Improvement of Weak Subgrade Materials Performance by Blending with Selected Materials from Quarry Sites: A Case Study in Agaro Area.

Abstract

Road pavements commonly consist of several layers of various materials and thickness. The performance of a pavement depends on the quality of its subgrade and subbase layers. There are many soil stabilization methods to gain the required engineering properties. These methods range from mechanical to chemical stabilization. Chemical treatments are relatively expensive to be implemented in most developing countries and the best way is to use locally available materials with relatively cheap costs and affordable. The native soil behavior of roads and their mode of failure were studied to establish the proper method of improving native soils using locally available materials. A wide variety of soil types occur across Agaro town, in-depth understanding of these subgrade soils where any pavement project is to be constructed is essential to sustain its design life. A laboratory experiment carried out in this study which aimed to highlight the physical mechanisms of improvement of weak subgrade materials performance by blending with selected materials. On the collected weak subgrade soils and selected materials from Agaro town quarry sites, a laboratory tests such as Atterberg’s limit test, Specific Gravity, Grain Size Analysis, Compaction test, CBR and CBR Swell test were done. The results of consistency test shows that the subgrade soils have a PI values more than 30% and according to AASHTO soil classification system the soils were Clayey Soils laying under A-7-5 soil type with a GI greater than 20. This is an indication of the soil section with high PI and GI values and very poor to support the traffic load. The Selected materials classified under A-2-6(1) are found to be [Silty or Clayey Gravel and Sand] material having a PI value of 17.05%. The maximum dry density for subgrade soils ranges from 1.57g/cc to 1.65g/cc, and 2.17g/cc for selected materials. The subgrade soil were not give CBR more than 8%, then to reduce the thickness of pavement, improvement of the subgrade material is done, when blended with the selected material ranging from 50% to 85% to attain a CBR value ranging between 10% and 20% when compacted to 95% MDD modified compaction. The provision of improved layer avoids the necessity of an extraordinary thick sub-base, and provides an adequate working platform for sub-base compaction as well as reduces the risk of damage to the subgrade during construction. This shows that a thinner pavement structure could be used on a soil with a higher CBR value than on a soil with a low CBR value.