Study On The Subgrade Treatment Of Black Cotton Soil Area In Africa

Black cotton soil is an expansive soil distributed in East Africa, it has a character ofwater swelling, drying shrinkage and repeated movement, which brings a great harm to safetyand quality of highway construction projects. The research object of this article is black cottonsoil on an expressway in Ethiopia, through specific working during geological annotation,geological survey, design and construction control of the project, the distribution, features,cause of formation, subgrade treatment scheme and construction process of the black cottonsoil are systematically studied, and achievements of which have been applied in the veryproject, and has a significance of reference for projects in similar areas. The research processand results of this study are as follows.1. Features and inflation level of the black cotton soil are analyzed according to the testindex variation of water content, plasticity index and swelling coefficient etc., which providea theory basis for the black cotton soil subgrade.2. Regional rainfall and influence depth of soil infiltration are analyzed, and safety workarea for subgrade and depth of treatment for black cotton soil are determined, which allprovide a design basis for the subgrade treatment of the black cotton soil.3. A subgrade treatment scheme which not only adapts to the project but also satisfies therequirements of the Ethiopian employer is proposed, by comparing the expansive soiltreatment scheme both home and abroad, as well as according to the characteristics of thisproject.4. Based on analysis of features of the black cotton soil, the subgrade treatment isconducted and construction technology process and test standard are proposed according tothe technical standards of the expressway.5. According to the distribution and properties of materials along the route of the project,requirements and notices for subgrade backfill materials of black cotton soil are proposed, byanalyzing physical mechanical index of padding, conducting penetration test and comparingtest sections in different seasons.6. According to the disease situation of test sections in different seasons, a low filledsubgrade optimization scheme is proposed.