The Manitowoc Containment Facility is an engineered structure designed to hold materials excavated during dredg- ing activities at the Manitowoc Harbor (Wisconsin). Confined Disposal Facilities (CDFs) like this remain a widely used strategy 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 struc- tures function as designed. The contained materials within CDFs typically comprise a mix of unconsolidated soft sediments, organic silts, and compressible materials generated from years of dredging operations. These soft-ground conditions translate to site access challenges for heavy equipment required for facility maintenance, dredge material handling/management, closure activities, and site redevelopment. The weak soils surrounding the Manitowoc Harbor were no different. Ex- hibiting a strength of less than 1 percent CBR, the soft soils could not support the repeated heavy loads required to keep up with dredging operations. Inherently Soft Soils Present Challenges for Equipment Access The CDF site is part of the Manitowoc Lakeshore Birding Area, which also includes Lake Michigan, the harbor, and the surrounding bluffs. The City of Manitowoc and the Woodland Dunes Nature Center work together to manage this en- vironmentally sensitive area. 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. To stabilize soft soils and utilize remaining CDF capacity along this sensitive shoreline, additional support was pro- vided by the US Department of Interior Fish & Wildlife Services, the US 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 cho- Engineers designed a 36,000-square-foot haul road over soft soils using the geocellular system. Due to the low sub- grade 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 filtra- tion. The construction crew filled the geosynthetic systemwith locally available low-maintenance crushed aggregate. As part of the complete GEOWEB system, ATRA® Keys were used to connect adjacent geocell panels. The ATRA Key Connection Device significantly reduces contractor installation time while tripling the connection strength versus metal staples. It is also a corrosion-free connection, making it appropriate for marine environments and applications where the systemwill remain submerged below the groundwater table or subjected to cyclic wetting and drying due to seasonal variations. Given the site’s location in an environmentally sensitive area, a low-impact solution was necessary. In addition to pro- viding a load-support structure, the GEOWEB system can also provide on-site stormwater detention/retention system through the use of the aggregate infill material. This approach that can help reduce, or even eliminate, requirements and costs for traditional 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 oper- ated 120-ton haul trucks and heavy tracked equipment over the geocell system without issue. sen for its exceptional load distribution, low maintenance, and cost-saving benefits. The GEOWEB® System Provides Sustainable, Low-Impact Solution for Haul Road Stabilizing Soft Soils at a Dredge Disposal Facility Using 3D Soil Confinement
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csengineermag.com
April 2021
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