Since the recent sinkhole news, many have asked not only how these sinkholes happen, but what can be done to avoid them in the first place. NTH recently won two awards for their work on the Oakland-Macomb Interceptor Drain Repair Program. The following is an account of this project and how NTH conducted investigations to try to find potential failure areas.
Innovation & Excellence Award:
Michigan Association of County Drain Commissions (MACDC)
Award of Merit for Engineering:
In August 2004 a developing sinkhole was encountered at the intersection of Fontana Drive and 15 Mile Road in the City of Sterling Heights over the Romeo Arm of the Detroit Water and Sewerage Department’s (DWSD) Oakland Macomb Interceptor System (OMIS). As the emergency repair work continued to restore the affected roads and subsurface infrastructure, another question was being raised, “How can we find and prevent future sinkholes.”
The interceptor that caused the sinkhole has an inside diameter of 11 feet and was located approximately 62 feet below the ground surface. Based on NTH research, the use of Multi-Channel Analysis of Surface Waves (MASW), a geophysical technique that uses seismic waves to determine subsurface conditions, was selected to initiate the search for potential failure areas. Following the restoration of the 2004 sinkhole collapse, MASW was used in conjunction with closed circuit television to inspect the balance of the Romeo Arm interceptor.
The geotechnical exploration confirmed the presence of disturbed soils and potential voids that were subsequently stabilized from inside the interceptor. Based on the initial findings and correlation between the MASW results and loose soils and voids surrounding the tunnel, NTH was tasked by DWSD to investigate the balance of the OMIS, including the Edison Corridor Interceptor (ECI), Oakland Arm Interceptor (OAI), and the Avon Arm Interceptor (AAI).
The investigation report identified the need to complete the geotechnical work and recommended a series of repairs. Ownership of the ECI, OAI, and AAI was later transferred to a Chapter 21 Inter-County Drain managed by the Oakland-Macomb Interceptor Drainage Board.
Based upon our knowledge of the conditions in the new Oakland-Macomb Interceptor Drain, a project team headed by NTH was selected to provide engineering services based on the compiled recommended repairs for the EEI and the OAI/AAI from the January 2008 reports. These reports also recommended performing a geotechnical investigation of identified anomalies and a MASW survey of the downstream portion of the OAI be completed.