Lois Lake Dam is a 59 m high double curvature arch dam with a crest length of 200 m and a thrust block supporting its right abutment. A gated intake is at the base of the dam’s body and its gate hoist steel tower is supported on the crest. A structurally independent spillway with six radial gates is on the right bank.

Klohn Crippen Berger (KCB) was retained by the dam owner, Evolugen (by Brookfield Renewable) in September 2019 to conduct a performance review of the dam and spillway structures and assess the seismic demand at the base of the hoist steel tower.

KCB used the Finite Element Analysis software LS-DYNA to analyze the dam foundation model, and hydrodynamic effects was applied to the upstream faces. Frictional contacts were used at the vertical contraction joints and the structure-foundation interface. Seismic records were implemented at the base of the foundation. Tied lateral foundation boundaries were used to ensure proper propagation of seismic waves.

KCB initiated the evaluation with a staged construction analysis, followed by normal and flood hydrostatic loads, and winter and summer thermal loads. We also performed dynamic earthquake and post-earthquake analyses, and developed design spectra at the base of the gate hoist tower.

As a result of this seismic performance study, KCB verified the strength and stability of the dam and the spillway for static and earthquake load cases. KCB also studied the influence of the analysis assumptions on the performance assessment.