Investigating Geotechnical Properties of Soils from Mambilla Plateau for Sustainable Infrastructural Development

Abstract

Investigation of geotechnical properties of soils from Mambila Plateau was carried out. Five Standard Penetration Test (SPT) boreholes carried to the depth of 12m each were conducted across a valley, two boreholes each at the opposite sides of the valley and one borehole at the base of the valley. Two significant strata (reddish brown silty soil layer and the grayish weathered rock layer) were observed from the soil samples retrieved from the boreholes except for borehole 3 sited at the base of the valley whose stratum showed relatively thick dark lacustrine deposit followed by yellowish brown sandy soil to terminating depth of 12m. Result of geotechnical properties of the soils relatively high natural moisture contents of between 27.6 and 46.6% for the reddish brown silty soil layer compared with the grayish weathered rock layer. Relatively high values of liquid limit ranging from 42.7 to 75.1% were also recorded at the reddish brown silty soil layer. The range of fines content were also observed to be higher for the reddish brown silty soil layer at between 40.4 and 85.6 compared to the grayish weathered rock layer. From the SPT results, it was deduced that the soil strata becomes stiff at an average depth of 3.0m and denser with depth. The result of the physico-chemical tests showed the soils to be mainly basic with pH ranging from 7.2 to 8.5. Although, no lateritic gravel were observed within the strata, oxides composition of the soils showed silicon-sesquaoxide ratios (SiO2/Al2O3+Fe2O3) of being generally lower than 1.33, indicating that the soils are lateritic. All these geotechnical properties coupled with the chemical and physico-chemical properties revealed that soil on Mambilla plateau can effectively support engineering structures of significant magnitudes.