Özet:

Subsoil engineering site condition and modeling of engineering parameters has been carried out in Ile Oluji, Ondo State, Southwestern Nigeria, using geotechnical investigation, geophysical method, borehole logging, groundwater level measurement, and laboratory studies. Findings revealed that the soils are clayey of low-high plasticity/compressibility, with AASHTO classification of A-7-6. Based on average values of cohesion (48.4 KN/m2), angle of friction (17.4°), unconfined compressive strength (186.8 KN/m2), coefficient of permeability (2.13E-06 cm/s), activity (0.48), soaked CBR (7 %), MDD/OMC (1980 kg/m3/14.8 %), plasticity index (20.2 %), group index (6 %), compression index (0.0443), coefficient of volume compressibility (0.2041 m2/KN), depth to basement rock (22.2 m), static water levels 5.5 m (in well) and 21.8 m (in borehole), the soil is unsuitable for highway subgrade, subbase, and base courses. Thus, if it is expedient to use it as subgrade soil, the minimum recommended thickness is 241 – 513 mm (avg. 395 mm). The average allowable bearing capacity of the soil for square and round foundations are 268.4 KN/m2 and 267.95 KN/m2 respectively, with average total settlement of 18.3 mm for structural pressure of 100 KN/m2. For embankment, the suitability index (1.21) of the soil suggests a fair/expanding not collapsible construction material. The rock units in the area have high compressive/shear strength, modulus of elasticity, high crushing strength, low deformability; and presumable bearing capacity of 8, 000 – 10, 000 KPa when fresh, and 5000 – 7000 KPa when partly or slightly weathered. Thus are valuable as foundation constructions, aggregate in pavement, building stone, and armourstones. The correlation coefficient of the parameters are: MDD/PI vs. CBR (0.0043), LL vs. coefficient of consolidation (0.0608), PI vs. undrained shear strength/effective overburden (0.2706), PI vs. angle of shearing (0.0117), dry density vs. angle of shearing (0.0058), suitability index vs. CBRs (0.3644), clay contents vs. PI (0.1355).

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