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Flying a flag for quality

Scarborough is a name synonymous with all things seaside and Yorkshire Water is investing £50M to ensure the resort’s bathing waters meet the highest standards. Claire Symes reports.

Scarborough

The work has attracted interest from tourists as well as local residents

Part of the charm of the North Yorkshire town of Scarborough lies in its history - the area claims to be the UK’s oldest seaside resort and Victorian architecture still dominates the promenade that skirts its beaches. But despite trading on its heritage, Scarborough will soon have a new high-tech claim to fame that will also help maintain its popularity as a top bathing spot.

Between the rocky promontory that separates the North Bay and South Bay Beaches and Marine Drive, joint venture contractor Morgan Sindall Grontmij (MSG) is working with piling specialist Bachy Soletanche to shoehorn in a new water treatment facility for Yorkshire Water that will help Scarborough’s waters meet thehighest European standards.

According to Yorkshire Water community engagement adviser Claire Glavina, the utility company is the only one working on schemes to target the highest water quality standard under the incoming EU Bathing Water Directive that comes into force in 2015.

“The rig and the tools are well suited to the job. The target was to achieve one pile per day and we’re meeting that.”

Andy Brennan, Bachy Soletanche

The £50M scheme at Scarborough is designed to provide more storage so that sewage can be stored and treated before discharge. At present if there is a period of heavy rain the storage capacity can be exceeded and untreated material can be discharged by the existing combined sewage overflow (CSO).

“There are two beaches at Scarborough that are central to its tourist industry - the North Bay Beach has had a blue flag for at least six years but the South BayBeach has not always gained one and would fall below the standard required under the new directive,” says Glavina. “The investment means that both beaches should gain blue flag status.”

The design of the scheme came about as a result of coastal modelling work carried out by Yorkshire Water in 2010 to help understand the problem and find a solution. The modelling was the result of the Price Review undertaken in 2009 ahead of AMP5 and allowed the water company to prioritise the work.

The scheme involves construction of a new CSO and a 4,000m3 storage tank, along with connection tunnels between the two and the existing facilities at Toll House that will provide the connection to Yorkshire Water’s main works on the coast 5km further north of Scarborough where MSG is building three new settlement tanks and an ultra-violet treatment facility.

Throughout the two-year scheme the existing facilities must be kept operational, which combined with the underlying ground conditions of hard rock, means the scheme is not straightforward. Its location means it is also on view to the public.

“We moved onto site in early 2012 and the site has proved to be an unexpected tourist attraction,” says MSG works manager John McGeever. “With the rigs sitting on top of the piling platform, the visitors on the promenade have a good view of the work. Some were even crossing the road to get a better view, so we have installed some information boards on the sea wall to explain the work and the techniques we are using.” The hoardings have also been specially designed to explain how the work will benefit the town and its beaches. MSG plans to update the display boards as work progresses.

High Peak

Netting was installed by high peak to reduce the risk of rockfalls

The main work on site started in mid-March with establishment of the construction site, with road diversions to cope with the work taking up one lane on the esplanade, and checking services to ensure the new development could be squeezed between the existing facilities. Location of the site up against a sheer cliff also called for some additional work and High Peak was called in to install rock netting to reduce the risk of rock falls onto the construction site, and also thefinished facility.

Work could then focus on gearing up for construction of the 30m deep, 24m diameter tank and the CSO, which will measure 15.5m by 10.5m in plan and be up to 24.5m deep.

According to Bachy, although the piling techniques and pile sizes planned at the site were relatively straightforward in themselves, it was the ground conditions that were the main concern. The rock at the site varies from mudstone to sandstone and the ground investigation suggested it became harder from 10m onwards.

“We hired in a Casegrande B400 rig and bought a Bauer centreless auger and a progressive auger to use with other coring tools to be sure that we could complete the work,” says Bachy Soletanche site supervisor Andy Brennan. “We have not had any problems - the rig and the tools are well-suited to the job. The target was to achieve one pile per day and we’re meeting that.”

Bachy is working on piles to form a retaining structure for the CSO, a retaining wall across the back of the site and piles to support the new equipment building.

The retaining wall is formed from 45, 750mm diameter contiguous piles bored to 10m below ground. “We managed to install three of these piles per day,” says Brennan.

The new building at the site will be supported by 10, 650mm diameter bearing piles cast to 15m depth using a 750mm casing. These were installed by a Bauer BG24 rig working alongside the Casegrande machine. “It was tight with both rigs on site at the same time,” adds Brennan.

Piling for the CSO was a little more complicated due to the varying depth. All the piles were 1,150mm in diameter and cased to the bottom. “The eight piles closestto the sewer only extend to 9.7m below ground level,” says Brennan. “There are 15 piles next to the cliff that are built to 24.5m depth that have a dual purpose of creating a retaining structure for the cliff and the side wall of the CSO. On the seaward side of the CSO, there are 19, 24m deep piles.”

“The rig and the tools are well suited to the job. The target was to achieve one pile per day and we’re meeting that.”

Andy Brennan, Bachy Soletanche

Brennan believes that another reason - beside the right choice of rig - that the work has gone smoothly is the use of an innovative splicing technique on the reinforced steel cages used in the piles at Scarborough. The cages were delivered to site in sections from Romtech and have the Easy Splice system that has fittings already in place to allow the cages to be bolted together. “It takes around 30 minutes to get the full cage into the ground rather than two to three hours that other systems take,” explains Brennan.

Once Bachy had finished on site, another subcontractor moved in to start work on the shaft. “Ward & Burke is forming the shaft using a cast insitu caisson that will be jacked down in three sections,” says McGeever.

The shaft construction is scheduled to take 200 days and once that is completed in spring next year, MSG will turn to the tunnelled connections.

“We will use an open face shield and mechanical excavation for the 2m diameter, 20m long tunnel between the CSO and the shaft,” says McGeever. “We are currently looking at the potential to use a tunnel boring machine for the other tunnel drive, but as it’s only 60m long and 2m in diameter, mechanical excavation may prove to be the best option there too.”

The facility is scheduled to be completed by December 2014 but the main construction is due to finish in spring 2014 to allow time for M&E fit-out andcommissioning.

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