Main Article Content
Gully erosion sites are increasingly becoming a threat to environmental sustainability, leading to severe environmental hazards. This study investigates the geotechnical and environmental risk assessment of two gully erosion sites in Nkwoegwu, Abia state. Four (4) Soil samples were collected at different depths ranging from 21.4 m - 20.3 m. The geotechnical properties of the soil samples were analyzed. Results of geotechnical investigations revealed that soils in Site A were composed of (Clay & Silt – 29.48%, Sand – 69.01%, Gravel – 1.51%); Soils in Site B composed of (Clay and Silt – 41.71%, Sand – 57.54%, Gravel – 0.75%) suggesting that they are nonplastic. The liquid limit values are 26% and %, plastic limit 19% while the plasticity index values are 7.0% and 6.0% for site A and site B respectively indicating that they were noncohesive. The maximum dry density (MDD) values are 1.99 mg/m3 and 2.02 mg/m for site A and site B showing their loose nature. The optimum moisture content (OMC) values are 12.1% and 13.3%; CBR values being 32% and 4% respectively. The moisture content of the erosive soil samples were 8.5% and 11.2%. The result for the bulk density gives 1.38 g/cm3 and 1.28 g/cm3 for site A and site B respectively, while the shear strength values comprising cohesion, C, and angle of internal friction, Ф, gave their C to be 34 N/m2 for both sites A and site B and Ф of 14° (site A) and 16° (site B) respectively. This revealed that the soils lack resistance to runoff. The soil materials were mostly loosed sands with a low percentage of silt/clay fractions and high porosity. Noncohesive properties of the soil materials make them vulnerable to agents of erosion such as rainfall, the slope of land-surface, and human activities. The topographical survey showed that gully sites are the lowest points in the area which is also the direction of drainage. The total surface runoff from the area of study is estimated to be 384000 m3/day. Environmental hazards such as loss of arable land, and the threat to lives and properties were identified as well. To mitigate against the expansion of the two gullies, terraces are recommended to be constructed. This will minimize the impact of surface runoff.
Albert AA, Samson AA, Peter OO, Olufunmilayo AO. An Assessment of the Socio Economic Impacts of Soil Erosion in South-Eastern Nigeria, Shaping the Change, XXIII FIG Congress Munich, Germany. 2006;12.
Akpokodje EG. Introduction to Engineering Geology. Pam Unique Publications. 2011;259.
Imasuen OI, Omali AO, Ibrahim I. Assessment of environmental impacts and remedies for gully erosion in Ankpa Metropolis and environs, Kogi State, Nigeria. Adv. in App. Sci Res. 2011;2(5) 372-384
Okogbue CO. Hydrocarbon Potentials of the Anambra Basin: Geology, Geochemistry and Geohistory Perspectives Proceedings of 1st PTDF (Chair) Senior in Geology, University of Nigeria, Nsukka. 2005;110.
Handy RL, Spangler MG. Geotechnical engineering: soil and foundation principles. McGraw-Hill 2007.
ASTM International (Standard practice for classification of soils for engineering purposes (Unified soil classification system). 2007;12.
British Standard Institution. Methods of Test for soils for Civil Engineering Properties (BS 1377) British Standard Institutions London, UK. 1990;143.
Okengwo ON, Okeke OC, Okereke CN. Paschal AC. Geological and Geotechnical Studies of Gully Erosion at Ekwulobia, Oko and Nanka Towns, Southeastern Nigeria. Elect J. Geot. Eng. 2015;20(1).
Ofomata GEK. Acrtual and Potential erosion in Nigeria and measures for control. Soil Science Society of Nigeria Special Monograph. 1981;1:151-165.
Okunlola IA, Abdulfatai IA, Kolawole LL, Amadi AN. Geological and Geotechnical Investigation of Gully Erosion along River Bosso, Minna, North Central Nigeria. J. Geosci. Geomat. 2014;2(2): 50-56.
O’Flaherty CA. Highway Engineering, Edward Arnold Publishers, London, Uk; 1988.
Ishaku JM, Adeleke JID. Negro SS. The Hydrogeological and Geotechnical characteristics of Rock Materials that Aid Gully Erosion in Lassa Area of Borno State, North Eastern Nigeria, Water Reso. J. Nig. 2002;13(53).
Okagbue CO, Ezechi JO. Geotechnical Characteristics of Soils Susceptible to Severe Gullying in Eastern Nigeria, Bulletin Int. Assoc. Eng. Geo. 1988;38(111).
Alao DA, Opaleye TS. Geotechnical analysis of slope failure of a Kaolin quarry at kurra, Jos of North-central Nigeria. Nigerian Mining and Geosciences Society Journal. 2011;1(2):87-102.
Nwachukwu MA, Osoro E. Assessment of Environmental Hazards: Linking borrow pits, gully erosion and pavement failure. J. Civil Eng. Constr Tech. 2013;4(6):199-210.