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Polyurethane Compaction Grouting

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Plural component polyurethanes can be used for soil grouting similarly to cement based grouts. Features and conditions which can be addressed with polyurethane compaction grouting include:

  • Karst feature & sinkhole sealing/filling
  • Loose or uncontrolled fill densification
  • Settlement correction

There are a few key differences between compaction grouting with cement grouts and compaction grouting with geotechnical polyurethanes.

  • Unlike low mobility cement grouts, where slump doesn’t change during placement, polyurethane grouts are highly mobile initially, then lose that mobility within seconds to minutes.
  • Polyurethane grouts used for compaction grouting generally have short gel times, so stop moving laterally before they stop expanding.

How Polyurethane Compaction Grouting Works

Polyurethane compaction grouting works just like traditional compaction grouting. The only difference is that instead of the mechanical force of the grout pump providing the compaction, the expansion of the polyurethane grout provides the compaction. Geotechnical polyurethane is injected through 1/2″ diameter tubing, which can be driven by hand. This makes the process significantly faster than cementitious compaction grouting, which typically requires 2″ or larger holes installed by drill rigs.

The CJGrout geotechnical polyurethane is injected through the tubing, and expands in the treatment zone, displacing and compressing the adjacent soil. Most CJGrout geotechnical polyurethanes cure to 95% within 15 minutes of injection. This is significantly faster cure time than cement-based low mobility grouts.

Settlement Correction

Settlement correction with geotechnical polyurethane grouting is a straightforward repair. Prior to grouting, exploratory bores or DCP testing are used to develop a grouting plan. Once the grouting plan is developed, sacrificial tubing is installed. Rotary lasers are typically used to monitor surface elevations at multiple points within the zone of influence. As grout is injected at various depths, compacting the soils within the target zone.

Vertical displacement happens after the target soils resist compaction more than the vertical loads. The process can be used to correct settlement of both slabs and shallow spread footings. CJGeo has performed compaction grouting using CJGrout to as deep as 35′ below grade.

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