International Journal of Earth Sciences Knowledge and Applications
Yazarlar: Falowo Olumuyiwa OLUSOLA
Konular:Yerbilimleri, Ortak Disiplinler
Anahtar Kelimeler:Geotechnical method,Cone penetration test,Borehole log,Hydraulic head,Resistivity structure
Özet: Engineering site investigation for shallow foundation design is carried out in Ose Local Government of Ondo State using integrated geotechnical, geophysical, hydrogeological measurements, and borehole logging. The northern part of the area is underlain by rocks of Migmatite-Gneiss Complex of Southwestern Nigeria, while the southern area is Cretaceous Ewekoro Formation. The static water level ranges from 3.1 to 15.9 m, while the hydraulic head varies between 38.9-371.8 m. Low static water level is observed in clay shale/sandstone lithology, while granite, migmatite and granite gneiss are characterized by high static water level. The hydraulic head map shows possible groundwater flow direction of south, as the values of hydraulic head in the study area reduce towards the south. The plasticity chart and clay mineral group indicate predominant high plasticity soil group (CH) with general AASHTO class of A-6 characteristic of poor soil material. All samples fall above the A-line, indicating clayey inorganic material. The mineral group of the soil is closer to illites. The soils are also characterized by high plasticity index (23.8% avg.) and show moderate to high shear parameters. The targeted CPT value of 100 kg/cm² corresponding to 245KN/m² is obtained at a depth of 3.0 m. The allowable bearing capacity of the soils (within upper 3 m) varies from 6 KN/m² to 309 KN/m² respectively, while the ultimate bearing capacity varies between 18 KN/m² and 927 KN/m², respectively. The settlement values obtained from the area are generally less than 20 mm from each of the subsurface layers. The minimum settlement values obtained vary from 0.68 mm to 0.80 mm at depth of 0.8 m and 3 m respectively. These depths would be appropriate for the design of foundation structure because they are characterized with low settlement with allowable bearing pressures greater than 100 KN/m².