GIN method applied to the consolidation of cracked rocks: case study of the Memve’ele hydroelectric dam (southern Cameroon)

Abstract

The empirical GIN (grouting intensity number) method is one of the most popular methods for structural stabilization and is increasingly used in many projects. The concept of this method is to limit the combination of pressure and volume injected to a specific grouting intensity number in order to control the energy induced in the rock fractures and to avoid heaving. In order to ensure the water tightness of the foundation of the Memve’ele hydroelectric dam, the treatment by the GIN method was implemented. The protocol implemented consisted to carry out a veil of injection drilling, consolidation, and control of effective treatment on each geotechnical hazard zone. Thus, 1240 injection boreholes were opened over a total length of 1600 m, i.e.: 613 pre-treatment boreholes and 627 consolidation boreholes. The results of the monitoring tests show that the 0.7 cement grouting treatment contributed to a reduction in crack permeability to less than 5 Lu (Lugeon units), a reduction of over 94%. This confinement of the rock was confirmed by geophysical imagery whose signature at the fractured interval varied after treatment. Geophysical and geohydrological characterization through permeability testing and electrical tomography revealed the existence of highly permeable discontinuity zones (over 90 Lu) below the bedrock surface, up to 15 m wide. Notwithstanding the volume of drilling carried out, the results obtained support the use of the GIN method in the stabilization of foundations of structures in the granite-gneissic basement zone.