Jet Grouting & Ground Improvement
Jet Grouting and Soil Improvement for Cutoff Walls and Underpinning
What Is Jet Grouting?
Jet grouting converts loose or water-bearing soil into an engineered soil-cement mass. High-pressure grout — and, in some systems, water and air — is injected through a rotating rod as it’s slowly withdrawn, eroding the soil in place and mixing it with cement grout to leave behind a column or panel of soil-cement with controlled strength and permeability. Jet Grouting Systems Choosing the right system is the first design step: • Single-fluid (Jet 1): only high-pressure grout is injected; produces smaller-diameter columns and is more sensitive to soil type.
• Double-fluid (Jet 2): the grout jet is shrouded by a coaxial air jet, increasing the erosion radius and column diameter.
• Triple-fluid (Jet 3): erosion (a water jet shrouded by air) is separated from grout injection, typically giving the largest and most uniformly mixed columns. Applications of Jet Grouting
• Cutoff walls: overlapping jet-grout columns form a low-permeability curtain to control groundwater seepage into the excavation.
• Base plugs: a horizontal layer of overlapping columns at the base of the excavation seals against upward groundwater flow and base heave, allowing dry excavation below the water table.
• Underpinning adjacent foundations: jet-grout columns installed beneath or beside a neighboring building’s foundation transfer load to stronger ground and prevent loss of bearing capacity from nearby excavation.
• Hardened zones behind the excavation face: targeted strength and stiffness improvement, often used to reinforce the passive resistance zone or pre-treat weak soil before installing nails or anchors.
Design and Execution Process
The system and execution parameters — injection pressure, rotation speed, withdrawal rate, water-cement ratio — are selected for each site’s actual soil conditions and verified with trial columns on-site, because jet-grout column diameter and quality depend strongly on soil type and can’t be reliably predicted from calculation alone. Column geometry (diameter, continuity, verticality) and strength — usually checked by coring and unconfined compressive strength testing — are then confirmed before the work relies on the production columns. Combined Use with Other Excavation Support Systems Jet grouting is usually a complement to other excavation support methods, not a replacement for them: a base plug, for instance, can be installed beneath a cross-lot bracing or truss bracing system, or a hardened zone can pre-treat weak soil ahead of installing a soil nailing and anchoring wall.
Construction Challenges
• Actual column diameter and quality are hard to predict before field trials.
• Significant spoil volume — a mix of displaced soil and excess grout — needs to be managed.
• Without careful pressure control, there’s a risk of ground heave or excessive lateral pressure on nearby structures.
• For cutoff walls, column overlap and continuity must be confirmed through careful quality control.
Where Does Jet Grouting Apply?
This method is widely used for sealing excavations against groundwater, underpinning neighboring buildings, and locally improving loose or water-bearing soils on urban excavation projects — particularly where other ground-improvement methods fall short due to soil heterogeneity or limited access.
Frequently Asked Questions
What’s the difference between single-, double-, and triple-fluid systems?
The main difference is how the soil is eroded: single-fluid uses grout alone, double-fluid adds an air shroud, and triple-fluid separates erosion (water plus air) from grout injection — generally, moving toward triple-fluid produces larger, more uniform columns.
Why are trial columns needed before production work?
Because actual column diameter and strength depend on each site’s soil, trial columns let the execution parameters be calibrated before the production columns are relied upon. At Ziggurat, we select the system and parameters for each site’s actual conditions and test them on-site, then verify column geometry and strength before the work depends on them.