Comparative Study of Geotechnical Assessment of Highway Subgrade Using In Situ DCPT and Laboratory Engineering Parameters


  • C. A. Oyelami, O. A. Ojo2, O. O. Owoyemi and A. Salako


UCS, CBR, Permeability, Geotechnical, Characterization.


A comparative study of the geotechnical assessment of subgrade soils using in situ Dynamic Cone Penetrometer (DCP) Test  and laboratory tests were carried out. The study was aimed at establishing the suitability of selected tropical soils as subgrade materials using the conventional laboratory test and in-situ DCPT method. The study involved sampling a total of 15 soil samples taken in a hand-dug pit at a minimum depth of 0.5m along Osogbo-Ilobu road. The in-situ test involved the use of a DCP in estimating the in-situ California Bearing Ratio (CBR) of the soil at 100m intervals through the 1.5 km stretch of the road. Laboratory tests carried out includes the grain size analysis, hydrometer test, Atterberg limits and specific gravity, CBR, permeability and Unconfined Compressive Strength (UCS). The results revealed a well-graded soils which are mostly clayey and silty sand (SC & SM) according to the Unified Soil Classification System (USCS) and A-2-4, A-2-6 to A-7 category of the American Association of State Highway and Transportation Officials (AASHTO) classification. The coarse fraction ranged between 48.3 - 90.5 % and fine fraction between 9.5 - 44.6 %. The UCS ranged from 148.8 - 214.5 kPa; unsoaked CBR from 54 – 148 %; soaked CBR from 42 – 106 %, reduction in strength due to soaking between 2.8 and 31.1 %; DCPT estimated CBR between 70 and 185. Conclusively, the soils were fairly suitable as subgrade, except for the clay contents in them, accounting for a very low rate of permeability which may be responsible for ponding and excessive soaking of the subgrade.

Author Biography

C. A. Oyelami, O. A. Ojo2, O. O. Owoyemi and A. Salako