Civil Engineering April 2021 | Vol 29 No 3

Civil Engineering April 2021 19 within the excavated hydro-power pit comprised unweathered, massive dolerite. Inspection of the excavated pit revealed several sets of discontinuities (Figure 7), broadly comprising the following: Q Q Sub-vertical or steeply dipping joints, striking roughly parallel to the dam centreline. Q Q Occasional sub-vertical, steeply dip- ping, or even shallow dipping joints that strike in an east-west direction, and dip towards the south. Q Q Non-continuous joints that strike north-south and dip at angles of about 40° in an upstream direction. Q Q Other random joints and occasional shear zones. The fortuitous location of the powerhouse entirely within the vertically orientated dolerite dyke indicated uniform founding conditions, and there were no concerns relating to possible variable excavation and founding conditions. Consideration was given to the stability of the cut faces, although only the temporary stability was relevant. Possible failure modes within these cut slopes were assessed, and appropriate options for stabilisation were addressed. IN CONCLUSION The evolution of the dam design, together with the geological conditions encountered, required a flexible and agile approach from the design team, supported by the geotechnical team, all working together with the contractor. The first filling of the dam was in 2017, while successful commissioning of the powerhouse, transmission line and substations followed in February 2020. The Kashimbila project is now making a significant contribution to the strained national power grid, as well as water supply, and providing flood protection.  REFERENCES G. Y. A. Soil and Foundation Engineering Ltd. 2009. Kashimbila Dam – Nigeria: Geotechnical Report: Factual and Interpretive Report of the Site Investigation Program. Report submitted to S.C.C. Levin, M. Geological and Geotechnical Surveys (G.G.S.) Ltd. Kashimbila Dam – Nigeria. Geological Report. 2006. Figure 5 Orthogonal lineaments exert clear structural controls on the drainage pattern Figure 6 Variable founding conditions within the original river course, comprising fractured, weak granite gneiss and minor dolerite intrusions Figure 7 The powerhouse footprint is located entirely within a high strength dolerite dyke The first filling of the dam was in 2017, while successful commissioning of the powerhouse, transmission line and substations followed in February 2020.