Compaction Grouting is the stabilization of poor soils under buildings, structures, roadbeds, railroads, or runways, by driving injection pipes down to stable ground and then injecting low-mobility grout to densify soft soils and form grout columns. Injection is continued in a pattern to cover all of the target area until the ground, building, or slab is raised back to original elevation, eliminating all voids. The amount of grout injected and pressures at each lift are closely monitored on every hole to adjust for differing soil conditions for quality control.
Filling voids or pipes can be as easy as plugging both ends of a pipe and filling with grout, or as complicated as figuring out the mix and method to inject grout 40' underground through a spring-loaded, expandable steel form with an inflatable plug to fill a void.
Slab jacking is the raising of sunken or settled concrete floors by drilling holes and Injecting grout underneath.
Determining what caused the settlement is important to determine the best method for a long term fix. Small test holes are drilled to find out the size of the voids and stability of soil underneath so that an accurate estimate can made. The same holes can also be used as vent holes when grouting. Custom packers are inserted and low density, lightweight cellular grout is injected to fill the voids and stabilize the ground, then lift the slab back to an acceptable elevation. Most slabs can be raised by only 1 psi.
Low-density cellular concrete, or grout is used to fill the annular space between an older damaged host pipe and a new plastic liner pipe, usually HDPE. The pipes can be for sewer lines, or culverts under roads or railroads. The grout density is usually kept between 40-55 pcf which is lighter than water so that the water-filled liner will not float. It also needs to be extremely flowable to keep injection pressure to a minimum, around 5 psi and travel long distances (800’) or very small spaces (1-2”) and still achieve 100-500 psi. QC is very critical on every load.
We use the same Putzmeister swing-tube line pumps for grouting as well as concrete. The difference for most applications is that we slow down the pumps to a minimum output. For underground grouting the volume measurements are in cu ft per min and with the TK20 we can pump down to 1 cu ft per min at 2000 psi line pressure. That is important for densifying deep soils and lifting heavy structures and buildings.
For small projects that are very difficult or costly to ship large pumps to we use a small hand-carried piston pump powered by a hydraulic power pack.
Polyurethane expanding foam can be used to fill voids and lift slab sections in some cases. There are many suppliers and many different types to do similar things. We use a two part polyurethane foam resin, heated, and injected under high pressure to fill voids and raise slabs. This works well for some applications but is limited in effectiveness and cost on many projects.