Mechanism And Engineering Application Of Side Grouting Reinforcement For Existing Pile Foundations In Silty Soil Layer

Bridges play an extremely important role in the process of transportation infrastructure construction and development in our country.Pile foundation is the main bearing structure of bridge and plays an important role in the safety of bridge structure.With the development of economy and society,many expressways show serious traffic jams and frequent safety accidents due to the rapid increase in traffic volume and insufficient traffic capacity,so it is urgent to implement reconstruction and expansion projects.However,a large number of bridge pile foundations in service cannot meet the bearing capacity requirements of reconstruction and expansion projects.Grouting method is widely used in the field of pile foundation bearing capacity improvement because of its high efficiency,economy and convenient technology advantages.However,the influence mechanism of grouting to improve the bearing capacity of pile foundation under existing load is unclear,and it is difficult to evaluate the lifting effect of grouting quantitatively.Therefore,it is of great scientific significance and engineering application value to carry out systematic and in-depth research on the mechanism of grouting reinforcement of existing pile foundation for the design of grouting reinforcement parameters and evaluation of bearing performance of existing bridge pile foundation.Through the method of literature review,model test,theoretical analysis,numerical simulation and engineering application test,this paper carried out the research on the mechanism of grouting reinforcement and improvement of load bearing performance of pile foundation in service of silt soil layer.The main achievements are as follows:(1)Taking compaction grouting reinforcement as the main consideration,a model test for grouting reinforcement of pile foundation in service was designed,and the variation laws of pile axial force,pile top reaction and displacement,side friction resistance and pile tip resistance during grouting of pile foundation in service were analyzed,and the bearing capacity of pile foundation side grouting under different overlying loads,grouting radius and grouting positions were obtained.The effect of pile side grouting on the improvement of load bearing performance of pile foundation in service is revealed.(2)Based on the load transfer mechanism between pile and soil,the basic principle of the load transfer model is analyzed,and its constitutive relationship and solution method are established.Based on the quantitative relationship formulas of pile side friction resistance,pile side displacement,pile end resistance,pile end displacement,etc.,the load transfer model of pile foundation in service under the condition of pile side grouting is established,which provides a theoretical basis for the reinforcement of pile foundation in service.(3)The load transfer model of in-service pile foundation was embedded into the finite element program through the subprogram,and the influence of pile length,pile diameter,grouting depth,grouting section length and grouting hole location on the grouting reinforcement effect of in-service pile foundation was analyzed,and the bearing capacity improvement of lateral grouting of existing pile foundation under different conditions was obtained,which provided a basis for the quantitative evaluation of grouting reinforcement effect of in-service pile foundation in silty soil layer.(4)In the Beijing-Taiwan high-speed reconstruction and expansion project,grouting reinforcement engineering in service was carried out,and the research results were used to guide the design of grouting parameters.According to the actual needs of the project,grouting materials and grouting technology were selected,and the grouting reinforcement effect was verified by static load test.