Piled walls – types of finish

Contiguous or Secant Piling infill and overlay

A contiguous bored pile wall is a retaining wall consisting of concrete bored piles installed in a linear configuration with a minimum spacing of 150mm between consecutive piles installed as a retaining structure.

A secant pile wall is a bored pile retaining wall formed by installing interlocking primary and secondary piles to form a homogeneous continuous retaining structure incorporating a capping beam. Secant pile walls are flexible in shape and design compared to diaphragm retaining walls and offer a significant lateral strength advantage compared to that of sheet piled walls.

Mass filling of pile cusps

This is the most cost effective application and is primarily used where contiguous piled walls are installed within dry and cohesive soils. A minimum amount of concrete is required, together with a light weight reinforcing mesh or L bars, and only a short working programme is necessary to complete this type of application.

Sprayed concrete is used to stabilise the gaps between contiguous piling and prevent further loss of material until the final facing is constructed. A false block wall, or a brick/ stone facing would typically be constructed up to the underside of the capping beam to complete the retaining wall and offer an aesthetic finish to the final structure.

As sprayed overlay to follow contours of piling

This application goes one step beyond the basic mass filling option and overlays the whole face of the piling with a minimal thickness, typically 25 – 50mm (dependant on design) to the front face of the piling.

By creating a monolithic layer of concrete, it offers additional structural support to the cusps of the piling and resists overburden from the gaps between a contiguous piled wall.

As sprayed finish to cover front face of piling

A structural facing will involve additional thickness of concrete with a higher specification reinforcing mesh and anchoring design. Photographs below show a structural facing that required two layers of mesh to support over 250mm depth of sprayed concrete.

Final finish was specified as an ‘as sprayed’ final finish. Increased thickness is applied to the cusps of the piling and softens out the profile of the undulations.

Screed finish to line and level

A flat finish is sometimes required where fine tolerances are necessary to accommodate additional works such as waterproof membranes or steel portal structures.

Timber levelling batons are fixed to the front face of the contiguous or secant piled wall and sprayed concrete is screeded flat but without the application or a wood or steel float in cases where the final surface finish is not considered critical to the completed structure.

Cut and flash finish

Where the final finish is considered important to the structure for aesthetic reason or technical design, a ‘cut and flash’ finish is a cost effective option. Once a screeded finish has been achieve (see previous steps) a final flash coat is applied to even out any surface imperfections or trowel screed marks and offer a uniform but textured finish.

Wood or steel float finish to line and level

More often utilised in concrete repair and cathodic protection work, wood or steel float finishes are occasionally required to complete a piled wall overlay, but inevitably the cost is prohibitive due to the time and labour involved to achieve a flat closed surface finish. This type of detail is only usually required where the final product is in public view.

Sheet Piling infill and overlay works

Sheet piling forms a structurally sound and often watertight retaining wall or barrier. Sheet piles are used to form cantilever, propped, and anchored retaining structures for many applications.

Steel sheet piles are manufactured as hot rolled sections with U or Z profiles. The interlocking sections are designed as both temporary and permanent works for retaining structures in both land based and marine environments.

Sheet piling overlay – screed finish

Tidal conditions allow short windows of opportunity to apply sprayed concrete
and as such, it is more important to achieve concrete cover to the secant piling and
steel reinforcement in one go, rather than have construction day joints that allow
water to ingress and create potential issues with oxidisation and subsequent spalling
of concrete.

Surface finish becomes secondary under these circumstances where
structural integrity and longevity is the main objective.

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