DERINER hydropower scheme – geotechnical issues related to the dam and HEPP construction

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Cane CEKEREVAC, Alexandre WOHNLICH, Philippe BELLWALD,
Abstract The Deriner hydropower scheme, which is still under construction, is located in the north-eastern Black sea region of Turkey. It is a part of Çoruh River regulation plan that will include 10 dams in total. It encompasses a 250 m high, double curvature arch dam with crest length of 720 m with all classic appurtenant structures and an underground powerhouse complex, which has been excavated on the right bank of the Çoruh River at a depth of approximately 100 m. Once completed, the Deriner hydropower scheme will have an installed production capacity of 670 MW.

The rock mass is mainly composed of two rock types: quartzdiorite and diabase, with a quite complex geological structure. Since the construction site covers a huge volume, the degree of weathering and the density of rock fractures change over the site and therefore affect the GSI-values attributed for the design of the various project items. In addition to that, presence of two major faults, named B-fault and C-fault have been observed, which led to some difficulties in relation to slope stability, dam foundation and overflow spillways excavations.

The paper addresses some geotechnical issues related to the construction of the Deriner dam and HEPP. Design considerations, follow-up on site during construction and rock stabilisation measures will be presented for the large open-air excavations in a highly fractured and weathered rock and for the underground powerhouse cavern, for which special attention to the rock support and structural wedge stability has been brought. Moreover, shallow excavations for the overflow spillways tunnels will be discussed. These present huge openings of 12 m in width and 18 m in height, with an overburden of approximately 20 m, for which numerical finite element analysis and structural discontinuity analysis have been performed to ensure safe excavation process and future operation.
Keywords: Highly fractured rock, Large open-air excavations, Numerical finite element analysis, Rock support, Weathered rock, Underground powerhouse cavern construction, Structural discontinuity analysis
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