Mini piling - at a glance:

Typical applications

Extensions, commercial buildings, rail, industrial

Suitable for

Weak ground and restricted access sites

Typical installation

Steel piles with grout or concrete

Alternative solution

Geopolymer ground improvement (where appropriate)

What is mini piling?

Mini piling, also known as micro piling, is a specialist foundation technique that uses small-diameter steel piles, typically installed with grout or concrete, to transfer structural loads through weak ground into stronger bearing strata.

Unlike conventional piling, mini piling rigs are designed for restricted access sites where larger equipment cannot operate.

Mini piling is commonly used for:

Although highly effective, mini piling is not always the most appropriate solution. Where the objective is to improve the engineering properties of existing ground rather than transfer loads to deeper strata, ground improvement techniques such as geopolymer injection may provide a faster and less disruptive alternative.

How does mini piling work?

Mini piling transfers structural loads from existing or proposed foundations into stronger soil or rock at depth.

The typical process involves:

  1. Drilling or driving small-diameter piles.
  2. Installing reinforcement or steel casing where required.
  3. Grouting or concreting the pile.
  4. Connecting piles to the existing foundation using pile caps or beams.
  5. Transferring structural loads onto the new piles.

The method is particularly suited where shallow foundations cannot safely support structural loads.

 

micro-piling-v-geopolymer

 

Where is mini piling used?

Mini piling is widely specified across the construction and infrastructure sectors.

Typical applications include:

  • Commercial buildings
  • Warehouses
  • Rail infrastructure
  • Airports
  • Bridges
  • Residential extensions
  • Historic buildings
  • Restricted access projects
  • Structures affected by settlement

How much does mini piling cost?

The cost of mini piling varies considerably depending on:

  • Number of piles required
  • Diameter of piles
  • Installation depth
  • Ground conditions
  • Site access
  • Structural loading
  • Temporary works
  • Reinforcement requirements

While individual piles can cost from approximately £2000–£4000 per pile, the overall project cost also includes mobilisation, excavation, spoil removal, concrete, reinforcement, testing and reinstatement. Costs vary significantly depending on project complexity.

 

Advantages of mini piling

Mini piling offers several engineering benefits:

  • Suitable for restricted access sites.
  • High load-bearing capacity.
  • Proven engineering solution.
  • Suitable beneath existing structures.
  • Can reach competent strata at significant depth.
  • Well suited where additional structural loads are being introduced.

Limitations of mini piling

Mini piling is not always the most efficient solution.

Potential limitations include:

  • Specialist drilling equipment required.
  • Spoil removal.
  • Concrete and grout curing.
  • Longer construction programmes.
  • Larger site compounds.
  • Noise and vibration.
  • Greater reinstatement works.
  • Higher embodied carbon than some ground improvement techniques.

These limitations do not make mini piling unsuitable, but they should be considered alongside alternative engineering solutions.

 

When is geopolymer injection a better alternative?

Geobear's geopolymer injection does not replace mini piling in every situation.

However, where the objective is to strengthen existing ground rather than transfer loads to deep bearing strata, geopolymer injection can often achieve the required engineering performance with significantly less disruption.

Typical applications include:

  • Improving bearing capacity.
  • Treating loose granular soils.
  • Filling underground voids.
  • Correcting settlement.
  • Re-levelling foundations.
  • Slab stabilisation.
  • Extending asset life.

Projects can often be completed in days rather than weeks, with no excavation and minimal disruption to ongoing operations.

comparison-chart

 

ilford-depot

case study

Mini piling avoided at Ilford Rail Depot

During the redevelopment of Ilford Rail Depot, conventional mini piling was initially considered to strengthen new foundations.Following engineering assessment, Geobear's geopolymer solution was selected to improve bearing capacity beneath 19 foundation pads and 168 metres of strip foundations.The required 350 kPa bearing capacity was achieved within a 10-day programme, compared with an estimated six-week mini piling programme. Performance was independently verified using pre- and post-treatment plate load testing.

Read full case study

No. Mini piling is one method that can be used as part of an underpinning scheme, but underpinning can also be achieved using other engineering techniques depending on the project requirements.

No. Some settlement and bearing capacity issues can be addressed by improving the existing ground rather than installing deep foundations.

Depending on the structural loading and ground conditions, yes. Geopolymer injection is frequently used as an alternative where the objective is to improve ground strength or correct settlement without excavation.

Programmes vary depending on the project, but can range from several days to several weeks depending on the number of piles and site conditions.

Costs depend on depth, access, structural loads and site constraints. The overall project cost should also consider programme duration, disruption, reinstatement and operational downtime.