Research On Engineering Characteristics And Treatment Of Expansive Soil In Subgrade On Chong-shang Second-grade Highway

Expansive soil, as a kind of special clay, distributed broadly in most places of our country and all around the world. These years, along with the swift development of our country economy and the large scale constructing of high-grade highway, some high-grade highways run across the area where the expansive soil develops. Because the expansive soil expands when absorbing water,shrinks and cracks when losing water, it has poor engineering property, and the roadbed will be damaged seriously if the expansive soil is filled in the roadbed directly. But if it's just abandoned simply as useless stuff, the cost of the project will grow and the environment around the road will be polluted. So it is an urgent task for our builders to work over roadbed with expansive soil.This thesis, based on the project of Chong-shang highway in Guangxi, studies and tests the expansive soil on its poor engineering property. By using highway project's conventional test indices and SOM neural network model, the thesis rationally identifies and classifies the swell-shrink grades of the expansive soil along the road, and verifies them through the tests. By a lot of laboratory tests of compacted expansive soil, the thesis establishes a quantitative relationship between the expansion deformation, expansive pressure, shear strength and the beginning water content, dried density and the overburden pressure, as a basis of the stability analysis of expansive soil slope. The thesis derives a safety factor equation of limit analysis which considers the effect of water content and expansive pressure on the stability of expansive soil slope, and calculates and analyzes data on the equation. We tests and studies the physical and mechanical property of expansive soil formed with different ratios of cement , sand and good soil to analyzes the variation rules of all kinds of engineering property indices under the condition of different ratios and water contents, and to provide a suggestion of reasonable economic improving programs, construction technologies, construction control measures. Earthwork fabric treatment method and sandwich interbedding method are introduced to build the test road in our study, and we evaluate the actual effect on the test road through spot-tracking survey and property indices examination of the test road. Analyzing the economy quality of the improving reinforcing project of expansive soil on the whole, we arrive at the conclusion that it has obvious economic and social benefit by using earthwork fabric treatment method and sandwich interbedding method to fill and build the roadbed with expansive soil.