To handle the growth of Markham and Pickering in Southern Ontario, a trunk sewer was contracted to accommodate the additional sanitary sewer flows projected from the future growth. The trunk sewer is about 8.7 miles long. The sewer is to be built at depths of 16 feet to more than 131 feet below the ground surface.
Doka supplied the custom benching formwork for 13 ventilation shafts in total, ranging between 32- and 197-foot depths. The custom formwork panels allowed Strabag, the contractor, to pour the U-shaped benching at the bottom of each ventilation shaft connecting the newly drilled tunnel openings with each other.
These custom formwork panels were based on Doka’s Large Area Formwork Top 50, including wooden gussets and custom splices. The formwork was particularly suitable for forming concrete that has to meet stringent specifications regarding its surface finish. Each formwork element was hand-built and assembled to the highest possible standards.
A major challenge was ensuring that the pipeline stayed within the Newmarket Till soil stratum, which is more conducive material for tunnel construction. To do so, a substantial drop in elevation of the pipeline over its length was needed. Using an Earth Pressure Balance Machine as a tunnel boring machine allowed for different modes of operation to accommodate the changing soils conditions.
The town of Markham required the use of Zemdrain, a form liner to be installed on every formwork element before a concrete pour. Zemdrain is a formliner that reduces the porosity of the concrete surface, thereby increasing the structure's durability. Doka’s custom formwork panels were epoxy-coated during assembly and shipped to the site ready to use. The achieved concrete finish was as anticipated when using Zemdrain.