Research purposes: In the collapsible loess area of Northwest China, the existing railway lines are widely distributed. The problem of subgrade settlement seriously puzzles the safety of line operation, which has become one of the most serious problems of the existing railway lines. Under the current situation of increasing speed and expansion of existing railway lines, it is of great significance to quickly and effectively control the subgrade settlement in loess areas to ensure the safe and stable operation of trains. 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, the technology has widely applied for existing railway subgrade reinforcement, and the prospect of application is good, but the relevant theoretical research is still less. This paper is based on the subgrade reinforcement project of K329～K331 section of Baoji-Zhongwei railway, the model test of oblique jet grouting pile composite foundation with different angles is designed, and the model test results are verified by FLAC^3D.
Research conclusions: (1) The bearing capacity of the oblique jet grouting pile composite foundation at different angles is obviously higher than that of the natural foundation;(2) The bearing capacity of the oblique jet grouting pile composite foundation in the 30 to 90 degree range is low in the middle and high in both sides; (3) Model tests and numerical simulations show that the characteristic values of the bearing capacity of composite foundations has little difference;(4) The larger the angle of the pile, the greater the axial pressure, the smaller the angle, the greater the maximum axial tension;(5) By comprehensive model test and numerical simulation, the formula of the bearing capacity of the oblique jet grouting pile composite foundation is preliminarily proposed;(6)When the jet grouting pile angle is small, it is suggested to control the strength of the pile with tensile strength; (7) The research result is mainly applied to the railway base line disease treatment works.