UNDERPINNING - NEEDLE BEAMS

TECHNICAL DATA SHEET 1.2

This method stabilises wall foundations by the use of piles installed either side of an existing wall. A small pocket is broken out below the ground level and a reinforced concrete needle beam is cast in-situ connecting the piles and supporting the wall.

Reducing the span between needle beams can accommodate very high loads. 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 traditional underpinning is not appropriate due to the existing foundations being too deep, or that good bearing strata is so deep that it is uneconomical to dig.(Depths greater than 1.5m)

Piles are installed in pairs at 1.0m - 1.5m intervals and approximately 1.0m - 1.5m apart.

Advantages of this system are:

• Suitable for restricted access.
• Needle beam constructed at a higher level if existing foundation too deep.
• Faster than traditional underpinning.
• High load capability.
• More economical at greater depths.
• Less disruption, less spoil generated and compleated quickly.

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