• Greater than a 50-year Life Cycle performance product

• Environmentally friendly

• Self-supporting arch system

• Quick and easy to install

• Simple capacity calculations

• Run other services alongside arch systems

and

• No crushed rock support required

• No geotextile fabric required

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The 50-year claim: Most plastic storage systems advertise a 50-year product life; that is, the plastic will last for 50 years or more when buried underground. Manufacturers use this as their warranty claim. However, this does not mean they are warranting the long-term infiltration performance of the system for 50 years.

Performance Life cycle difference: It is now widely acknowledged that storage systems using geotextile fabrics will eventually block up or become heavily clogged over time by impurities which enter the storage systems. Impurities from roads such as hydrocarbons, brake pad debris, oil film washed in from roads, carparks or hardstand areas and the like. Other impurities such as fine particles carried in the stormwater from point of collection and worst of all, the “fines” found in the crushed rock used to provide structural strength to all current competitor arch storage systems on the market today. All these factors and impurities eventually block the geotextile fabric over time. The timelines for blocking vary from system to system, but generally between 9 and 20 years these systems using geotextile fabrics become attenuation tanks, not infiltration tanks, and are no longer effective and need to be retrofitted. The geotextile fabric cannot be cleaned or reinstated to its original condition while buried underground.

Tunnelwell® was designed from the outset to eliminate the use of geotextile screening fabrics. Instead, the novel integrated side wall louvre system infiltrates stormwater laterally from the arch chamber as well as horizontally through the base, meaning it does not block. A Tunnelwell® system will require periodic maintenance where a simple mechanical rake is sent down tunnels to break up hydrocarbon films over the sand base to ensure a >50-year lifecycle.

Also see: What maintenance needs to be done on a Tunnelwell® Arch System?

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You can purchase direct from Tunnelwell®. Contact us

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We do not advise this installation configuration and do not warrant it.

Many other systems on the market do claim they can be stacked, but do not warrant that installation should they fail. The liability will stay with the buyer/contractor/design engineer who would likely be held fully liable for the collapse and all costs associated with that installation. Warranty statements can be found on most product data sheets.

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That is very simple. Tunnelwell® arches have been designed to hold their volume for each lineal metre of arch.

Example: a TW 1000 arch holds and infiltrates 1000 litres or 1.0m³ of effluent per lineal metre.

We provide a basic product calculator to assist with system design. This is available to download from the Resources section of our website once you have signed up to access it.

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The Tunnelwell® Arch System will retain its performance proficiency 50 years or longer and is 25% more efficient than other competitor infiltration systems. The degradation in filtering characteristics of geotextile fabrics buried underground is becoming apparent. Since the early 2000’s plastic storage systems started to become mainstream in engineering design, but few considerations had been given to the longevity these systems would provide to end users who may inherit that design/development.

Local governments are now retrofitting systems which employ geotextile fabrics from anywhere between 10-16 years later depending on the type of system initially specified and installed. The average time between and installation and a retrofit is around 10-16 years and sometimes maybe 20 years. However, the screening fabric cannot be reinstated to its original condition without removing and replacing it. While the plastic arches or crates are themselves re-usable, the retrofit is effectively a new install.

Cost Implications: The cost of excavating a system, re-clothing it with geotextile fabric and re-installing it is considerable; estimated to be approximately twice the initial install costs each time. If a system were to be fitted, retrofitted and retrofitted again within a 50 year period, this could equate to twenty times the original cost of installation.

Note: Restoration costs such as resurfacing carparks or re-landscaping costs in addition to the above statement.

Installing Tunnelwell® is a once only install for the 50 year period and while it does need to be maintained like any other piece of infrastructure, Tunnelwell® has been designed to be serviced, not buried™

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You only remove the actual arch volumes and allow for a bulking factor, which is 40% less than competitor arch systems using crushed rock support.

