The communities of the Presqu’île de Quiberon in France, united in the Syndicat Mixte d’Auray Belz-Quiberon, awarded the contract for the design and installation of an outfall system for a new water treatment facility at Port Kerné to VBMS (as part of Visser & Smit Hanab). This project was executed as a semi-turnkey project in close co-operation with joint venture partner Betom.
The Quiberon outfall system, consisting of three separate 250-millimetre effluent disposal pipelines, was built in the granite of the Atlantic coast, at a location where construction time was limited by the predominant westerly winds and offshore wave patterns. The pipelines were built from 250-millimetre SDR 17.6 PEHD pipe installed directly into the rock face using Visser & Smit Hanab’s horizontal directional drilling technology. The length of each disposal pipeline was approximately 415 metres, which required drilling some 1,245 metres through the solid granite rock of Brittany. Each pipeline was fitted with a submarine diffuser installed at a water depth of approximately 7 metres, a design unique to the company and resistant to the severe offshore climate.
The drilling operations through the rock face, using a 250-tonne drill rig, took a total of three weeks. The preparation and actual welding of the 1,245-metre outfall pipe into strings, performed under tight quality control, was completed within a week. The strings were pulled into place with a land-based 30-tonne capstan winch and offshore sheave block and anchoring system. Each of the three pull-in operations was performed in a single shift. The diffuser systems (stainless steel diffusers with mechanical protection against drag nets) were installed with a workboat and surface supplied air divers.
Once the sea end of the outfall system was completed, a manifold and manifold chamber were installed at the water treatment facility and connected to the effluent basin. The system will accommodate 1,035 cubic metres of treated water per hour.
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