Geotechnical Investigation Of A Swampy Soil For Foundation Design And Construction In Buguma City, Rivers State, Nigeria
Joseph Chukwuka Okah
Department of Building Technology, Port Harcourt Polytechnic, Rumuola, Port Harcourt, Rivers State, Nigeria
Keywords: Soil stratigraphy, swamp, consolidation, compressibility, settlement, cohesion, shear strength, Allowable Bearing capacity
Abstract
Buguma City, in Asari Toru LGA of Rivers State had witnessed population upsurge on account of O&G, fishing and trading activities in the city, exerting pressure on lands available for buildings and driving development into swampy areas causing frequent building collapses that needed urgent attention. To this end, geotechnical investigation was conducted to determine the engineering properties of the soil for foundation design and future construction. In doing this, 4 boreholes; BH¬¬1, BH2, BH3 and BH4 were drilled at a landed space located at 4.7133170N and 6.863660E in Buguma City using cable percussion equipment to the depth of 25m and soil samples were collected for laboratory tests (Particle size analysis, consolidation etc) according to BS 1377 (1990). The Soil stratigraphy revealed near surface dark brown compressible silty clay from 0-750mm and grey to light silty clay of high plasticity from 0.6-8m depth for BH1, BH2 and BH3 while BH4 contains a grey to light silty clay of medium compressibility. Below the 8m is brown medium-grained loose sand to 13m depth which increases in density to a coarse-dense sand beneath. The Atterberge limit test result shows that the L.L, 49% and P.L, 26% sufficiently indicate relatively compressible silty clay. Result also revealed a Bulk unit weight γ, MDD and OMC of 18KN/m3, 1.73g/cm3 and 13.20% respectively. The soil produced a coefficient of compressibility mv of 0.687m2/MN and Cc of 0.29, while the shear strength parameters were; c = 38KN/m2 and Ø = 3.00 which produced bearing capacities (BC) of 98.25KN/m2 and 104.9KN/m2 and settlements of 63.76mm and 42.5mm for shallow foundation at depths 1m and 3m respectively under a water level of 1.8m. Finally, it was concluded that the soil is weak silty clay which is unsuitable for strip and pad foundations. However, it is recommended that a raft and beam/slab-raft foundation be adopted for bungalows and 1-storey buildings respectively otherwise pile foundation to the stratum of 25m depth should be adopted for more than 2 storey buildings