Permeation grouting is the use of low viscosity grouts to uniformly saturate soil and fill materials to reduce its permeability, increase its stability and/or increase its bearing capacity. This is in contrast with low mobility grouting, which is primarily focused on increasing the density of soils by displacing treated materials.
How Permeation Grouting Works
The goal of permeation grouting is for the selected grout to permeate the soils, binding the individual soil particles together to increase the bearing capacity and reduce mobility and permeability of the treated zone. CJGeo performs permeation grouting using chemical & mineral grouts, including expansive resins, non-expansive resins, colloidal silica, and acrylic grouts.
Prepolymer grouts tend to provide the highest compressive strengths within the treated mass. However prepolymers are higher viscosity, so best utilized in larger grained soils such as gravels and coarse sands. Acrylic grouts are suitable for use in sands, silts, and sandy/silty clays. They are primarily utilized to reduce soil mobility and groundwater permeability. Colloidal silica is nearly the viscosity of water, so is effective in sands, silts, and sandy/silty clays.
Acrylic Grouting
Acrylic grouts are exceptionally low viscosity–they can be difficult to distinguish from water. Because of this, acrylic grouts are know for their ability to very uniformly permeate fine grained soils, such as silty sands and silty clays. Similar to prepolymers, acrylic grout set times are field-adjustable by varying the catalyst dosage.
In place, acrylic grouts range from the consistency of a cooked egg white to a hard silicone rubber. Cured acrylic grout is highly elastic. Above the water table, outside of temporary support, acrylics are usually not the best choice.
Colloidal Silica Grouting
Similar to acrylate, colloidal silica is exceptionally low viscosity. Colloidal silica grout is a colloidal suspension of silica nanoparticles in water, typically at either 15 percent or 30 percent by mass. The grout is pumped with a sodium chloride solution ranging from one to ten percent by mass. The ratio of grout to salt water, in combination with the salt concentration, is used to control set time.
Because colloidal silica is a mineral grout and not a chemical grout, the reaction generates no heat. Temperature has a significantly lower impact on reaction times compared to chemical grouts, as well. Colloidal silica grouts are exceptionally safe–it’s just very small sand particles and table salt. Treated soils are effectively impermeable, and friable.
Prepolymer Grouting
Prepolymer chemical grouts are particularly advantageous for grouting gravels and course sands. Sand treated with prepolymer chemical grouts can achieve unconfined compressive strengths greater than 1000psi. Prepolymers don’t permeate find sands, silts or clays very well.
Catalyst dosing controls set times. Prepolymer permeation grouts react with existing moisture in the ground. They expand a few times their liquid volume, which allows for reducing the amount of material needed to treat a given volume of soil.
Prepolymer grouts are also excellent for addressing high velocity water flows through soils without washing out. The reaction time can be set to be nearly instantaneous from contact with groundwater.
Advantages of Permeation Grouting
Permeation grouting is an excellent alternative to jet grouting in the case of unconsolidated granular soils below concrete slabs and foundations. In case of settlement, chemical grouting soil stabilization is generally paired with a shallow foundation repair such as polyurethane grouting. Compared to deep foundation repairs, chemical grout soil stabilization is:
Cleaner
Permeation grouting equipment is compact & electrically-powered. Dustless drilling is typical for interior applications. Mechanical connections in all components of the injection equipment ensure no loose material.
Less Disruptive
Compared to underpinning, permeation grouting 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, with 1/2″ diameter injection pipes driven into the treatment area.
Faster
Permeation 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.
Other Permeation Grouts
Alternative permeation grout materials include sodium silicate and microfine cement. Microfine cement is very economical at scale, but not as clean as resin, colloidal silica, or acrylic grout. Sodium silicate is exceptionally effective in sands, and similar in price to acrylic grouting.
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