Optimization Of Large Diameter Silo Pile Foundation Based On Automatic Grouping Genetic Algorithm

The silo has the advantages of small floor space,large capacity,high efficiency and environmental protection,and is often used as the best way to store bulk materials.With the increase of the volume of the silo,the requirements for the deformation and bearing capacity of the foundation are getting higher and higher.The pile foundation has gradually become the first choice for large diameter silos.The traditional pile foundation usually adopts the equal stiffness design concept.The settlement deformation will be large in the middle of the foundation and small in the side of the foundation.The deformation just likes a dish.The uneven settlement will cause the internal force of the pile cap to increase,resulting in the increase of the thickness and reinforcement of the pile cap,and increasing the foundation cost.In view of the defects of the stiffness design concept of pile foundation,the optimization design of pile foundation of large diameter silo is particularly important.In this thesis,the pile foundation of a large coal storage silo in Shijiazhuang,Hebei Province is studied.The main research work and conclusions are as follows:(1)Based on the variable stiffness design principle of pile foundation,the automatic grouping genetic algorithm is introduced into the optimization design of large diameter silo pile foundation.Aiming at the problems of immature convergence and late convergence difficulty of automatic grouping genetic algorithm,two measures are proposed to make improvements.First,the power function is introduced into the Lemonge penalty function to reduce the punishment for individuals which violate the constraints slightly.Secondly,the genetic operator is constructed based on the hyperbolic tangent function.The change speed of the function is between the cosine function and the Sigmoid function,which can better balance the population renewal and stability.Finally,through three standard function tests,it is proved that the improved automatic grouping genetic algorithm has better optimization accuracy and stability.(2)The three-dimensional finite element model of superstructure-soil-foundation interaction of large diameter silo is established by finite element software ANSYS.The influence of geometric parameters(pile length,pile diameter and pile cap thickness)of pile foundation on the maximum uneven settlement in the pile cap is analyzed,and the influence degree of each parameter is quantified by sensitivity analysis.The results show that the change of pile cap thickness has the greatest influence on the maximum uneven settlement in pile cap,followed by pile diameter and pile length.The reasonable ranges of pile cap thickness,pile length and pile diameter are 1.7～2.3m,11.8～19.3m and 0.6～1.2m respectively.(3)Combined with the mathematical model of pile foundation optimization,an improved automatic grouping genetic algorithm optimization program is written by Matlab language and applied to this project.Comparing the optimized scheme with the original scheme,the results show that the optimization scheme adopts long thin piles instead of short thick piles,the total number of piles increases by 34,but the total amount of foundation concrete decreases by 39.2%.The optimized pile group presents a variable stiffness layout of "strong inside and weak outside".The maximum and minimum values of raft settlement are 38.722 mm and 32.321 mm,respectively,which increase by 6.401 mm and 11.066 mm,while the maximum uneven settlement of raft decreases from 6.348 mm to 1.683 mm,which decreases by 4.665 mm.The uneven settlement of raft is significantly reduced,thus reducing the secondary internal force of superstructure and raft and improving the structure safety.Therefore,long and thin piles should be used as much as possible to reduce the amount of concrete when the bearing capacity of foundation deformation is met.When the structure has low requirements for the overall settlement of the foundation,the pile layout method of "strong inside and weak outside" can be adopted to reduce the uneven settlement.