Civil Engineering July 2021 | Vol 29 No 6

Civil Engineering July 2021 25 I n 2013 the Liberian Ministry of Publics Works awarded a contract to the China Henan International Cooperation Group (CHICO) for the design, rehabilitation and maintenance of the road between Gbarnga and the Guinea border (70.14 km). The work is carried out under an Output and Performance-based Road Contract (OPRC) and comprises initial rehabilita- tion of the road, maintaining the road for the full ten-year contract period and provision for a periodic maintenance intervention in year eight. Quarterly monitoring of the pave- ment condition was specified to ensure that the performance criteria, as set in the contract, are met. The monitoring includes regular measurement of road roughness (IRI), deflections (FWD) and visual condition assessment. JG Afrika was appointed by CHICO as its consulting engineerings for the reha- bilitation and upgrade of the road section for the initial implementation and future maintenance stage, which included the evaluation of the performance of the current pavement design for the future planned overlay. Determining the 20-year design traffic and effective life of the existing pavement are key aspects in designing the asphalt overlay thickness. In accordance with the contract documents, the design was carried out following the guidelines given in the AASHTO Guide for Design of Pavement Structures, 1993. Asphalt overlay design for Gbarnga Road, Liberia Surita Madsen-Leibold Pr Eng Senior Engineer: pavement engineering JG Afrika madsen-leibolds@jgafrika.com 800 000 792 000 784 000 776 000 768 000 800 000 792 000 784 000 776 000 768 000 450 000 460 000 470 000 490 000 480 000 500 000 450 000 460 000 470 000 490 000 480 000 500 000 Figure 1 Road alignment and key features 0 1 2 4 6 8 10 Kilometres N Shalen Jangali Pr Eng Technical Director: highway engineering JG Afrika jangaliS@jgafrika.com PROJECT TEAM Project Manager Shalen Jangali Pr Eng, Technical Director: Highway Engineering, JG Afrika jangaliS@jgafrika.com Design Engineer Surita Madsen-Leibold Pr Eng, Senior Engineer: Highway Engineering, JG Afrika madsen-leibolds@jgafrika.com Contractor Zhang Youtao, China Henan International Cooperation Group (CHICO), Liberia zhangyoutao@chico.com