Back River Outfall Interceptor Emergency Rehab

Project Scope

The Back River Outfall Interceptor (BROI) project involved rehabilitation of 1522 LF of a 132” x 147” inside diameter arched interceptor constructed in 1907 made of unreinforced concrete with a brick lining at the lower third. The downstream 200 LF section of the BROI was severely deteriorated due to the two 30” force mains (Easterly and Westerly FM) entering into the BROI at the crown, where a sinkhole from a deteriorated manhole had developed. Boyer performed the heavy debris removal and cleaning prior to starting the rehabilitation, removing 114 tons of silt and concrete debris, then hydro-blasting with 8-10K psi water pressure to get to stable and competent concrete. Once cleaned, a CCTV and 3D laser scan revealed a 56 LF long crack visible in the side and crown, a condition assessment was performed, and the engineered rehab design was provided. The Danby PL3E, 1” profile flat panels and curved corner panels were installed for the floor and transition to walls, then the floor and curved corners were grouted. Side and top rebar were installed according to the engineers' rehab design, then the 25’ long top Danby panels began. The top panels were grouted in 14 controlled lifts. The approved mix design was a blend of Portland cement, Type “F” Fly Ash, admixtures and water that met the Danby manufacturer's requirement of 5,000 psi minimum compressive strength in 28 days. Although some wet weather events did occur, Boyer was able to successfully rehabilitate the BROI with no major interruptions, allowing this project to be completed in 8 months.