Ballyhalbert LSO

Overview

ABCO Marine Ltd were contracted as specialist marine subcontractor on Northern Ireland Water long sea outfall project. The project design detailed a 280mm OD pipe, 780lin/m long taken from the shore to a discharge point in 12m deep water in the Irish Sea.

During the marine trench excavation three large rock outcrops were encountered, resulting in a revision to the work methodology and programme. Substantial amount of rock some 237lin/m of the marine trench had to be removed to formation level, with the ‘drill and blast method’ of underwater blasting utilised. Drilling was conducted from our C59 Emotion Jack-Up Barge, with explosives placed by our commercial diving company ‘ABCO Divers Ltd’. To also ensure with compliance with the marine & blasting licence we had to complete property surveys, seismograph blast monitoring, enforce blast exclusion zone and marine mammal observing.

Project Information

Long Sea Outfall into Irish Sea, employed as specialist subcontractor for outfall installation on behalf of Northern Ireland Water.

280mm Outside Diameter Pipe and associated diffuser fittings were placed from Ch0+220 on shore to ‘Low Water Mark’ (LWM) to the diffuser outlet point at Ch1+000. ABCO sourced and procured the all materials utilised in the project, pipe lengths with associated fittings, concrete collars/mattress and granular backfill material.

Mobilised C5 Jack-Up Barge c/w excavator, Tug and support vessels to support the marine excavations through clay, with material side cast for backfill. Excavation of trench in 12m deep water, using long reach excavator, with level control maintained from GPS dig system. Prepared blast design and works methodology for Underwater Blasting operations, detailing ‘zip pattern’ drill and blast profile for a 2m wide x 2m deep trench detail. Charges placed by ABCO Divers Ltd, in line with prepared documentation, in close liaison with local police authority and HSE NI.

Pipe length was prepared in Ballyhalbert, with all pipe welding, concrete collaring and connections completed on site. Bathymetric and topographical surveys of the existing seabed and beach were completed, bathymetric survey were also utilised during the project, both pre/post sink surveys of the marine trench.

Preparation of project as-built reports and drawings, including all pipe testing results and pipe welding logs for quality control. Additional had to complete reports in line with license in relation to archaeological monitoring and to UK Hydrographic Office.

Client

Graham for NI Water

Date

May 2012 – April 2013

Client Representatives

Mr Gerard McKeever, Graham Construction Ltd

Category

Long Sea Outfalls

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