Micro Piles for restricted access and underpinning
Micro piles, also written micropiles or mini piles, are small-diameter drilled and grouted piles, reinforced with steel bars or tubes. They can be installed with compact rigs in restricted access or low headroom, and they carry load mainly through the bond between grout and ground.
Suitable ground conditions and applications
Can be considered where…
- Underpinning and strengthening existing foundations.
- Restricted access and low headroom.
- Tension (uplift) as well as compression loads.
- Ground with obstructions or rock.
Limitations
- Each pile carries less load, so more piles may be needed.
- Slender piles need checking for buckling in very soft soils.
- Permanent piles need designed corrosion protection.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
A hole is drilled, often with a casing or a hollow self-drilling bar. Steel reinforcement is installed.
The hole is filled with cement grout, by gravity or under pressure, and may be post-grouted to increase bond. Load is transferred to the ground along the grouted length.
Design inputs
- Site investigation.
- Loads: compression and tension.
- Pile diameter, bond length and reinforcement.
- Grout specification.
- Corrosion protection and design life.
Trial and calibration
- Sacrificial test piles loaded to confirm bond, where specified.
Execution controls
- Drilling records.
- Reinforcement type and length.
- Grout mix, volume and pressure.
- Grout samples.
- Pile records.
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
Design loads and acceptance criteria agreed with the consultant.
What was done
Drilling and grouting records for each pile.
What was proven
Compression or tension load tests and grout strength tests.
Deliverables
- Method statement and risk assessment
- Pile layout drawings
- Pile records
- Grout test results
- Load test reports
Common questions
When are micro piles used?
For underpinning existing foundations, in restricted access or low headroom, for tension loads and in difficult ground.
How do micro piles carry load?
Mainly through the bond between the grout and the ground along the grouted length.
Can micro piles be installed inside an existing building?
Yes. Compact rigs can work in restricted access and low headroom.
Discuss whether Micro Piles fits your ground conditions.
Share the site location, the investigation report and the performance requirement.