66-Inch Steel Sewer River Crossing

Project Overview

A 66-inch diameter sewer line that is the primary influent line for the Clinton River Water Resource Recovery Facility crosses above the Clinton River in Pontiac, Michigan, as it enters the plant. During a 2015 video inspection of the sewer, which is constructed of carbon steel pipe above the river and of reinforced concrete elsewhere, Oakland County Water Resources Commissioner’s Office (OCWRC) staff observed cracks in the sewer at two locations in the middle span over the river. The OCWRC retained NTH to study the potential causes of, and suggest repair approaches for, the cracking. NTH used a variety of techniques to measure the existing geometry and conditions of the steel pipe in order to evaluate the pipe, which was constructed in the early 1960s, and be able to recommend appropriate immediate and long-term repairs. Subsequently, OCWRC engaged NTH to provide design services for a permanent repair of the steel pipe.

Project Scope

NTH developed an initial repair approach that OCWRC crews would be able to implement to reestablish closure of the pipe wall on the day following completion of our field exploration activities using the same crane that our staff used to access the middle span for the pipe measurement and testing and the surveying, thereby avoiding an additional mobilization charge for the crane. OCWRC staff installed patches over both cracks in a single work shift using NTH’s repair plan in order to complete an effective temporary repair that will last until a permanent repair can be constructed.

Client Benefit

NTH developed an initial repair approach that could be implemented by OCWRC crews using the same crane that was used for conducting the field exploration, saving OCWRC considerable time and money by not needing a second crane mobilization. NTH’s structural analysis of the steel pipe section allowed for a repair design that maintains service and avoids a very costly external bypass system.