CLIENT CASE 1
CLYDEBANK RETAINING WALL

Clydebank Railway Station, near Glasgow is situated on an elevated section of electrified railway which is supported by a series of bridges, retaining walls and embankments. When it became apparent that the existing dilapidated brickwork retaining wall supporting the rear of Platform No 2 was displaying signs of lateral movement leading to localised subsidence to the platform surface, Network Rail procured the services of a leading structural designer to design a new retaining structure.

Following approval of the final design, CK Contracts Ltd were contracted to construct a new 50m long x 2.4m high x 1.34m thick solid core Class B brickwork retaining wall offset from the existing wall by 2 metres. Following construction, the new wall was to be backfilled with granular material against the existing wall to arrest any further lateral movement. The design allowed for the new wall to be constructed during normal working hours without the need for railway possessions or isolations. Because of the close proximity of the existing wall, temporary structural raking props were installed prior to construction commencing in order to maintain the wall’s stability during the deep excavations required.

The site was located within a narrow strip of sloping ground situated between the rear of Platform 2 and the gable wall of an existing tenement building and could only be accessed from one end. A temporary access road was required to be ‘cut through’ the existing embankment to allow the site to be serviced with plant and materials. Due to the restricted nature of the site, the access road required to be formed over an area of the proposed wall’s footprint. Consequently, it was necessary to carry out the works in three phases, with each phase requiring to be completed in its entirety prior to removing the associated section of access road and retreating along the site to the subsequent phase.

During the initial phase of the works, the existing embankment ground levels combined with the steep embankment slope gradients prohibited the installation of a founded retaining wall and forced a change of design. CK Contracts Ltd put forward an alternative design solution in the form of a 1.5m high gabion wall installed along an 8m section of the embankment toe, backfilled to the crest of the embankment with granular fill. This alternative design was adopted and successfully constructed.

The new retaining wall, constructed during phase 2 & phase 3, was formed using 35,000 Class B engineering bricks constructed on top of a 500mm deep x 1750mm reinforced concrete foundation, complete with and 850mm deep toe beam, all of which was cast into the existing embankment slope. The foundation was stepped at two locations in order to negotiate the geometry of a step-out in the exiting wall. Drainage to the rear of the new wall was provided via of sloping weep pipes installed at 2m centres combined with a 150mm diameter slotted pipe out-falling to a formed granular soakaway.

The entire project was successfully completed within an agreed 10 week programme and delivered within the tendered contract sum.

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