Geotechnical appraisal of abandoned borrow pits as potential landfill sites in Abuja and Environs, North Central, Nigeria

Abstract

Abandoned borrow pits pose significant environmental hazards such as landslides, gully erosion, road failure and groundwater contamination if not properly reclaimed. This study investigates the geotechnical features of abandoned borrow pits with a view to converting suitable sites to a modern sanitary landfill. Twelve abandoned borrow pits were assessed using geotechnical parameters such as particle size distribution, Atterberg limits, bulk density and permeability. Results showed that the sites are underlain by gneisses, migmatites and granites, which are fresh to provide enough support for the conversion of these borrow pits to a modern sanitary landfill. Geotechnically, the soils at these sites are predominantly sand with a gradual increase in clay content. Sand is 55 – 75%, clay is 12 – 16% and silt is 12 – 30%, respectively. Values of plasticity range from 12 – 26%, liquid limit ranges from 40 – 48%, shrinkage limit ranges from 14 – 22%, bulk density ranges from 1.75 – 1.95 g/cm3 and permeability ranges from 9.00 x 10-6 to 1.8 x 10-5 Cm/S. Some of the borrow pits possess favourable features such as high bulk density and well-graded soils that are suitable for the construction of an engineered landfill. The majority of the pits exhibit significant challenges that could affect their use for waste disposal.