Frequently Asked Questions

  • Whole of Life-Cycle solution
  • Environmentally friendly
  • Self-supporting arch systems
  • No blue-metal/gravel support required
  • No geotextile cloths required
  • Quick and easy to install
  • Simple capacity calculations
  • Designed to be serviced not buried
  • Run other services alongside arch systems
Tunnelwell® is located in Western Australia at corporate headquarters.
Tunnelwell® is wholly privately owned by Sentry Holdings Pty Ltd, ABN: 59 476 597 054.
No it cannot. Note: You should be aware that competitor systems which claim they can do this do not warrant that installation should they fail. The liability stays with the supplier/contractor who will be held fully liable for the collapse and all costs associated with that installation. Refer to competitor Warranty statements.
That is very simple. Tunnelwell® arches have been designed to hold their volume for each lineal metre of arch. No tricks, no hidden calculations or supplier spreadsheets to download in order for you to calculate required quantities. Example: a TW 1000 holds 1000 litres or 1.0m³ of effluent per lineal metre; TW 2000 holds 2000 litres or 2.0m³ of effluent per lineal metre Calculating some competitor systems you need to measure the volume of the stone/gravel support and calculate the 40% void claim as added storage for the volume arch measurement and then work out how much geotextile cloth you need and ALSO calculate how much soil the stone/gravel occupies to allow to remove that amount of soil off site. Using Tunnelwell®, all that soil goes back into the excavation – “Value engineering at its finest!”
You only remove the actual arch volumes and allow for a bulking factor which is 40% less than competitor arch systems using stone/gravel support - “Value engineering at its finest!”
The patented louvre/side wall orifice design has a formula called the “X” factor theory developed by Michael Wynne which negates the need for geotextile cloths because the angle of the louvre in the wall of the arch is set so not to allow and ingress of soil back into the arch chamber when backfill and or compaction is taking place.
The parabolic design of the arch is such that it has a much thicker wall thickness than competitor injection moulded products and is made from polyethylene and not polypropylene which has greater flexural properties than polypropylene. Tunnelwell’s unique design of the larger arch ribs which increase in width towards the base of the arch is what provides its strength with the addition of gussets as the foot/toe piece of the arch to strengthen these area load capacities. Each size of arch design has undergone structural engineering analysis and as well as finite element analysis (FEA) to verify these design capabilities. In addition to the theory, Tunnelwell® arches have been subjected to great physical testing to validate the FEA and structural calculations.
The steel pegs are there so that when backfill commences, the arches do not move and the base/side of the arch does not move inwards. Once the arch has been completely backfilled and compacted, the steel pegs are not required for any other purpose as the top load offsets the side wall loads balancing the earth and traffic load requirements. They are there to facilitate backfill only.
Tunnelwell® has had more than $1.5m spent of R & D to date. The directors are committed to being at the forefront of world’s best practise in engineering development and have also pledged to continue to allocate funding for continual R & D to keep up with technological and materials advancements in the future. An example of this is the research and development grant by Sentry and the Federal Government of Australia to engage with Deakin University’s, Institute for Frontier Materials to develop world’s best polymers so Sentry can design even larger, lighter and or stronger arch systems requested of Sentry by regulators, local governments and major civil and geotechnical engineers from around the world. That research grant will start in February 2018 and will continue until finished which is estimated to be approximately 1 year. This research will be directed by Russell Varley, PhD, Professor of Composite Materials and his team of scientists.
YES. Because of the unique design characteristics of Tunnelwell®, all services (third party) can be run adjacent or over the top of the arches, depending on cover requirements for both the services and Tunnelwell®. This also saves costs to developers and construction companies as it allows for common trenching principles to be adopted. Note: any services installed in or around a Tunnelwell® arch system must have the Tunnelwel®l design engineer’s approval as well as the services design engineers approval to be installed near the Tunnelwell® arch systems and the installation and backfill requirements of those third party services must comply and meet all services manufacturers installation requirements. Tunnelwell® does not accept any responsibility or claims whatsoever for any third party services installations within or around a Tunnelwell® arch system. Failure of third party services rests entirely with the services design engineers.
Top of arch inlet sizes are: 150mm and 225mm UPVC spigot connections. Smaller connections can be provided using reducing sockets such as 90mm and 100mm UPVC.
Flow rates for horizontal stormwater discharges into TunnelWell® arch system end caps should be:
  • ≤1.50msˉ¹ for 100mm pipes up to 300mm diameter; and
  • ≤1.00msˉ¹ for all pipes over 300mm diameter.
  These criteria may involve the installation of a deceleration chamber(s) depending on the inflow rates of the designed system catchment(s). Apparatus such as concrete liners* sized for appropriate catchment inflow with suitable lids or concrete liners*with baffles installed are an acceptable method for velocity reduction of inflow stormwater. * Denotes that concrete liners need to be adequately vented to allow for air relief to prevent any backpressure on the upstream catchment systems.   Flow rates for vertical stormwater discharges into TunnelWell® arch system arch crest inlets (pre-set at 150mm or 225mm NB) should be ≤1.00msˉ¹ for all pipe sizes. NOTE: All inflow discharges into Tunnelwell® arch systems must occur over a correctly sized “stormwater dispersion mat” and the length taking into consideration the discharge velocity rate for the distance that stormwater will travel before settling on the base of the arch system to avoid any scouring of the base material upon which the arches are laid. Note: Siphonic discharges are not permitted directly into Tunnelwell® arches whatsoever.
