Allen Park Tunnel
Upstream Storage and Conveyance Tunnel
NTH Consultants, Ltd. (NTH) provided geotechnical engineering and instrumentation investigation and design services followed by construction material testing and geotechnical instrumentation monitoring services for a proposed 96-inch inside diameter upstream storage and conveyance tunnel with pump station in Allen Park, MI. The existing system is over-whelmed during wet weather conditions causing untreated overflows into surrounding waterways and backups into residential basements. The existing sanitary system does not conform to the clean water act that the State of Michigan has required the City of Allen Park to be complaint with by 2018. To achieve compliance, a soft ground tunnel was to be constructed in close proximity to sensitive utilities and existing infrastructure.
NTH implemented an extensive geotechnical investigation including 12 testing borings and one rock core and completed Phase I and II environmental assessments. The information obtained was utilized to provide design guidelines that would be used to assist contractor related designs for temporary earth retention systems (TERS) and the tunnel. NTH designed and installed the geotechnical instrumentation monitoring plan and assisted WTA in preliminary design elements for TERS (both rigid and flexible systems) design requirements, primary and secondary tunnel liners, and construction specifications.
The NTH geotechnical monitoring program was comprised of inclinometers, tell-tales, monitoring point arrays, and deformation monitoring points. These instruments were used to monitor soil movement and utility settlement / heave from shaft, tunnel, and open-cut sewer construction activities.
The instrumentation program was vital to the success of the project since
construction activities were performed within the influence zone of a 54-inch diameter watermain and numerous fuel/oil pipelines all located adjacent to the I-94 expressway. During construction, the contractor experienced difficulties in controlling surface settlement and lateral soil displacement due to tunneling and shaft construction activities. The geotechnical instrumentation program allowed settlements to be closely monitored and timely adjustments implemented to mitigate further settlements and protect surrounding utilities and infrastructure.
As part of the construction administration team, NTH reviewed project submittals, provided construction inspection services, and performed construction material testing including laboratory testing.
NTH years of experience with soft ground tunnels and construction of TERS within soft clay proved to be an important asset to the construction of the Upstream Storage and Conveyance Tunnel. NTH provided recommendations to the contractor for ways to control settlement of existing utilities and the surface during tunneling. These recommendations were utilized by the contractor and settlement was decreased by almost 50 percent when passing directly under major underground utilities.