About Mini Piles

Mini piles, also known as micro piles, are used in underpinning applications to strengthen existing structures such as bridges, retaining walls and floor slabs. Mini piles are generally made from steel and come in various sizes, from 100mm in diameter to 600mm in diameter. They are often used in areas with limited access or headroom, making them ideal for works inside buildings or on sites with restrictive access. [1]

With various applications, these small-diameter piles can be used in conjunction with steel-reinforced ground beams to replace traditional footings when ground conditions become unfavourable.

Klemm 702 piling rig at Durham Castle project

How Does Mini Piling Work?

Mini piles are driven or drilled into the ground by a piling rig and equipment. Instead of a traditional piling rig, mini piling rigs are used. These rigs are smaller in size, providing more flexibility in getting into restricted access sites. The dimensions of mini piling rigs can vary from 720mm to 2500mm wide. Some rigs can be so compact that they can enter through a 3.3ft wide door.

Mini piles can be installed in different methods or techniques. The most suitable method depends on the ground conditions and project requirements. Here are three common methods of mini piling:

  1. Sectional Flight Auger (SFA) – SFA piling is used in low headroom or very restricted job sites where a CFA rig is not possible. The piles are formed using sectional lengths of hollow stem continuous flight augers. SFA is typically considered for use in all unobstructed ground conditions, including made up ground and ground with high water tables. Due to the size of the rigs used, they are ideally suited for areas with restricted access or low working height.
  2. Augered Piling –  Augered piling is generally used in cohesive soils where segmental augers are rotated into the ground and the soil being penetrated is flighted to the surface by the augers. Where the ground is unstable, temporary casings can be installed in conjunction with the augers to progress the bore. When the desired pile length has been achieved, the steel reinforcement is placed, and the pile bore is filled with either concrete or grout. This technique is particularly time-efficient and cost-effective where open boring is possible.
  3. Mini Bottom-Driven Piling – Mini bottom-driven piling is efficient and suitable for most ground conditions. A closed-ended, thin-walled steel tube is driven in lengths between 2m and 6m using an internal drop hammer onto a dry concrete plug. The tubes are joined by a full but non-structural fillet weld as the installation proceeds until the pile is driven to a predetermined set or design length criteria. Once the required depth is reached the tube is filled with high slump concrete or grout and a single bar or cage is inserted.

How Are Mini Piles Installed?

Here is a step-by-step guide on how mini piles are generally installed [2]:

  1. Site Investigation – Before any piling work begins, a site investigation is conducted. This includes geological surveys to understand the soil profile, which helps in designing the piles according to the load requirements and soil conditions. Engineers also consider the proximity of adjacent structures and any existing below-ground utilities.
  2. Design – Based on the site investigation, engineers will design the pile system, choosing appropriate diameters, materials, and depths for the piles. This will also include specifying the layout and spacing of the piles.
  3. Site Preparation – The site is prepped and the exact pile positions are marked out.
  4. Pile Installation – The mini piles are installed according to the chosen method or technique.
  5. Grouting – In some cases, grouting is conducted to improve the load-bearing capacities of the piles.
  6. Testing – Once the piles are installed, tests are often carried out to verify their load-bearing capacity and integrity.
Piling project at Redhills, Durham

Advantages of Mini Piling

The advantages of using mini piling systems include:

  • Work extremely well both in tension and compression
  • Enables builders to create extensions to homes in tight spaces that would have been out of bounds
  • Speedy installation, depending on ground conditions
  • Causes minimal disturbance and vibration to adjacent structures during the installation
  • With suitable ground conditions, they can be installed cost-effectively with high load capacities
  • Greater depths can be reached with ease
  • Can be structurally incorporated into existing foundation systems
  • Can work within low headroom in restricted working conditions
  • Ideal for sites with environmental sensitivity or close to buildings
  • Use less concrete and steel than other piling systems, reducing the foundation’s carbon footprint

Written by Aarsleff UK
17 February 2025

Aarsleff Ground Engineering is a leading sheet piling supplier and contractor. We specialise in designing and delivering sheet piling solutions across the UK.

Headshot of Mark Fuller, Aarsleff's Piling Director

Reviewed by Mark Fuller, Piling Director
17 February 2025

Mark Fuller is the Piling Director at Aarsleff Ground Engineering. He has amassed a wealth of experience and knowledge within the specialist piling and ground engineering industry throughout his 20 years of experience in the industry. Mark is directly responsible for the overall driven piling within the business, including technical and operational management of awarded contracts, development of strategic long-term plans and planning of recruitment and resource.

A leading UK ground engineering specialist, focusing on multi-discipline excellence and value engineering. We design and deliver some of the UK’s largest ground engineering projects.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

Our vision is to bring confidence to those constructing the landscape of tomorrow .

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

1947. Central Jutland, Denmark. Per Aarsleff borrowed 10,000 Danish Kroner from his father’s life insurance, bought an excavator, and founded Northern Europe’s leading contracting company.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

Our biggest asset, our team is composed of the leading experts in ground engineering. Working with collaboration and cohesion at the core of our business, we can guarantee a quick and founded answer to all your questions.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

We recruit and reward our people based on our ‘Step into the Blue’ company culture, where we embrace the core values of Life and Health, Trust, and Responsibility.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

We do everything to ensure our team and yours work safely on our sites. With our core value of Life & Health, we see safety as a cultural pillar.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

Our ISO accreditations are an assurance to you that we take governance seriously. Read our policies to discover more.

An Aarsleff construction worker wearing a high-visibility jacket and hard hat on a site.

The projects that keep society running. Bridges, buildings, transit and rail facilities, embankment support, marine and offshore facilities, mines, airports, and water projects.

Close-up view of steel reinforcement cages at a construction site. A yellow KLEMM drilling rig is in the background.

Keeping things turning. Sewage Treatment Works, Waste Water Treatment Works, Wind Farms and Wind Turbines, Biomass Plants, and Power stations.

Aarsleff's Junttan PM 20HLC piling rig in operation with two workers present. Another piling rig can be seen in the background.

Meeting society’s needs. Nursing and care homes, MOD buildings, Schools and Universities, and small or large-sized residential developments.

Three piling rigs positioned on a muddy site under a blue sky. Construction workers are seen near the rigs.

Staying on the move. Remediation, bridges, and foundation work are integral to keeping the industry running smoothly.

Aarsleff worker kneeing down on one knee with a yellow piling rig and concrete piles in the background. The worker is wearing high-visibility clothing and a white hard hat.

The landscape of the marketplace. Mega-retail sheds, distribution warehouses, University accommodation, and major supermarket and household name units.

Commercial piling projects

Keeping things afloat. Ports and harbours, coastal defences, river embankments and inland waterways.

An aerial view of the Port of Hanstholm.