Installation
Underground concrete rainwater tank installation
Correct site preparation and delivery access are essential to the successful installation and long-term performance of an underground concrete rainwater tank. Please review the following requirements with your plumber, builder or installer before delivery.
Delivery access and unloading
- Check delivery access with Ri-Industries before the tank is dispatched.
- A minimum height clearance of 8 metres is required when unloading.
- A clearance of 4.7 metres is required for the truck to pass beneath trees and overhead power lines.
- A minimum clearance of 4 metres is required between gate posts.
- Identify the position of underground drains, cables and other services before delivery.
- The unloading site must be level, firm and accessible.
- Ri-Industries trucks will not drive over concrete, sealed areas or foundations unless the required indemnity has been signed.
If you are uncertain about site access, contact Ri-Industries to discuss whether a site inspection is required.
Excavation and base preparation
- Over-excavate by 300mm on all sides to allow for backfilling.
- Prepare a flat, uniform base below the required tank level and backfill with 10–12mm gravel or screenings so the tank can be placed on a level base.
- Where the natural ground is extremely soft, over excavate by 200mm, compact 100mm of 50-75mm ballast into the surface and backfill to the required level with 10-12mm grave
- Ensure the gutter outlet is above the tank inlet and allows the required fall.
- Underground rain water tanks can be installed down to a maximum of 1750 mm below
the ground but this requires riser pipes to allow access at ground level and a heavy duty concrete cover.
Backfilling
- Use an approved granular material, such as sand, compacted in 150mm layers to 90% maximum dry density in accordance with AS 3798.
- Raise the backfill evenly around the tank, with a maximum backfill height differential of 400mm at any time.
- Where the tank is installed at greater depth, risers must provide access at ground level and the appropriate heavy-duty cover must be used.
After placement
- Ri-Industries advises that all underground tanks are filled at least 50%-75% with water in all chambers to stop floatation.
- Do not leave the tank empty for an extended period.
- Fill the tank with water after placement to provide stability while the surrounding backfill compacts.
- Keep access points clear and ensure the selected cover is appropriate for the installation area.
Important
Installation requirements can vary according to the tank, burial depth, ground conditions, traffic loads and site design. The plumber, builder or installer remains responsible for ensuring that the installation meets the applicable engineering and regulatory requirements.