Effect of Compaction and Moisture on the California Bearing Ratio of Residual Lateritic Soils in Kontagora, Niger State

Abstract

 The research explores impact of compaction and moisture on the California Bearing Ratio (CBR) of residual lateritic soils collected from Kontagora and its surrounding areas in Niger State, Nigeria. 20 disturbed soil samples were used in laboratory testing to exermine the effects of the variables on CBR values. The tests conducted include: Sieve analysis, Atterberg limit, Compaction test and CBR using both British Standard Light (BSL) and British Standard Heavy (BSH) compaction efforts. The results show that soils compacted using heavy compaction effort achieved higher compaction, with an average MDD values of 1.95 g/cc when compared to 1.84 g/cc for BSL. Samples compacted with light compaction effort generally showed higher OMC, averaging 13.91%, eventhough both compaction efforts exhibited good consistency in MDD values. When the samples were soaked, there was a significant reduction on CBR values for both compactive efforts. Under the heavy compaction, the mean CBR decreased from 89.83% (unsoaked) to 69.22% (soaked) with a total reduction of 20.61%. Samples under BSL experienced a more pronounced decline, with the mean CBR dropping from 74.96% to 52.09%, projecting a 22.87% reduction. The statistical analysis indicated that these reductions were significant, reinforcing the critical role of moisture in diminishing soil strength. Although the heavy compacted soil samples consistently showed higher CBR values than BSL compacted samples in both soaked and unsoaked conditions. The high loss in CBR value of the soil samples when soaked in water stresses the importance of adequate moisture control. Based on these findings, the study recommends the adoption of heavy compaction combined with effective moisture control and drainage measures to enhance pavement durability and ensure reliable road performance in the study area.