Soil stabilization is the application of chemical grouting to modify the characteristics of soil for geotechnical or structural purposes. Chemical grouting for soil stabilization is also referred to as soil modification. It is different than the use of chemical grouting for water intrusion repair. We do not perform lime-based stabilization for cohesive soils.
How Soil Stabilization Works
Chemical grout is injected into soils in place, and reacts with native or introduced water to cure into a solidified mass. A catalyst may be added to speed the reaction time. Depending on the chemical grout being used, it may expand as part of the reaction process. Non-cohesive soils are the best candidates for chemical grouting soil modification. Layers of uncontrolled sandy fills commonly found under slab floors and slab foundations that are raised above finished grade are generally excellent candidates for chemical grouting soil modification. Generally, soil stabilization is done on a grid pattern in conjunction with a shallow foundation repair method such as polyurethane grouting. This is a low-disruption alternative to deep foundation installation below slab floors.
Advantages of Soil Stabilization
Chemical grouting is an excellent alternative to deep foundation repairs in the case of unconsolidated granular soils below concrete slabs and foundations. Chemical grouting is generally paired with a shallow foundation repair such as polyurethane grouting in the case of settlement. Compared to deep foundation repairs, chemical grout soil stabilization is:
Chemical grouting is performed with compact, electrically-powered equipment. Dustless drilling is easily accomplished for interior applications, and mechanical connections in all components of the injection equipment ensure no loose material.
Compared to underpinning, soil stabilization is phenomenally less disruptive. Typical deep foundation repairs require 8″ diameter holes drilled through floors, and large access pits dug next to foundations. Deep soil stabilization only requires 1 5/8″ access holes drilled through floors and 3/8″ diameter injection pipes driven into the soil to be treated.
Chemical grouting is generally faster than underpinning repairs or other deep grout injection processes due to its compact equipment and ease of installation. Because of its compact equipment, fast reaction times and minimal surface disruption, work can easily be scheduled and planned to accommodate an area’s or structure’s normal use.
Disadvantages of Soil Stabilization
The primary disadvantage of chemical grouting compared to deep foundation repairs is that it does not allow for elevation correction. For slabs on grade structures, chemical grouting can be partnered with polyurethane grouting to correct settlement. In conjunction with polyurethane grouting for settlement correction, chemical grouting is used to stabilize the underlying soils to reduce the chances of resettlement.
For more heavily-loaded elements, such as mat footings & spread footings, chemical grouting can be used to reduce further settlement, but can’t be used to correct settlement. Therefore, helical piles or resistance piers are generally better. However, the mess and disruption associated with deep foundation repairs is often not worth the benefits of settlement correction. In cases like this, using chemical grouting soil stabilization to arrest settlement is often a much more practical solution.
Common Applications for Soil Stabilization
One of the most common applications of chemical modification of soils is treating relatively thin bands of non-cohesive soils below slabs. Polyurethane grouting is used for filling voids below the slab and lifting it back into place. Then, chemical grouting is used to treat columns of soil from the bottom of the slab down to a layer of soil with higher bearing capacity. This can be used to bypass uncontrolled fill which was placed during slab prep for floors elevated above the surrounding soil. Read about CJGeo doing chemical & polyurethane grouting to address slab settlement & treat the underlying thin band of unstable soils here.
Another common application is reducing vibration of equipment inside of facilities using chemical grouting. Modern machine bases are generally much larger than older styles. This is to provide additional mass to counteract vibrations. If the soils below the inadequate machine base are primarily non-cohesive, chemical grouting can be used for soil modification to turn the soil into a solid mass. This is not as predictable as removing the equipment and installing a new base, but it can generally be done in a day or two with little disruption to operations. That definitely can’t be said for replacement. Read about CJGeo doing chemical & polyurethane grouting to address compressor slab vibrations here.