Jet Grouting for soil columns, cut-off walls and underpinning
Jet grouting forms columns or panels of cemented soil, called soilcrete, by eroding the ground with a high-pressure jet of grout, sometimes shrouded by air or preceded by a water jet, while the drill rod is rotated and withdrawn. The jet mixes the eroded soil with the grout in place. Overlapping columns can form cut-off walls, bottom plugs for excavations, underpinning beneath existing foundations or ground improvement blocks, in soils from gravel to clay.
Suitable ground conditions and applications
Can be considered where…
- Underpinning and protecting existing foundations.
- Groundwater cut-offs and base plugs for excavations.
- Strengthening soft or loose soils where access is restricted.
- Tunnel and shaft support, and treatment around obstructions.
Limitations
- Column diameter and strength vary with soil type and must be proven on a trial.
- Spoil (returned slurry) is produced in large volumes and must be handled and disposed of.
- High pressures can cause ground heave near structures; monitoring is needed.
- Strong clays and very coarse soils reduce column diameter.
- Quality depends on strict control of the jetting parameters.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
A small-diameter hole is drilled to the base of the treatment. Grout is then pumped at high pressure through nozzles near the bottom of the rod, which is rotated and lifted at a controlled rate. The jet cuts a cylinder of soil and mixes it with grout.
Single-fluid (grout only), double-fluid (grout with an air shroud) or triple-fluid (water and air to cut, grout to fill) systems are chosen for the soil and the column size. Excess slurry returns up the hole and is collected.
Design inputs
- Site investigation: soil types, grading, strength and groundwater.
- Purpose: cut-off, underpinning, bearing or retention.
- Required column diameter, strength, permeability and overlap.
- Existing structures and services nearby.
- Spoil handling and disposal route.
Trial and calibration
- Trial columns at the project site with the proposed parameters.
- Columns exposed or cored to measure diameter, continuity and strength.
- Laboratory testing of cores; parameters confirmed before production.
Execution controls
- Jetting pressure, flow, rotation and lift speed recorded continuously.
- Grout mix, density and quantity per column.
- Hole position, depth and inclination.
- Spoil return observed for consistency.
- Heave and movement of nearby structures monitored.
Verification and acceptance
Design intent, production control and acceptance verification are kept separate, so it is always clear what was required, what was done and what was proven.
What is required
Column diameter, strength, overlap and permeability criteria agreed with the consultant.
What was done
Automated jetting records for each column.
What was proven
Coring, unconfined compressive strength tests and, for cut-offs, permeability or pumping tests.
Deliverables
- Method statement and risk assessment
- Column layout plan
- Trial column report
- Jetting records
- Core and laboratory test results
- Monitoring records
Discuss whether Jet Grouting fits your ground conditions.
Share the site location, the investigation report and the performance requirement.