Experimental Study On Enhancing Effect Of Soft Soil For Express Railway With Deep Mixing Pile

To break out of international financial crisis by stimulating domestic demand of the Chinese central government, railway construction began to enter an era of rapid development in China. In the past year, a number of new railways began to be constructed in succession, with rapidly growing adverse geological conditions encountered, especially the soft ground conditions.In order to meet the high standard of post construction settlement of high-speed railway, soft soil foundation must be treated. There are many methods to treat soft soil foundation with different applicable scopes, engineering costs, effects and construction period, so it is necessary to do researches on these methods for the purpose of finding out a suitablemethod for treating the soft soil foundation ofhigh-speed railway.Under the large, dynamic load of the express train, it is necessary to study enhancing soft soil with deep mixing pile for the railway foundation to meet the strength, settlement and seismic design requirements as well as to save construction funds.Around the demand of lowering post-construction settlement, the indoor and outdoor soil-cement tests were carried out. The relationships of unconfined compressice strength with curing age, and with mixing ratio, for the indoor soil-cement specimen and the the specimen from deep mixing piles, are systematically analyzed.By core drilling, cone penetration, dynamic sounding, low-strain test, load test, standard penetration test and cross-hole wave velocity test etc., the quality of the deep mixing piles was inspected; the variations of pile body strength with curing age and with the depth were achieved; and if the bearing capacity of sigle pile or composite foundation meet the design requirement was known.Tested by laying the relevant sensors and long-term observation, the settlement and deformation law of the composite foundation in the course of construction and after was studied and analyzed.The settlement calculation software for mixing pile composite foundation was coded and used to calculate settlement for test section. By the comparison of observed and calculated foundation settlement the rationality and accuracy of input parameters were validated. Several numerical analysis methods were used to fit the test deformation results to find a most approaching one.By using finite element software MIDAS GTS, in considering nonlinear properties of pile and the soil in composite foundation, the deformation characteristics of the mixing pile composite foundation were numerical simulated, the results of which were compared with the observed ones.The author has got good results in such research, and the main contributions are as follows.1.The quality of the deep mixing piles should be inspected by core drilling, cone penetration and load test.2. Mixing pile composite foundation has relative high strength and vertical as well as lateral stiffness, with small settlement, and it can withstand the fast loading speed. The deformation characteristics of side displacement and the deformation characteristics of the slope toe and outside of it indicate that the composite foundation has fewer side effects on the surrounding environment.3. The software was coded that based on the settlement calculation of reinforced area use composite modulus method, the additional stress calculation of underlying layer use diffusion angle method and the stress ratio is 0.1. And used to calculate settlement for test section. The results are idential with the results in the actual practice.4. Of the Settlement after the hyperbolic method to predict the recommended use, the method calculates accurate, high precision and easy operation and convenience.5. Numerical simulation and experimental results show that the settlement after construction of express railway can meet the restrict limits.Through this experimental study, settlement deformation characteristics of mixing pile used in enhancing soft-soil foundation are held. The rationality of the calculation and design method was validated. The study is of great importantance in ensuring the success of the Beijing-Shanghai express railway construction, and if of important referrence to other espress railway construction.