| Baotou to Maoming national expressway is the seventh vertical line in national expressway network. It’s a longitudinal main artery which connecting northwest and southwest China. The Guangdong Province section is122.3kilometers long, expected to be completed in2016. It will become one of the important access to the sea of Guangxi and the inland provinces, Guangdong. Baomao expressway(Guangdong section) through many rivers and ditches. At the same time, there are a lot of intermountain depression and paddy field, the special rock-soil mainly are drowned valley soft soil and wet soil, accounting for about11%of the length of the line. The "Specifications for design of expressway"(JTG D30-2004) stipulates the design of soil subgrade that including the settlement calculation, stability checking and corresponding methods of treatment. This paper will according to the specific situation of Baomao expressway(Guangdong section), choose representative soft soil section, using different methods to analyze the settlement and stability of soft soil subgrade. The soft soil subgrade treatment measures will be raised to ensure the expressway itself of higher quality and more stable. Meanwhile provide reference for expressway design and construction of the same area of Guangdong.In this paper, the following works are completed:①A comparative analysis of two methods for settlement calculation has been done. Using the methods to calculate the settlement of four typical sections that come from the drowned valley soft soil subgrade. Through the comparative analysis of the results of two methods, the specification method is more suitable for the study area. And six major factors affecting the settlement of Baomao expressway are analyzed.②Stability of the selected four section subgrade are calculated and analyzed by using Bishop method and Janbu method. Due to the provisions of the stability coefficient is less than the value of "Specifications for design of expressway"(JTG D30-2004), it’s necessary to treat soft soil subgrade. The Janbu method by comparison is more suitable for the analysis of the engineering stability.③Using VC++6.0to modify the header files and source files of Mohr-Coulomb constitutive model which comes with the FLAC3D software, this paper developed a nonlinear elastic constitutive model named Duncan-Chang E-B. The simulation of three axis test confirmed that it is available. Building a model with a cross section of subgrade in this project, then a numerical simulation analysis is carried out by using Duncan-Chang E-B model. It outputs the shear strain increment contours, velocity vector diagram and vertical displace ment contour. The subgrade settlement value and stability coefficient is close to compared with the traditional method,it has important practical significance.④Discussion on the treatment principle of the drowned valley soft soil, putforward a economic and effective treatment scheme. The construction points of each scheme are described in detail. All of the drowned valley soft soil are classified and corresponded to the right treatment scheme. |
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