With its upgrade to Howth Middle Pier, John Sisk & Son has demonstrated its ability to think outside the box

Completing a substantial, complex project to the highest quality on solid ground, without any health and safety incidents during construction, requires diligence, care and consideration. Building a project in the sea is a totally different ballgame. This year, John Sisk & Son completed a significant upgrade to Howth Middle Pier for the Department of Agriculture, Food and the Marine, the purpose of which was to allow for additional primary trawler mooring facilities. Sisk isn’t a stranger to marine projects; over the past 15 years the company has worked on marine jobs in the UK and Ireland, including Greystones Harbour in 2011. Work on Howth Middle Pier kicked off in September 2020, which coincided with Howth’s new status as a designated port. Before the project even completed, the seaside village had already started to receive a steady stream of new traffic both from the North of Ireland as well as trawlers from the continent, all of whom have had to change tack and chart a different course post Brexit.

Alan Tully, Project Manager at John Sisk & Son, led the team on the Howth Middle Pier project. An upgrade was essential as originally, Howth Pier was more of a breakwater than a pier. “It wouldn’t have been possible to moor any trawlers up against it. Our brief was to widen the existing middle pier and create a vertical space 134m long on the western side, which would create mooring for trawlers. On the eastern side, a new line of revetment was also outlined in the brief,” said Alan Tully. A huge amount of dredging along the western side of the Middle Pier was required in order to facilitate the construction of the new vertical wall. That dredging increased the overall footprint of the middle pier from 8000m2 to 14000m2. During the dredging process, approximately 11600m3 of material was dredged, processed, treated and used as structural fill material within the land reclamation area on the eastern side of the middle pier. A dredge pocket extending 20m beyond the face of the new quay wall was also created to accommodate the new structure and facilitate berthing. Dredging works were carried out using a combination of land-based, long reach excavators and floating plant (hopper barges, spud barges, long reach excavators). The dredge material was stabilised by applying the Allu stabilisation method.

On other projects that require dredging, dredge materials are quite often excavated and either dumped at sea and/or brought to tip. On the Howth Middle Pier project, this material was stored in cells on site to form part of the permanent works. “We had to come up with a mechanism to actually stabilise the material in situ, which hadn’t really been done before. This was a project that required us to be innovative and open to new ideas. We engaged with Newton Engineering who purchased equipment from Germany to carry out the stabilisation of the dredge material. We mixed the dredge in cells with wet grout and conducted a lot of trials before and during Covid to get the right combination. When we came out of Covid, we knew exactly what mix we were going with and we knew the equipment we needed to get.” Reusing the dredge also significantly reduced the nett importation of material and impact to the locality and carbon footprint. Utilising the wet mixed Allu Stabilisation method also allowed for structural and environmental benefits which in turn, helped to reduce the impact to the surrounding environment. \

Headquartered in Northern Ireland, Newton Ground Engineering Ltd provides innovative solutions in civil engineering and construction projects across the UK and Ireland. Part of the CAB Group, the company specialises in soil stabilisation and ground engineering for the development of highways, building infrastructure and complex logistics of renewable energy. On the Howth Middle Pier project, services provided included soil stabilisation, deep soil mixing and remediation. “For us, this was a slightly unusual project in that we purchased the equipment that was specific to the works, namely an Allu mixing processing head and a Bauer grout plant,” said Dominic Flanagan, Contracts Manager at Newton Ground Engineering. Working space on such a tight site was limited, says Dominic, requiring high levels of coordination between all teams. “We stabilised the dredge materials taken out by Sisk along the outer perimeter using a cementitious grout, working our way inwards to cover the whole area.”

An existing relationship with Sisk helped make the project a smooth, incident free job. “We’ve worked with Sisk on previous projects and in 2021, we actually won the ‘Supply Chain Partner of the Year – Civils Ireland’ at Sisk’s Supply Chain Awards.”

Dominic attributes the company’s success on Howth Middle Pier to a collaborative approach. “On all projects we undertake and on this project in particular, we engaged early on with the contractor. We bring value engineering to design solutions to give clients the best value for money and in line with that, we strive to provide a high quality, environmental approach to all the projects we work on. With the Howth project, sustainability was key; the binder we used contained a significant portion of GGBS, which has less of a carbon footprint than cement alone.”

Rock removal
Will Merriman, Managing Director for Ireland Civils at Sisk, says one of the main challenges on the project was processing the dredge and material from the original pier structure and converting what would otherwise have been waste material into something new. “We managed to sort and treat all that material, from silt through to rock, retain it on site and reuse it in a variety of ways to double the footprint of the pier. In civil engineering, we don’t always get the opportunity to do something that is sustainable and has a low carbon footprint. When you’re building roads, for instance, you often need to dispose of existing material off site and import stone and blacktop to construct a new road. This project gave us an opportunity to incorporate the existing material into the new works. For the staff who worked on the job, that was certainly something that struck a chord with them.”

