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A civil answer

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Peter Watt reports on a scheme which looks to the future, while harnessing brickwork's traditional strengths

The Gillingham Northern Link is Phase Two of the Medway Towns Northern Relief Road, a major transportation improvement project, Phase One of which was a new road tunnel under the River Medway. The new 3km relief road forms the A289 bypassing Chatham and Gillingham, linking with the New Medway Tunnel and also with the historical Chatham Docks and Maritime areas. Built to dual carriageway standard, it is part new construction and part upgrade of the existing highway infrastructure.

Work commenced on Gillingham Northern Link in late 1997 with site preparation and drainage installation.

Principal access and structures were built mainly between the summer of 1998 and the following spring. The road and full access to the new tunnel were opened to public traffic in June 1999.

Brickwork structures

The Medway Towns have a long historical tradition, and brickwork in buildings and in infrastructure plays a major role in the vernacular. A significant part of the link road passes through historically sensitive old dockyard and maritime areas which boast some very fine free-standing boundary walls in brick that have stood for well over 100 years. Some of these are very substantial structures.

Similar boundary walls can also be seen in the towns of Gillingham and Chatham and many are constructed around former naval facilities in the area. For these reasons the choice of new brickwork structures for the Gillingham Northern Link formed part of complementary planning decisions. The good durability and low maintenance factors associated with brickwork construction were also influential in the choices made.

The two principal brickwork walling structures in the scheme are the north and south boundary walls, which meet the new Medway Tunnel slip roads. The north wall runs adjacent to the Chatham Docks and Maritime areas and is about 1km in continuous length. It complements and integrates with existing dockyard walling, parts of which are retained as fully serviceable construction. The 1km long south wall is entirely new.

Both walls are built as part earthretaining, part free-standing brickwork walling structures, the earth retaining function being required because of level differences at the carriageway edges. Like their older counterparts they are substantial structures. In parts of the north wall for example, the earth retaining section starts 2m below ground: above ground free-standing elements can rise up to 3m high above finished ground level.

Earth retaining wall stems are formed mainly of reinforced grouted cavity brick construction with a typical overall wall stem thickness of 300mm. The free-standing wall stems are constructed using mainly 215mm thick unreinforced brickwork in English bond but collar jointed with tie systems rather than bonded through, a technique which helps achieve fair faced brickwork on both sides of a wall when using stock bricks.

Piers are provided to strengthen the taller free-standing structures of the north wall.

The simplicity of the structural brickwork forms used enabled rapid on-site construction and the brickwork was completed to schedule despite bad weather which continued while most of the principal walling was being built.

In addition to the north and south walls the Gillingham Northern Link includes a number of less substantial freestanding and earth-retaining brick wall structures at various locations. In many cases the height of these walls is less than 1.5m and economical, fully structural solutions have been provided by mass brickwork walling, of 215mm or 328mm stem thickness. Earth retaining planter walls also use this form of mass brickwork construction, providing beneficial environmental aspects to the link road.

Brickwork is also deployed as cladding to other structural forms and features.

Abutments to pedestrian and railway overbridges are of reinforced concrete clad in single 102mm thickness brickwork. The approach ramp to one pedestrian bridge has been executed as a series of increasing radii arches with both arch spandrels and soffits being fully brick clad to match the aesthetics of the overall scheme.

Demolishing a fewmisconceptions

The majority of both structural and cladding brickwork has been built in stock brickwork using a pre-blended mix of 15 per cent yellow and 85 per cent red stock bricks to match old existing walling.

The use of a moderate compressive strength brick unit with higher than 7 per cent water absorption demonstrates that major brickwork free-standing and retaining wall structures do not rely upon the use of high strength, low water absorption clay bricks to achieve adequate structural and durability performance.

Damp proof courses in walls have been formed using low water absorption bricks in a Designation (i) mortar as an integral part of wall stems, thus avoiding the need for separate (and structurally disruptive) sheet damp proof courses in structural walls. Detailing to the head of the north wall is flush, using special shaped brick capping, again in sympathy with existing brickwork.

Gillingham Northern Link demonstrates the benefits to the built environment when a major civil engineering project exploits both the aesthetic and structural possibilities of brickwork. When used to its full structural potential, brickwork can help achieve highly competitive and economic walling solutions. It also provides an original and attractive alternative to conventional approaches, while enhancing the built environment.

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