Grouting Reinforcement Mechanism And Engineering Application Of Existing Bridge Pile Foundation In Expressway Reconstruction And Extension

Pile foundation is a common foundation form in bridge construction.As the bearing member of the bridge substructure,the safety and stability of pile foundation is very important for the normal operation of the bridge.Most of the existing bridges in China were built in the1990 s and the beginning of the 21 st century.With the rapid development of society,the traffic volume is increasing and the vehicle load is also increasing.Some bridges in service can not meet the current demand,so it is necessary to reconstruct and expand the existing highway.Grouting,as a technology to enhance the bearing capacity of pile foundation,is widely used in pile foundation reinforcement engineering,which can greatly improve the bearing capacity of pile foundation,and the reinforcement process does not affect the normal use of the bridge.However,because the slurry flow is related to permeability,strength and grouting pressure,the grouting slurry diffusion mode is not ideal spherical and column shape,and the flow of slurry is not easy to control.The actual slurry diffusion is to penetrate through soft split or large pore,forming irregular grout vein,and the grouting reinforcement mechanism,construction method and construction technology are not mature,so relevant research is needed.In order to control the flow of slurry in the specified range and improve the efficiency of slurry,DJS method is proposed to strengthen the existing pile foundation.Based on the reconstruction and expansion project of Dezhou(Shandong Hebei boundary)to Qihe section of Beijing Taiwan expressway,this paper uses the research methods of theoretical analysis,indoor test,numerical simulation and field test to establish the calculation formula of bearing capacity of existing pile foundation after grouting reinforcement,optimize the key construction parameters of existing pile foundation grouting,and clarify the effect of different schemes on strengthening existing pile foundation,A set of efficient construction technology of existing pile foundation reinforcement is formed.The main research contents and achievements are as follows:(1)Based on the theory of the injectivity of geotechnical media,the paper puts forward the method of " Disturbance before grouting " method to reinforce the existing pile foundation and deduces the calculation method of DJS engineering method related design parameters.Based on method in staticmethod β,DJS method is introducedΔto determine the quantitative relationship between the lift range of pile bearing capacity and grouting parameters,and the formula for calculating the bearing capacity of pile side after reinforcement is established.(2)The key construction parameters optimization tests such as disturbance pressure,dynamic grouting pressure,static grouting pressure,rotating speed,lifting speed and water cement ratio in DJS method are carried out.Through the comparison and analysis of solid strength,the local optimization grouting parameters and the law of slurry diffusion are obtained.Considering the reinforcement effect,construction progress and construction cost of grouting parameters,the analytic hierarchy process is used to get the global optimal parameter combination,which provides theoretical guidance for the selection of grouting parameters in field engineering application.(3)The finite element software ABAQUS is used to establish the numerical model of bearing capacity of pile foundation with different grouting depth and solid thickness.The distribution law of pile side friction,shaft force and load settlement are analyzed.The numerical simulation results show that the ultimate bearing capacity of pile foundation increases with the increase of grouting reinforcement depth;the ultimate bearing capacity of pile foundation increases with the increase of grouting plus solid thickness,but there is not always a positive proportion relationship.When other conditions are the same,the thickness of adding solid has the most reasonable value,and the influence of adding solid thickness after exceeding the reasonable value on the vertical ultimate bearing capacity of single pile is increased Not obvious.(4)Combined with the reconstruction and expansion project of Dezhou to Qihe section of Beijing Taiwan high speed,the bearing deformation,load transfer law and the performance of friction resistance of pile side are analyzed by comparing and analyzing the bearing deformation characteristics of grouting and non grouting piles,and the effect of DJS method is explored.The static load test results show that the bearing capacity of DJS is better than that of the grouting pile,which shows that the DJS method has a significant effect on strengthening the pile foundation,which greatly improves the ultimate bearing capacity of the existing pile foundation.(5)The results of SEM test before and after grouting of silty clay and silt,which are representative of the plain and in-situ layer of alluvial proluvial of the Yellow River,are analyzed.The improvement effect of DJS method on the side soil of the existing pile foundation is analyzed from the micro mechanism.The results show that the pore number and cementation degree of the soil particles decrease after grouting,and the aggregate formed by the mutual inclusion of the slurry and soil can effectively improve the shear strength of the soil,thus improving the bearing capacity of the pile foundation.