Low mobility (compaction) grouting involves the injection of a low slump, mortar grout to densify loose, granular soils and stabilise subsurface voids or sinkholes.

Keller rig performing compaction grouting

Common uses

Suitable for rubble fills, poorly placed fills, loosened or collapsible soils, karst conditions, and liquefiable soils
Often selected for treatment beneath existing structures because the columns do not require a structural connection to the foundations
Reduce liquefaction potential
Decrease or correct settlement
Increase bearing capacity
Stabilise sinkholes or reduce sinkhole potential

Process

An injection pipe is inserted, typically to maximum treatment depth, and the grout then injected as the pipe is slowly removed in lifts, creating a column of overlapping grout bulbs. The expansion of the grout bulbs displaces surrounding soils and the grouting increases the density, friction angle, and stiffness of surrounding granular soils.

You can increase effectiveness by sequencing the compaction grouting from primary to secondary to tertiary locations. In all soils, the high modulus grout column reinforces the treatment zone.

Advantages

Often more economic than conventional approaches such as removal and replacement, or piling
Allows the improvement of discrete soft or loose zones at depth without the need to treat to the surface
Can be done where access is difficult and in limited space

Quality assurance

Keller can provide complete solutions which combine compaction grouting with real-time monitoring of affected structures, and has a variety of rig types to accommodate access constraints.

Typically improvement is demonstrated by pre and post work in ground testing by CPT or DCP for example.  Where possible a working verification section is incorporated into the start of the works to demonstrate and finesse the injection process.