Study On The Application Of Pile-plank For Reinforcing Soft Foundations Of Highways

There are many kinds of soft soil foundation in China with the complicated condition.The current methods of soft soil foundation treatment are limited.Sometimes it can not solve the problems in practical engineering economically and effectively,which has adverse effects on the quality,schedule and cost of the project.In order to control the subsidence and differential settlement of roadbed and reduce the cost,this paper proposes a kind of pile-plank as the new road soft soil foundation treatment method.The characteristics of pile-plank structure of highway foundation are explored and optimized from the applicability analysis,indoor model test,finite element analysis and optimization analysis.The conclusions are as follows:(1)According to the analysis of the limitations of current methods for highway soft soil foundation treatment method,combined with the characteristics of pile-plank structure,it shows that the pile-plank structure have enough suitable space and development prospects in soft soil foundation treatment of highway.(2)In the indoor model experiments,the standard value of bearing capacity of pile-plank composite foundation is two times as large as that of natural foundation.It shows that the pile-plank structure has obvious effect in dealing with soft soil foundation.The results of indoor model test and finite element calculation are consistent,which can be verified by each other,and also shows that the finite element modeling is accurate and effective.The post construction settlement value of subgrade decreases with the increase of plank thickness,but the post construction settlement value will not change significantly when the thickness increases to a certain extent.The pile arranged in triangle has lower settlement after construction than rectangular.(3)The finite element model of pile-plank structure of highway foundation is established,and the response of each factor to its settlement characteristics and the maximum tensile stress at the bottom of plank is analyzed.It is concluded that the decrease of the pile spacing,the increase of the width of the plank and the increase of the plank thickness will lead to the decrease of the post construction settlement and differential settlement of the subgrade and the maximum tensile stress at the bottom of the plank.The pile material has an important influence on the settlement,but it has the smallest influence on the maximum tensile stress at the bottom of the plank.The width of the plank and the arrangement of pile has little influence on the settlement.The plank thickness is the dominant factor in the post construction settlement and differential settlement of subgrade and the maximum tensile stress at the bottom of plank.(4)Based on the response surface method the design scheme of pile-plank structure of highway foundation is optimized.According to the weight of each response,four optimal design schemes are given.This method can complete the optimization of design scheme according to the requirement of the project.