Underpinning Raft


This method stabilises existing wall foundations to whole rooms or buildings. Mini-piles are installed within the property and capped with an integral reinforced concrete raft. Needle beams project from the slab into the walls below ground level.

Reducing the span between projecting needle beams and increasing pile numbers can accomodate highly loaded structures. However, the bearing capacity of the underlying strata will determine the number, diameter and spacing of piles used.

Load Capabilities using mini-piles:

  • 105mm diameter SWL 60KN per pile
  • 150mm diameter SWL 90KN per pile

This system is used where whole rooms or whole structures are to be underpinned and includes the provision of a new integral floor slab. It is appropriate when existing foundations are deep, or that good bearing strata is so deep that it is uneconomical to dig. (Depths greater than 1.0m)

Piles are installed at centers determined by loadings. Pockets are then broken out and reinforced needle beams are placed to pick up the walls. A ring beam is constructed and linked to the needles, mesh is laid and the whole stucture poured.

Advantages of this system are:

  • Provides lateral and traverse ties throughout the structure.
  • Provides new floor slab upon compleation.
  • Economical at depths greater than 1.5m.
  • No need for external access.
  • Minimises disruption to drainage and services.
  • High load capability.