Installing liner pools using products such as butyl are relatively simple operations, providing that certain ‘rules’ are followed, especially on larger projects. As liner pools vary in size and scale, it is better to understand the requirements of larger schemes, then apply a standard ‘check-list’ as appropriate, to all installations.
Pre-design Site Appraisals – Check List
- Google Earth historic photographic survey undertaken to establish previous site conditions especially regarding tree removals and changes of ground levels?
- Topographical Survey, checking surrounding ground levels?
- Any SuDS compliance issues apparent, bearing in mind any local strategies?
- Hydrological Survey undertaken to establish likely ground-water movements across the site, both to and from the site location?
- Any Riparian Rights & Responsibilities surrounding the project including water run-off and ground water interruptions. Any ditches, culverts, streams etc identified?
- Planning permission required? (Any change of ground level more than 30cm requires permission. Is the site in a National Park or Restricted Development area?)
- Soil analysis undertaken to check for soil type/contamination?
- Has the excavated material been assessed for volume (including bulking factor, which varies by soil type) and including any surface material e.g. vegetation and rubbish?)
- Any trees or invasive shrubs within close proximity – especially willow and bamboo. (Some willows will colonise and disrupt liners externally by entering the water and growing on top of the liner. Bamboo roots will penetrate liners)
- Any animals likely to affect the liner – especially deer, cats/squirrels and moles?
- Logistics reference vehicle access/entrance to site, subjected to Method Statements?
- Any Banksman/road sweeping requirements. Risk Assessments conducted and scheduled?
- Site vehicle ground boards required (include in project preliminary costs) ?
Site Excavations – Check List
- Assuming all spoil remains on site – has an area been stripped of topsoil ready to receive the excavated spoil?
- Level pegs installed and checked for accuracy?
- Following excavation and ground formation – is the hole free of sharp objects/tree roots?
- Any sign of and underground land drains or drainage systems leading to or from the excavation?
- Depth of excavation satisfactory, bearing in mind any sharp sand lining. Is sand lining deemed necessary to prevent physical damage from potentially sharp objects?
- Any requirement assessed to prevent methane gas build-up (dependent of soil type) pipes to be installed under/within any sand layer?
- Any signs of ground water pressure likely to disrupt/lift the liner requiring drainage pipes to be installed under/within any sand layer?
Following excavation and shaping ………….
- Liner trench (to the top of the banks) or other method of securing the liner in place formed, cleared and ready to receive the liner? (See cross sectional drawing below for suggested method of installation)
- Geotextile or other membrane in place over any sand lining and ready to receive the liner?
- Do you have sufficient man-power and suitable lifting equipment on site to cope with the weight of the liner?
- Liner folding plan received with the delivery? (As folded and placed on a pallet at the factory)
- Orientation and placing of the liner pre-unwrapping clearly understood by everyone involved in unfolding the liner? It is very difficult to manoeuvre once unfolded.
- Once currently positioned, do you have sufficient soil in place to secure the liner at the boundaries?
- Ensure that any off-cuts are made cleanly, without tearing the liner, by having a suitably very sharp knife ready at all times.
- If required, add another layer of geotextile membrane over the liner, and cover with 100 – 150mm of clayey soil (especially if a wildlife pond) to disguise the liner and edging method.
- If required, instal lengths of black or brown rope secured firmly to pegs in the area beyond the pool as safety ropes especially on steeply sloping pool sides. These should not be obvious unless part of the design risk assessments. Drape the ropes on top of the clay lining at suitable intervals if deemed necessary as safety lines.
- Once the project is completed, avoid using any mechanical equipment e.g. rotovators near to the liner channel at the edges of the pool.
- If clay soil lined, take care if planting any shelves or upper regions, using hands only if possible. Plants to the bottom of the pool should be lowered and placed with ropes from the banks, or from a flat-bottomed boat to avoid damage to the liner.
- On completion, provide the client with a detailed cross-sectional drawing showing the composition of the project, underlining the importance of not using any sharp tools in future maintenance works.
SUMMARY
In summary, by following these guide lines and checking off each item will ensure that you are able to safely install a liner, correctly positioned to avoid attempting to realign a heavy material that may be easily damaged without due care and diligence.
A common problem when creating liner pools is to underestimate the amount of labour and time involved in following correct procedures in a safe manner.
Alan Sargent
Landscape Library Limited www.landscapelibrary.co.uk
