We construct low permeability slurry walls for groundwater management and infrastructure protection.
Cutoff and barrier walls, also known as slurry walls, offer numerous benefits for subsurface groundwater management and infrastructure protection. These low-permeability barriers effectively contain groundwater, control contaminated groundwater hydraulically, and mitigate seepage through critical infrastructure such as levees and dams.
Slurry walls are versatile; they can divert water when placed upgradient, capture contamination when placed downgradient, or encircle and contain areas of concern. The construction process typically involves excavating a vertical trench under slurry (bentonite or biopolymer) and backfilling it with low-permeability or reactive materials. The success of slurry wall construction hinges on proper excavation, mixing, slurry and backfill preparation, as well as ensuring trench stability while avoiding damage to nearby structures.
Forgen has constructed over 110 million square feet of slurry cutoff walls, demonstrating our capability and experience in this industry. We offer comprehensive slurry wall services, including design assistance, and overall construction using various methods and materials tailored to specific site conditions and performance requirements.
Types of Cutoff & Barrier Walls
We excel at selecting the appropriate type of barrier walls based on site-specific conditions and project-specific requirements for strength and permeability.
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Soil-cement-bentonite slurry walls use bentonite slurry as support for excavation. Then, excavated or local soil is blended with bentonite and cement to create a low-permeability backfill with strength. These walls are ideal for scenarios requiring hydraulic containment and strength where excavated or local soils can be re-used.
They are used to control groundwater for sites requiring flood control, groundwater management, remediation and infrastructure protection.
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Cement-bentonite slurry walls are self-hardening slurry containing cement, bentonite, and other reagents, integrating the impermeability of bentonite with the strength and durability of cement. These walls are ideal for scenarios requiring both hydraulic containment and unconfined compressive strength.
We construct cement-bentonite walls using a slurry that self-hardens in the trench after excavation, ensuring safety and effectiveness in challenging soil conditions. Slag cement (ground granulated blast furnace slag, GGBFS) is often added to cement-bentonite (CB) slurry walls to enhance the wall’s properties and performance. These walls can offer effective containment for hazardous materials, preventing contaminant spread in groundwater, and can be tailored to meet specific project needs. Their adaptability and long-lasting performance make cement-bentonite walls a reliable choice for a variety of engineering challenges.
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A permeable reactive barrier (PRB) filters and treats contaminated groundwater below ground. This wall allows groundwater to flow through it, treating the water that passes through it. The reactive materials inside the wall treat and trap contaminants, making them less dangerous for the environment. We install the PRB down gradient, allowing the funneled groundwater to flow through the wall and react with the treatment media.
To build a PRB, we dig a long, narrow trench in the path of contaminated groundwater flow and fill it with reactive material such as zero-valent iron, limestone, carbon, or mulch. We design and construct PRBs to treat the impacted groundwater, reaching depths exceeding 75 feet by excavation.
Different reactive materials remove contaminants in various ways:
These mechanisms ensure that PRBs effectively treat contaminated groundwater, providing a safer environment.
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Biopolymer collection trenches function similarly to French drains by capturing groundwater on a project site for treatment. Biopolymer collection trenches are more cost-effective because they use slurry for support instead of trench boxes or other shoring methods, reducing both cost and schedule. These collection trenches can be combined with horizontal conveyance piping, extraction wells, sumps, lift stations, or other methods to capture freely draining groundwater efficiently.
In the construction of biopolymer collection trenches, Forgen uses engineered slurry made of biodegradable materials, such as guar gum, instead of bentonite slurry. This natural, high molecular weight material provides stability during the installation of collection trenches. Unlike traditional slurries, the biopolymer slurry does not form a filter cake on the side walls and naturally degrades to the viscosity of water once drainage media is placed.
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Construction Methods
Our extensive experience includes working in diverse weather conditions and challenging terrains, ensuring successful project execution under various circumstances. We manage complex scheduling requirements, including tight deadlines and round-the-clock operations to meet project goals efficiently. Our expertise allows us to adapt techniques to extreme temperatures, high moisture levels, and rocky landscapes, ensuring optimal performance.
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Clamshell trenching is a slurry wall construction method used for depths exceeding 90 feet. When using clamshell trenching, we consider the different rates of excavation between excavator and clamshell to ensure optimal operations. Forgen ensure trench stability by considering the weight of the crane into the work platform design and/or using different methods to increase trench stability. This method allows us to achieve greater depths while maintaining the structural integrity of the trench walls.
At Forgen, we have successfully employed clamshell trenching to dig walls in excess of 170 feet below the ground surface. In these projects, we initially use conventional trenching with an excavator to reach depths of 90 feet, and then switch to a clamshell attached to a crane for deeper excavation.
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The deep mixing method (DMM) of cutoff wall construction enhances soil strength and stiffness by mixing soil with stabilizing agents, such as cement, lime, or other binding materials. This technique forms a solid, durable wall or improves soil properties to prevent shear of embankment soils and control groundwater. DMM significantly improves the soil’s load-bearing capacity and reduces permeability, making it ideal for robust containment and support applications.
DMM walls are versatile and effective solutions for creating strong, stable barriers in challenging soil conditions. They are particularly effective in weak or loose soils, controlling groundwater flow, and stabilizing slopes. Their adaptability to various soil types and conditions, coupled with reduced disruption during construction, makes them suitable for both urban and remote projects.
At Forgen, we have extensive experience in both self-performing and managing DMM on projects ranging from tailings ponds management to levee seepage repair at depths of up to 135 feet below the ground surface. Our expertise ensures the successful application of DMM in a variety of settings, providing strong, stable, and reliable solutions for our clients.
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Cutter soil mixing enhances soil stability and strength by using a cutter head with counter-rotating wheels fixed onto the end of a Kelly bar to mix rectangular panels of soil. Cement slurry is injected through the cutter head as it cuts the surrounding soil. This method is effective in most soil types, with the option of adding specialized teeth for harder materials. Cutter soil mixing technology can reach depths of up to 150 feet below the ground surface.
At Forgen, we have extensive experience as a prime contractor managing cutter soil mixing scopes on environmental and flood control projects.
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Alternative Delivery
We specialize in delivering projects through alternative contracting methods, aiming to improve quality, reduce costs, enhance efficiency, and manage risks.
Our expertise in heavy civil, geotechnical construction, and environmental remediation allows us to provide innovative solutions with agility. Early stakeholder engagement ensures alignment of project goals, fostering transparency and accountability. By combining technical expertise with innovative problem-solving and strong client communication, we tailor our services to meet each project’s unique challenges, ensuring successful outcomes.
