- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 19 Sep 2018
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. Very broadly, foundations can be categorised as shallow foundations or deep foundations.
Pile foundations are deep foundations. They are formed by long, slender, columnar elements typically made from steel or reinforced concrete or sometimes timber. A foundation is described as piled when its depth is more than three times its breadth.
Micropiles are piles that have a relatively small diameter, typically in the range of 100-250 mm. They can also be described as:
- Minipiles (generally mini piles are smaller than micro piles)
- Pin piles.
- Needle piles.
- Root piles.
- Lightweight piles.
They can be driven or screw piles and tend to be used where access is restricted, for example underpinning structures affected by settlement. They were first used in Italy in the 1950s in response to the demand for innovative underpinning techniques that could be used for historic buildings and monuments.
They are particularly suited to:
- Shallow bedrock.
- Boulders and cavities.
- Immediate hard strata.
- Where underpinning is required, such as for foundations adjacent to planned excavations.
In a typical installation process a high-strength steel casing is drilled down to the design depth. A reinforcing bar is inserted and high-strength cement grout pumped into the casing. The casing may extend along the full length of the pile, or it may only extend along part of the length of the pile, with the reinforcing bar extending along the full length.
Drilling may be achieved by a removable bit, or by a sacrificial head to the steel casing.
They can be installed in restricted access sites where there is low headroom by the use of lagging. This is where wood, steel or precast concrete panels are inserted behind the pile as the excavation proceeds so as to resist the load of the retained soil and transfer it to the pile. Greater capacity can be achieved by post-grouting within the bond length to increase frictional forces with surrounding soils.
There are advantages of micropiles include:
- They are small and relatively light.
- They are relatively inexpensive.
- They can be installed through almost any ground condition, making them suitable for installation in environmentally-challenging conditions, such as for wind turbine towers.
- The limited vibration and noise causes little disturbance.
- Piling rigs can be low-emission or even electrically driven.
- They can be installed while avoiding existing utilities, meaning that expensive utility re-routing is not required.
- They can beinstalled close to existing walls with limited headroom and congested site conditions.
- They have a high load capacity and an ability to resist compressive, tensile and lateral loads.
 Related articles on Designing Buildings Wiki
- Bored piles.
- Continuous flight auger piles.
- Driven piles.
- Geothermal pile foundations.
- Ground anchor.
- Grouting in civil engineering.
- Pad foundation.
- Pile cap.
- Pile foundations.
- Raft foundation.
- Retaining walls.
- Screw piles.
- Sheet piles.
- Soil nailing.
Featured articles and news
BSRIA publication provides guidance about the capture and analysis of big data.
Gove launches a waste and resources strategy for England.
Only 9% of construction workers are 24 or younger.
Blighting local areas, preventing investment and and encouraging anti-social behaviour.
Sharing knowledge about the conservation of the built and historic environment.
CIOB launches a call to improve quality in the built environment.
Vastint gets permission for a 6.6 hectare site to support the expansion of Leeds’ city core.
One of the Isle of Man’s best 1960s buildings.
Using renewable energy in developing countries - QSAND and Loughborough University Research collaboration.
From frost damage to sulphate attack, common causes of defects in brickwork.
Precautions to take when making advance payments.