Geotechnical and environmental problems related to shales in the Abakaliki area, Southeastern Nigeria

Abstract

Six (6) samples of shale and five (5) water samples from hand-dug wells and boreholes, from different locations within the Abakaliki shale formation, have been assessed to evaluate the impact of the shale formation to the geotechnical and hydrogeo-environmental problems prevalent in the Abakaliki area (Southeastern Nigeria). Results indicated that the shale samples have Atterberg limits that might be considered moderate to high; while Liquid Limit (LL) ranged from 49 – 54, the Plasticity Index (PI) ranged from 34 – 38. These relatively high LL and PI suggested presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 20%) was also significantly high. Hydrochemical analyses, on the other hand, revealed that the water samples had comparatively high content of ions and dissolved particles; Ca²⁺ ranged from 8.0 – 134.0 mg/l, Mg²⁺ ranged from 0.2 – 3.3 mg/l, HCO^-₃ ranged from 21.8 – 1176.1 mg/l and total dissolved solids ranged 56.9 – 1415.0 mg/l. Dissolution of soluble minerals (predominantly calcite and other rock salts) contained in the shale might likely be responsible for the release of these particles. Geotechnical behaviours of the shale and hydrogeochemical characteristics of water samples from the shale formation, thus, provided insights into the probable causes of seasonal waterlogging, consistent poor groundwater quantity and quality, structural and foundation problems that are prevalent in the Abakaliki area.

Key words: Abakaliki shale, dissolution, environmental problems, geotechnical analysis, groundwater quality, structural failure.