Appropriateness of soils as media bearing in a freshwater swamp terrain in the Niger Delta area

Abstract

Umaru G. H

This study evaluates the subsurface lithologies as well as examines the properties of the soils at a University location within the fresh water swamp terrain in the Niger Delta. Borings for subsurface exploration in the area were made at five well spaced locations with a hand auger to a maximum depth of 4.00 m in each borehole. Soil samples were retrieved at 0.5 m interval and at positions where changes in lithology were noticed during the boring process. Laboratory tests were carried out on selected and representative soil samples recovered from the borings in accordance with BS 1377 (1975) and ASTM (1979) standards. Moisture content range from 20.6% to a maximum of 26.5% in the silty clay and gravelly, silty clay soils located at 2 m depth and low to medium plasticity range (12 to 18%). The undrained friction angle was determined to be 30 while the undrained cohesion has a value of 58 KN/m2 , the computed coefficient of volume compressibility (Mv) gave 1.24 m2 /MN while the coefficient of consolidation (Cv) resulted in 3.38 m2 /year. Computed total settlements of 69 mm are within design limits for shallow foundation. Borehole 1 (BH1) was dry while BH2 recorded 3.80 m as the ground water level. Observed water table depths in BH3, BH4 and BH5 were 2.00 m, 1.70 and 1.50 m, respectively, at the time of the subsurface investigations. Higher values are expected especially at the peak of the rainy months. Foundation systems in the area must take special precaution to prevent seepage into the structures. This could be by drainage or waterproofing or a combination of both methods.