Geological and Geotechnical Investigation of Gully Erosion along River Bosso, Minna, North Central Nigeria

Abstract

Geological and geotechnical investigation along River Bosso, Minna to determine the soil characteristics contributing to gully erosion in the area was done. Field mapping showed that granite, granite-gneiss and schist of Basement complex suite underlie the area and granite is more prominent than granite-gneiss and schist. The index test results for the natural moisture content ranges from 11.19 - 24.08%; the plasticity index ranges from 0 - 5.21%; the sieve analysis result shows that coefficient of uniformity, Cu ranges from 3.37 and 29.00 while coefficient of curvature, Cc ranges from 0.17 - 0.89; the undisturbed bulk density is between 0.87 - 1.11kg/m3 and the compacted bulk density is between 1.25 - 1.49kg/m3; the specific gravity ranges from 2.16 - 2.67. For the performance test; the compaction result shows that the optimum moisture content (OMC) ranges from 8.90 - 14.85% while the maximum dry density (MDD) ranges from 1.880 - 2.09mg/m3; the triaxial shear test result shows that the angle of internal friction is between 60 - 90 and the cohesion ranges from 28 - 42kg/m2; the permeability is between 1.42 - 10-3 and 1.93 - 10-3 cm/sec. The relatively high sand content and low plasticity of the soil is susceptible to erosion which is attributed to the dominant granitic rock of the study area with high affinity for gully erosion. The anthropogenic factors found to have contributed to gully growth are farm practice, mining activities and residential buildings on the flood plain.