Predicted and measured stresses and displacements around the Darlington intake tunnel

The C.W. Intake Tunnel of the Darlington Nuclear Station is D-shaped in section with a span of 8 m and a length of 925 m beneath Lake Ontario. The tunnel is located in a horizontally bedded limestone with variable shaly interbeds. The geotechnical investigation including in-situ rock stress measurements, and laboratory determination of strength and deformation properties as well as time-dependent behaviour are reported. Design of the tunnel, in particular provisions for rock squeeze, is described in detail. To verify the design approach adopted and the provisions made, field instrumentation was performed during excavation of the tunnel. The results of field measurements of stresses and displacements were compared with premonitoring analysis. Postmonitoring analyses were also performed using the as-constructed condition. It is shown that the performance of the tunnel is in general agreement with the predicted behaviour in both short and long term conditions