DWSD Primary Clarifiers #17 and #18
Geotechnical, Environmental and Field Engineering
To comply with state requirements, the Detroit Water and Sewerage Department (DWSD) commissioned the design and construction of new primary clarifier capacity at the Detroit Wastewater Treatment Plant. The project was awarded to Malcolm Pirnie, Inc. in 1998. NTH was a major subconsultant to Malcolm Pirnie providing geotechnical engineering and related field engineering services.
NTH performed the geotechnical investigation to gather design data for these structures, including assembly of historical subsurface information for adjacent projects, and performing additional test borings. We installed open-stand pipe piezometers in some test borings to measure artesian groundwater pressure in the hardpan and bedrock beneath the site to address this potential site challenge.
NTH conducted an environmental sampling program to characterize the soils that would be excavated. We completed ash and soil sampling, analytical testing, evaluation of worker safety issues, and evaluation of disposal options.
The design included two 250-foot diameter clarifiers, influent tunnels, sinking caisson shafts, and other underground structures. NTH designed an extensive construction staging plan to include acceptable factors of safety and to minimize impacts on existing structures and completed aspects of the work. Geotechnical instrumentation was specified to monitor soil and structure movement during construction. NTH used finite element analysis to analyze construction impacts on a portion of an existing tunnel, and then designed a reinforcement system using that data.
Construction is ongoing. NTH provided field engineering for underground construction including submittal review, construction claim review assistance, and as needed design services. NTH performed a condition survey and evaluation of a major primary influent tunnel while it was dewatered as part of the construction and found several large cracks that required repair. NTH designed the repair system, prepared plans and specifications, and provided the field engineering during the repair.
NTH reviewed geotechnical instrumentation data daily to evaluate the design and contractor operations. Changes to the construction procedures were made, allowing the contractor to be more aggressive in some areas, saving construction schedule and budget.