Rigid Inclusions for settlement control on soft ground
Rigid inclusions are grouted or concrete columns installed in the ground without a direct structural connection to the foundation. Together with a granular load transfer platform, they carry part of the load down to more competent layers and reduce settlement.
Suitable ground conditions and applications
Can be considered where…
- Soft, compressible soils that are too weak for stone columns.
- Large slabs, tanks, warehouses, embankments and buildings where settlement must be tightly controlled.
- An alternative to piled foundations where a load transfer platform is acceptable.
Limitations
- A load transfer platform must be designed and built between the inclusions and the structure.
- Inclusions are not structural piles: they are not connected to the foundation.
- Obstructions and hard layers can limit installation.
- Grout or concrete supply and quality must be tightly controlled.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
Inclusions are usually installed with a displacement auger, which pushes the soil sideways with little spoil. Grout or concrete is pumped through the auger as it is withdrawn, forming a continuous column.
A compacted granular load transfer platform is placed on top. It spreads the load between the stiff inclusions and the soil between them, so most of the load is carried by the inclusions and settlement is reduced. The platform is sometimes reinforced with geogrid.
Design inputs
- Site investigation: soft layer thickness and strength, bearing layer.
- Loads and settlement criteria.
- Inclusion diameter, length and spacing.
- Load transfer platform thickness and material.
- Grout or concrete strength.
Trial and calibration
- Test inclusions installed with production equipment.
- Static load tests on test inclusions.
- Installation parameters agreed.
Execution controls
- Depth, torque and penetration rate from the rig instruments.
- Grout pressure and volume against depth for every inclusion.
- Position and cut-off level.
- Grout or concrete samples for strength testing.
- Platform placement and compaction.
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
Settlement criteria and inclusion capacity agreed with the consultant.
What was done
Rig records of depth, grout volume and pressure for each inclusion.
What was proven
Static load tests, integrity tests, material strength tests and platform compaction tests.
Deliverables
- Method statement and risk assessment
- Inclusion layout drawings
- Test inclusion reports
- Rig records for every inclusion
- Material test results
- As-built records
Common questions
What is the difference between rigid inclusions and piles?
Piles are structurally connected to the foundation and carry its load directly. Rigid inclusions are not connected: a load transfer platform shares the load between the inclusions and the soil.
What is a load transfer platform?
Typically a compacted granular layer between the inclusions and the structure. It spreads the load so that most of it is carried by the inclusions.
When are rigid inclusions considered?
On soft, compressible soils where settlement must be tightly controlled, for slabs, tanks, warehouses and embankments.
Discuss whether Rigid Inclusions fits your ground conditions.
Share the site location, the investigation report and the performance requirement.