Geotechnical Investigation of Sub-Soiland Rock Characteristics in Parts of Shiroro-Muya-Chanchaga Area of Niger State, Nigeria

Abstract

This study aims at determining the litho-stratigraphic sequence to ascertain the engineering properties of the underlying soils and rocks in Shiroro-Muya-Chanchagaarea of Niger State, Nigeria and recommend appropriate foundation types for road construction, bridge and pavement design. Ten boring points/rock coring to 10m below existing ground level were made, out of which six along the piers/abutment alignment and two confirmatory borings each at the abutments. Four (4) boring points were located in water (BH-1, BH-3, BH-4 and BH-5) and two on land (BH-2 and BH-6).The bearing capacities for pile diameters of 406mm, 600mm, 750mm and 1000 mm were computed. Generally, the rocks encountered at the top layer were predominantly weathered and highly fractured with discontinuity in the rock formation due to fractures. However, rocks encountered at lower depths were granitic formation with appropriate recovery lengths. The depths of overburden averaged 4.50m on water and 0.5m on land. The rocks encountered at the near surface werefragmented due to the excavation activities that have taken place while the soils encountered during burrow pitting were hydromorphic soils with clays of moderate saturation. It is recommended that reinforced concrete bored piles be adopted to support steel and for road pavement. It is also suggested that the sub-grades should have average thickness of 150mm with a minimum practical value for spreading and compaction with the load carrying capacity verified by conducting pile load test.