Project At-a-Glance
- Approximately 10,000 feet of 36-inch diameter wastewater interceptor
- The alignment runs beneath mixed residential, commercial, and industrial property with ground contamination
- Crossing beneath the Fox River via HDD
- Drill and Blast, Microtunneling and conventional open cut construction methodologies
- 70-ft deep secant pile-supported shafts
- Ground challenges included cobbles, boulders, dolomite with chert nodules, and high hydraulic conductivity
Project Narrative
The City of Waukesha saw an opportunity to upgrade their aging wastewater infrastructure by converting the existing Greenmeadow Forcemain Sewer into a gravity-flow system, a solution that eliminates the long-term operating, maintenance, and replacement costs of the deteriorating force main and two pump stations. Brierley and its partner, Donohue & Associates, Inc., performed the geotechnical investigation and designed the replacement gravity interceptor comprising about 10,000 feet of 36-inch diameter gravity conveyance. Challenging conditions were encountered including glacial till containing large cobbles and boulders; zones of high hydraulic conductivity; hard dolomite with chert nodules; and contaminated soil from previous industrial activities.
Given the dense residential area and concerns about contaminated ground conditions, tunneling, trenchless, and over 7,000-ft of open-cut techniques were incorporated into the final design to enhance project efficiency and reduce project costs.
Due to adverse soft ground conditions, our team designed a 2,300-ft of 72-in diameter microtunnel, within cherty dolomite, to host a 36-in diameter Hobas carrier pipe. This required three shafts located in residential areas ranging from 6 to 23-ft in diameter and approximately 70-ft deep. The terminal ends of the microtunneled section connect to the open-cut pipe segment ranging from 15- to 40-ft in-depth in glacial clays, tills, and outwash soils. Approximately 500-LF of the deep open-cut was completed in saturated sands and required extensive dewatering and staged excavation.
Horizontal Directional Drilling (HDD) was the selected means to install 600-ft of 18-in diameter HDPE pipe to construct a dual siphon structure to cross beneath: a recreational trail, an active rail line, and the Fox River. The HDD alignment was challenged by not only a tight radius geometry and complex ground conditions, but also ground contaminants associated with an adjacent inactive manufacturing site.
Brierley also provided construction phase engineering services and monitoring.
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