Most other arch systems require you to measure the volume of the crushed rock 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 what volume the cruched rock occupies to allow to remove that amount of soil off site.

 Using Tunnelwell®, all that soil goes back into the excavation.

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The patented louvre/side wall orifice design has a formula called the “X” factor theory, developed by Tunnelwell® founder Michael Wynne which negates the need for geotextile fabric because the angle of the louvre in the wall of the arch is set so as not to allow ingress of soil back into the arch chamber when backfill or compaction is taking place.

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All other arch systems on the market today require crushed rock backfill. This is what provides the structural support for the arch void. The arch itself does not do this. Tunnewell® is different; it was designed from the outset to be self supporting.

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. Polyethylene 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 load capacities of these areas.

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.

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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 no longer perform any function as the top load offsets the side wall loads balancing the earth and traffic load requirements. They are there to facilitate backfill only.

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Yes. Because of the unique design characteristics of Tunnelwell®, all services (third party) can be run adjacent at 600mm from the side of the bottom edge/base of the arch or over the top of the arches at 90° to the arch system, depending on cover requirements for both the services and Tunnelwell®. If proper coordination between contractors is organised such as electrical contractors and civil contractors, electrical conduits (cover requirements must be observed) can be run at any angles across the top of the arches provided final backfill by civil contractor has not occurred and the civil contractor agrees to undertake final backfill and compaction processes.

Note: any services installed in or around a Tunnelwell® Arch System must have the Tunnelwell® design engineer’s approval as well as the services design engineer’s approval to be installed near the Tunnelwell® Arch Systems. The installation and backfill requirements of those third-party services must comply with Tunnelwell® installation instructions and meet all services manufacturer’s installation requirements.

Tunnelwell® does not accept any responsibility or claims whatsoever for any arch failures related to any third-party services installations within or around a Tunnelwell® arch system. Responsibility for third-party services rests entirely with the project services design engineers.

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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.

End Cap pipe inlet sizes are:

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End caps with pipe sizes of >100mm can be ordered with Enviropipes PE pipes butt welded into the end caps to ensure a perfect seal and no sand ingress later after backfilling due to settlement or earth movements breaking mastic seals on larger systems.

It is a Tunnelwell® mandatory requirement to have the spigots welded in on any commercial installation – Tunnelwell® will include these costs when quoting such large systems. If a contractor is using UPVC pipes where PE spigots have been butt welded onto the end caps, they must supply a slip coupling to connect to PE spigot and switch back to UPVC pipework. Slip couplings are available from plumbling suppliers but only come in 100mm and 150mm sizes. Alternatively, the switch can be done by connecting the UPVC pipe to a GPT or deceleration chamber and then connecting from that chamber to the Tunnelwell® Arch System using PE corrugated pipes using a PE socket. This applies to both overt and invert connection pipe selections by the design engineer.

Note: for invert level connections the gabion must be cut into the soil base so the inlet pipe is flush with the top of the gabion. For overt level connections the gabion may sit on top of the soil base area.

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Flow rates for horizontal stormwater discharges into Tunnelwell® Arch System end caps should be:

• ≤1.00msˉ¹ for 100mm pipes up to 300mm diameter; and

• ≤1.00msˉ¹ for all pipes over 300mm diameter.

These criteria may necessitate 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.

* 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 (Gabion)” 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. The minimum gabion length for horizontal discharges is 2m.

Note: Siphonic discharges are not permitted directly into Tunnelwell® arches whatsoever.

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Balancing pipes are only required where more than one or more Tunnelwell® Arch systems are manifolded together or where the design engineer wants to balance overflow/excessive water flows between multiple arch systems. The balancing pipe size is 100mm diameter UPVC size and must overlap into the top of the arch chamber by not less than 100mm before being sealed. The number of balancing pipes required is at the discretion of the design engineer.

Note: The balancing pipe inlet may also be used as the air relief connection point if the required pipe cover is not available for a top arch connection point.

