Piling in Made Ground
Made ground can present significant challenges when designing foundations for a residential or commercial development.
Fill layers may be weak, variable or contain obstructions, making it difficult to rely on conventional shallow foundations. In these circumstances, piling may be used to transfer the structural loads through the unsuitable material and into stronger ground at greater depth.
There is no single piling method that is suitable for every site containing made ground. The correct solution will depend on the depth and condition of the fill, the underlying natural strata, structural loading, groundwater, site access and any obstructions encountered.
Understanding these conditions begins with appropriate investigation. Read more about why site investigation is important for pile design.
What Is Made Ground?
Made ground generally refers to material that has been placed, filled, disturbed or reworked rather than remaining in its original natural condition.
It may be encountered on previously developed land, sites where levels have been raised, former industrial areas or plots containing historic construction and demolition material.
The composition and thickness of made ground can vary considerably across a site. It may include:
- Soil and granular fill
- Construction and demolition material
- Loose or poorly compacted material
- Existing foundations or buried concrete
- Cobbles, boulders or other obstructions
- Contaminated or variable ground
This variability is one of the main reasons why foundation design cannot be based on assumptions about the ground beneath the proposed structure.
Why Can Made Ground Cause Foundation Problems?
Shallow foundations rely on the near-surface ground being capable of safely supporting the loads from the building.
Where made ground is weak, inconsistent or poorly compacted, it may not provide reliable support. Different areas of fill can also behave differently under loading, increasing the risk of movement or settlement.
Potential concerns include:
- Variable bearing capacity across the building footprint
- Weak or compressible fill layers
- Unknown depth to suitable bearing strata
- Buried foundations, concrete, cobbles or boulders
- Groundwater affecting installation conditions
- Contaminated material and spoil-handling requirements
A piled foundation can bypass unsuitable near-surface material and transfer the building loads into stronger strata below.
How Does Site Investigation Identify Made Ground?
A site investigation provides information about the ground conditions beneath the proposed development.
The investigation can help identify:
- The type, strength and consistency of the fill
- The thickness of the made-ground layers
- The depth and condition of the natural ground beneath
- Groundwater levels
- Buried obstructions such as old foundations or boulders
- The depth of suitable load-bearing material
This information allows the engineer to assess which piling methods may be appropriate and determine the required pile depth, diameter and capacity.
Good ground information can also reduce the risk of delays, redesigns and unexpected costs after piling has started.
How Made Ground Affects Pile Design
The term made ground does not describe one consistent soil type. Its effect on pile design will depend on what the fill contains, how it was placed and what lies beneath it.
| Ground condition | Potential effect on piling |
|---|---|
| Weak or loose fill | Piles may need to pass through the fill and transfer loads into stronger ground below. |
| Variable fill thickness | Pile lengths may vary across the site according to the depth of suitable bearing strata. |
| Concrete or buried foundations | Obstructions may affect installation and require a method capable of drilling through difficult material. |
| Cobbles and boulders | Driven or augered piles may encounter refusal, making a specialist drill-and-case system more appropriate. |
| Groundwater | The water table may influence pile selection, installation and concreting requirements. |
| Contaminated ground | The amount of spoil generated and how it is handled may influence the preferred piling method. |
Which Piling Methods Can Be Used in Made Ground?
Several piling methods may be considered for made-ground sites. The correct choice depends on the ground investigation, structural requirements, access and the type of obstructions present.
Mini Piling
Mini piling is commonly used where ground conditions are weak or variable and where larger piling equipment may not be practical.
The term covers several bored, driven, drilled and screwed piling systems installed using compact equipment. This provides flexibility when working on residential developments, restricted-access sites, underpinning projects and smaller commercial schemes.
Mini piles can pass through unsuitable fill layers and transfer structural loads into more competent ground below.
For an overview of the available systems, read Different Types of Mini Piling Methods Explained.
Bottom Driven Steel Cased Piles
Bottom driven steel cased piles are installed by driving a closed-ended steel casing into the ground until the required depth or resistance is achieved.
The pile is then filled with concrete or grout and reinforced as required.
This method uses compact equipment, requires relatively little site preparation and does not create significant spoil during pile installation. It can therefore be useful on residential, restricted-access and internal projects where spoil removal would be difficult.
However, the presence of substantial buried concrete, boulders or other hard obstructions may prevent a driven pile from reaching the required depth.
Continuous Flight Auger Piles
Continuous Flight Auger piling is a bored piling method in which a hollow-stem auger is drilled into the ground in one continuous pass. Concrete is pumped through the auger as it is withdrawn.
