Study On The Bearing Performance For Cement Mixing Pile Composite Foundation At Jinan-Qingdao Dedicated Line

As the national economy increases, the project of construction makes rapid progress. In order to meet the demand of groundsill intension, deformation and anti-seismic etc, the crude soft soil must be dealt with artificially. Composite foundation with cement mixing piles is widely used in varies projects due to its remarkable economical benefits, convenient construction and no circumstance pollution. However, the history of cement mixing piles reinforcement technique is only about tens years. Not only mechanisms of reinforcement but also design and computing methods have some faultiness. Some are still in discussion. Based on the cement mixing piles' field test results at Qingzhou Straightened Section (DKK225+950～DKK238+890) of Jinan-Qingdao Dedicated Line, this paper focuses on the questions as followings:(1) The cement mixing pile composite foundation's bearing capacity and deformation behavior are studied by the field test and theoretic analysis. The bearing capacity as well as the elastic modulus of each pile and composite foundation is obtained by field tests on original soil, the soil between piles, single pile and one-pile composite foundation. The results show that the loessial silty clay reinforced by cement-soil piles has better performance in bearing capacity and deformation. The strength and elastic modulus of soil areobviously improved.(2) Numerical model is set up. The model of the interaction between piles and soil is built based on the interaction between piles and soil. Numerical simulations are carried out on the bearing performances of the cement mixing pile composite foundation , one pile group and 4×4 piles group, respectively, by using the finite software called FLAC3D. Then, by analyzing the influences of such factors as load, cushion modulus, cushion thickness, the ratio of length-radius of the pile, the modulus of pile and the replacement ratio on the settlement of compound foundation and the stress ratio between pile and soil, it is found that there have the best modulus of pile, the best ratio of length-radius of the pile and the best replacement ratio. Based on the comparison between the results of computing analysis and the experiment, it is demonstrated that the cement mixing pile composite foundation has better reliability on the bearing capacity and the bearing characteristics.(3) Due to the importance of pile-soil stress ratio n of the cement mixing pile composite foundation in the design, the test method, the numerical method and the analytical method are summed up in this paper to calculate this important parameter. Based on this project, three methods have certain feasibility in some extent. Each one has its own advantages as well as disadvantages. The conclusions in this paper have some reference value for designing and constructing of composite foundation in the future.