loading conditions were selected.And the influence of construction process on the frame core tube structure-pile raft foundation with equal pile spacing-soil working system under the condition of considering the interaction was emphatically studied.(5)Four different pile spacing schemes were set up by reducing the number of piles and changing the pile spacing.Considering the influence of construction process,the effects of adjusting pile spacing on the internal force of upper structure,settlement characteristics of pile-raft foundation,raft internal force,distribution of soil reaction at raft bottom,distribution of pile top reaction and load sharing between raft and piles in the frame core tube structure-pile raft foundation-soil working system under the layer-by-layer loading calculation model were studied and analyzed.The scheme of the pile-group foundation with variable pile spacing studied in this paper can effectively optimize the working performance of the interaction system.Compared to change pile length or pile diameter,it has stronger applicability and operational ability in engineering.It can also provide a certain theoretical basis for the optimized design of pile foundation stiffness to reduce differential settlement.