Study On The Reinforcement Mechanism Of Oblique Jet Grouping Pile In Loess Foundation Of Bao (Ji) Zhong (Wei) Railway

In the collapsible loess area of Northwest China,the existing railway lines are widely distributed.The loess foundation is usually composed of silt soil,the pores are visible to the naked eye and vertical joints are developed.The most obvious feature is that it has strong structure.Before encountering water,the strength of soil is higher,once encountering water,it is extremely prone to collapse,the strength of the foundation is reduced rapidly.As a result,the problem of subgrade settlement is common.The oblique high pressure jet grouting technology has the advantages of simple mechanical operation,fast construction speed and no need to interrupt operation.At present,it has been successfully applied in some existing line foundation reinforcement projects,achieved remarkable effect of reinforcement and the prospect of application is good.But the relevant theoretical research is still less.For example,the reinforcement mechanism of oblique jet grouting pile and the calculation of bearing capacity of composite foundation.This article is based on the foundation reinforcement project of the K329 to K331 section of bao?ji?zhong?wei?railway,the following studies have been done,in order to provide relevant references and suggestions for the use of oblique jet grouting pile to control the settlement of subgrade on existing railway lines in the loess region.?1?Based on the development history of high pressure jet grouting technology of domestic and foreign,the main features of the high pressure jet grouting technology,grouting method classification,grouting material,suitable soil layer and application range are systematically described.The characteristics of high pressure jet flow are introduced,and the detailed research on the reinforcement mechanism of oblique jet grouting piles was carried out.At last,the characteristics of the pile body of oblique jet grouting pile are summarized.?2?In order to study the bearing capacity difference of oblique jet grouting pile composite foundation at different angles,a model test of composite foundation with oblique jet grouting pile is designed.The results show that the bearing capacity of composite foundation is obviously higher than the natural foundation.According to the test results,a formula for the bearing capacity of oblique jet grouting pile composite foundation is preliminarily proposed.?3?The finite difference software FLAC^3D is used to carry out numerical analysis of the model test.The trend of P-S curve is basically the same between numerical simulation and model test.Based on the numerical simulation results,a formula for the bearing capacity of oblique jet grouting pile composite foundation is proposed,and the axial force of the pile is also analyzed.By comparing the two types composite foundation bearing capacity formulas proposed by model test and numerical simulation,it is found that the difference between the calculation results of the two formulas is very small.Comprehensive model test and numerical simulation results,the formula of the bearing capacity of the oblique jet grouting pile composite foundation is preliminarily proposed.?4?The reinforcement effect of oblique jet grouting pile is evaluated from three aspects:sample scanning electron microscope,subgrade settlement observation and bearing capacity of composite foundation.It is proved that the reinforcement effect is remarkable.