Deep Foundations in Formations with Thick Layers of Intermediate Geomaterials and Deep Stable Strata
This work entails the foundation studies, analysis and design that was conducted for a proposed development in the central area of the federal capital of Nigeria. The work encompasses extensive field work, experimental regime, laboratory testing and analyses of the deduced data. The work entails boring of twenty (20 Nos.) rotary drillings with rock coring as well as fifty (50 Nos.) mechanised percussion drilling with standard penetration tests (SPT). The latter gave refusal at between 8.15 and 9.65m while the rotary drilling depths were between 21 – 40m. These revealed sandy silt, silty sand, laterite, lateritic clay and concretionary laterite as the overburden material. Weathered and fresh basement rock were proved between 15 and 40m. Geophysical survey, by the use of vertical electrical sounding predicted weathered and fresh basement rock at varying depth of 18 -50m. The bearing capacity of the overburden material range from 28 – 400kN/m2 ( Factor of safety of 2.5) and >1000kN/m2 for fresh basement rock. 600mm and 900mm bored and cased piles were recommended as foundation for the facility up to depth of 50m below the ground level. This is to take care of the depth to the stable strata resulting from the thickness of the intermediate geomaterial.
