Suitability Assessment of Selected Lateritic Soils For Highway Construction In Anambra State, Nigeria

Abstract

Fifteen samples of coarse-grained lateritic soils obtained from different parts of Anambra State were assessed for their suitability as materials for highway construction. The soil samples were subjected to laboratory tests to obtain their index properties, compaction and California bearing ratio (CBR) characteristics. Three compactive efforts namely, British Standard Light (BSL) compaction, West African Standard (WAS) and British Standard Heavy (BSH) compaction were employed in the compaction tests. Samples were soaked for 48hrs prior to CBR testing. The index properties of the soils were used to classify the soils as   silty sand (SM) or silty sand/clayey sand (SM-SC) based on the Unified Soil Classification System (USCS) classification as well as silty soils (A – 4) or silty/clayey gravel and Sand (A – 2 -4) based on American Association of State Highway and Transportation Officials (AASHTO) classification. All the fifteen soils fell under “grading F” based on AASHTO standard specification designations for particle size distribution. The maximum dry unit weight (MDUW) of the soil samples ranged from 16.203 kN/m3 to 19.424 kN/m3,17.385 kN/m3 to 19.996 kN/m3 and from 18.126 kN/m3 to 21.473 kN/m3 with  corresponding optimum moisture content of 11.4% to 21.4%, 12.45% to 12.5%  and 8.5% to 11.75% for BSL, WAS and BSH respectively. The CBR values ranged between 7.92% and 18.87%. Most of the soil (more than 50%) did not meet the lower values of MDUW while only 20% of the soils had CBR values above 10% which is specified for subgrade soils by the AASHTO standard and the Nigerian Highway Design Manual, Federal Ministry of works and Housing.Keywords: coarse-grained, lateritic soils, highway pavement materials, USCS, AASHTO