HomeTechniquesRetaining-wallsPile wallsContiguous Pile Wall

Contiguous Pile Wall

A series of adjacent piles constructed to form an earth retaining structure as a cantilever or a propped cantilever wall. Contiguous piled walls consist of a row of successive unconnected cast-in-situ concrete piles constructed with small gaps between the adjacent piles, formed using CFA or rotary bored piles (replacement piles techniques). Compared to other lateral soil supporting systems, contiguous pile walls are a more simple and economical supporting system due to reduction in cost and construction period when considering small to medium scale depths of excavations.

Construction sequence

1. Construct pile by either rotary bored or CFA technique (Continuous Flight Auger) techniques.
2. Install pile cage reinforcement to allow the pile to carry the bending forces.
3. Allow concrete to gain its design strength.
4. Install a capping beam to tie piles together; ensuring the wall acts as a monolithic structure.
5. Commence reduced level dig to formation level.
6. Install temporary and/or permanent propping where design requires.

Fields of application

New basement structures, especially in urban areas
Additional support for highways subject to embankment slippage (slope stability)
Bridge abutments carrying horizontal loads
Embankment cuttings

Environmental impact

Has a positive environmental impact by facilitating earth retaining solutions with the minimum amount of excavation (rather simple "production / installation" procedure).
Piling with comparatively low level of noise, vibration and deformation of adjacent soil mass, therefore suitable in crowded urban or industrial contexts.

Technical specifications

Temporary or permanent earth-retaining structure: restricting movements of the soil on the retained side.
The unconnected piles are not suitable for retaining water or groundwater ingress unless jet grouting, 'gunite' or 'shotcreting' seal the piles and remedy ingress.
Due to rotary drilling techniques, system is applicable in a wide range of soil conditions: granular soils, most cohesive soils, soft layers of rock. However, the contiguous wall (with a gap between the piles) usually renders unsuitable for structures retaining fine granular soils with a high water table, soft clay and weak organic soils due loss of fines between the piles.
Unsuitable in hard clay and hard rocks.
Piles are usually constructed with a nominal gap between the piles of 100 mm to 150 mm typically.
The piles are designed to carry lateral bending forces and are normally tied together at the top with a capping beam to ensure they act monolithically.
Depth of excavation is limited by the length of the pile cage reinforcement introduced into the piles (maximum 18.0 m for CFA and may become more economical for diaphragm wall systems at depth).
Ability to support an axial loading (point load and/or line load distributed through capping beam.

Franki Foundations UK

Martello Piling

Atlas Fondations

Franki Grondtechnieken

Franki Foundations

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