RECONNAISSANCE GEOTECHNICAL MAPPING OF ENUGU AND ENVIRONS

Abstract

The geotechnical mapping of Enugu and environs was carried out and relevant field tests were performed in the process. The soils in the project area are derived from four dominant geologic formations- Ajali, Awgu( Agbani Sandstone),and Mamu Formations and the Enugu Shales. Available data from field and laboratory analyses have indicated that the soils derived from Ajali Formation have the lowest allowable bearing capacity (qa) and low to medium permeability; shear strength parameter c and ø of 24.2kN/m2 and 16º respectively. They also have Activity and Liquidity Indices of 0.37 and -0.05 respectively. Other geotechnical data gathered and presented in this report for all four geologic lithologies encountered in the study area include compaction, SPT, direct shear and Atterberg Limits. Geophysical and Soil geochemical data have also been employed to facilitate deductions, conclusions and recommendations presented in this report. Thematic maps indicating areas prone to landslide and inundation have been produced. Landform and permeability as well as slope instability maps for study area have been presented to aid investors and land developers to identify areas suitable for residential, waste disposal and industrial purposes. Both the Activity and the liquidity indices of the clay-size fractions of the soils of the project area indicate that the soils derived from the lithologies are stable, not sensitive and hence not expansive. Causes of cracking and excessive settlement of structures in the study area could be explained through further work aimed at accurate identification of clays sampled at both shallow and deeper depths.