Vibro Compaction (VC) for densification of sands
Vibro Compaction (VC), also known as vibroflotation, densifies loose sands at depth using a depth vibrator. Horizontal vibration temporarily reduces the friction between sand grains, which rearrange into a denser packing; the space created is filled by the surrounding sand or by added sand.
Suitable ground conditions and applications
Can be considered where…
- Clean, loose sands and gravels with a low fines content.
- Hydraulic fills and land reclamation.
- Reducing liquefaction potential in suitable sands.
- Thick loose deposits that surface methods cannot reach.
Limitations
- Effectiveness drops as silt and clay content rises, and Vibro Replacement may then be considered.
- Needs a reliable water supply and site water management.
- Cemented layers or obstructions may need pre-drilling.
- Not suitable for cohesive soils.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
The vibrator penetrates to the design depth under its own weight, assisted by vibration and water jetting. It is then withdrawn in stages, held at each level until the sand around it is compacted.
As the sand densifies, a cone-shaped depression forms at the surface, which is filled with sand. Points are installed on a regular, usually triangular, grid so the compacted zones overlap.
Design inputs
- Grading and fines content of the sand.
- CPT profile and target cone resistance or relative density.
- Required treatment depth.
- Point spacing and grid pattern.
- Groundwater level and liquefaction criteria where relevant.
Trial and calibration
- Baseline CPT before treatment.
- Trial points at more than one spacing, logging vibrator power and holding time per stage.
- Post-treatment CPT at the centroid between points, after an agreed waiting period.
- Spacing and stage criteria agreed for production.
Execution controls
- Depth reached at each point.
- Holding time and vibrator power at each stage.
- Sand backfill volume per point.
- Data logs for every point.
- Water and spoil management.
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
Target cone resistance or relative density agreed with the consultant.
What was done
Data-logged depth, power and time for each point.
What was proven
Post-treatment CPT compared with the baseline and the target; plate load tests where specified.
Deliverables
- Method statement and risk assessment
- Point layout drawings
- Trial report
- Data logs for every point
- Verification CPT reports
- As-built records
Common questions
Which soils can be treated by Vibro Compaction?
Clean sands and gravels with a low fines content. As the silt and clay content rises, the method becomes less effective and stone columns may be considered instead.
What is the difference between Vibro Compaction and Vibro Replacement?
Vibro Compaction densifies the existing sand. Vibro Replacement builds stone columns in soils that cannot be densified by vibration alone.
How is Vibro Compaction verified?
By CPT before and after treatment, usually at the centre point between treatment positions, compared with the target cone resistance.
Discuss whether Vibro Compaction (VC) fits your ground conditions.
Share the site location, the investigation report and the performance requirement.