REBUILDING COASTAL DEFENCES DEMANDS BIG MACHINES 
Maintaining the integrity of the sea defences along the Norfolk coastline is essential to prevent flooding of thousands of acres of rich farm land. Massive sea bunds/dunes, built up over many year to a height of 6 m in places, provide a high level of protection from flooding and a natural habitat for rare plants, birds, reptiles and small animals.
Following a massive breach of the flood defences in 1953 with the loss of many lives, the coast has, over the years been further protected by installing artificial reefs, refreshing beaches, rebuilding sea walls and construction of groynes. However, this work is ongoing and Abeko UK, specialist marine and coastal engineering contractor, in partnership with Team Van Oord has recently completed works on the latest Environment Agency contract to replace some old sea defences.
Abeko worked on an 18 km long stretch of beach between Happisburgh and Winterton, replacing groynes and construction a new revetment, while Team Van Oord provided technical support and took responsibility for beach replenishment works.
Quantities involved included 35,000 t of fresh granite rock, an estimated 25,000 m³ of rock which had, over the years become buried in the sand as well as 280,000 m³ of dredged sand for beach replenishment. The work involved removing the 10 badly deteriorated 80 m long, timber groynes. This involved excavating down to clay and then pulling out the old timbers. Because some parts of the groynes were still partially submerged at low tide, the contractors had to wait for the Spring tides to gain access. .
The groynes were replaced with much more substantial rock armour groynes, to the same length, 80 m. With the old groynes removed, the beach was levelled and excavated down to clay – being careful not to damage the existing concrete stepped sea wall, which have become covered by sand over the years.
Extreme care throughout the excavations was essential as the Environment Agency wanted to minimise disturbance of the clay beds. Built 90 degrees to the beach, the first 8 m is level, after which it follows the natural slope of the beach. Once the excavation had been measured and passed to meeting specifications, a 6 m wide geotextile bed was put in place. On to this was placed a base line of three granite boulders across the width. These measured 1.5~2 m diameter and weighed 10~15 tonnes. A second layer of two similar sized rocks was then placed on top. Space between the rocks had to be kept to a minimum so the operator was required to place the rocks taking into consideration their shape.
Although built to close specifications, there was a permissible tolerance for settlement and also for the top alignment given the unpredictable shape of the rocks. As each groyne was completed, the excavation was backfilled and surplus sand used to create a ramp to allow the trucks and other equipment to travel along the beach.
Modified Heavy Duty Equipment
Excavating to exact levels and placing heavy rocks of varying dimensions and shape with precision required large machines and skilled operators. Abeko UK, with many years experience in marine and coastal engineering, had both the skills and the equipment.
The rock for the groynes was sourced from waste material and brought in on high tide by sea going barge from Norway. Bringing in 32,000 t. of rock from Norway was the simplest and most environmentally beneficial solution.
 The rocks were unloaded by a Cat 988 wheel loader working from the barge. Once the load of 13,500 tonnes of rock was unloaded, the barge was taken back out to see before the retreating tide left it stranded on the beach.
With all the rock on the beach, a 78 t. O&K RH25.5 heavy-duty tracked excavator, with extra counter weight and heavy-duty cylinders began recovery work. The excavator was equipped with a 6.7 t. large grab manufactured by Flynn Welding Services. The work was shared with a Hitachi Zaxis 470LCH which had also been fitted with extra counterweight.
To avoid damaging the body and the suspension of the Cat 740 and Volvo A35D articulated dump trucks, the rocks were gently placed in the dump-body and moved clear of the high water line, where they could be easily redistributed for construction of the groynes.
Heavy loads and soft sand do not make a good combination and the soft sand rutted very easily as the fully laden trucks struggled for traction. Although the haul was only to the top of the beach, it put great demand on the dump trucks as they required all available power and drive to gain traction.
Logistical Nightmare
 Project Manager, Gareth Shape, has many years experience in such works and knows that even with the best equipment, configured for the works and with a skilled team of operators, the work was still going to be challenging because of circumstance which cannot be controlled.
“As the rock was coming from Norway, any schedule was subject to disruption due to bad sea conditions so there were the inevitable delays, especially at the time of the year. When a delivery came in, moving it to higher ground became a priority. We also had to schedule some work around the tide time tables.
Operators had to be flexible with their time. Team work is vital for this type of project, and the Norfolk coastline is not the most pleasant of places at times. It can be very cold, very windy and very wet.
Getting the large equipment on to the beach was another challenge. The access roads across the farmland to the beach are designed more for tractors than delivering 80 tonnes excavators and dump trucks.
Of course, the fine sand played havoc with the machines and maintenance was an ongoing process. Loss of traction when under full load and deep rutting often resulted in the dump trucks bottoming out. As we began to carry the rock over longer distances, I did considered bringing in a Cat dozer to help maintain some sort of haul road, but this was not required in the end.
 Because of the nature of the work we do, we also had to be extremely conscious of the environment, which can be extremely sensitive to disruption in some areas. For me, and Abeko, these were nothing unusual, but typical of the challenges we face on every job.”
Environmental Considerations
The Environment Agency and environmentalist watched the works very closely to see that the contractors did not disturb the existing sand dunes, contaminate the beach or endanger the local habitat. Some of the work was also undertaken under the watchful glare of seals that populate part of the beach. As it was the breeding season, part of the beach was closed off to the public but the construction works continued although under the watchful eye of an ecologist.
On-going Work
Once the ten groynes had been replaced, Abeko started work on 275 m of revetment work at Eccles. To be built against the existing sea wall, the same size rock armour as for the groynes was used on top of geotextile which, were there were joints, had to overlap by a minimum of 2 rocks or approximately 4 m.
The revetment is built on top of the clay layer predicted to be between 0.15 m OD and 0.35 m OD. The top of the revetment is between 2.4 and 2.9 m OD and, after 4 m of near level rock, the revetment slopes down at 25º to a total length of almost 10 m.
During the Abeko works, Team Van Oord used the 280,000 m³ of sand being pumped ashore from the trailing suction hopper dredger, “Geopotes 15”. The dredger, fitted with screens to ensure material met beach specifications, worked some 15 km off shore and then discharged on to the beach from inshore, via pipeline, to recharge the beach at Sea Palling.
With the completion of the works, the beach was fully restored along the full length of the works enabling unrestricted access for the public.
The works went to schedule and, despite the tough weather and sea conditions, the works were completed early in February 2009. Abeko UK worked as subcontractor to Team Van Oord on behalf of the Environment Agency.
With a fleet of over 150 pieces of heavy plant, including dozers excavators, loaders, screening and crushing equipment, Abeko is able to undertake any marine or coastal engineering contract or provide plant and operators under hire around the world.
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