December 1, 2020
JET GROUTING PROCEDURES
Typically, jet grouting is done in a "bottom-up" fashion. There are numerous varieties, though. A larger borehole annulus can be opened by precutting while drilling. To remove a higher proportion of cohesive soil and/or to improve the soilcrete's quality, the design zone might be cut twice.
When the erosive action of the jet grouting procedure is repeated right after the initial cut, this is known as double cutting. To guarantee full mixing of the grout slurry and in situ soil as well as the removal of cohesive material, the second cut, which can span the whole design zone, is performed with calculated lift and rotation rates.
Double cutting is most frequently employed in cohesive soils since the first cut can leave big chunks of highly flexible clay in the design zone.
Depending on the type of cutting fluid being used, care must be taken when double cutting. For instance, using too much water can result in weaker materials, but using too much grout can result in material waste. Additionally, it is simple to modify techniques to account for changes in soil conditions, although doing so needs the jet grout practitioner to have a thorough understanding of the subsurface conditions as well as focus.
Procedures may need to change because of spoiler returns and their control. Numerous elements can be changed to help with its restoration and control because this is the most crucial component.
• alteration of grout viscosity
• altering airflow and pressure
• using casing to lessen friction in the up-hole
• preparing the cuts
• an additional airlift system
• adjusting the borehole size
• reaming the hole by hand
• decreased jetting power
Many things can be responsible for a loss of spoil return, such as:
1. a borehole limitation... Too little of a hole through a footing; soft clays that squeeze; unyielding gravel.
2. a reduction in air return zones with open pores and gravel; very soft clays; and fibrous peats.
3. cohesion-related soil erosion If the soil is too thick, the air stops returning up the borehole and chooses a path of less resistance. If the spoil is plastic, it can cut up into chunks and clog the annulus. If the step height is too high, it will cut into larger chunks and plug up.
JET GROUTING PARAMETERS
The drilling rig equipment is frequently somewhat under the control of the jet grouting parameters used. Even yet, the process has its limitations and each component must be in good functioning order. It should be mentioned that numerous systems may produce outstanding results when the right procedures are followed in order to produce soilcrete of high quality. Only specialized contractors should choose the parameters due to equipment limitations and knowledge of systems and procedures. With this knowledge, pre-qualifying specialized contractors and performance standards will be the preferred means of ensuring the task.
Ranges of Jet Grouting Parameters
|Single Fluid||Double Fluid||Triple Fluid|
|Nozzle Sizes (mm)||na||na||1.5–3.0|
|Volume (m3 /min)||na||8–30||4–15|
|Grout Slurry||Pressure (bar)||400–700||300–700||7–100|
|Nozzle Sizes (mm)||1.0–4||2–7||5–10|
|Lift||Step Height (cm)||0.5–60||2.5–40||2–5|
|Step Time (sec)||4–30||4–30||4–20|