Cope Construction is undertaking the civil site works as part of the large Co-Generation plant currently under construction in Sarnia. The project required that a 48” diameter cooling water outflow be connected to the existing 96’diameter sewer.

The location for the connection was constrained by various site issues and had to be made at an intersection with several existing underground services. The coffer dam was bounded on all four sides by existing services. Three large diameter pipes (96”, 78”
and 48” had to be maintained through the coffer dam at different elevations. The
contractor also had to excavate to approximately 9 metres below grade outside
of one wall of the cofferdam at one point during the installation.

Riggs Engineering designed a system incorporating steel sheet piles and H-piles with timber lagging to facilitate the existing piping. Active earth pressures were calculated using Rankine theory. Passive soil pressures were calculated using the modulus of sub-grade reaction. We carried out finite element analyses of the various stages of excavation and backfilling and designed all of the structural elements and connections.

The location of struts and reinforcing elements were selected in close consultation with the contractor to accommodate their concrete forming needs and to allow for excavation to
the specified depths.