Permeation Grouting
Been There. Grouted That.™
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.
CJGeo performs most permeation grouting through TAM tubing installed with sonic drilling. Most permeation grouting is done with acrylic grouts, though occasionally colloidal silica or polyurethanes are best suited to the soils being treated.
How permeation grouting works
Fundamentals
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, sodium silicate, and acrylic grouts.
Options
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. Sodium silicate is relatively low viscosity and well suited for increasing the stability and strength of sands.
Types of Permeation grouts
Acrylic
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.
silica
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.
Installation Methods
tube-a-manchette
Manchette tubes are PVC pipes with cross-drilled holes on pre-determined intervals that are installed via drilling into the grouting zone. The holes are generally ever 15″, and protected by rubber sleeves.
After installation, down drill casing, the casing’s removed, and a cement bentonite grout is placed around the tubes. Straddle packers capable of isolating individual sets of tubes are then sent down each Manchette pipe to grout specific zones.
CJGeo utilizes a computerized manifold system capable of placing through up to 10 individual placement locations at once.
sacrificial tubing
Instead of Manchette tubing, driven or washed small diameter tubing can be used to install permeation grouts. The tubing is typically 0.5 inch steel tubing, which is driven to a particular depth for injection.
After injection at an individual stage, the tubing is either pulled up for the next stage, or abandoned in place.
Driven tubing is generally less expensive per linear foot than TAM tubing. However, it does not allow for multiple passes, and is less precise, as the tubing is much more likely to deflect during installation than the sonic drill casing used to install TAMs.
The Advantages
Cleanliness
Permeation grouting with acrylic and colloidal silica grouts is generally much cleaner than soil mixing or jet grouting. There are trade-offs, however, as the treated soils generally are not as strong as those treated with cement-based processes.
Small Footprint
The equipment for performing permeation grouting is generally very adaptable to tight conditions. CJGeo’s sonic drill is small enough that it can be craned into tunnel shafts, driven into buildings, etc. Once there, if the TAM can be installed, it can be grouted easily.
Increase Speed
Because the equipment is compact, and the process clean, permeation grouting in tight sites tends to be very efficient, though placement speeds are typically limited by the ability of the soil to take grout (coarser soils take grout faster).
On large, wide open sites, deep soil mixing, jet grouting, etc., are generally faster.
Speak With An Expert
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