ScaffFloat is a U.K.-based start-up in Cornwall that has invented a line of durable floats made from recycled plastic that integrate with standard scaffold components to make pontoons, rafts and workboats.
ScaffFloat recently completed a project in North Wales where the company provided a full marine package to clients Pennys Demolition and Alun Griffiths to help remove the old and then install a new bridge for Network Rail across a tidal estuary in Barmouth, North Wales. The ScaffFloat floats were used on the project to transport 25-tonne sections of the demolished bridge to the beach, and then to transport deck sections for the new bridge.
Mobilization
First, the pontoons were assembled at the top of the beach by hand. The tracked excavators used for the demolition then lifted and carried them down the beach at low tide where they were moored before floating off on the flood tide.
Demolition
Demolition of the old bridge started as soon as the ScaffFloat team had mobilized. To support the weight of the old bridge sections after they were cut, a gantry on the new bridge was used to take their weight. As soon as the bridge sections were hanging free, a ScaffFloat pontoon was push towed into place under the bridge an hour before slack water. A mooring line was run from the pontoon bow to one of the pre-laid anchors and then tension was taken up on the windlass capstan which held the pontoon against the flow. Two lines were then run out sideways from the deck winch on the pontoon to the bridge piers. The crew onboard could then fine tune the position of the pontoon to the 100mm of tolerance needed to get the bridge section onto the pre-laid deck chocks.
Once the weight was taken by the pontoon, the lifting strops were removed, the deck winches released and the pontoon’s capstan was used to pull the pontoon and bridge section into clear water before the workboat behind would take over control and the anchor line let go. As all moves had to be done at high tide, there was hardly any space to get the old bridge sections out into clear water, often less than 100 millimeters.
Once in clear water, the ScaffFloat skippers had the challenge of pushing the laden pontoons across the estuary, through the moorings and onto the beach. Delays in the bridge lowering meant that on occasion this was done after the ebb tide had started to flow. In this situation, the tide would be flowing out the estuary mouth with some power which made it imperative that the critical turn round the starboard channel marker into the beach was done without error. In these situations, the second workboat would sit on the outside of the turn to push against the pontoon as it made the tight turn.
Over the course of several weeks this process was repeated as the weather and tides allowed, with the team managing three pontoon moves on a single high tide to help make up for lost time.
New Bridge Decks
Once the last bridge section was on the beach and cut up, the next phase of the project began. The heavy lift pontoons were all dried out on the beach. Attridge Scaffolding pre-installed the suspended scaffold on the decks of the pontoons. The new bridge deck sections, complete with rail track, were then lifted on top of this scaffold and connected. The bridge sections were taken, one by one, out to the bridge. Once the new deck sections were in place, the scaffold would hang underneath, which saved a lot of work having to install it in the air.
Hoisted for Access
At various stages during the project, access was needed to the underside of the bridge when the scaffold had been removed or not yet installed. The ScaffFloat had been designed so that as well as floating, the units could be hoisted up under the bridge on a four-point lift with the gantry. They could then be secured to provide an access platform.
Weather and Tides
One of the biggest challenges to the marine element of the project was working around the tide and weather. Given the large volume of water held by the estuary upstream of the bridge, there was only a very short period of slack water, often under half an hour, when all the marine work had to be completed. The project was also completed during the autumn with very changeable weather and during which several named storms passed through the region putting work on hold.
Design and Certification
The team at ScaffFloat provided a full set of RAMS [Risk Assessment and Method Statement], as well as designs for all the ScaffFloat pontoons and moorings. In addition, the advisory firm Richter provided a full Cat 3 threat and risk assessment for the heavy lift pontoons and hoisting, which included full structural, stability and buoyancy analyses.
Toby Budd, ScaffFloat’s managing director commented, “On a calm day at slack water you would let your kids swim under the bridge it looked so benign. But a few hours later you could have one-meter standing waves with five knots of flow against a full gale.’’
He added, “It was a great project delivered by a top team. We worked well with the team from Pennys and Alun Griffiths, everyone had a ‘let’s get it done’ attitude, tempered with a sensible level of safety and risk management. Being such an innovative engineering project, problem-solving was a daily practice, and we loved being part of the team that overcame a long list of challenges to get the job done and it was great to see the line reopen and a train cross on December 8.”
Reprinted from Marine Construction Magazine, Issue II, 2024.
