Aging hydraulic infrastructure across North America is increasingly affected by concrete deterioration while remaining constrained by limited outage windows and challenging underwater access. This paper presents a case study on the rehabilitation of submerged diffuser (manifold) structures in a high-lift navigation lock dam on the U.S. side of the St. Lawrence Seaway that has been in service since 1959. Diffuser structures are critical components of the lock emptying system, functioning as hydraulic energy dissipators that distribute large volumes of water through multiple ports within minutes. Their performance directly influences lockage time and vessel safety under turbulence-induced forces.
After nearly six decades of operation, the original cast-in-place diffuser components experienced significant deterioration due to aging, operational demands, and environmental exposure. In addition, their compact arrangement and short annual winter shutdown periods restrict using typical construction methods. To address the tight dewatering schedule and constructability constraints, a segmental precast and post-tensioned replacement strategy was developed. However, transferring high static and dynamic loads from the precast diffuser segments to the existing concrete foundation within very limited geometric clearances posed significant design challenges, requiring specialized connection detailing and post-tensioning to ensure structural integrity.
Nonlinear finite element analyses were conducted to evaluate load transfer mechanisms, governing failure modes, and system performance under transient hydraulic pressures during lock emptying. Challenges associated with the parametric design of diffuser segments and connections, as well as construction constraints during a nine-week shutdown period, are presented and discussed. The findings provide insight into the structural behaviour and constructability of precast, post-tensioned systems for the rehabilitation and replacement of aging hydraulic structures within limited construction windows.
