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Long Underwater Effluent Discharge Pipelines Experience Gained from the Thessaloniki Outfall

Author(s): K. S. Spyropoulos; E. G. Andrianis

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Keywords: Long pipeline; Concrete; Cast iron; Mattresses

Abstract: A twin pipeline was constructed to discharge effluents, at a design flow rate of 4.5m3/sec, from the biological treatment plant of the city of Thessaloniki towards the sea and finally in the Thermaikos gulf. The onshore pipeline measures a length of 10.4 km, while the underwater pipeline is 2.6 km long, discharging through two diffusers at a water depth of –23m. The diffusers are 400m long with 25 risers at 8m axial distances. Concrete pipes/HDPE risers was the material for the underwater pipelines, with the exception of the last 200m of the diffusers where cast iron pipes and diffusers were used. The internal diameter of each of the two pipeline branches is 1600mm and the pipes are made out of 10m sections connected together through a bell and spigot joint. The pipeline has been armoured against wave action in the surf zone and against dragging anchors along its whole length with stone rip-rap and concrete mattresses. The pipeline has been buried under the sea bottom mainly in order to overcome geotechnical difficulties encountered due to the very soft sea bottom material. An «installation horse» performed the major part of the underwater construction of the pipeline with the assistance of which the pipe sections were positioned on the sea bottom, aligned, jointed and hydraulically tested. The underwater pipeline construction lasted for 18 months. Design and construction matters of this pipeline are discussed in this paper.


Year: 2003

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