A surface depression in the northbound traffic lane of Middlebelt Road in Farmington Hills, Mich., eventually expanded and collapsed, leaving the Oakland County Water Resources Commissioner with an emergency repair situation. The sinkhole was located directly over a 35-ft deep, 36-in. sewer servicing central Oakland County. Nearby 300-psi and 90-psi gas transmission mains, water mains and other utilities continued to complicate the project.

NTH Consultants Ltd. determined the expanding sinkhole threatened failure and/or explosion of the 300-psi gas main, as well as the adjacent homes. Initial phases of the project included installation of a by-pass system pumping 26 cfs, stabilization of the ground and protection of the medium-pressure gas main. In addition to design data, a geotechnical investigation included an instrumentation program to monitor ground movements to protect the adjacent utilities and homes, as well as groundwater monitoring/consultation to protect adjacent residential wells exposed to sewage due to the break.

CCTV inspection revealed weepers and boils on the invert of the sewer resulting in soil fines being piped into the sewer. The remainder of the sewer was relined using CIPP after leaks were sealed. The failed section was repaired and remedial measures were performed to prevent future failures in the area.



Owner: Oakland County Water Resources Commissioner
Engineer: NTH Consultants Ltd.
Contractor: Aqua Group, IPR, Pacitto Forest Construction Co.

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