System Construction Of The Information Management And The Risk Assessment For Residual Soil Slope With The Unsaturated Soil Theory

As a geological hazard with occurring frequently and harmful, slope disasters have occurred in Fujian Expressway slope, causing enormous loss of life and property. Fujian Expressway slope is usually composed of unsaturated residual soils. And landslide risk assessment generally uses the regional landslide assessment method or the safety coefficient method. Affected by rains, the soil suction and the initial water content change, and the shear behavior of unsaturated residual soil, and then the accuracy of the stability analysis results of the single slope; Further investigations on the landslide risk assessment theory, the scholars find that safety coefficient in the real-time risk assessment for slope cannot fully reflect the actual situation. And a single method of slope stability analysis by means of safety coefficient or regional landslide assessment is unable to fully assess the landslide disaster risk. So this thesis analyzes the influence of the change of the initial water content on the shear behavior of soils after the moistening process by performing the unsaturated residual soil direct shear tests. Qgis software is used to study the methods of the landslide risk assessment, and to construct the information management and risk assessment system by combining with the test results. The main content of this thesis is as follows:Firstly, research background and significance is presented, and the objectives and specific issues to be investigated, as well as the organization of the thesis are introduced..Secondly, the concepts of unsaturated soil are reviewed and the researches on the strength characteristics of unsaturated soil are summarized.Thirdly, the direct shear tests and analyses are performed:1) The unsaturated residual soil direct shear tests are performed, the moistening process is used to simulate the increasing soil water content when rains fall, and the influences of moistening on the shear strength characteristics are investigated. When the matrix suction of soil reduces to 0 in the moistening process, the tests start. The experimental results show that the moistening process slashes the soil cohesion, and the influence on the internal friction angle was negligible.2) The unsaturated residual soil direct sheaf tests with the initial water content changing after the moistening process are conducted, and the influences on the strength characteristics of the changed initial water content are studied. The experimental results show that under the same net normal stress, the shear strength parameters decrease with the increasing initial water content, and the change of the effective cohesion is by far greater than that of the effective internal friction angle. Numerical analyses with the shear strength parameters obtained from the experiments are performed, and the safety coefficient and the reliability are used as the safety indicators in the calculations. The results show that the reliability is much more suitable for the landslide risk assessment.Then the Qgis software is used again to analyze the laws of landslide hazards in Fujian province, and the evident relationship between landslide distribution and every influencing factor of landslide has been found. The influencing factors of landslide are slope, exposure, elevation, petrofabric types, geologic structure, rainfall, land use and the distance between the slope and water. These influence factors of landslide were chosen to make analyses, and information value method is used to assess the risk of landslides in Fuyin Expressway.Finally the Qgis software and the Geo-Studio software are combined to perform the single slope stability analysis, and then the regional landslide risk assessment of system is conducted with a combination of the Qgis software and the Google Earth technique, thus achieving the risk assessment functions of the slope management system and the landslide risk assessment system. After the risk assessment results, the images and the data are collected, sorted and saved in a sequence, the completed slope information management database is constructed, and the system of regional landslide risk assessment in Fuyin Expressway is formed.