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

Low mobility compaction grouting technique illustration

Common uses

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

Process

Low Mobility Grouting densifies loose granular soils (Compaction Grouting), reinforces fine grained soils, and stabilizes subsurface voids or sinkholes by the staged injection of low-slump, low mobility aggregate grout. When performing soil improvement, an injection pipe is first inserted typically to the maximum treatment depth. The grout is then injected as the pipe is slowly removed in lifts, creating a column of overlapping grout bulbs. The expansion of the low mobility grout bulbs displaces surrounding soils. Compaction grouting increases the density, friction angle, and stiffness of surrounding granular soils. The effectiveness of the improvement can be increased by sequencing the low mobility (compaction) grouting work from primary to secondary to tertiary locations. In all soils, the high modulus grout column reinforces the treatment zone.

Compaction grouting was developed in the 1950s as a remedial measure for the correction of building settlement. Over the past 25 years, low mobility grouting technology has evolved to treat a wide range of subsurface conditions for new and corrective construction. These include rubble fills, poorly placed fills, loosened or collapsible soils, karst conditions, and liquefiable soils.

Low mobility grouting often offers an economic advantage over conventional approaches such as removal and replacement, or piling, and can be accomplished where access is difficult and space is limited. Low mobility grouting for treatment beneath existing structures is often selected because the low mobility grout columns do not require structural connection to the foundations.

Advantages

Economic alternative to removal and replacement or piling
Can be performed in very tight access and low headroom conditions
Able to reach depths unattainable by other methods
Non-destructive and adaptable to existing foundations
Effective in a variety of soil conditions

Quality assurance

Keller's quality control includes procedural inspection and documentation of the work activity, testing to ensure proper mix design and injection rates, and verification of ground  improvement where applicable. Ground improvement can be assessed by Standard Peneteration Testing, Cone Penetrometer Testing, or other similar methods. Data recording of important grouting parameters has been utilized on sensitive projects.