Award of Merit: Water Structures Category
Preventative Repairs to a Large Diameter Interceptor Sewer
Submitted by NTH Consultants, Ltd.
Detroit Water and
NTH Consultants, Ltd.
Kerneos Aluminate Technologies
XYPEX Chemical Corporation
Mt. Morris, Michigan
The Macomb Sewer System was constructed by the Detroit Water and Sewerage Department (DWSD) in the early 1970s. Since that time, the system has experienced deterioration of the concrete liner due to hydrogen sulfide and ground movements. The sewer was inspected and areas were identified that required repair. Sewer inspections were done using man entry, CCTV inspections, geophysical multiple analysis of surface waves (MASW) methods, and test borings in isolated areas, and identified several reaches that required immediate repair.
Repair methods were designed that included grouting behind the liner in suspected loose soil areas, chemical grouting in leaking areas, and shotcreting using conventional and calcium aluminate materials.
A major design challenge was managing flow in the sewer to allow physical access to perform the repairs. Flow quantities, operation methods, and acceptable working conditions were identified to develop a flow control sequence. This included shutting down pumping stations on a temporary basis, operating existing flow control gates, and construction of flow control weirs within the sewer. A platform was constructed within the sewer to allow work to continue over flow. To control flow from one branch of the system, a large flow control structure was designed that included a drilled secant pier temporary earth retention system, groundwater dewatering, a cast-in-place concrete structure, and installation of a flow control gate. Given the urban location of the structure, support of an existing adjacent five-lane roadway, utility relocations, and traffic control were significant design aspects.