What we were asked to do
European Directive 2004/54, transposed in Italy in 2006 (with Legislative Decree 264/2006), established minimum safety requirements for road tunnels, and interventions were therefore planned to adapt them to these measures.
For tunnels longer than 1,000 meters, the works involve, among others, the creation of a drainage system for spilled hazardous liquids.
To this end, Greenpipe was asked to design and implement a drainage solution for the A23 Motorway, with the fundamental characteristic of preventing the spread of a fire caused by flammable fluids.
Greenpipe studied and implemented a solution that proved applicable to many other cases.
To date, there are:
4,900
flame traps sold
(as of September 2021)
8 motorway
sections
involved
245 km
of motorway tunnels
upgraded
The context
In tunnels, as they are covered sections of road not subject to direct precipitation, a drainage system different from that used on open roads is generally provided, designed primarily to drain rainwater carried in by vehicles or originating from infiltration from the surrounding rock mass.
However, regulations required solutions that also allowed for the collection of flammable liquids from accidental spills (e.g., fuel leaks from vehicles in the event of an accident or from tankers) and guaranteed an effective fire propagation prevention action in case of fire, as well as the collection of water from the fire-fighting system.
The project
A major construction company specializing in infrastructure and civil and industrial engineering works contacted Greenpipe requesting a solution to upgrade 26 km of tunnels on the A23 Motorway in the Udine Sud – Tarvisio section managed by Autostrade per l’Italia.
Specifically, the intervention referred to 5 tunnels (Del Lago, Campiolo, Moggio Udinese, Zannier, and Raccolana tunnels) that required upgrading according to regulations and for which Autostrade per l’Italia had designed a suitable drainage system schematically composed of:
- a gravity collection system for water infiltrating through the rock walls;
- firebreak manholes designed to collect liquids spilled on the road surface in order to reduce the size of the liquid pool and prevent the spread of flames to other parts of the tunnel;
- an underground pipe running the entire length of the tunnel, into which the fluids are discharged;
- special manholes outside the tunnels, through which the underground pipe will be intercepted. A probe system is located inside these manholes, capable of detecting the presence of hazardous fluids and, if necessary, providing an alarm to the system for their correct management: this will allow for direct discharge into the final receptor or, in the event of the actual presence of hazardous liquids, their conveyance towards a storage and treatment tank.
In particular, Greenpipe handled the firebreak manholes to be installed, as per the Autostrade per l’Italia project, every 30 or 50 meters (depending on the existing conditions in each tunnel) along the entire hard shoulder, and to be connected via transverse pipes to the main line, i.e., the underground pipe.
The Greenpipe solution: SMART PRO 150 FIREBREAK SIPHON MANHOLE or “P” SIPHON
For its project, Autostrade per l’Italia required a product with characteristics that we found matched those of our SMART PRO 150H210 drainage channel.
From this product, with the appropriate modifications designed and developed by the Greenpipe Technical Office, the flame trap was born, combining the main characteristics of the channel and those of the accessories.
FLAME TRAP BODY
The flame trap body is represented by the aforementioned channel, the Smart Pro 150H210, made of vibro-compressed concrete with steel fibers, featuring high compressive strength (Rck > 45 N/mm2), resistance to freeze/thaw cycles in the presence of stagnant water containing de-icing salts and to aggression from atmospheric agents, to which the galvanized steel containment profiles for the gratings are firmly anchored;
“P” SIPHON and FILTER
The bottom of the channel is perforated and equipped with an additional external pipe of appropriate length and 110 mm diameter anchored to the channel body with a high elastic modulus single-component polyurethane joint sealant.
Connected to the lower protruding part of the additional pipe is a Φ110 “P” siphon and, in the upper part (i.e., inside the channel), a debris and rodent filter. The connections to the additional pipe for both the siphon and the filter are made via a socket joint with an NBR gasket. The additional pipe, the “P” siphon, and the filter are made of AISI 316 stainless steel.
GRATINGS
Two Smart 150 drainage gratings in GJS 500/7 grade spheroidal cast iron, class D400, are bolted to the channel.
PLATES
At both ends, the channel is equipped with two galvanized steel plates press-fitted to close and compartmentalize the unit.
The connection of the flame trap to the main underground pipeline, or line backbone, is made via transverse pipes (not supplied by Greenpipe) that start from the P-siphon and intersect it.
The 3D and 2D graphic design was submitted for review to the engineers of Autostrade per l’Italia, who validated it also based on the technical reassurances that Greenpipe, after initial prototyping, was able to provide regarding the dischargeable water flow rate, the type of gaskets used, and the type and thickness of the stainless steel employed.
The flame trap’s objective of preventing the spread of flames inside the underground drainage pipe is guaranteed by the “P” siphon and the presence of water inside its “gooseneck”.
Each flame trap, normally installed at a distance of between 25 and 50 meters from one another, is connected to the main drainage pipe running the length of the tunnel, and the configuration of its gooseneck siphon ensures the isolation of the firebreak manhole from the rest of the drainage system, preventing the spread of any flames.
