Virtual Gas Curtain

Introduction to Virtual Gas Curtain Principles

The virtual gas curtain is an innovative ground gas remediation technology comprising a series of driven vent nodes that form a connected venting system. This system operates based on the forced dilution principle, creating a low-pressure zone that attracts and dilutes ground-borne gases to acceptable levels prior to venting. In doing so, it provides an effective pathway break for mitigating gas migration risks.

Unlike impermeable membranes, the virtual curtain wall does not interfere with the groundwater characteristics of a site. Groundwater continues to behave naturally, avoiding potential issues like flooding, water abstraction complications, settlement, or heave. Regarding gas, the system functions as both a pathway interruption and a controlled venting conduit, ensuring safe passive venting into the atmosphere.

The venting system relies on purpose-built stacks or bollards designed to exert a Venturi effect within the ground. This effect facilitates gas migration to the virtual curtain, introduces clean air for dilution to prevent odours, and enables passive venting to the atmosphere. These stacks and bollards are highly customisable—they can be crafted to resemble traditional urban street furniture and even offset from the curtain itself, offering unparalleled flexibility for site development projects.

Key Advantages of the Virtual Curtain Wall System:

Minimal Disruption: Does not alter groundwater flow or site hydrology.
Versatile Application: Functions as both a gas pathway break and a venting solution.
Customisable Design: Vent stacks can blend into urban environments, maintaining aesthetic considerations.
Development-Friendly: Can be offset to accommodate construction requirements.

Explore complementary soil processing techniques for preparing contaminated sites.

Learn how pump and treat systems integrate with gas mitigation solutions.

Contaminants Addressed by Virtual Gas Curtain Systems

The virtual curtain wall system effectively mitigates ground gases, including:

Methane (CH4)
Carbon Dioxide (CO2)
Carbon Monoxide (CO)

Design and Installation of Virtual Gas Curtain Systems

The design of a virtual curtain system is highly site-specific, considering factors such as gas types, concentrations, and flow rates. These parameters are critical for calculating the size and spacing of vent nodes.

Key Installation Steps:

Node Installation: Vent nodes are driven into the ground with minimal excavation.
Connection to Geo-Cellular Ducts: Nodes are connected to a geo-cellular collector duct system wrapped in a protective membrane.
Shallow Trench Construction: The duct system is installed in shallow trenches and backfilled upon completion.
Above-Ground Venting Infrastructure: Venting bollards or stacks are installed based on calculated capacity, spacing, and design preferences.

This system is virtually maintenance-free and has gained widespread approval from UK regulators for its efficiency and minimal disruption.

Learn about stabilisation and solidification techniques that can further mitigate site risks.

Example: Virtual Curtain Wall Installation

Project Overview:

VertaseFLI was commissioned to design and construct a virtual gas curtain wall to prevent gas migration from a landfill into a proposed residential development. The site posed unique challenges:

Contaminated Soils: Exporting soils would have incurred high disposal costs.
Groundwater Monitoring: Maintaining the groundwater regime was critical under local Part 2A obligations.
Public Perception: The client wanted to avoid sterilising parts of the site while addressing community concerns.

Solution:

VertaseFLI successfully designed and installed a 690m long and 6.5m deep virtual curtain wall. The system achieved the following:

Prevented the generation of contaminated soil.
Maintained the existing groundwater regime.
Enabled residential development to proceed.

Customisation:

To minimise visual intrusion, the client specified aesthetic stainless steel bollards, which were installed at calculated intervals. Some bollards were offset to allow for internal road construction, demonstrating the system’s flexibility and adaptability.

Advantages and Limitations of Virtual Gas Curtains

Advantages:

Provides gas pathway breaks while allowing for passive venting to the atmosphere.
Avoids altering groundwater flow, ensuring compliance with hydrological requirements.
Low-maintenance system with proven effectiveness on UK sites.
Bollards and vent stacks can be customised to blend into urban environments.
Flexible installation options support site development needs.

Limitations:

Requires detailed site-specific design and engineering.
Not suitable for sites with complex contaminant mixtures beyond gases.
Installation may be limited by subsurface access constraints.

Learn how pump and treat systems integrate with gas mitigation solutions for comprehensive remediation.

All works exceeded all expectations of our QHSE Team. Would highly recommend VertaseFLI for all ground remediation works for the future.

Louie Sharp

Civil Engineer, Vistry Northern Home Counties

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