Geotechnical characterization of a highway route alignment with light weight penetrometer (LRS 10), in southeastern Nigeria

摘要

Abstract Background It is required to carry out geotechnical characterization of the subgrade for a proposed 18 km dual carriageway alignment. A light weight penetrometer, LRS 10 was chosen as an exploratory tool to carry out the investigation. Methods The LRS 10 penetrometer was deployed at an average interval of 250 m along the proposed alignment, and was used to sound the soil consistency up to 6.0 m depth. Trial pits were dug at locations closed to the LRS 10 sounding positions from which soil samples were collected for laboratory analysis. A software, UK DCP version 3.1 was employed to analyze the LRS 10 field data. Results The LRS 10 results classified the highway alignment into three zones based on in situ relative density while the UK DCP software gives penetration index and CBR values of soil layers from the ground surface up to 1.5m depth. Laboratory analyses places the dominant soils in the area into clayey sand (SC, A-2- 4, A-2- 6), silty sand (SM, A-2-7), and a combination of the two (SM-SC, A-6). Exception is the occurrence of Inorganic silt MH and ML, and organic silt OH (A-7-5) in a few locations along the alignment. These soils are predominantly nonexpansive (plasticity index less than 15 %) but a few are moderately expansive (plasticity index between 15 and 25 %). Sub-grade stiffness as indicated by resilient modulus values were estimated from the largest penetration index values (lowest strength) using established correlation equations; this gives resilient modulus values between 27 MPa to 304 MPa. Conclusion The soil types dominant along the proposed highway alignment were classified and characterized in strength. The soil types is consistent with the geology of the area the alignment transects. The subgrade stiffness of some sections of the alignment will need improvement to meet minimum strength required for a highway pavement. Some useful correlations of strength parameters were proposed.