Study On The Mechanism Of Lifting The Bearing Capacity Of Existed Pile Foundation By Pile Side Grouting In Silty Clay Stratum

As the main bearing structure of bridge,pile foundation can greatly improve the bearing capacity and stability of foundation.However,due to the large accumulated deformation of foundation and local change of geological conditions,the surrounding factors of engineering distribution,a large number of bridges in service appear uneven settlement and the pile foundation bearing capacity is insufficient,especially in silty clay,sandy soil and other weak strata of bridge pile foundation.The problem of insufficient bearing capacity of pile foundation is particularly common and serious.In addition,with the rapid development of the economy and society,many expressways have to carry out reconstruction and expansion projects due to traffic saturation,insufficient capacity and increase of safety accidents.As a technical means to enhance the bearing capacity of pile foundation,pile side grouting technology is widely used in practical engineering.It can enhance the bearing capacity of pile foundation without affecting the normal use of buildings.Besides,the grouting reinforcement technology of pile foundation has the advantages of low cost,saving manpower,material resources and time.However,due to the complexity of the service environment around the pile,the grouting reinforcement mechanism of the pile side is not clear,and the intrinsic correlation mechanism among the stratum characteristics,grouting effect and bearing performance of the pile foundation needs to be further studied.This paper aims at the key scientific problem of grouting mechanism of bearing capacity enhancement in silty clay foundation.Model test,numerical simulation and theoretical analysis methods were used to study the bearing capacity of pile foundation after pile side grouting,reveals the pile side grouting reinforcement mechanism of the silty clay strata,and bring insight into the effect of pile side grouting on the bearing characteristics.Furthermore,an optimal control method for the bearing capacity of pile foundation by grouting in silty clay is proposed combined with the systematic numerical simulation analysis.The results of this paper are as follows:(1)Based on the existed calculation methods of pile foundation bearing capacity and method of ?,the concept of pile side grouting coefficient a is introduced,the quantitative relationship between grouting parameters and the lifting range of pile foundation bearing capacity is determined,and the calculation formula of pile side grouting bearing capacity of pile foundation is established.(2)The grouting parameters and geological parameters are analyzed through the self-developed grouting model device.Based on the effect of grouting parameters and geological parameters on the slurry diffusion mode and grouting reinforcement effect of silty clay stratum,the design method of grouting parameters is put forward,which can be used to guide the field construction of pile-side grouting to lift the bearing capacity of pile foundation in silty clay stratum.(3)Based on simulation experiment of pile foundation by pile grouting,the shaft force distribution of pile,pile side friction,load(Q)-displacement(S)curve in different grouting condition were analyzed,and revealed the mechanism of grouting around pile on the bearing capacity.Finally,the calculation method of pile foundation bearing capacity was corrected.(4)The finite difference software FLAC3D was used to establish the calculation model of pile foundation bearing capacity at different reinforcement positions,pile length,pile diameter and grouting pressure.The law of action of the reinforcement position on pile lateral friction resistance,pile end resistance,load-settlement and other data was monitored,and the key control method of improvement of pile foundation bearing capacity was proposed in silty clay stratum.