MOORE & TABER                     

 

 

Soil Grouting and Ground Improvement Specialists

 

         

Compaction grout is defined as: "Grout Injected with less than 1 in. (25 mm) slump.  Normally a soil-cement with sufficient silt sizes to provide plasticity together with sufficient sand sizes to develop internal friction.  The grout generally does not enter soil pores but remains in a homogenous mass that gives controlled displacement to compact loose soils, gives controlled displacement for lifting structures, or both (1980).  It is a specialized application of a much broader-based class of Limited Mobility Displacement (LMD) Grouting, a term used to describe the injection of stiff grout that does not mix with or penetrate the soil, displaces the substrate into which it is injected, and does not travel far from the point of injection (Byle, 1997).  It is also commonly referred to as "Low-Mobility Grouting", although the most common application of this type of grouting is "compaction grouting" (Warner, 2003).

In order for pump pressure to be transferred through the grout, and ultimately to the target treatment soils, the grout material must not only be quite stiff, but must possess a favorable grain size distribution in order to develop sufficient internal friction.  A typical gradation consists of silty sand with between 10 and 30 percent passing the No. 200 sieve.  It is important that the "fines" portion contain very little clay (if any).

The purpose of the "fines" content is to prevent the water in the mix from traveling ahead of the particulate portion while in the grout hose or casing.  If that were to happen, the casing would develop a blockage or "pack-off", as it is commonly described in the field.  Once the grout material exits the bottom of the injection casing, some of the grout's mix water migrates from the grout mass to the surrounding soils.  This process promotes further "stiffening" of the grout, keeping the grout mass very near the point of injection, and allowing mechanical displacement of the surrounding soils (Byle, 2000).