Confined Space Legislation and AS 2865 – 1195 Entering a Tunnelwell® arch system via an access arch section is dangerous and confined space regulations should be followed. The installer should procure third party confined space signs and fix them inside each cover and grate to warn personnel entering the chambers of that danger. Only qualified and certified holders of confined space certificates should enter a Tunnelwell® arch system. All required documentation and certified personnel should be on site when an entry is performed.
When rainwater runoff enters a Tunnelwell® arch system, the air inside the chambers needs to be displaced by venting each row of arches to atmosphere as is the case with any other well designed buried underground storage system.   Air relief provisions   All sealed rainwater chambers should be designed to allow air to expel from within the chamber to prevent any backpressure on the upstream discharge pipe systems connecting to the rainwater storage system. If access arch chambers are not designed into a Tunnelwell arch system, then vents should be incorporated using the pre-set holes in the top of each arch section to connect onto that opening provision and extend a 150mm pipe to the surface and provide a vented connection to the Tunnelwell® arch system – refer to Diagram 1 below. The number of vents should be established by the design engineer. If no engineer is engaged for the design or installation processes, provide at least 1 x 150mm air relief vent to each 30m3 of storage capacity provided or 1 x 225mm air relief vent to each 50m3 of storage capacity provided.
A Tunnelwell® arch system can be accessed by two methods:  
  1. Design in an access arch section to allow for human entry; or
  2. Provide inspection/access opening in the roof of the arches for cleaning and maintenance.
  Inspection or Cleaning Access   All buried rainwater chambers should be designed to allow for inspection/monitoring and or cleaning provisions. An inspection access should be incorporated using the pre-set holes in the top of each arch section to connect to that opening provision and extend a 225mm pipe to the surface and provide an inspection point to the Tunnelwell® arch system – refer to Diagram 2 below. The number of inspection points should be established by the design engineer. If no engineer is engaged for the design, provide at least 1 x 225mm inspection point to each 30 metres of arch chambers as a recommended minimum requirement.
Maintenance on Tunnelwell® arch system is very low.  
  • The only maintenance requirements are for grated covers and hold down bolt checks and perhaps replacement on galvanised grates should they become corroded or sheared off by third parties during installation.
  • Annually remove manhole covers and re-grease in accordance with manufacturer’s specifications and reset covers.
  • Inspect chambers annually for any compression from wheel loads and if found notify Tunnelwell® immediately so an engineer can come to site and check for any unknown issues.
  • Rake over bottom of chambers to turn over soils and remove hydrocarbons impregnated in the sand from roadways and carparks caused by brake pads and leaking oil from vehicles.
  • Check rainwater dispersion mat locations for any gouging and or degradation from constant water inflows. Replace as required.
  • Clear any debris that may have entered the chamber from infill flows of rainwater should no pre-treatment system have been installed prior to the Tunnelwell® arch system.
Compaction has to be in 200mm deep compacted layers and compaction has to be to 98% Modified Dry Density (MDD) ±2% from optimum moisture content or 8 blows to the foot/300mm for a PSP for backfills without cohesion. Each compacted layer of backfill has to be installed evenly on each side of the Tunnelwell® arch system prior to going to the next layer of back fill and compaction. Repeat this process until the crest of the arches is reached. Ensure that the compactor is kept a minimum of 100mm from the edge of the vibrating plate away from the arch side walls.   DO NOT install backfill using a front end loader or backhoe bucket directly over the top of the arches. Once the backfill has reached the top of the arches and access risers have been connected, backfill the next 200mm layer and compact over the whole surface of the arches. Lower the vibration intensity of the compactor when going over the actual crests of the arches as the compactor will tend to “bounce” slightly until the final 200mm layer of backfill and compaction is undertaken – minimum cover of 600mm of sand over the top of the arch. The PSP testing has to be done on the sides of the arches not right over the top of the arch. The offset from centre of the arch to the compaction test point is 600mm. See table below:  
Tunnelwell Arch Systems (TWAS) Compaction Regime
Cover over the arch Test Point - Offset or Centreline
Minimum cover – 600mm Offset from centreline of 600mm
600mm to 900mm Offset from centreline of 600mm
≥ 900mm to 2500mm Centreline
Yes. The 1m3 arch system has been approved by the Chief Health Officer of the Health Department of Western Australia. The infiltrative area rating from the Health Department is 2.53m²/m which is the highest rating ever provided. This means a significantly reduced foot print saving excavation, time and money on the installation. Tunnelwell has also been approved for NO-GEOTEXTILE cloth cover required.