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SEL Environmental Ltd offer high quality, value-engineered solutions for stormwater management (SuDS) and contaminated land redevelopment throughout the UK and Europe |
| The Virtual Curtain Gas Migration System The virtual curtain is a no-dig gas migration interception system and can form a major element of the solution to satisfy a Part 2A determination. To date over 45,000m of virtual curtain vent nodes have been installed. The vent nodes are installed to intercept the pathway of ground gases and provide a new preferential pathway (route of least resistance) to atmosphere for these gases. The vent nodes are installed by vibro-inserting 'vent chimneys' up to 10m deep into the ground. These vent chimneys also introduce a zone of low pressure in to the surrounding ground which will attract ground gas to itself from both sides of the virtual curtain installation. Once within the virtual curtain system the ground gas will be diluted with fresh air to safe levels before dispersal to atmosphere via a vent bollard or vent stack. This is all achieved using passive ventilation technologies. Click for info on our dedicated vent bollard Click for info on our dedicated vent stack |
The virtual curtain wall is not an impermeable membrane and will not change the groundwater characteristics of a site. Groundwater will continue to act in the same manner avoiding any potential issues with flooding, water abstraction and settlement / heave. In respect of gas, it acts as both a pathway break and conduit for controlled and safe passive venting to atmosphere.
The virtual curtain is vented through purpose made hdpe steel stacks or bollards which have independant high and low-level vents. This creates a pressure differential and encourages gas migration to the virtual curtain and provides clean air for mixing / dilution and allows passive venting to atmosphere. The vent stacks and bollards can be be off-set from the virtual curtain proving even more flexibility for subsequent construction. Contaminants Virtual curtain systems are devised to mitigate ground gases such as: - Methane (CH4) - Carbon dioxide (CO2) - Carbon monoxide (CO) - Diesel range organics (DRO) - Petroleum range organics (PRO) - Volatile organic hydrocarbons (VOCs) Design & Installation The virtual curtain must be specifically designed for each site. Gas types, concentrations and flows are used to calculate the size and spacing of vent nodes that are driven into the ground using a method that minimises the amount of excavation required. Normally a virtual curtain system will displace appx. 0.05m3 of soil per linear metre. This is usually from the overlying inert material and can be regraded to suit original levels which means there are no arisings requiring off-site disposal. The individual nodes are connected to a geo-cellular collector duct system which is wrapped in a membrane. The duct system is located within a shallow trench which is backfilled on completion of the wall. The design will confirm the capacity, number and spacing of the above ground venting infrastructure. The system is virtually maintenance free and has been widely accepted by regulators all over the UK.
Further information can be found at www.virtual-curtain.com SEL also offer a hdpe vertical membrane gas migration barrier system, click here for more info. |
