Hydro Québec’s 520 MW Toulnustouc Hydroelectric Project is located on the Toulnustouc river approximately 150 km north of the city of Baie-Comeau, Québec, Canada (Figure 1).

Construction started in 2001 and the power plant was commissioned in 2005. The project includes:

– a 77 m high concrete-face dam and a 45 m high nearby cut-off dike;

– a 10 km long, 13 m 11 m unlined pressure tunnel operating under a maximum static head of 183 m;

– a 138 m long, 8 m diameter steel lined pressure penstock;

– a 526 MW surface powerhouse with two Francis units;

ABSTRACT: The Hydro-Québec Toulnustouc Hydroelectric Project was commissioned in July 2005. The 520 MW surface powerhouse includes a 10 km long, 13 m 11 m unlined pressure tunnel operating under a maximum static head of 183 m. The tunnel was excavated using drill and blast techniques in a good quality, gneissic rock mass of Precambrian age. The paper describes the testing and the results for 117 hydro-jacking tests performed in the tunnel at two separate locations. For the first test zone, 41 tests were done near the powerhouse to optimize the steel liner length. In the second test zone, 76 tests were done some 3 km upstream from the powerhouse, in a zone where the river valley is close to the tunnel alignment and rock cover is reduced. For both sites, test results locally indicate minimum confining stresses lower than the water pressure in the tunnel. The measured values were also lower than the stress predicted by topographic rock cover criteria. On the basis of the test results, the steel liner was extended to reach a zone having adequate measured minimum confining stresses. For the other test site, a surface drainage solution was implemented in order to limit the extension of potential hydro jacking phenomena and also to preclude high pore pressure and seepage reaching surface and destabilizing the overburden located above the tunnel. The tunnel was filled in March 2005 and has performed very satisfactorily since then, with acceptable water losses.