Highway Subgrade Treatment Technology Of The Expansive Soil In Longnan Legion

Expansive soil is the main cause of highway foundation subsidence, collapse, uplift. When the expansive soil cracks by the soil swelling and shrinking, the repeatability of the destructive effect is stronger, that seriously affect the project progress and increase the difficulty of highway construction, is the hidden trouble of highway construction quality and highway operation safety. When expansibility of expansive soil is weak, it can be used in the engineering construction, but the weak expansive soil classification is relatively rough and pertinence is not strong. Therefore, the experimental study on the weak expansive soil, the development of the weak expansive soil classification standard, subgrade filling classification standard and grade of side slope classification standard are important for developing subgrade treatment control methods of the weak expansive soil area.Through systematic analysis of relevant research results at home and abroad, based on the combination of theoretical research and experimental analysis method, weak expansive soil classification standard, subgrade filling classification standard and grade of side slope classification standard for Longnan region are researched.By using the test of SEM and XRD, the weak expansive soil in the Gansu province Longnan region from the microscopic view is analyzed. Through qualitative and quantitative research on microstructure on mineral composition of expansive soil, the internal mechanism of the weak expansive soil was revealed, that provide the basis for analysis of the engineering properties of weak expansive soil.Through geotechnical test of expansive soil, the basic properties of weak expansive soil in the area of Longnan in Gansu province are analyzed, on the basis of research on no-load and load expansion rate test, the relevance of between the influence factors such as moisture content, dry density etc and the swell of expansive soil is researched, and the estimation formulas of no-load and load expansion rate on weak expansive soil are deduced, that lay the foundation of weak expansive soil classification standard, subgrade filling classification standard and grade of side slope classification standard.The discriminant index of expansibility on expansive soil is analyzed, combined with the expansibility of the weak expansive soil in the Gansu province Longnan region, classification index of expansive soil expansibility is refined and classification index of expansive soil expansibility on weak expansive soil is formulated. Based on experimental data of expansive soil expansibility, classification index of expansive soil expansibility on weak expansive soil is contrasted and analyzed.Based on the swelling force experiment, by using the ideas on balance of expansive soil overlying load stress and the expansive force, the overlying embankment thickness standards of weak expansive soil as the filler is formulated. weak expansive soil subgrade filling classification standard is verified by FLAC-3D.According to the weak expansive soil classification standard, weak expansive soil slope was graded. The treatment plan on expansive soil distribution sections of Shi-tian expressway in gansu province is formulated.