SADE Special Works connects Brittany!
Intervention in the framework of a colossal project for GRT Gaz. Due for commissioning in 2021, the Landivisiau natural gas-fired combined cycle power station will strengthen the security of electricity supply in Brittany. At present, the region produces only 10% to 15% of the electricity it consumes and is therefore highly dependent on its neighbours.
To enable its connection to the natural gas supply distribution network, GRT Gaz must lay 22km of 400mm-diameter gas pipeline across the Finistère region. The new network will cross some ten municipalities, starting from a point located on the existing Saint Eloy-Dirinon gas pipeline and arriving at the Landivisiau power plant facility.
Calling on the SADE Special Works experts
This is a highly complex project. In particular, it runs through a Natura 2000 protected area (the famous Quimper snail), the Elorn river and its geological fault, and SNCF railway lines that can only be crossed via micro-tunnelling.
GRT Gaz thus called on SADE Special Works to lay 530m of concrete priming pipes using a 1,800mm-diameter micro-tunneller.
The works started at a depth of 8m, on the same level as the water table, with a 17% incline, before passing under the Elorn. The profile will thus consist of a drop of more than 40m with a water load of over 4 bars. A curved path and the presence of highly abrasive rock add to the technical challenge of this project for the teams.
Along the entire route, the ground is very rocky (alternating gneiss and shale), which increases the wear and tear of the cutting wheels (rotaries and scrapers) on the front of the micro-tunneller, which our operators need to replace about every 70m to 80m. The borehole is progressing at an average speed of 8m per day.
To facilitate the replacement of cutting tools and offset the pressure of the water table exerted on the tip of the micro-tunneller, hyperbaric equipment has been installed; located to the rear of the micro-tunneller, a chamber with inner pressure enables dry and safe operations.
Once this priming pipe is completed, and with CSR in mind, GRT Gaz will naturally be able to provide other utility providers with the possibility of laying their networks through it, i.e. water supply, drainage or optic fibre.
Sade Special Works is currently working on the first bend passing under the Elorn and the railway lines. The first metres of digging have proceeded smoothly.
Completion of the borehole up to the natural ground level is scheduled before 15 August.