Underscour
Structures in contact with flowing water or waves can experience scour of their foundations over time. If the scour is permitted to continue, it can cause a number of issues:
- Undermine the structure
- Cause excessive settlement
- Loss of fill material
- Collapse of the structure
Commonly used methods for filling scour holes often mask the problem without providing a permanent solution. Stacked concrete bags or rock bags placed in and around a void may prevent additional scour, but they do not prevent the loss of further fill material or provide guaranteed support to the undermined foundation.
Grouted Repair
Underpinning grout bags can fully fill a void with mass structural concrete, preventing further scour, halting losses of fill material and critically providing support to the undermined structure.
The mass concrete fill cannot be plucked out of the void by high currents or wave impact pressures, resulting in a permanent repair so long as the bed is prevented from scouring below the filled grout bag.
Installation
Underpinning grout bags are pushed into the void, restrained in position and pump filled in tremie fashion until a back pressure of 10 kPa is generated. This back pressure ensures that the fabric fully fills the void and achieves guaranteed soffit contact on the underside of the void for a complete structural repair.
Advantages
Underpinning grout bags:
- Fully fill the void with a permanent repair
- Guarantee full soffit contact for structural underpinning
- Achieve high durability concrete
- Can be combined with concrete mattress to avoid future scour beneath the grout bag repair
