Teamwork triumphs in Heysham bridge demolition

 

It was a ‘sprint to the line’ as Controlled Group and fellow contractors battled to complete the demolition of Berth No.1 before the new link span bridge arrived at Heysham Port, near Lancaster, after its five day journey by sea from Rotterdam. With the divers still in the water burning out the last of the foundation reinforcing as the new bridge appeared on the horizon, it was a dramatic scene.

 

Since the start of the demolition Controlled Group had removed the winch house, portal cross beam and supporting column and blasted the buttress and foundation above and below the waterline. This was a project that proved to be a true test of man’s struggle with the extremes of nature, culminating in the nail-biting climax that now faced them.

 

 

The old link span bridge with its concrete portal and winch house is one of three berths for the ferries and freightliners travelling across the Irish Sea between Heysham and the Isle of Man and Belfast. The other two berths remained operational during the demolition. The new £5.2m link span bridge is a two-lane carriageway, twice as wide as the old bridge, which will halve the ferry turn-around times for Berth No.1.

 

Planning for the 18-day project began back in October 2006. Surveys and inspections were carried out and the weight of each element accurately calculated as most of the structure was to be lifted out by floating crane. The lower part of the reinforced concrete buttress was to be blasted.

 

With only minutes to spare, the Mersey Mammoth and long-reach machine finished removing the last of the demolition debris before the new link-span bridge was floated into the harbour. The three sea-going tugs manoeuvred the bridge so it could be tirfored the last few feet onto its new bearings and bank-seat, prepared by Nuttall John Martin.

 

 

 

 

“Possession of the old Berth No.1 was taken on the 28th December 2006 and in only three days all the heavy lifting had been completed. This was a tribute to the previous month of meticulous planning” says Rob Clarke, Controlled Group’s in-house Structural Engineer.

 

  

 

Phase 1 – The Heavy Lifting

 

The Winch House

 

The first task was to remove the winch house, which was used to automatically raise and lower the old bridge with the changing tide. The cables and bolts between the winch house and bridge had to be cut and burned through. Two lifting beams were specially fabricated to lift the winch house, complete with 50 tonnes of winding gear. It was removed using the Mersey Mammoth – a floating crane with the capacity to lift up to 300 tonnes. “The Mammoth with its eight-man crew is a marvellously versatile tool,” enthuses Rob.

 

The Portal Cross-beam

 

The Mersey Mammoth was also used to remove the portal cross-beam between the two columns. An old locomotive lifting beam was dusted down to suspend the 100 tonne capacity wire ropes used to lift the 160 tonne reinforced concrete cross-beam. Early partial diamond wire saw cuts were made through the beam prior to the full possession. Therefore once the final cuts through the 2.4m sq, 10m long reinforced concrete beam had been made, it was raised using wire rope slings. Each 100 tonne capacity sling was 4 inches in diameter. The difficulty here was safely climbing onto the beam to pull the wire ropes down and up round the other side to hook them onto the lifting beam. A 50 tonne mobile crane had to be used to hold the ends of the slings while they were secured.

 

The supporting column

 

 

Nationwide Diamond Drilling cored a 7-inch diameter hole through the middle of the remaining 2.4m sq 7m tall column. Then a 6 inch mild steel shaft was inserted for lifting. After a four hour long final saw-cut was made, the slings were attached to each end of the shaft, and the 110 tonne monolith was hoisted away by the Mammoth.

 

The link-span bridge

 

 

With the high level structure gone, there was now space to lift out the 150 tonne steel trussed bridge. However, the team had to move quickly. Strong westerly winds were being forecast for the next two weeks. In addition, the far end of the bridge was resting on the seabed and the chains and shackles had to be secured around the bottom boom before the bridge became submerged by the advancing tide.

 

Access was difficult, but using a 50ton mobile crane and man-basket, shackles carried in two safety boats and the Mammoth holding the slings, everything was connected for the lift. With great skill the Mammoth kept the bridge steady in three directions, made a clean lift and transported the old steel structure to the south quay for processing, all just before the wind became too strong.

 

Phase 2 – The Explosives

 

With the heavy lifting completed, now it was time for the explosives. This was going to be the fastest and safest way to destroy the massive reinforced concrete buttress and foundation that now stood isolated, 10m from the quayside. Charging holes were drilled three metres deep into the top of the buttress. Heavy purpose made blast-mats were craned into position over the buttress. The blast-mats prevent any fly, fragments of concrete and steel, from being ejected by the blast.

 

 

After evacuating the 150-metre exclusion zone area the first section was detonated. The concrete shattered and was held loosely in place by the reinforcement cage. A 30 ton long-reach machine, equipped with hammer and

bucket, standing on a floating pontoon working platform, then cleaned away the shattered concrete debris. After the reinforcement was burnt off, the process was repeated and the next level of charging-holes were drilled. This procedure was repeated four times until cut-off level was reached, 3m below low-tide level.

 

“In practice this was not at all easy,” says Controlled Group’s Explosives Director, Mick Williams. “Burning the rebar had to be done from a man-basket suspended from a crane on the quay side. And this was during the period when the high winds were at their worst.

 

“Overnight, the pontoon which was carrying the 30 tonne long-reach machine became damaged whilst moored against the north quay. Lorries were being blown over on the M6 by the westerly winds and the conditions in the harbour were horrendous” says Mick. “The pontoon’s steel box panels began to leak and it slowly sank with the long-reach machine chained securely to it. We couldn’t believe our bad luck. The Mersey Mammoth had to return from its home in Liverpool to recover the pontoon and the long-reach!”

 

Noisy neighbours

 

Heysham Nuclear Power Station is a mere 500m from the blast site and not surprisingly power station officials were a little apprehensive about the potential power of the blasts and vibration coming from the Port area.

 

“We provided them with predictions of expected vibration levels, and carried out a test blast before beginning the operation,” says Mick. “As expected the vibration levels were negligible,”

 

 

Dealing with the unexpected

 

Meanwhile, unusually low river levels in Holland delayed the launch and departure of the new link span bridge.  As it turned out, this allowed the demolition team extra time to deal with another unexpected problem.

 

“We discovered a lot of steel temporary works cast into the foundations of the bridge,” explains Rob. “Old railway lines had been cast into the concrete base and were supported on a steel frame during the pour. The final blast using 70kg of explosives was not enough to rip this out. We had to use a team of divers to burn away the remaining buried steelwork with thermic lances.”

 

The divers’ work was synchronised with the long-reach machine hammering and clearing debris, a job that continued round the clock for 48 hours, working around the tides and in between ferry manoeuvres.

 

Just in time!

 

The new bridge was now on its way from Rotterdam.  But burning steel under water in the murky Irish Sea is no easy task. Visibility was so poor that the divers couldn’t tell which piece of steel they were cutting and how many times they had cut it. Somehow, however, the divers and machine driver managed to clear away all the concrete and reinforcement debris in the channel to make space for the new bridge with just three minutes to spare!

 

 

“As you can imagine we were so relieved,” says Rob. “This project had consisted of a series of highs and lows and the constant pressure of the tight timescale, so it was great to be able to go out on a high.”

 

Rob concludes that the demolition of the Heysham link bridge was one of the most unusual challenges of his career and a large part of its ultimate success was due to the high standards of cooperation between all those involved.

 

 “It was a great example of teamwork in practice and I would certainly work with any of the contractors involved again,” he says. “The Port staff, the Mersey Mammoth crew, the Diamond Drillers, crane drivers, long-reach drivers and Nuttall John Martin all worked together really well. Despite having to deal with the tides, the ferry movements and some of the severest weather conditions, remarkably, we pulled it off.