F2A along with the client EMA and the building company Colas Rail, have been involved in the extension of line 1 of alger’s subway untill the Bachdjara 1 and 2, El Harrach Gare and Centre stations
The extension started in 2008 and the tunnel’s drilling was finished in 2012. The rails and other equipments were set up by the end of 2013.
The total length of the tunnel is 4km long and will have costed over 85 million euros.
Air handling and acoustic requirements :
The noise emergence has been controlled by our Acoustics specialist in order to comply with the specifications set by the Client both inside and outside the tunnel.
Outside the tunnel, the acoustic objectives were set based on the 2006-1099 decree of 31 august 2006 regarding neighboring noise (french regulation):
This decree sets the noise emegences’ standard values that ventilation equipments must comply with regarding their proximity to neighbors : they are 5dB(A) by day and 3dB(A) by night compared to the residual existing noise (see tunnel regulation).
Inside the tunnel in soft ventilation mode:
- 60-65 dB(A) in the stations at dock level
- 60-65 dB(A) in the ventilation wells at dock level
These acoustic requirements are very complex to reach, for air intake and air exhaust fans both reach airflows over 100 000 m3/h in soft ventilation mode (the airflow is almost twice as big when the installation passes in smoke exhaust mode) and generates a noise over 100 dB(A) in the ventilation shafts and 90 dB(A) in the stations. 2 fans near one another in the stations and 4 fans in the wells must also be accounted for whose emerging noises accumulates, making the 60-65dB(A) in the stations extremely demanding.
The project manager also set very demanding requirements in the design of acoustic equipments:
- The pressure loss generated by the silencers must not reach 100 Pa or more in smoke exhaust mode which sets the value at 25 Pa in soft ventilation mode.
- Air velocity inside the acoustic splitters must remain under 12 m/s
- The gap between each splitter must be at least 90mm.
There is also a dimension constraint, caused by the arched shape of the air exhaust. Splitters with custom sizes were designed to fit the rounded shape of the arch.
Transversal section of a ventilation well
F2A Solution :
After 9months of study, thanks to a close collaboration with Colas Rail, F2A offered the following acoustic measures: a wall of splitters 5m high and 2m thick. F2A managed to reach the set acoustic levels by mounting silencers on both sides of the fan, in air exhaust and air intake.