Compaction grouting, also known as low mobility grouting, is a grouting technique that displaces and densifies loose granular soils, reinforces fine grained soils, and stabilizes subsurface voids or sinkholes by the staged injection of low-slump, low mobility aggregate grout. Typically, an injection pipe is first advanced to the maximum treatment depth. The low mobility grout is then injected as the pipe is slowly extracted in lifts creating a column of overlapping grout bulbs. The expansion of the low mobility grout bulbs displaces surrounding soils. When performed in granular soil compaction grouting increases the surrounding soil’s density, friction angle, and stiffness. In all soils the high modulus grout column reinforces the soils within the treatment zone. By sequencing the work from primary to secondary to tertiary locations the densification process can be performed to achieve significant improvement. Compaction grouting has been used to increase bearing capacity and decrease settlement and liquefaction potential for planned and existing structures. In karst geologies compaction grouting has been used to treat existing sinkholes or to reduce the sinkhole potential in sinkhole prone areas.
Compaction grouting was developed in the 1950’s as a remedial measure for the correction of building settlement and used almost exclusively for that purpose for many years. Over the past 25 years, however, compaction grouting technology has evolved to treat a wide range of subsurface conditions for new and remedial construction. These include rubble fills, poorly placed fills, loosened or collapsible soils, sinkhole sites, and liquefiable soils.
This technique also 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. Compaction grouting for treatment beneath existing structures is often selected because the low mobility grout columns do not require structural connection to the foundations.