Dam Wall Cavity Collapse Repair

What happened and how was it repaired?

The edge of a dam wall had collapsed into a cavity, leaving an open void beneath the stonework. Highveld Group excavated the collapsed area to expose the full extent of the damage, compacted the base, and backfilled the void with 30 MPa pumped concrete, so the wall edge is solid again instead of hollow.

Dam wall repair
Excavation
Compaction
30 MPa pumped concrete backfill
Civil & concrete works

Collapsed cavity at the edge of a dam wall with a dark void opening beneath the stonework — The collapse at the edge of the dam wall: a void opening beneath the stonework.

The problem

A collapsed cavity at the edge of the dam wall

From above, the wall edge looked like grass and soil. Underneath, the ground had given way and a void had opened up behind the stonework.

A cavity like this is easy to miss because most of it is hidden. Once the stonework is undermined, loose stone and soil sit over an open hollow, and the edge of the wall has nothing solid beneath it. Water movement can carry more material out and widen the opening, which is why a cavity in a dam wall needs a structural repair rather than a surface patch.

Looking into the cavity beneath the dam wall stonework — Inside the cavity: a dark void beneath the stonework.

Loose stone and soil sitting above an open void in the dam wall — Loose stone and soil over the open void.

Our approach

Excavate, compact, backfill with pumped concrete

Excavate to expose the cavity
We opened up the ground around the collapse to see how far the void ran and to clear loose and unsound material, so the repair would be built on solid ground and not on top of the problem.
Compact the base
Once the extent of the cavity was clear, the base of the excavation was compacted to give the backfill a firm, stable foundation.
Backfill with 30 MPa pumped concrete
The void was filled with 30 MPa concrete delivered by pump hose. Pumping lets us place concrete into tight spaces beneath and behind stonework that cannot be reached by hand, and fill the cavity completely.

Scope