Piled Retaining Walls

In urban ground engineering and sub-structure construction, piled walls have become ubiquitous, allowing basement construction to extend many storeys below ground level. Used as either temporary or permanent works, piled walls can provide high stiffness retaining elements affording large excavation depths with minimal disturbance to surrounding structures, properties or utilities.

Using either CFA or Large Diameter Piling (LDP) techniques we offer both secant and contiguous piled retaining walls. Bored piled walls can reach much greater depths and are suitable in wider range of soil conditions when compared with sheet piling.

Our piling division works closely with our wider group function to provide a comprehensive solution for deep basement construction including piling, excavation, propping and concrete works.


Piled retaining walls:

Contiguous piled wall technique:

Contiguous piled walls are utilised when groundwater ingress is not an issue. Installed using either CFA or rotary bored techniques, piles are typically arranged at centres 150mm greater than the pile diameter. Following pile installation a reinforced concrete capping beam is installed connecting the piles together and these act together in supporting the required surcharge loads. Contiguous piled walls are less expensive and have a faster speed of installation when compared with secant piled walls.

Secant piled wall technique:

Secant piled walls consist of a series of interlocking piles which can provide an impermeable piled wall thus retaining groundwater to the rear of the wall. In advance of piling, a temporary scalloped guide wall is installed along the line of the proposed wall in order to assist with pile positioning and alignment. Unreinforced primary piles are installed first using a lower initial strength concrete mix. Secondary piles are then installed between the primary piles, cutting into either side of the primary piles, then cast using a higher strength concrete mix with steel reinforcing. A pile capping beam links the top of the piles so that they act as a single element.

King Post wall technique:

King post walls can provide a lower cost piled retaining wall solution for some projects.   This technique is most suitable for above ground installation to provide earth retention for backfill placed to the rear of one side of the wall.   Bored piled are first installed at pre-determined spacing, a steel H section is then fixed vertically into the pile. Timber sleepers or pre-cast concrete panels are then inserted between the steel H sections to complete the retaining wall.


Advantages of Piled Walls:

  • Piled walls can be constructed using either CFA or rotary methods and therefore almost all ground conditions can be accommodated
  • Tolerances on verticality, particularly for rotary piling, mean that excavation of three to four storeys depth are achievable
  • Large diameter and high capacity / stiffness piles can be constructed which means that negative impacts on beyond the site boundary can be mitigated

Sectors: commercial (multi-storey), commercial (tower), civils