Investigation of Suitable Foundation for Storey Building in Surcharged Swampy Soil (A Case Study of Lagos State)

In Lagos, Southwestern Nigeria, the land area has been developed such that there are insufficient land spaces for building construction. It therefore becomes imperative that construction of storey buildings is inevitable to accommodate buildings within the limited land spaces. The percentage of swampy – land is high, thus restricting people to build on the little available land with little or no convenience and to effectively utilize the available land, there is need to improve the large percentage of swampy–land for construction of storey building with suitable foundation. This study therefore focused on determination of soil properties for building foundations at 1.5km South of Lagos – Epe Expressway Oloja, Ibeju Lekki Local Government Area of Lagos State.Soil samples were collected from open pits in five different locations within the study area. The undisturbed samples were obtained at depths of 3m and were carefully transported by putting each of the samples in polythene bag and then kept in sealed container before being transported.The particle size distribution analysis of selected soil samples from the study area was carried out in accordance with the provision of BS1377: Part 2, 1990. Compaction test, Unconfined compression Strength (UCS) test and bearing capacity test were all carried out on the collected soil samples.The results of the tests carried out on the selected soil samples showed that the soil in the study area was largely made up of silty-clay material with OMC and MDD ranging from 9.60-12.5% and 1.82-1.91 g/cm3 respectively; UCS values between 22.24 – 56.67 kN/m2 and allowable soil bearing capacity ranging from 90.95 to 106.26 kN/m2. It is recommended that Raft foundation be used for bungalows while beam/slab raft should be used for structures that have 2-5 storeys and pile foundation for structures above 5 storeys in order to cater for silt-clay nature of the soil and to prevent differential settlement in future. Keywords: Swampy Soil, consolidation, foundation, storey building