CFA piling can provide efficient installation across larger sites where sufficient access and headroom are available.
The suitability of CFA piling in made ground will depend on the composition of the fill, the presence of obstructions, groundwater and the depth of the required pile.
Sectional Flight Auger Piles
Sectional Flight Auger piling may be considered where a bored pile is required but access or headroom prevents the use of a larger continuous-flight rig.
The bore is formed using auger sections added progressively during installation. The method selected must still be capable of passing through the made ground and reaching the required bearing material.
Overburden Drill and Case Piles
Overburden drill and case piles, including ODEX systems, may be used where made ground contains dense granular material, cobbles, boulders, buried concrete or other obstructions.
The system installs a steel casing through the overburden before forming a socket within competent rock beneath.
This can allow piles to progress through ground where driven or augered systems may otherwise encounter refusal.
Read more in our guide: What Is ODEX Piling?
How Deep Do Piles Need to Go Through Made Ground?
There is no standard pile depth for a made-ground site.
Piles must extend through the unsuitable material and reach ground capable of supporting the required structural loads. The depth will therefore depend on:
- The thickness of the made ground
- The strength and consistency of the underlying soils
- The depth of suitable bearing strata
- The pile type and diameter
- The structural loads being supported
- The engineering design requirements
The depth of made ground may also vary across the footprint of a building, meaning pile lengths are not necessarily identical throughout a project.
Further information is available in our guide to how deep mini piles can go.
Does Made Ground Increase Piling Costs?
Made ground can influence the cost of piling because it may affect the pile type, depth, installation equipment and level of investigation required.
Factors that may affect cost include:
- Greater pile depths where fill layers are substantial
- Variable pile lengths across the site
- Specialist drilling equipment where obstructions are present
- Working-platform or access requirements
- Groundwater and concreting considerations
- Contaminated spoil and disposal requirements
- Ground beams, pile caps and associated reinforced-concrete works
Although investigation adds an initial project cost, reliable ground information can reduce the risk of unexpected changes, delays and unsuitable pile designs.
Read more about the factors influencing piling costs in the UK.
Piling in Made Ground for House Extensions
Made ground is often encountered on residential sites where land has previously been developed, filled or altered.
If the near-surface material cannot safely support a proposed extension, mini piling may be used to transfer the loads through the fill and into stronger ground.
Compact piling rigs can also be useful where access to a rear or side extension is restricted.
The foundation design may include piles combined with reinforced-concrete ground beams, pile caps or a slab, depending on the proposed structure.
Read more in our guide: When Do You Need Mini Piling for a House Extension?
Piling in Made Ground for Commercial Developments
Commercial and redevelopment sites may contain variable fill, former foundations, buried structures or contaminated material from previous uses.
These conditions can influence both the piling method and the wider construction programme.
A commercial piling assessment should consider:
- The available ground-investigation information
- The extent and variability of the made ground
- The structural loads and proposed pile layout
- Existing foundations and buried obstructions
- Site access and working-platform requirements
- Noise, vibration and environmental constraints
- The management of spoil and contaminated material
Visit our Commercial Piling page for more information about Dawson Foundation Engineering’s capabilities.
Working Platform and Access Considerations
Safe piling installation requires suitable access and a stable working area for the selected rig.
Made ground may be soft, loose or inconsistent, so the existing surface should not automatically be assumed to provide suitable support for piling equipment.
The working area may need to account for:
- The weight and dimensions of the piling rig
- Delivery and storage of pile materials
- Concrete, reinforcement and support equipment
- Safe movement around the installation area
- Changes in level or areas of weak fill
Read more about what a working platform is and why it may be required.
How Is the Right Piling Method Selected?
The most suitable pile system cannot be selected from the term made ground alone.
The engineer and piling contractor must consider:
- The nature and depth of the fill
- The underlying natural ground
- The presence of groundwater or obstructions
- The required pile capacity
- Site access and headroom
- Noise and vibration restrictions
- The amount of spoil generated
- The proposed foundation connection
- The project programme and budget
One project may be suitable for a compact driven pile, while another may require an augered or overburden drill-and-case system.
A site-specific assessment is therefore essential before the foundation design and installation method are confirmed.
Discuss Your Made-Ground Project
Dawson Foundation Engineering provides piling solutions for residential and commercial projects involving weak, variable, filled or obstructed ground.
Our team can review the available site investigation information, drawings, loading requirements and access constraints before recommending an appropriate piling method.
We can also support associated reinforced-concrete works, including ground beams, floor slabs and pile caps, where required.
To discuss your project, call 0333 224 5196 or contact our team to arrange a free site visit and no-obligation quotation.