Dissertation > Transportation > Rail transport > Railway Line Project > Line constructed > Subgrade > Subgrade reinforcement and protection > Embankment construction compaction and roadbed subsidence

Characteristics Study on Settlement of Expansive Soil Cfg Pile Composite Foundation of Liuzhou-Nanning Passenger Dedicated Line

Author YuanShengYang
Tutor JiangGuanLu
School Southwest Jiaotong University
Course Road and Railway Engineering
Keywords expensive soil foundation microstructural characteristic compressioncharacteristic basal stress calculation and forecast for settlement site settlementmonitoring
CLC U213.157
Type Master's thesis
Year 2012
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This paper had fully studied the basic physical and mechanic and settlement characteristic of the foundation soil of Liu Nan passenger dedicated line. In order to decide the calculations and forecast method for foundation settlement, the laboratory experiment, field in-situ tests, embankments settlement monitoring tests had been done. The main results are as foll wings:1、The SEM test and X-ray diffraction test images had illustrated that the basic structural unit of Liu Nan soil was granular particles and flake assemblage which clay flakes in face-face association. The structural unit didn’t have obvious arrangement and the whole structure was loose. The results of X-ray diffraction test had shown that the main clay mineral was kaolinite, the next was chlorite, the content of Montmorillonite was the lowest.2、The stress-strain curves in compression test and triaxial test correspond to hyperbolic model. The model of stress and time had been built via studying the relationship among stress, strain and time. The compression modulus of Liu Nan soil was varied from12.61to17.98MPa, so this soil was defined as low or moderate compressed soils.3、The varying pattern of soils’mechanical index which had gotten by different field in-situ test was basically the same, but the values were different. The standard penetration test change in a small range, then the static cone penetration test changes in a larger range, the preboring pressuremeter test changes in the largest range. The standard penetration test result is close to the consolidation test result.4、The stress distribution forms which got by common used methods, i.e. Proportional Stress method and Uniformly Distributed load method, were different form the real one. The results through using Elastic Subgrade were close to the real, however it was complex to use it. On the other hand, amended the Proportional Stress method based on Elastic Subgrade data, the results can be close to the real one. As convenient this method was, this paper recommended using this method to calculate the distributed form of additional stress on the surface of subgrade.5、The load in the pile-net supported embankments will focus on the pile that is soil arching effect. The basal stress analysis revealed that the pile-soil stress ratio and bearing ratio increased with the increasing of embankments height, nevertheless, when the height got to a certain value, those two indexes began to stabilize. The average values of the pile-soil stress ratio of the two sections were3.6and5.9separately, while the bearing ratio was0.508, this declared that the existing of pile in the subgrade can affect the stress state which lead to more load focusing on the pile. What’s more it showed that the capacity of soil had been fully used.6、Compared the results of theoretical calculation with the data got by field settlement monitoring, L/3method which considered the deformation of reinforced area, the additional stress on the surface of subgrade using the uniform stress distribution, while using the compressed modulus gotten by standard penetration test, to calculate settlement of foundation was proposed by this paper. The results were close to the real one. Relation the settlement of natural foundation to that of CFG composed foundation, using CFG to reinforce the subgrade, the settlement of foundation had been decreased sharply. In other word, CFG piles could limit the deformation well.7、If to forecast the deformation changing model along time under one stage, this paper recommended exponential model. While if it is the final stage, hyperbolic model was advised in order to consider the soil’s creep deformation. For multistage loading, Asaoka method could forecast each stage’s ultimate deformation. Its results were close to the monitored data.

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