Engineering Subsoil Characterization for Shallow Foundation Using DCPT at the Permanent S

Abstract

Geotechnical investigations for foundation design have proved to be good veritable tool in effective foundation design and construction. This study was carried out to investigate the efficiency of DCPT in geotechnical characterization of subsoils for foundations around Ondo Town in Ondo State with the aim of establishing a relationship between the in-situ and laboratory parameters. The study involved in-situ assessment of the shear strength of the soil using the Dynamic Cone Penetrometer (DCP) to determine its Allowable Bearing Pressure (ABP) and bulk sampling of disturbed soils taken from five (5) borrow pits at depths ranging between 1.0 to 1.5m. Laboratory tests were carried out to determine their index properties (grain size analysis, hydrometer test, Atterberg limits, natural moisture contents and specific gravity) and engineering properties (compaction test, unconfined compressive strength test (UCS), direct shear test and unit weights). The study area is mostly a flat-lying terrain except for quartzite which outcrops at the southern part of the study area. Three horizons identified include; the topsoil (Azone) with depths ranging between 0.2 to 0.4 m, the gravelly stone layer (B zone) with depths ranging from 0.4 to 0.5 m and the lateritic horizon (C zone) for 0.5 to 1.5 m where the pits terminated. Soils in the study area are well graded clayey sand (SC) according to the Unified Soil Classification System (USCS). The percentage of coarse fraction (Gravel and Sand) ranged between 53.7-67.6% and fine fraction between 32.4-46.4%. Atterberg limits revealed an inorganic medium plasticity soil (CI) with plasticity index ranging from 13.90-21.30. Specific gravity confirmed the soils as lateritic soil that ranged between 2.68 and 2.74; their bulk unit weight (ã ) ranged from 22.01- t 3 23.25 kN/m ; optimum moisture contents (OMC) from 13.3-18.0%, maximum dry density (MDD) from 1942-2078 3 kg/m and unconfined compressive strengths (UCS) from 169.3-280.7 KPA. Statistical correlation between ABP and geotechnical parameters returned a positive regression lines with equations for possible estimation of soil geotechnical parameter from in-situ test. Results obtained for ultimate bearing capacity (q ) ranged between ult 2 2 1129.35-1842.95 KN/m while the allowable bearing capacity (q ) ranged between 376.45-614.30 KN/m . This is in all agreement with the allowable bearing pressure as obtained from the DCPT. In conclusion, DCPT proved to be an effective, cheap and easy-to-use device for sub-soil geotechnical characterisation in civil engineering constructions.

Publication Info:

Author: Oyelami, C.A. *, Obaromi, O. , Omoyajowo, B.T. , 1 1 Oluyem

Volume: 59

Issue: September

Published By: Journal of Mining and Geology Vol. 59(2) 2023. pp. 103 - 116, 2023-09-01