Mark Halsall, National Manager – Storm Water Control at ACO Water Management, looks at five of the most common issues and misconceptions when specifying and installing geocellular structures.
Geocellular structures are an integral part of managing rainwater on site. However, despite this critical role, there remain a number of pervasive misunderstandings surrounding their specification and installation, which can have a damaging impact on their efficacy.
1. Assess the conditions
When it comes to specifying drainage solutions, there is a tendency towards focusing solely on the impact of rainwater and determining the volume of storage required. While this is undeniably a crucial factor when designing geocellular structures, there must also be consideration of other factors, such as loadings on the tank.
It is important for ground conditions to be confirmed, such as the type of soil or whether ground water is present, as well as understanding what types of vehicles are going to traffic the structure, both during and post installation. Understanding these factors will allow consultants, contractors and suppliers to accurately offer the most appropriate solution.
2. Correct installation
Not all geocellular structures are installed in the same way and understanding how and why specific products are most effectively built will ensure attenuation performs at the level it needs to. Often, crates are simply put into the ground individually and then clipped together, but some products can benefit from a more thorough installation technique.
ACO StormBrixx, for example, offers superior stability thanks to its patented brick-bonding and cross bonding structure. Although it can be fitted in the traditional way, the long-term benefits and improved construction speed associated with brick-bonding is something that contractors should be conscious of during installation.
3. Excavation size
A common error which can really hamper installation times is failing to excavate a large enough area to install the tank. Suitable working space needs to be created around the footprint of the geocellular system, and safe access/egress should be accounted for through a suitably stepped excavation, or alternative excavation shoring methods.
For example, if the structure requires a 12m2 space, then the excavation site must be slightly larger than this to allow for installation and maintenance. Adequate space must be left around the edge of the structure to allow personnel to fit side panels or install the membrane.
4. Excavation base
The base of an excavation should be sufficiently compacted and stable enough to ensure the geocellular structures remain in place. When doing so consider the California bearing ratio (CBR), which reflects the mechanical strength of the soil and therefore the integrity of the system. A low CBR will flex under weight and sink, so it is critical that contractors achieve a high CBR to provide a steady base to build their tank on.
5. Fit and forget
This is an issue across all types of drainage, but it can be particularly prevalent with attenuation tanks Far-too-often, they are installed and then rarely, revisited. Guidance documentation exists to provide an indication of how often they should be maintained and emptied, and contractors should ensure they are routinely checking the drainage systems.
When you consider that products such as ACO StormBrixx contain accessibility features, specifically to facilitate more straightforward maintenance, this is something that needs to be addressed.
For further information on ACO StormBrixx visit https://www.aco.co.uk/products/stormbrixx/
Geocellular structures are a powerful tool in managing water on a site, but they are only as effective as those installing them. To help contractors get to grips with the key installation, specification, and maintenance issues associated with geocellular structures, ACO Water Management has created a free CPD. For more information and to sign up visit https://app.livestorm.co/aco-technologies/geocellular-structures-design-specification-and-maintenance