For more information on balancing the system, refer to section 5 of the installation instructions located in the Technical Resources section.

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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.

For more information refer to Confined Space Legislation and AS 2865 – 1195

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 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 manhole 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 to provide a vented connection to the Tunnelwell® Arch System. 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 tunnel section or 30m³ of storage capacity provided, or 2 x 150mm air relief vent, to each 50m³ of storage capacity provided.

NOTE: Cut a hole in top of arch at 150mm diameter so the OD of the pipe meets the outer rim of the hole so that a mastic seal can be effective and the pipe rests on top of the arch to avoid “push through” where a load could be applied.

Balancing pipe locations can be used for air relief locations if the required pipe cover cannot be achieved from the top of the arch. The balancing pipe size is 100mm diameter so the design engineer may increase the number of air reliefs required to relieve the amount of air necessary.

For more information on system air relief, refer to section 10 of the installation instructions located in the Technical Resources section.

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A Tunnelwell® Arch System can be accessed by two methods:

1. Design in an access manhole section to allow for human entry; or

2. Provide inspection/access opening in the top of the arches for cleaning and maintenance.

Inspection or Cleaning Access

All buried rainwater storage 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. The number of inspection points should be established by the design engineer. If no engineer is engaged for the design, provide at least 1 each tunnel section or 1 x 225mm inspection point to each 30 metres of arch chambers as a recommended minimum requirement or one at each end of the Tunnelwell® sections.

NOTE: Cut a hole in top of arch at 225mm diameter so the OD of the pipe meets the outer rim of the hole so that a mastic seal can be effective and the pipe rests on top of the arch to avoid “push through” where a load could be applied.

For more information on system cleaning and maintenance, refer to the section on the installation instructions located in the Technical Resources section.

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 Maintenance on Tunnelwell® Arch System is very low.

• 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 (Gabion) 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.

Important Maintenance Note: Access for any maintenance of any buried storage system is paramount!

Tunnelwell® Arch Systems have been designed without the need for any geotextile geotextile fabric surround or crushed rock support. Proper maintenance on other systems is not possible as geotextile fabrics can never be reinstated to their original performance criteria without retrofitting that fabric or the entire system installation. Tunnelwell® claims it has a >50year performance life cycle but for that to occur, Tunnelwell® Arch Systems need to serviced. Each Tunnelwell® Arch System should be designed for end cap access in the future so that the arch end can be excavated and accessed via removal of the end cap to allow a mechanical rake to turn over the soil to break up any hydrocarbon films built up over the soil base and remove any debris which may have entered the arches. Once this has occurred, the soil will infiltrate the stormwater as it did when initially installed.

Competitor systems can only be partially cleaned to enhance performance. Unless the geotextile fabric is replaced which can only be done by retrofitting the installation, reinstatement of their original performance criteria can never be achieved.

Note: Out of 13 functions Tunnelwell® only has 6 functions to perform!

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Compaction must be in 300mm 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 must be installed evenly on each side of the Tunnelwell® Arch System prior to going to the next layer of back fill and compaction. The maximum differential in compacted backfill level on either side of the arch shall not exceed 150mm. 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.

For more information on compaction, refer to sections 8 and 9 of the installation instructions.

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The proper compaction around and over the Tunnelwell® Arch System is paramount as it is the compaction of the sand/soil which provides the structural support much like the crushed rock support used by competitor injection moulded arch systems. If compaction and installation is not to specification, then the arch system could fail and no liability claim with be considered by Tunnelwell®. If there is anything not clear to the installer prior to installation, please contact us.

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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 fabric cover required.

Leach drain separation measurements

Arch is 1740mm toe to toe BUT side walls are only 1400mm therefore separation measurements need only be 1400mm then the 1.8m for boundaries and 3.6m apart if Dept. of Health require.

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No. Tunnelwell® should not be installed in water-charged ground. A minimum separation of 500mm is required between the high-water level and the bottom of the arch system.

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