Research On Moisture Field Of Unsaturated Loess Foundation By Numerical Analysis

In the northwest China, a great mount of lands are covered by collapsible loess. The strength of loess decreases quickly when water infiltrate into loess foundation, which will cause extremely damage to the buildings.The purpose of this study is to explore the law of water seepage in loess foundation and obtain the rule, thus we can propose the reasonable foundation treatment methods, construction control standards and the possible prevention and control measures for the buildings in loess area. Finally, the law of water seepage will ensure the security of the gymnasium during the post-stage operation period.The paper carried out a detailed survey and sampling near the gymnasium of new campus of Qinghai Communication Technical College. Combined with the relevant literatures, the laboratory tests were designed to analyse the moisture field.The SEEP/W, unsaturated seepage analysis software, was adopted to simulate the distribution of moisture filed under different dry densities loess foundations.The main content of the paper:(1) The Van Genuchten model, Fredlund and Xing model、 Modified Kovacs model were applied to fit all the saturation(volumetric water content)-matric suction data. Root mean squared error (RMSE), residual sum of squares (RSS), squared normalized residuals (SSNR) and coefficient of determination (R2) were used to evaluate the reliability of the three soil-water characteristic curves model, which shows that the Fredlund and Xing model performs the best in all the three models while fitting the saturation(volumetric water content)-matric suction data. (2) The coefficient of permeability of unsaturated soils was calculated by combining the Fredlund and Xing model and the pore-size distribution function proposed by Childs and Colli-Geoge. Three different dry densities loess samples were calculated in this paper, which were 1.5g/cm3,1.6g/cm3,1.7g/cm3. (3) Taken foundation with three different dry densities as the representative to analyze the changing trend of moisture field in the vertical and horizontal directions under line-source seepage condition, which is using the SEEP/W finite element software to analyze it in three different time periods. The changing areas of wetting front of three different types of dry densities foundation were simulated by the SEEP/W finite element software. It shows that the vertical distance and the horizontal distance both increase with time going on. (4) The vertical distance and the horizontal distance of saturation zone also increase with time going on under line-source seepage condition. Compared with the area of the wetting front, the area of the saturation zone is much smaller.