The project required the contractor to excavate within 25m of Beaumaris Castle – a UNESCO World Heritage site and one of the best examples of 13th and 14th century architecture in Europe attracting over 100,000 visitors last year.

Faced with the challenge of installing 600m of 1.5m diameter polypipe in 6m sections between existing manholes, John Kelly Construction spent time researching the products available on the market, before finding that MGF’s High Clearance Trench Boxes were ideal for the job.

The 7m x 2.9m wide High Clearance Trench Boxes coupled with Top Boxes saved time and money to the contractor when compared to sheets and frames. The strength of the box allows suitability and capability of going to 5m depth and having high clearance struts on both ends of the box allows access at both sides – ideal for installing larger diameter pipes.

Paul Cowen, Technical Sales for MGF commented: 

“Beaumaris’ most recent floods in 2017 was the catalyst that something needed to be done regarding the surface water drainage system. MGF became involved to supply the excavation support equipment to alleviate the threat of flooding to protect the natural beauty and tourism trade in the area”.

MGF’s stock logistics team confirmed availability of the kit at our Dartford depot and coordinated transfer to the Astley depot before delivery to site with three 40ft articulated vehicles and two 15t wagons to ensure the order was met.

John Kelly, Managing Director of John Kelly Construction, stated:

"I was very impressed with MGF as a company as they were very quick to respond to our queries, provided designs and all equipment ordered arrived on site with no delays."

Sector: Water & Utilities
Client: Isle of Anglesey County Council
Contractor: John Kelly Construction
MGF depot: North West - Astley
Products hired: High clearance trench box, top boxes & titan manhole box

The purpose of the job was to design and supply temporary and permanent support for a hydro power house and turbine chamber (plus associated inlet channel and tailrace) constructed at the side of an existing weir on the banks of the River Derwent in the centre of Derby.

The design incorporated a single level of modular 406UC Hydraulic Brace system in conjunction with Larssen piles up to 10m in length, toed in mudstone, covering a perimeter of over 150m.

MGF's design allowed early removal of the brace by using a permanent concrete base slab as a low propped cantilever. The design had to take into consideration the complicated construction sequence; and the location of a large crane during installation and removal of the river piles.

During the project Balfour Beatty and MGF collaborated to develop the Stairsafe system (the UK's first temporary steel stair system designed specifically for excavations). The system proved a great success in providing rapid and safe access into excavations leading to greater site productivity. The system is now being used throughout the UK on excavations up to 6.5m in depth.

From early in the tender process MGF have been heavily involved with Balfour Beatty to develop an innovative, cost effective and highly complicated cofferdam design; which helped make Balfour Beatty's tender attractive to the client, Derby City Council.

Michael Rummens, Balfour Beatty Site Agent, commented:

"MGF were brought in at tender stage to assist in the value engineering of the cofferdam and support frames. Upon contract award, MGF's technical team were extremely proactive in producing a workable design in line with the projects requirements. The professional, amenable and expedient attitude continued throughout the process from design, technical support, plant hire and delivery and site assistance."

Sector: Energy & Waste
Client: Derby County Council
Contractor: Balfour Beatty
Consulting Engineer: WS Atkins
MGF Depot: Midlands - Rugeley
Product hired: 406UC Hydraulic Brace, 10M Larssen Piles

A support system was required for the installation of a new foul pumping chamber tank and customers D.B Cummins (Jersey) Ltd called for MGF’s assistance to meet a tight construction programme. The report from the sub-contractor, D.B.Cummins Ltd, detailed a 15m x 12m x 3m deep excavation with groundwater at 2m, with poor clay conditions throughout – requiring engineering designs and advice on the most efficient and safe support system.

Managing Director, Pierce Cummins, praised MGF’s efforts here noting:

“... the technical design and information was very helpful to present to our client. I couldn’t have asked for better customer service. Chris and his team looked after us from initial design all the way through to shipping equipment back to the UK."

Chris Whitworth, MGF’s International Sales Manager added:

“... it was important to Pierce to ensure that we met their construction programme. The design was completed and approved by their external consultant and equipment was on site, on time, as assured.”

Equipment was pre-assembled at MGF’s Tring Depot – including 254UC, 203UC braces complete with a 60T cross strut – and delivered to Southampton docks for shipping direct to site.

• Sector: Exports
• Contractor: DB Cummins (Ltd)
• MGF Depot: South East - Tring
• Product hired: 254UC, 203UC with cross struts

MGF have supplied specialist hire company Trench Shoring New Zealand (TSNZ) for the last 8 years during an excellent period of growth. During this time, TSNZ have expanded their fleet and added a variety of MGF equipment, including hydraulic brace systems and the breakthrough range GRiPSHORE^®.

TSNZ proposed a temporary works solution for major sewer upgrades in Auckland, New Zealand. General Manager, Frank Swanberg identified hydraulic brace systems as the most effective solution for tank installations. The contractor required an open pit to work on stormwater and sewer diversion upgrades as part of the Waterview Dual 3 Lane Tunnel Project.

