Cavity Probing & Grouting to locate and treat voids
Cavity probing and grouting locates and treats voids and weak zones, such as solution features in limestone or gypsum, old excavations or loosened ground, by drilling probe holes on a grid and filling detected voids with cement-based grout.
Suitable ground conditions and applications
Can be considered where…
- Karstic limestone or gypsum-bearing ground where solution cavities are suspected.
- Sites with a history of sinkholes or ground loss.
- Beneath foundations, tanks, roads and pipelines.
- Voids or loosened ground beneath existing slabs.
Limitations
- Probing tests the ground only at drilled points, so the grid spacing sets the risk of missing a cavity.
- Open cavities connected to large voids can take large volumes of grout; staged grouting or stiffer grout may be needed.
- Grout must be prevented from travelling into services or neighbouring land.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
Probe holes are drilled on a grid with rotary-percussive equipment. Drilling parameters (rate of penetration, flush loss, sudden rod drops) are recorded to identify voids and soft zones.
Where anomalies are found, closer secondary holes define their extent. Voids are then filled with cement-based grout in stages until agreed refusal criteria are met, and check holes confirm the treatment.
Design inputs
- Geology and site investigation, including any geophysical survey.
- Foundation layout and loads.
- Probing grid spacing and depth.
- Grout mix design, with sulfate-resisting cement where gypsum is present.
- Grouting pressures, volumes and refusal criteria.
Trial and calibration
- Initial probing on the primary grid.
- Grout mix trials for flow and strength.
- Grouting procedure confirmed on the first treated zones.
Execution controls
- Drilling parameters logged for every hole.
- Grout volume and pressure per stage.
- Refusal criteria checked at every hole.
- Hole location and depth records.
- Monitoring for grout escape.
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
Treatment zone and acceptance criteria agreed with the consultant.
What was done
Drilling logs, grout takes and pressures for each hole.
What was proven
Check holes after grouting, grout strength tests and comparison of grout takes.
Deliverables
- Method statement and risk assessment
- Probing grid drawings
- Drilling logs
- Grouting records
- Check hole results
- Void and treatment plans
Common questions
When is cavity probing needed?
In limestone or gypsum-bearing ground where solution cavities are suspected, or where a site has a history of sinkholes, especially beneath foundations.
How are cavities detected?
From the drilling record: a sudden drop of the drill rods, loss of the drilling flush or unusually fast penetration indicates a void or weak zone.
How do you know the grouting is complete?
Grouting continues until agreed refusal criteria are met, and check holes are drilled afterwards to confirm the treatment.
Discuss whether Cavity Probing & Grouting fits your ground conditions.
Share the site location, the investigation report and the performance requirement.