Staged Reconstruction Of A Major Interceptor Without Service Interruption

Rehabilitation Of The Oakland Macomb Interceptor Drain
By Harry Price, Fritz Klingler and Mike McMahon | November 2012, Vol. 67, No. 11
Shaft Number 6, north side of flume installed

Inspections conducted by NTH in 2006 through 2009 included extensive CCTV surveys, man-entry inspections and Multiple Analysis of Surface Waves (MASW) studies to identify loosened soil areas and potential voids. The inspections revealed significant and widespread deterioration, microbially induced corrosion and loss of ground through cracks in the monolithic concrete sewer liner. The conditions resulted in a range of recommended repair options including chemical grout injection to stop active leaks, epoxy repair of fractures, void grouting with cementitious grout, shotcrete lining repair and Xypex treatment of minor deteriorated areas.

Flow control

Due to high flows in the interceptor, an extensive flow control plan was developed to allow entry to the sewer to conduct the repairs. The developed flow control program involves installation of four new flow control gates and a new dewatering pump station, as well as utilization of three existing gates and an existing pumping station. The flow control plan was designed to accomplish in-system storage of flow to allow access of all of the deteriorated sections of the sewer, for repair periods ranging from six to 15 hours. Depending on the area of the sewer to be accessed and the repair period, the system will store up to about 45 million gallons which will be released between subsequent storage/repair periods.

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To solve the difficulty of operating and monitoring gates located miles apart, the owner and design team have designed an innovative system of remotely operated sluice gates that can be monitored and controlled through a SCADA system. Design for installation of the flow control gates was complicated by a number of factors, including limited right-of-way for some of the structures, poor soil conditions, high groundwater and the fact that three of the structures were to be installed directly below high-voltage power lines supplying most of the population in the area and to the north. In addition, live-tapping and fluming of the existing flow during the shaft installation was a major challenge. These flow control structures were constructed under Segment 1 of the OMID reconstruction.