km182 Landslip


African Minerals Limited


Tonkolili, Sierra Leone



African Minerals Tonkolili iron ore mine is located in the Sula Mountains and served by circa 200km of newly constructed rail line running from the port of Pepel, near Freetown.

Construction of the rail on sidelong ground in the mountainous upper portion of the route lead to reactivation of an historic landslide at chainage km182. Following an extensive emergency remedial earthworks operation during construction; ongoing mass movement particularly during the annual wet season meant a ground investigation and detailed stability analysis was required.

Our investigation included a detailed geomorphological mapping exercise together with a technical review of all previous investigation works undertaken in the vicinity of the failure as well as a review of the construction and failure history of the site. We provided two drilling rigs to undertake a ground investigation within the limits of the marginally stable slope. 11 boreholes with depths up to 40m and sampling methods consisting of dynamic sampling, rotary coring and Shelby Tube sampling were undertaken together with the installation of vibrating wire piezometers and inclinometers. Laboratory testing was undertaken at the Dawnus soils laboratory at the Tonkolili mine site.

We provided a detailed interpretive report covering the investigation and monitoring which included slope stability modelling for a range of potential groundwater scenarios. The report concluded with detailed recommendations for ongoing assessment, remedial earthworks and effective groundwater control.

All works were undertaken by our own team of experienced site engineers and operatives using our own specialist drilling and testing equipment imported from the UK.