| The completely decomposed granite is widely distributed in Southeast China. with the rapid development of transport infrastructure, the high-speed railway, highway constructed on the granite geographical distribution is inevitable. The high-speed railway construction is a systems engineering, high strength, stiffness, and changes in uniform, long-term stability of the embankment is to ensure critically high-speed train safety and running smoothly. However, for this particular completely decomposed granite soil widely distributed in our country, its engineering properties, extensive research has not yet commenced. There are some questions must to be pay attention to and be solved, such as the completely decomposed granite used in railway and highway, the design and subgrade settlement control, the foundation reinforcement measures. Especially in completely decomposed granite soil, construction high-speed railway which has strict requirements for settlement after construction. Therefore, it is necessary to completely systematic research on the decomposed granite road, for providing the basis for engineering design.This paper relied on scientific research "Research on settlement characteristics and processing technology of high-speed railway which constructed on medium compression soil". Based on the comprehension of the special properties of Hainan completely decomposed granite, relying on the design and calculation theory, indoor soil test, field test on high-speed railway around the east of HaiNan, centrifuge model test, numerical analysis, the research on soil arching effect of Pile-Net composite foundation, stress distribution under embankment, ground lateral deformation were carried out. The settlement and foundation reinforcement mechanism of the completely decomposed granite in HaiNan was carried out. The deformation characteristics of the completely decomposed granite foundation which high-speed railway was built on was carried out. The deformation theory of the completely decomposed granite foundation which adapt engineering practice was put forwarded.Research work of this paper includes the following aspects.(1)The pressure distribution under embankment of high-speed railway around the east of HaiNan was researched through the design and calculation theory, centrifuge model test, numerical analysis. Field test of stress distribution under embankment was carried out. By the comparative study analysis, the pressure under embankment does not equal to the product value of fill specific density and filling height, also does not equal to the pressure value calculated by uniform load method. The pressure under embankment is not uniform and presents a curve which intermediate large and small on both sides. Pressure under embankment increases with the filling height increasing. When we study the relationship between pressure under embankment and the embankment shape, scale, we found that nondimensionalization value ?/?h and b/h have high correlation. By further analysis, the calculation method pressure under embankment central was derived, which amended the proportion load method. The high-speed railway roadbed width and slope ratio was provided in "high-speed railway design specification (Trial)" (TB10621-2009), according the roadbed width and slope ratio, correction factor of pressure under embankment central was ?=1-0.3e-43/h, correction of pressure distribution under embankment was carried out.(2)When analysis the pile-net structure in high-speed railway around the east of HaiNan, supposing the load form which loads on geogrid's reinforced cushion strip was anti triangular distribution, formula of the deformation and force calculating of geogrid was Inferenced. The calculation formula for upward reaction force of soil between piles was Inferenced, when geogrid's reinforced cushion strip was divided as diamond between piles, Vertical reaction force of the soil between piles was considerd completely. Treated geogrid reinforced cushion, pile, soil between piles of as three different part, In considering the pile on piercing, piercing the lower, analyzing interaction between piles-Cushion-oil between piles, the stress ratio between pile and soil method was deduced. By Comparative analysis and calculation, There are still large differences between Calculation value and measured values. But among all calculation value by other methods, the value of algorithm deduceed in this paper, was the closest value compared tomeasured and calculated values of the finite element method.(3)Based on Gray additional stress solution, the lateral load strain formula of soil under embankment was deduceed. Based on Boussinesq's displacement solution of semi-infinite under concentrated force, the lateral deformation formula of soil under embankment was deduceed.For medium compression and completely decomposed granite of high-speed railway around the east of HaiNan, Characteristic deformation curves from filed test, theoretical calculations, numerical analysis were consistent characteristics. When Forecast Analysis of medium compression and completely decomposed granite, Lorenz curve equation may be used. Filed test and theoretical calculations wascarried on high-speed railway around the east of HaiNan. Looking at the results from the observed, the lateral deformation curve with depth shows "bow" shaped features. There is a maximum lateral deformation point in the curve. The lateral deformation increases with depth to a maximum and then decreases with increasing depth. The lateral deformation is not zero on the soil surface. For the completely decomposed granite soil in HaiNan, when the railway embankment height wass between 3.2m-7.7m, the maximum lateral deformation Dm was about 7mm?11mm, the lateral deformation on surface Do observations was about 4mm-6mm.(4) For medium compression and completely decomposed granite of high-speed railway around the east of HaiNan, when we calculate settlement the foundation which was unreinforced, if the pressure distribution under embankmen using the proposed amendments stress load ratio method, the additional stress using Boussinesq's solution, modulus using the compressive modulus results of standard penetration test, and consider the impact of lateral deformation on the settlement, the calculations was high accuracy. For medium compression and completely decomposed granite of high-speed railway around the east of HaiNan, when we calculate settlement the foundation which was reinforced, the settlement calculations value which calculated by the composite modulus, was much smaller than the measured value and unsafe. When we calculate settlement the foundation which was reinforced by L/3 method, if considering the settlement caused by the lateral deformation, the settlement calculation was very close to the measured value. L/3 method is a appropriate method for calculating settlement of HaiNan completely decomposed granite foundation.(5) Comprehensive analysis of field settlement observation, centrifugal model tests and numerical simulation,we can found the settlement law of the completely decomposed granite in HaiNan. During filling, the settlement rate is high, in the rest period settlement development is slow. The settlement value of the end of Filling was about 85% of the end of the rest. The settlement was gradually stabilized after three months, post-construction settlement can meet the requirements. We can see from the settlement observation data, The settlement value of the end of filling was about 74.6%-94.4% of the settlement before laying, The average is 85.6%. The settlement value of the end of filling was about 67.1%-85.4% of the settlement, The average is 78.0%. The settlement value before laying was about 87.5%-93.6% of the settlement, The average is 91.1%. The post-construction settlement was about 7-13mm, meet the requirements.(6) Depending on the settlement law of the deep completely decomposed granite in HaiNan, the principles and measures proposed to build high-speed railway in HaiNan were concluded. When ballasted track was builded on the deep completely decomposed granite in HaiNan, after layered filling, the settlement gradually stabilized after rest for 3 months. The sections of which the settlement meet the requirements need not treat. But the soft soil surface must be reinforced by replacement, cement mixing pile, CFG pile reinforcement.The sections of which the settlement don't meet the requirements need to be reinforced by cement mixing pile, CFG pile reinforcement.If the medium compression deep completely decomposed granite in HaiNan was not treated, after layered filling and rest for 6 months, the post-construction settlement can meet the requirements of ballastless track. when ballastless track constructed on the deep completely decomposed granite in HaiNan, it was recommended that shallow foundation which was deep 6-8m need to be treated by cement mixing pile, CFG pile reinforcement, preloading. The sections of transition should be treated more deeply, and combined preloading also needed. |
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