The Manitowoc Containment Facility is an engineered structure designed to hold materials excavated during dredging activities in Manitowoc Harbor (Wisconsin). Confined Disposal Facilities (CDFs) like this one are one of the most widely used strategies for managing and containing dredge materials. Also known in some areas as Dredge Material Management Areas (DMMAs), these facilities require long-term maintenance to ensure the confinement dikes and drainage structures function as designed.
The materials contained within CDFs typically comprise a mix of unconsolidated soft sediments, organic silts, and compressible materials generated from years of dredging operations. For heavy equipment, these soft ground conditions translate to site access challenges for facility maintenance, dredge material handling/management, closure activities, and site redevelopment. The weak soils surrounding the Manitowoc Harbor were no different. Exhibiting a strength of less than 1% CBR, the soft soils were unable to support the repeated heavy loads required to keep up with dredging operations.
Presto Geosystems worked with the project team to provide a long-term, efficient solution for load support and site access.
SUSTAINABLE HAUL ROAD ON SOFT SOILS
The CDF site is part of the Manitowoc Lakeshore Birding Area, which includes Lake Michigan, the harbor, and the surrounding bluffs. Management is shared by the City of Manitowoc and the Woodland Dunes Nature Center. The containment facility, which is essentially an island situated along the Lake Michigan shore, has become an integral part of the physical landscape for both wildlife habitats and recreational activities.
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To shore up the soft soils and secure continuing dredge spoil disposal along this sensitive shoreline, additional support was provided the US Department of Interior Fish & Wildlife Services, the U.S. Army Corps of Engineers (USACE), and the Lakeshore Natural Resource Partnership.
Presto Geosystems worked closely with the US Army Corps to develop a sustainable solution to provide equipment access to the CDF and overcome the facility’s soft ground issues. The GEOWEB® 3D Soil Stabilization System was chosen for its exceptional load distribution, low maintenance, and cost-saving benefits.
Engineers designed a 36,000-square-foot haul road over soft soils using the geocellular system. Due to the low subgrade strength and anticipated heavy traffic patterns, a dual-layer of GEOWEB GW30V6 (6-inch-deep) reinforcement was required. An enhanced woven geotextile was installed on the prepared subgrade to provide separation and filtration. The geosynthetic system was filled with low-maintenance crushed aggregate.
As part of the complete GEOWEB system, ATRA® Keys were used to connect adjacent geocell panels. The key connection device significantly reduces contractor installation time while tripling the connection strength versus metal staples. It is also a corrosion-free connection that’s appropriate for marine environments and applications where the system will remain submerged below the groundwater table or subjected to cyclic wetting and drying due to seasonal variations.
Additionally, given the site’s location in an environmentally sensitive area, a low-impact solution was necessary. The system utilized not only provided load support structure but stormwater detention/retention through the aggregate infill material.
It’s an approach that can help reduce, or even eliminate, requirements and costs for on-site stormwater containment systems.
LOW-IMPACT DESIGN GETS RESULTS
Since the installation, the haul road has withstood repeated heavy traffic and significant rain events. Crews have operated 120-ton haul trucks and heavy tracked equipment over the geocell system without issue.
One of Wisconsin’s most popular birdwatching destinations, with more than 300 recorded species of birds—some nesting, others feeding or resting during migration—continues to thrive. Furthermore, the responsible management of the site means that someday, when the CDF is no longer needed, the site can be evaluated for beneficial reuse. These type of enhancements may include new development, additional green space, boat launches, recreational areas, and even new habitat for wildlife.
It’s an exemplary project, providing high impact for the clients but low impact on the environment.
For more information about Presto Geosystems’ engineering solutions, visit www.prestogeo.com.