The geotechnical survey of Enugu metropolis and its environs was carried out. The area covers approximately 625km2 and includes parts of Udi, Enugu metropolis, Oliemba, Emene and Ukana. The topography of the area is rugged with the Enugu Escarpment as a prominent feature. East of the Escarpment are Rivers Ekulu, Asata, Iyaka, Nyaba and Nvenen dissecting the area and flowing into the Cross River system.
The area is underlain by the following Cretaceous rocks: the Agbani Sandstone, the Enugu Shale, the Mamu Formation and the Nsukka Formation. There is also alluvium deposit of Quaternary to Tertiary age.
The soils derived from the Enugu Shale and the Mamu Formation are stiff and have swelling characteristics while those derived from the Agbani Sandstone and the Ajali Formation are loose and more permeable.
The predominant geotechnical factors observed in the area are: Problem soils, inundation, slope instability and acidity problems.
Problem soils are mainly those derived from the Enugu Shale, the Mamu Formation and the Alluvium deposits along the flood plains of Rivers Iyaka, Ekulu, Asata, Nyaba and Nvenen. Approximately 42% of the study area is covered by problem soils.
Slope stability problems occur along the scarp of the Enugu escarpment, especially the area underlain by the Ajali Formation. About 17.4% of the total study area is affected by slope instability. Inundation occurs along the banks of down streams of Rivers Iyaka, Ekulu, Asata, Nyaba and Nvenen. Approximately 0.07% of the total area is affected by inundation. Soils with acidity problems cover about 92.5% of the study area. These are areas underlain by the Enugu Shale, The Mamu and the Ajali Formations.
Remedial measures that are suggested when developing on the problem soils include: Provision of foundations as deep as 1.5m or more to avoid the zone of volume change, isolating the foundation below ground level from the surrounding soil by various means such as two coats of bitumen or polythene liners to minimize friction between the foundation and the soil, sand-filling the foundation to a height of 30cm before laying the sand Crete blocks on top to avoid friction between the foundation soils and the block work, using ordinary Portland cement not less than 400kg /m3 , water/cement ratio of 0.5 for soils with pH less than 5 and carrying proper study of slope instability before construction or avoiding all areas of active slope failures during development on those areas.