Geotechnical Characterization of Geological Formation at Slump Sites within South-Western Outskirts of Zungeru, North Central Nigeria

Slumping is destroying farmlands on the south-western outskirts of Zungeru. Sieve analysis and Atterberg limit tests were conducted on samples of geological formation from the slump and stable sites to ascertain the geotechnical attributes that make the area susceptible to slumping. Surface geological reconnaissance revealed that the area is underlain by schist, amphibolite and granite. The schist unconformably underlay Doko member of Bida Formation, which is the lithostratigraphic unit undergoing slumping. Coefficient of Uniformity (C U ) ranges from 0.57 to 3.48 at the slump sites. This indicates that the slump sites' geological formation is poorly graded. Formation C U at stable site is 5, which indicates fair particle size grading. Natural Moisture Content (NMC) is 1.9% at the stable site. The value tripled (2.2 to 6.6%) at the slump sites. Atterberg limits' value is similar at all the sites. Their liquid limit is less than 40%. Their plastic limit and plastic index are less than 20% and 7% respectively. The low Atterberg limits' value indicates that clay shrinkage and swelling is not responsible for observed slumping. Poor formation particle size grading and high NMC caused slumping in the area. Retaining walls with drain pipes, and vegetation will arrest observed slumping.