I&M Canal Aqueduct over Nettle Creek
This project features a single-span, 150’ long, post-tensioned CIP concrete aqueduct carrying I&M canal over Nettle Creek. It replaces an existing 100-year-old aqueduct that had recently collapsed and been decommissioned.
The New Aqueduct
Credit: JLK Architects
Credit: JLK Architects
Credit: EXP
The cross section of the new aqueduct consists of a 6’ deep, 20’ wide trough for the canal water, saddled by two post-tensioned 8’ x 8’ concrete beams. The post-tensioning was used to eliminate large long-term deflections caused by creep from heavy weight of the concrete and water. A middle pier was considered to limit deflection, however the client, IL Capital Development Board, did not prefer this option due to concerns about scour and debris build-up in the creek.
Design challenges included staged tensioning to prevent cracking in the anchorage zones. The anchorage zone also included unique rebar detailing to provide adequate confinement of the bursting stresses. Another challenge was preventing the superstructure from excessively prying on the 20’ tall abutments due to its anticipated long-term creep and shrinkage displacement. Large elastomeric pads were used to decouple the longitudinal movement of the superstructure from abutments.
Credit: EXP
Rebar dowels were placed at relatively close spaces between the trough and beams to transfer shear flow. This ensured that all components in the cross section would act together as one unified composite member. Waterproofing was placed along the inside faces of the trough to prevent water from seeping into the concrete. Each post-tensioning duct was filled with hot wax to provide long-term corrosion protection for the PT tendons. The wax also allows for tendon replacement in the future if needed.
Credit: EXP
