Abstract
Engineering geological investigation of some unstable and stable sections of the Ibadan-Iwo-Osogbo highway was undertaken to unravel the intrinsic reasons responsible for continuous pavement failure along this road. Eighty disturbed and forty undisturbed soil samples were collected at different depths from twenty test pits of six selected failed sections (FS) and two stable sections (SS). Road construction analysis was done on these soil samples using standard methods. Liquid limit (22 - 64% and 32 - 40%), plasticity index (13 - 41% and 12 - 18%) and percentage fines (47 - 59% and 32 - 41%) indicated fair to poor and fair to good subgrade materials of FS and SS respectively. Medium to high plasticity and high clay content of soils of FS are indicative that the soils possess medium to high swelling potential. The activity of clay in soils of FS was approximately 0.3 – 1.2 and classified as inactive to normal clay. High linear shrinkage (> 10%), low compacted density and predominance of fines in soils of FS caused the instability. Exposure to excessive moisture led to strength reduction of the soils. Triaxial compression showed cohesion (72.6 - 127.0 kN/m2) and internal friction (12.7° - 33.3°) indicating moderate to good shearing strength of the soils. A coefficient of compressibility of 0.1 – 0.5 kN/m2 indicated incompetency of the soils for road construction and the coefficient of consolidation was 0.01 – 0.30 m2 /year. The subsoil of the FS is impervious with a relatively low coefficient of permeability, indicative high saturation in the region. Thus, the pavement failure was caused by water absorbing clayey soil, poor geotechnical parameters of the soils and a poor drainage network.
Highlights
The role of roads in trade and transportation globally cannot be overemphasized as they serve as links between towns, states and countries
Soils of the stable portions have percentage fines of 32 – 41% with an average of 38%, with little clay content within group A-2-4 to A-4 of AASHTO rating system as fair to good highway construction material. It is slightly greater than the threshold value but does not exceed the limit of 35% stipulated by the FMWH, 2000 for highway construction material
The high clay content of the soils is responsible for its high plasticity index (33.1 - 49.7%) as presented in Table 1, which is an indication of high swelling potential of the soils
Summary
The role of roads in trade and transportation globally cannot be overemphasized as they serve as links between towns, states and countries. Sub-Saharan Africa roads are relatively unsafe due to their deplorable state with incessant losses from accidents. The occurrence of soil makes it available as a construction material in engineering works. Most engineering works are either erected on rocks for a strong foundation or on soil, which supports the structure. The engineering properties of soil define its applicability for different uses. They facilitate the estimation of soil response to different conditions that may be applied to it as a construction material or foundation. The performance of engineering works will depend on a correct assessment and prediction of soil performance for the intended use. Most structural failures can be attributed to inadequate knowledge of the competency of substandard materials
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
