Analysis Of Subgrade Performance Of Black Cotton Soil In Zambia

The performance of highways is mainly dependent on the properties of theunderlying subgrade. The subgrade soil supports the entire pavement structures and all theloads transmitted on it from the upper layers of the pavement. Its performance is greatlyaffected by load bearing capacity, moisture content, shrinkage and swelling characteristics.The black cotton soil is extensively distributed in Zambia. Many highways areconstructed in black cotton soil region. The engineering properties of black cotton soil arevery poor. The subgrade performance in black cotton soil region is the key issue inhighway construction. The performance of subgrade in black cotton soil is studied in thisthesis, field and laboratory tests have been conducted and numerical analysis has beenperformed.Field and laboratory tests of subgrade performance of highways constructed in blackcotton soil region in Zambia have been conducted. Experimental investigation involvedfield visitation and conducting of laboratory experiments to determine the behavior ofblack cotton soil under moisture variations by conducting California Bearing Ratio test onsoaked and unsoaked conditions. Samples were taken from Mbala-Nakonde Roadallocated in Northern Province of Zambia on five different points along the road.Using the field and laboratory tests data, a numerical simulation was performed undertwo different conditions derived from soaked and unsoaked CBR values in saturated andunsaturated conditions. The pavement was subjected to static loading. In this analysis,much focus is on subgrade response to stress, strain and displacement rather than on baseand asphalt layers of the pavement. A two-dimensional (2D) finite element method wasadopted for computation using ABAQUS software. The interpretation of the results ofnumerical simulation was based on load transfer, stress concentration, contours and vertical displacements in the subgrade.Based on the experiment results and numerical simulation, some valuableconclusions have been drawn. The achievements in this thesis can be beneficial for theconstruction of roads in black cotton soil region.