Britain’s seaside resorts frequently have manmade seawalls and built up beach areas constructed in Victorian times, but in many towns they need replacing. One of the largest resorts in the UK, Blackpool, is famous for its Eiffel-like tower, three piers, and a beach tramway. The resort is now two years into a four year £73m (EUR104m) programme to reconstruct 3km (2mi) of its seafront. Neighbouring Cleveleys, a smaller resort town, is rebuilding its 1km seafront for £19m (EUR27m).

Both resorts are taking out old vertical seawalls and putting modern sloping revetments, with embankments faced with concrete steps, behind the beach areas. In Blackpool’s case these will direct damaging wave reflections away from the Victorian stone walls. At Cleveleys they will soften the impact of a high seawall which cuts the town off from the beach.

The walls are needed because of very high tides, which can reach 10m, and strong storms in the winter, which can cause significant damage and flooding. They will absorb and diminish the energy in the waves’ impacts.

The nearby projects are separate works, but both contracts were won by Birse Coastal Engineering, part of Balfour Beatty Group. A key feature of the winning bids was Birse’s plan to use precast facing units for the seawalls.

The facing units are odd shapes with steps on the front surface, and it is awkward to position them at the angles needed. Working with SLP Precast, Birse developed a vacuum lifting system, which will allow them to place the units carefully and quickly without damaging them. The common solution helped keep prices down when bidding for the work.

Placing the precast units with a normal hook and sling would have put them under flexing and bending stresses that could crack the concrete and perhaps let in seawater. This would have meant that they would need steel reinforcement that, in combination with seawater, could damage the concrete. As steel is exposed to sea water and its damaging chlorine ions, it corrodes, expands and eventually breaks up the concrete. Also, lifting points would need to link on to internal steel, providing another route for seawater to enter. The sea walls are expected to survive for 100 years in a very harsh environment, so protecting them is vital.

Using the vacuum lifters reduces these bending and flexing forces, which means the precast blocks can be made without steel reinforcement. The only reinforcement in the units at Blackpool is some fibre. At Cleveleys, a very small amount of steel is used at the back of the units, which have to resist aggressive pounding from gravel in the water. The Blackpool units are installed on a sandy beach, and so don’t need even this minimal steel reinforcement.

The units each weigh up to 18t, and the lifter adds another 3t–5t to the load. The vacuum lifters hang from the crane hook and hold the loads with seven pairs of suction pads fitting on to each of the seven steps. At Blackpool, a Kobelco 180 crawler crane lifted the units with a 33m long lattice boom giving a 19m reach and lifting capacity of up to 26t. At Clevelys a smaller Kobelco CKE 1350 did the job again with a 33m lattice boom and 19.5m reach, though this time lifting 21t maximum, plenty for the smaller units on this more northerly job. Both cranes were hired in from Birse’s own plant hire company BP.

The lifter

“Power for the lifting vacuum is from self-contained diesel motors in the units,” explains Graham Hoole at SLP, which helped develop the units for Birse. A special additional signaller controls the units with a simple handheld radio remote control device.

The precast cladding units are delivered on low loaders with a specially shaped cradle that holds them at the angle they will be seated in on the embankment; this allows the lifter to be placed against the steps easily. They are swept clean of any sand and grit that may affect the suction grip.

“The lifters are positioned with the pads on the steps and then carefully pushed back against the riser,” Hoole says, “The vacuum is created and the pads tighten onto the concrete.” The easiest lifts are when the concrete is damp.

A green light indicates when the vacuum has built up sufficiently. A set of detectors monitors the vacuum level. If the vacuum should fail, red warning lights flash and a klaxon sounds. Hoole says that it would take 20 minutes after the vacuum begins to fail before the load drops, for safety.

Once the units are sitting on the prepared rough concrete facing on the new embankment they are released and grouted into position.

A piece of the puzzle

The shape of the lifters was worked out in discussions with Dutch firm Moderniek, which built them to order. The lifters do not fit simply against the steps, but need to match various changes in the units’ shapes caused by their positioning along the 3km of embankment.

“The new seawall has been designed to make a curving form along the beach in a plan to create various ‘headlands’ for promenaders’ interest,” says Anthony Hill, principal engineer for Blackpool Council.

“But that means there are many variations of the basic shape of the precast elements at various points in the curves,” says the contractor’s managing director Phillip Enright. “Something over 200 slightly different shapes are required for the several thousand units.”

There are architectural curves to cope with at the smaller scheme for Cleveleys as well, though that lifter has only 12 pads.

Moderniek worked closely with the contractors, designers and SLP Precast to tailor the lifters and the units together so that everything would fit.

SLP designed and opened a new factory nearby for the project, which will be used on other jobs later. Moderniek supplied a third lifter for the factory. This is used to lift the new units out of their steel moulds. It has only two pads, because the concrete sections are poured with the steps facing down, and present a flat back surface.

The factory vacuum lifter is electrical rather than diesel. It is suspended from a 30t overhead travelling crane built by Street Crane of the UK, and is powered by electrical cable and electronic remote control. It has the same red-green light ‘vacuum achieved’ safety systems used on the lifters at the job site.

The concrete sections are placed in a yard where they are cured to full strength, and then turned over by a simple rotating lifter, supplied by Moderniek. It has web slings at either end and a small electrical motor which turns the slings to rotate the units to their placing orientation.

“That is a normal system,” says Hoole, “but the device is interesting because it has an automatic centre of gravity detector and a ram to position the units properly between the slings. It will not lift until the unit is balanced; we need this because they are rather complex shapes and not easy to balance exactly.”

Blackpool’s job finishes in 2009. The work has been conducted at a slow pace deliberately, in order to minimise disruption to the tens of thousands of visitors to the beach. It has been phased so that they can access the beach with ease. Cleveleys will finish this year, although Wyre Borough Council may do a further phase of works.