Civil Engineering July 2021 | Vol 29 No 6

Civil Engineering July 2021 27 km 225+000, which is at a low point of the alignment. The road alignment and key features are shown on Figure 1, while the route profile is shown in Figure 2. The original road had a carriageway width of 7 m to 7.4 m, with 1 m to 1.5 m wide shoulders. The road from Gbarnga and Ganta originally had an asphalt sur- face, but it deteriorated to the point where most of the asphalt was gone, leaving a badly potholed gravel surface. The last 1.83 km of the road, between Ganta and the Guinea border, had a gravel surface. As part of the rehabilitation, the existing pavement was strengthened by overlaying it with a crushed aggregate base and asphalt layers while the road was slightly widened. Climate The available rainfall and temperature data are provided in Figure 3 and Figure 4. Based on the climatic data available, the project is in an area which experi- ences high average temperatures all year round. The rainy season is between July and September, with the highest monthly rainfall of 419 mm experienced in September. The project area has a high annual rainfall and a wet climate. ASSESSMENT OF PAVEMENT DATA As built pavement data The as built drawings indicate that the new pavement was constructed to the following design: Q Q 40 mm asphalt wearing course Q Q 70 mm asphalt binder course Q Q 150 mm crushed aggregate base (min CBR of 100), compacted to 98% Mod AASHTO density Q Q 250 mm gravel subbase (min CBR of 30), rip and compact in situ to 98% Mod AASHTO density Q Q Subgrade (min CBR of 20). The original pavement was widened on the left-hand side to achieve a uniform roadway width of 7.5 m and 1.5 m wide surfaced shoulders. As part of the widening, a side fill and new pavement layers were placed. Based on the material data in the geotechnical report, the upper (imported) pavement layers of the original pavement mostly consist of nodular laterite gravel to sandy, silty gravel. This is underlain by residual material comprising gravelly, silty sand to clayey sandy silt, a weathering product of the underlying granitic gneiss bedrock. Based on limited trial pit profile Rainfall (mm) 500 200 100 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 18 66 143 172 191 217 248 224 419 203 144 41 Figure 4 Rainfall in mm for Ganta 400 300 Figure 5 Pavement defects (cracking) observed in April 2021 Location (SV, km) Area (m 2 ) 250 240 230 220 210 200 30 20 25 15 5 10 0 Paving underway