Study On Settlement Control Optimization Of Soft Composite Foundation Reinforced By Screw Pile

In this paper,based on the soft soil quality in the southwestern region and the specific design problems of pile foundations for specific railway projects,field tests compare and analyze the reinforcement effects and reinforcement schemes of cement fly ash gravel piles(CFG),cement mixing piles and compact thread piles.The group pile model system was established by finite element method,the load transfer characteristics of soft ground reinforced by screw piles and the change law of additional stress of foundation were analyzed,and settlement was proposed as an important design index to control the reinforcement of soft ground.The Mindlin-Geddes solution principle is used to give the vertical additional stress solution of the foundation soil,and the coefficient of frictional resistance increase of the screw pile is calculated.The settlement calculation formula of the soft soil foundation reinforced by the screw pile is studied through theoretical analysis The simulation analysis was conducted to study the influence of screw pile length,pile diameter,pile spacing,pile thread pitch,cushion layer and ground soil quality on foundation settlement,and the design optimization value range of screw pile parameters was obtained.According to the results of settlement analysis,the settlement of the reinforced area of the soft soil composite foundation with screw piles is small,accounting for only about 5%,and the settlement of the underlying layer is as high as about 95%.Therefore,it is proposed that the soft soil composite foundation treatment should be combined with the soil.It is recommended to choose the pile length reasonably or deepen the underlying layer.In the course of the research,in view of the traditional passive design method of composite foundation,there are disadvantages of passive repeated analysis and comparison,and the limited number of design options.It is proposed to combine mathematical methods with computer technology and apply optimal control theory to engineering design.The basic idea is: to establish a mathematical model ? select an optimization algorithm ? optimized design ? optimal conclusion,which belongs to active design,there are a large number of feasible schemes to choose from,and it can reach the optimal under feasible conditions.An optimization model was established for the soft soil foundation reinforced by thread piles according to settlement control,and the optimization objective function and design variable constraints were determined.Use numerical optimization software,rationally select the nonlinear quadratic programming(SQP)algorithm according to the type of design variable constraint function,apply the optimization model to the engineering example for verification,and find the optimal under the conditions of ensuring engineering design performance requirements,especially settlement control Value,can greatly save the amount of piles used.The optimization design model of reinforced soft ground also has the problems of complicated parameter setting and difficulty in establishing the objective function and constraints in the application process.It should be improved and simplified in conjunction with the reliability theory,and secondary software development should be carried out to facilitate engineering application.Key research directions.