Geotechnical Evaluation of the Causes of Road Pavement Failure Along the Mbaitoli-Ikeduru-Mbaise Highway, Southeastern Nigeria

Abstract

The incessant failed spots in the road pavement along the 27.61km Mbaitolu-Ikeduru-Ahiara Mbaise highway in Imo state, southeastern Nigeria, has necessitated this geotechnical study to evaluate the impact of the subgrade material quality on the road pavement failure. The study entailed both physical and geological assessment of the predominantly sandy to clayey silt Benin Formation underlying the area, as well as field and laboratory engineering tests on the subgrade materials underlying the road alignment. The engineering tests carried out included the grain size distribution, specific gravity, natural moisture content, Atterberg (liquid and plastic) limits, compaction (to determine maximum dry density and optimum moisture content), California bearing ratio (CBR), and shear strength (to determine cohesion and angle of internal friction). The engineering test results indicate that the natural moisture content values range between 10.4 and 18.9%, liquid limit between 36.0 and 48.6%, plastic limit ranges from 26.1 to 31.6, with corresponding plasticity index values that range from 9.2 to 17.0%. The grain size distribution test results connote the predominance of sand, with number of fines-sized particles that ranges from 22 to 38% and amount coarse to medium sand-sized particles ranging from 62 to 78%.Maximum dry density ranges from 1.29to 1.93 kg/m3. (CBR) ranges from 3.7 and 91.9%. Specific gravity ranges between 2.56and 2.61, while cohesion and angle of internal friction range from 39 to 42 kPa, and 14 to 20°, respectively. Some failed portion especially in Inyishi area were likely due to moisture fluctuation in the subgrade due to closeness of the water table. Proper compaction, chemical stabilization, and appropriate drainage would likely boost the efficiency of the subgrade material and the durability of the road pavement.