Study On Experiments And Load-bearing Mechanism Of Post Grouting For Pile Foundation Of High-speed Railway In The Deep Soft Soil Region

Cast-in-place pile has been widely used in civil and traffic construction projects. It is a new issue on how to control post construction settlement and standing time effectively after the use of post-grouting technique in deep soft soil, whether in construction field and theoretical research field. As the principal of a key project in Ministry Railways of "the experimental study of post grouting pile in the Beijing-Shanghai high-speed railway", author collected the study on the subject and used site experiments, theoretical analysis and means of numerical simulations on the basis of the site construction, the organization and the results of the application. After this, the design and construction technology of high-speed rail pile and theoretical foundation in deep soft soil are developed. Study results can be summarized as the following four aspects:(1) Through the site experimental, the following rule is found:When the load of pile top is reached about460tons, the displacement of pile top can be reduced about22.2%to27.1%for pile side in deep soft soil, the displacement of pile end can be reduced about30.1%to40.0%, the joint of pile end and pile side can be reduced about32.4%to43.2%.(2) Based on the modified Cam-clay model, they analyzed the mechanical mechanism of pile post-grouting in deep soft soil; Based on cavity expansion theory and non-associated flow rule, the calculation method of pile post-grouting pressure in deep soft soil is established.(3) A hyperbolic model of the load transfer mechanism analysis of no-grouting pile in elastic state, a hyperbolic model of the load transfer mechanism analysis of pile in the damaged soil and the model of shear displacement method of load transfer analysis considering damage are established; They studied the mechanism of pile load transfer after post grouting at pile side through using the model of shear-lag theory and the introduction of damage theory and established the model of pile load transfer mechanism analysis based on the injury shear-lag model and considered the date of engineering test to verify the validity of the model. (4) Based on the parameters back analysis and numerical simulation methods, it has a large pre-settlement under the design load conditions, the latter creep effect is not very obvious, the change of settlement rate is very small after30days, thus the pile standing time can be reduced.