Influence of Spatial Variation in Subgrade Properties on the Design of Highway Flexible Pavements
American Journal of Applied Scientific Research
Volume 2, Issue 6, November 2016, Pages: 65-74
Received: Oct. 1, 2016; Accepted: Nov. 18, 2016; Published: Dec. 21, 2016
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Nwakaire Chidozie Madu, Department of Civil Engineering, Nnamdi Azikiwe University, Awka, Nigeria
Chukwu Chinagorom Joshua, Department of Civil Engineering, Nnamdi Azikiwe University, Awka, Nigeria
Udemba Jonathan Nwachukwu, National Inland Waterways Authority, Warri, Nigeria
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Influence of spatial variation in subgrade properties on the integrity of highway pavement design is the burden of this research. Interruption, delay and discomfort in transportation flow that characterize roads across the globe due to poor pavement conditions are pathetic experiences. This work is an attempt to investigate the influence of subgrade variation on the design thicknesses of highway flexible pavements, using subgrade properties and traffic characteristics encountered along the Enugu-Onitsha expressway. Soil samples collected from selected sections of the expressway were subjected to geotechnical laboratory tests like particles size distribution, Atterberg’s limits, compaction and California bearing ratio in order to analyse their properties. The results generated from these three samples from different stations across the road showed that the soil materials along the Enugu-Onitsha expressway vary significantly. Sample from Nkpor, Awkuzu and Kwata stations contain 15%, 45% and 80% fines (silt and clay) respectively, likewise their MDD and OMC are 1852KN/m3, 1980KN/m3 and 1788KN/m3; 11.7%, 11%, and 14.6% respectively. The 48 hour soaked CBR values of soil samples from Nkpor and Awkuzu stations are 8% and 9% respectively while Kwata station is 2.3%. The plasticity index and liquid limit results were also 11%; 31% and 9%; 27.4% for Awkuzu and Kwata samples while Nkpor sample in a non-plastic soil. Based on ASSHTO classification, the soils fall within A-2-4, A-6 and A-4 categories which depicted a significant variation in properties, fair to bad. Based on the design outputs for pavement thicknesses, it was concluded that designing a length of highway with a single CBR value will be uneconomical for areas with significantly higher surface modulus as well as providing insufficient thicknesses for areas with lower actual CBR than the observed. Sectional pavement design at not more than 1km intervals was recommended.
Pavement, Design, Subgrade, Variation, CBR, Asphalt
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Nwakaire Chidozie Madu, Chukwu Chinagorom Joshua, Udemba Jonathan Nwachukwu, Influence of Spatial Variation in Subgrade Properties on the Design of Highway Flexible Pavements, American Journal of Applied Scientific Research. Vol. 2, No. 6, 2016, pp. 65-74. doi: 10.11648/j.ajasr.20160206.16
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This article is an open access article distributed under the Creative Commons Attribution License ( which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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