Dun Si St Marnocks Bay

Project Name

Dun Si St Marnocks Bay


Lone Star




Station Road, Portmarnock

Main Contractor:

D|Res Properties

Contract Period:

Aug 18- 2020

M&N Civil Engineering were subcontracted in 2018 by Dres Developments for the St Marnocks Bay Phase 1B, the scope of which involved extensive civil and substructure advanced works to facilitate the construction of 150 residential units as outlined below.

675m3 Retaining Structure which was cast in-situ element 15m x 15m x 3m deep. It was constructed with a 350mm deep RC slab, 250mm thick RC wall, and a 250mm deep roof slab consisting of the hollow-core slab had a 150mm concrete screed, which was laid to falls. Additionally, galvanized ladders, handrails, and grills were designed and installed.

Sutra Weir Manhole: A 2100mm diameter x 4.5-meter-deep sutra weir manhole was constructed as part of the stormwater management system. Within the 2100mm manhole, a 150mm thick sutra wall was constructed in RC. Upon completion, bespoke 15mm & 25mm thick stainless plates were installed on the wall using stainless steel fixings. This enabled the manhole to be closed with a 2100mm x 300mm deep cover slab, featuring 2 nr 600mm openings to accommodate hoist entry/exit and installation and removal of sutra weir plate sections if required. Surface-mounted galvanized davit sockets were installed on the 300mm deep cover slab for a davit lifting arm for future entry and exit.

The project also included a 28m long box culvert (1200mm deep x 1800mm wide x 2000mm Culvert Sections) which was in 14 nr section units which were contractor designed. Culvert installation included extensive traffic management with a contraflow from our traffic management partner CHM Group who designed and implemented the traffic managemen for us.Headwalls were also installed to facilitate outfall into the existing Baldoyle estuary which required the use of cranage to lift the 9 sections of the bespoke panels into place.

Other key components of this project included the construction of a regional wetland which required the excavation of an area of 175.00m x 75.00m x 2.5m deep including channels, bunds and storage of excavated material on site into berms.

These crucial tasks at the location of the road crossings were executed under the vigilant supervision of Fingal County Council, adhering to strict working hours from 10 am to 4 pm as outlined in the Traffic Management Plan (TMP) devised by CHM Group. This meticulous planning helped minimise disruptions in the densely populated area.

Tide restrictions posed an additional challenge when connecting to the existing estuary. Initially, the plan was to discharge into the estuary via a 525mm concrete pipe through a headwall. However, during our preliminary advance exploratory work and trial holes, we encountered existing services along the coast road at the crossing site. We conducted a thorough survey of these services and proposed an innovative alternative to the Employer which involved installing a twin 375mm pipes side by side, effectively avoiding impact with the services which didn’t ultimately need to be diverted. This strategic decision ensured the project’s efficiency and safety.

The project also encompassed significant foul sewer works, including:

  • Sewer SN8 Pipework: Laying 1300 meters of sewer SN8 pipework with diameters of up to 300mm at depths up to 3.5metres including all associated manholes.
  • Foul Pumping Station with a design capacity of 80,000 litres and a design flow of 15 l/s: Procuring a foul pumping station (Klargester GRP PSTOR-13) equipped with a valve chamber, 2 pumps, 4 float switches, 1 control panel featuring ammeters, hours run meter, cyclic changeover, and a high-level beacon, along with 1 set of 150mm Ductile Iron pipework and valves.
  • Rising Main: Installing a 240-meter-long rising main with a diameter of 150mm, leading to a new rising main discharge stand-off manhole, following STD-WW-29 standards. This rising main eventually connected to an existing sewer line through an existing manhole.

Furthermore, the project involved the installation of a watermain, consisting of 1.9Km of water main pipes conforming to Irish Water standards. These pipes included:

  • 1100 meters of 110mm SDR17 PE pipes
  • 450 meters of 160mm SDR17 PE pipes
  • 200 meters of 250mm Ductile iron pipes in accordance with EN545 standards.
  • 214 meters of 450mm Ductile iron pipes in accordance with EN545 standards.

This comprehensive infrastructure work aimed to provide essential utilities and services for the St Marnocks Bay Phase 1B development.


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