Assessment of geotechnical strength properties of road construction soils stabilized with lime in Southwestern Nigeria

Abstract

The quality of the roads in Southwestern Nigeria is appalling; most are inaccessible owing to pavement failures, prompting research into the feasibility of underlying soil courses if lime is used to stabilize them. Eighteen (18) borrow pit soil samples for road construction (one from each Senatorial district in Southwestern Nigeria) was used for this study. The index properties of the natural soil and strength properties (compaction, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS)) of both the natural and stabilized soils were assessed following BS 1377 (1990) standard procedures. Lime of 2, 4, 6, 8, and 10% of the dry weight of soil was used to obtain the varied stabilized soil samples. The particle size distribution results showed that EK1, EK2, OS2, OS3, OG1, LG1 were predominantly fine (Clay + Silt) soils while samples from Oyo, Ogun and Lagos states are predominantly sand as well as OD1 and OD2. The gravelly-rich soils are EK3, OD3, OS1. The subgrade rating (AASHTO) of the natural soils is Fair – Poor for EK1, OD1, OS2, OS3, OY1, OG1, OG2, and LG2 soils while the Excellent – Good soils are EK2, EK3, OD2, OD3, OS1, OY2, OY3, OG3, LG1, and LG3 soil samples. The Maximum Dry Density (MDD), CBR, and UCS values all improved as the lime content increased, with the optimum being obtained at 6% lime addition. Although, there was an exception for OMC, which continued to increase with the increase in lime content by up to 10%. Evidently, unsuitable soil samples became suitable as pavement layer materials after stabilization with 6% lime. MDD results showed % gain ranging from 3.6 %, 16.4 %, 7.8 %, 21.0 %, 14.9 % and 11.7 % for Ekiti, Ondo, Osun, Oyo, Ogun and Lagos states. The Soaked CBR % gain are 72.8 %, 145.8 %,708.0 %, 1861.5 %, 525.9 % and 54.0 % while UCS % gain are 208.1 %, 132.1 %, 305.4 %,43.4 %, 25.0 % and 95.6 % for the states respectively. Comparatively, the effect of the optimal 6 % lime addition on soil was prominent in Oyo state soils. Hence, due to the improvement in the properties of the lime-stabilized soil, the subgrade soil in Southwestern Nigeria roadways may be stabilized with 6% lime content for construction of durable pavements.