Works on the eastern side of the Middle Pier consisted of the construction of the rock armour revetment, constructed on the outer face of the reclaimed land. A pedestrian walkway and crestwall was constructed, along with mooring bollards for light recreational vessels. To build the 134m-long, 10m high quay wall at the western face of the pier, the team at Sisk had to excavate 4m into bedrock, casting in-situ underwater concrete foundation and placement of double height precast panels, in-situ concrete massfill stitch, tie-rods and in-situ capping beam. “For the excavation, we created a 3D model of the breakout line that we wanted to achieve in the bedrock. That was uploaded to the excavators, which then went about breaking the rock. We used rock breakers and a rock wheel to grind down some of the rocks and once it was broken out, we used an airlift that we manufactured ourselves to lift out all the loose material.” Hard quartz sections within the rock made it difficult to break. “We had to replace quite a few of the pins in the rock breakers after breaking them on the very hard rocks. The extraction and removal of rock took us a bit longer than we anticipated.”

After the required surveys were carried out, a steel screed frame was placed on the rockbed and positioned at the right level. Concrete was then poured, with the screed frame used to level off the concrete before the precast walls were positioned.

Precast elements
Next up was bringing in the precast concrete walls, manufactured by FLI Precast Solutions in collaboration with ByrneLooby, FLI Precast Solutions came up with an offsite, prefabricated solution to create the pier wall. “There were two elements to our design – the manufacture and the delivery of an inverted T wall, along with an L wall that sat on top to create the full height of the pier wall. We were tasked with manufacturing it in a way that was simple for the divers to install. This was an extremely challenging installation; some of the walls were between 12 to 16 tonnes in weight. We worked closely with Sisk to come up with the most efficient way of fitting the walls under the water, while simultaneously meeting the specific design requirements in a marine situation,” said David Walsh, Contracts Director – Europe at FLI. An amount of fine tuning was involved, with all parties ultimately agreeing on an appropriate solution.

“We cast certain elements into the wall such as platforms for people to work on and additional elements to make the units moveable under the water. To come up with a solution that worked for all of us, it really was a team effort.” As the units were cast off site, the likes of steel fixers, sheet piling, formwork and access and egress dams were all taken off site. “That helped reduce the environmental impact of the project significantly. Health and safety risks were minimised. Utilising a precast method also made the project more cost effective for Sisk.”

Howth Middle Pier was FLI’s first marine project in Ireland. “As this project was so successful for us, we would definitely be interested in more marine work going forward. This project was very much a collaborative effort with all teams involved and I think the benefits of going down the precast route far outweighed the advantages of opting for traditional methods.”

Specialist commercial dive teams placed approximately 61 wall panels on the lower part of the wall, with a total of 140 precast concrete panels placed under water during the construction. About 4000 cubic metres of concrete backfill going onto the land-side wall. “At low tide, the concrete was poured up to 300ml from the top of the first precast wall. A good, level platform was achieved, which was essential as another wall would be placed on top. The initial brief had called for traditional, full in-situ wall but after engaging with ByrneLooby, we redesigned that full in-situ wall to two precast walls. Our solution resulted in a faster, more efficient build period. It also reduced the number of man hours on the site.”

The team of divers engaged by Sisk were faced with very specific challenges. At 7m down visibility was impaired, while any level of turbidity made the project more difficult. “They were also working in a live working harbour and although the mariners were very clearly notified each time the divers were in the water, there was still turbidity from the trawlers. The divers did an excellent job in a challenging environment.”

Although Sisk has experience working on marine developments, the Howth Middle Pier project still presented the team with a particular set of challenges. “It’s a real challenge to be involved in a job where a lot of the critical work – creating foundation for the seawall and putting in the new precast panels – was underwater. You can’t see what’s going on, you’re relying on feedback from divers who are under the water. There’s a lot of potential for error there, but thankfully a high level of expertise from all the teams on the project helped avoid any issues,” said Will.

Covid lockdowns created issues for Sisk around supply chains. UK or Dutch contractors that were originally to supply some of the larger pieces of equipment to the project were reluctant to make the journey to Ireland due to the required isolation periods. “Restrictions had eased in other parts of the world, so asking equipment companies to isolate before delivering the equipment and also after was a big ask.”

Once lockdown lifted, Sisk sourced Irish drivers and Irish based plant equipment suppliers. “Lockdown certainly changed how we went about the works. That led to using smaller equipment with a shorter reach but luckily, we were able to source most of what we needed in Ireland.”

Health and safety was paramount on the Howth Middle Pier project. Regular briefings with divers ensured coordination between all teams.

“Health and safety played a major role on this project. With people in the water that we couldn’t physically see and trawlers moving on the seaward side, we had to stay vigilant at all times. A huge amount of coordination was required between senior engineers, site agents and the site general foreman,” says Alan. A full-time crane coordinator was on site at all times, as was a safety boat. “We implemented man overboard safety procedures and engaged with the RNLI who came to site to deliver toolbox talks. We completed the project incident and accident free, which was a great achievement.”
The commitment and dedication shown by the Sisk team on the project guaranteed its success, says Alan. “A huge effort was made by all involved to complete the project to the highest standard and also to ensure it was an accident free build.” Kudos must also go to the Department and to Malachy Walsh and Partners, the consultant engineer on the project.”

“From project inception right through to delivery, this was an extremely well thought out project. The Department procured the project with the perfect blend of client and contractor design and in collaboration with Malachy Walsh and Partners, Sisk was able to develop innovative solutions for construction of the sea wall and reuse of the dredged material. The entire Sisk team is very proud to have been involved in this project,” said Will.

John Sisk & Son would like to thank the project team on the Howth Middle Pier project – John O’Connor, Michael Boran, Anthony Gannon, Martin McLoughlin and Cian O’Regan



Denise Maguire   Editor of Irish Construction Industry Magazine & Plan Magazine