TSNZ have found they are recommending hydraulic systems more frequently to local clients due to ease of installation, providing stronger working environments and overall reduction in time.

Chris Whitworth, International Sales Manager at MGF, stated:

"We delivered a 203 series brace system, 200 series struts, 60-tonne cross struts and multiple extensions to suit the specific dimensions of the cofferdam."

Sector: Exports
Contractor: Trench Shoring New Zealand (TSNZ)
Products hired: 203, 200, Cross-Struts & Extensions

Excavation works began in 2017 at the Dancing Hill Reservoir site as part of a £6 million project to upgrade the Water Supply GRID for Bridgwater and the surrounding areas. Major upgrades are required due to large-scale developments in the area.

The design was particularly challenging due to the complicated nature of the ground surrounding the reservoir tank. A sizeable berm was built on the ground profile around Cofferdam 4 to ensure a safe and stable excavation. This exaction also had to accept other loadings from Cofferdams 1, 2 and 3. Multiple 203UC tank brace frames were used due to the strict lift plan limit of 1 tonne. Larger or heavier brace systems could risk the collapse of existing foundations.

Vibration pile driving was not permitted due to the detrimental effect it could have on the high-pressure water mains that supplies customers. There was also a HV cable running through the site that had to be avoided. The exact location of other services created additional challenges and ongoing surveys had to be monitored throughout the duration of works.

As of 2017 there are four connected cofferdams in place allowing safe working space to combine new pipeworks to the main reservoir tank. Multiple back-to-back 203UC tank braces with special alignment of bracing has been key in the design, combined with KKD 600 sheets to secure the trench. Several Lightweight DavitSafe systems allow safe access into the 10m deep cofferdams.

Sector: Water & Utilities
Client: Wessex Water
Location: Bridgewater, Somerset
Scheme: Water Supply GRID Upgrade
MGF depot: Bristol
Products hired: Multiple 203UC brace, KKD 600 sheets, lightweight davit

National Grid, working with North Lincolnshire Council and East Riding of Yorkshire Council, developed a plan to construct a tunnel under the River Humber to replace the existing pipeline. The three-year project will provide National Grid with a 5km long, 3.65m diameter tunnel bored 30m under the river bed. A single 1200mm concrete-weight coated steel pipe will be inserted into the tunnel in a single string, making it the longest gas pipeline insertion of this kind in the world.

The River Humber pipeline is an important pipeline - connecting an import location for gas at Easington, on the East Yorkshire coast, to the national network – delivering gas supplies to millions of households throughout the UK.

The original pipeline, Feeder 9, is buried in a cut-and-cover trench under the river bed where tidal patterns have eroded the river bed uncovering the pipeline. Remedial work was undertaken to provide a short-term solution while a long-term solution was developed.

Working with the joint venture consisting of Skanska, PORR Bau GmbH and A.Hak, MGF’s in-house design engineers developed and manufactured a bespoke temporary works propping solution for the tunnel boring machine (TBM) launch pit excavation.

The contractor required the design to allow for the following key factors:

• Use of a load monitoring system.
• Design of bespoke connection details to sheet piles or capping beams where steel walers were not used.
• Design of bespoke 'headwall' beam to eliminate knee bracing at the end of the tunnel portal to increase working space.
• Design of prop connections to withstand 10 tonne accidental load.

The excavation was 209m long by 8m at its widest point, ramping from ground level to 11m depth. The deepest section, including the portal wall, was constructed with secant piles with PU32 sheet piles forming the remaining walls. The propping solution consisted of 406UC hydraulic braces with 2500kN 400 series struts. To accommodate the TBM installation the longer, high-level props were twinned with spans of up to 11m between pairs of props. The headwall beam was primarily required for ease of excavation as knee braces are notoriously hard to navigate around with an excavator. This ensured that the temporary works was sufficiently robust whilst maintaining an accessible working space; a technical aspect which separated us from the competition and was completed to Eurocodes.

Additionally, there were concerns that accidental impact of the struts by plant could cause failure of the system, particularly during the TBM lift, as there was only 200mm space between the paired props. To mitigate this risk MGF designed bespoke connections to the capping beam, wailing beams and sheet piles to withstand an impact of 10-tonnes.

MGF used its in-house load monitoring system which actively measured the load and temperature of each individual prop, waler axial loads and bending and axil load in the headwall beam. The data collected during the monitoring regime will have a significant impact on creating efficiencies in the design of hydraulic strutting and support of narrow closed trenches going forward.

Stephen Barker, Major Projects Engineer said:

"This project was particularly challenging due to the multiple levels of framing, high loads and strict robustness criteria. As the design was required to survive the loss or damage of a prop and withstand a 10-tonne impact load more props were required, however we had to balance this with ensuring that the contractor had sufficient space to excavate efficiently. The design of the headwall beam contributed significantly to this as it removed the requirement of having knee bracing at the end of the excavation, opening space and making bulk excavation easier."

The project will take approximately two years to complete and top level of the temporary works will stay in place during this time. In an adjoining field, the pipework is being welded in top strings in readiness for insertion. The tunnelling is currently underway with a slurry TBM.