The Kichi Sipi Bridge, as part of Manitoba’s Northern Development Strategy, represents an investment in both transportation infrastructure in the region and in the well-being of the Pimicikamak Cree Nation and Cross Lake communities. The Kichi Sipi Bridge is a 260 metre long, four-span structure with an innovative concrete foundation system supporting steel plate girders and a composite concrete deck. The Kichi Sipi, which means “Great River” in Cree, replaces temporary, seasonal ferry service and a winter ice road across the Nelson River on PR 374 to provide year-round access to the remote northern Manitoba community. The project provided many challenges, including the remote location, high cost of construction, and degree of difficulty of the site. Water depths reach up to 20 metres, the bedrock is a very hard basalt/granite with sudden elevation changes, and the ice is up to 1 metre thick with a high crushing strength. These factors result in a tremendous load on the tall piers, and a conventionally constructed foundation system would have added enormous cost to the project. A unique foundation system was developed to minimize the effect of the ice loads. The foundation system also reduced risk during construction and the initial capital cost of the project. Each pier consists of a group of six relatively small diameter battered rock-socketed concrete caissons that extend into the bedrock, and are tied together with a submerged pile cap. The pile cap supports a narrow, sloped pier shaft, which results in minimal ice contact area with the piers and greatly reduced loads. The system provides stable foundations, reduced time and costs for drilling smaller caissons, and reduced concrete quantities and costs. In addition, the system provided redundancy and enhanced constructability. The foundation system required innovative construction techniques that were investigated during the design phase to ensure constructability. This included the use of a steel-tub form, which acted as both the caisson template and the submerged cofferdam. Cost and schedule dictated that coring the caissons for quality assurance was impractical. As a result Crosshole Sonic Logging (CSL), a non-destructive testing method, was specified. During construction this method identified a major defect near the bottom of one caisson. A repair method was developed to adequately restore the caisson capacity and to allow the repair to proceed while construction of the substructure and placement of the girders continued above. Significant knowledge was gained on the Kichi Sipi Bridge project through the success of several design and construction innovations, as well as through the remediation of the defective caisson. Recommendations and lessons learned include the following: (1.) Redundancy for high risk elements is critical. With the innovative foundation design developed, redundancy reduced risk and allowed for the defective caisson to be remediated without delaying the project schedule. (2.) Submission of specific tremie concrete procedures by the Contractor should be made a requirement, even if detailed specifications are provided by the Owner. (3.) On this project the only locally available aggregate source was the rock blasted and crushed for the project, however it would have been beneficial to import smooth aggregate specifically for the caisson concrete to provide a more pumpable mix. (4.) CSL testing was very effective in identifying a major caisson defect and provided sufficient information to allow acceptance of the final repair. (5.) The use of hydrodemolition to remove poor concrete in a submerged condition was ineffective on this project. (6.) Grouting the defective concrete with preplaced aggregate in a tremie condition proved to be highly successful as evidenced by above-ground trials, coring and final CSL testing. In conclusion, despite the many challenges encountered, this project was completed successfully, within the project budget, and the bridge was opened ahead of schedule.
Thank you to our Premier Sponsors
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