Grundomat Piles Explained
The Go-To Choice for Domestic Projects
A Grundomat is a compact pneumatic piling hammer commonly used to install small-diameter bottom-driven steel-cased piles.
Its portability and compact dimensions make the system particularly useful for house extensions, rear gardens, internal works and other projects where access for a conventional piling rig is restricted.
Dawson Foundation Engineering recently used a Grundomat piling system to install 150mm diameter bottom-driven piles to a depth of 10 metres for a domestic extension project.
This guide explains how Grundomat piles are installed, why they are frequently used for residential foundations and the limitations that must be considered before selecting the method.
What Is a Grundomat?
The term Grundomat refers to a compact pneumatic, or air-driven, hammer. It was originally developed as a brand name but is now commonly used within the piling industry when describing this type of equipment.
The Grundomat is a cylindrical tool powered by compressed air. An internal piston produces repeated high-frequency impacts, which drive the steel pile casing into the ground.
Unlike a conventional tracked piling rig, the Grundomat operates from inside the steel casing. This keeps the installation equipment compact and allows the system to work in locations that would otherwise be difficult to reach.
Grundomat hammers are available in different sizes. Dawson Foundation Engineering commonly uses:
- A 95mm Grundomat to install 100mm diameter piles
- A 130mm Grundomat to install 150mm diameter piles
Grundomat piling is one form of bottom-driven steel-cased piling.
How Does Grundomat Piling Work?
A Grundomat is used to drive a permanent steel casing into the ground.
The pile begins with a closed-ended steel tube known as the starter section. The bottom of the casing is sealed with a welded plate, and limestone is placed inside the tube to form a driving pack.
The Grundomat is lowered into the casing and repeatedly strikes the driving pack. These impacts transfer force through the closed base of the starter section and advance the casing into the ground.
Once the starter section has been driven to slightly above ground level, an open-ended follower section is welded onto it. The Grundomat is repositioned inside the new section, and the driving process continues.
Further casing sections are added until the pile reaches:
- The specified design depth
- The required rate of penetration
- The driving resistance stated within the pile design
The completed steel casing is then filled with concrete or grout and reinforced as required.
For a fuller explanation of the system, read What Are Bottom-Driven Steel-Cased Piles and When Can They Be Used?
Grundomat Piling Installation Process
A typical Grundomat piling sequence involves:
- Setting out the pile position in accordance with the foundation design
- Placing the closed-ended starter casing at the required location
- Adding limestone to create the driving pack
- Lowering the Grundomat hammer into the casing
- Using compressed air to drive the starter section into the ground
- Welding additional follower casings onto the pile
- Continuing installation until the required depth or resistance is achieved
- Removing the Grundomat equipment
- Filling the permanent casing with concrete or grout
- Installing the specified reinforcement
- Connecting the pile to a ground beam, pile cap or other foundation detail
The exact sequence will depend on the pile design, ground conditions and layout of the proposed foundation.
Why Are Grundomat Piles Used for Domestic Projects?
Domestic piling projects frequently involve access and space restrictions that make conventional piling equipment impractical.
Rear extensions, side extensions and underpinning projects may be located behind an existing house, within an excavated trench or close to neighbouring properties.
A Grundomat system can provide a practical solution because the main hammer is compact enough to be transported through narrow access routes.
| Benefit | Why It Helps on Residential Projects |
|---|---|
| Portable equipment | The Grundomat can be moved by two operatives using a small mechanical aid such as a trolley. |
| Restricted-access installation | The system can reach rear gardens, internal spaces and areas inaccessible to larger tracked rigs. |
| Compact working arrangement | The hammer operates inside the casing and can be used within foundation trenches and confined spaces. |
| No bored spoil | The steel casing displaces the ground rather than excavating it, reducing spoil-handling requirements. |
| Low vibration for a driven system | The high-frequency, low-impact action can produce less vibration than some other driven piling methods. |
| Cost-effective for suitable schemes | Compact equipment and straightforward mobilisation can provide an economical solution for smaller residential foundations. |
Visit our Residential and Domestic Piling page for further information about foundation solutions for extensions and new-build properties.
Can Grundomat Equipment Reach a Rear Garden?
Grundomat equipment is particularly useful where the proposed foundations are located behind an existing property.
The hammer can be manually transported using a trolley or similar mechanical aid, avoiding the need to bring a large piling rig through the house or along a narrow side passage.
Access planning must still account for:
- The Grundomat hammer
- The compressed-air equipment and hoses
- Steel casing sections
- Welding equipment
- Concrete or grout
- Reinforcement
- Safe access for the installation team
The casing sections must also be transported to the pile positions and safely handled within the available working area.
Read more about the challenges involved in restricted-access piling.
Grundomat Piling in Foundation Trenches
Grundomat systems can operate from within excavated foundation trenches, making them useful where piles are being installed beneath reinforced-concrete ground beams.
This can allow the pile positions and ground-beam excavations to form part of a coordinated foundation layout.
The trench must provide sufficient room for:
- Safe positioning of the casing
- Operation of the pneumatic hammer
- Welding additional casing sections
- Concrete and reinforcement installation
- Safe access and escape for operatives
The stability and safety of any excavation must be considered before personnel or equipment enter the trench.
What Loads Can Grundomat Piles Support?
Grundomat-installed piles are generally used for modest structural loads associated with domestic and small-scale projects.
The Dawson Foundation Engineering project information describes typical Grundomat pile capacities of up to approximately 100kN.
This can be sufficient for many single-storey and two-storey residential structures, subject to the structural and geotechnical design.
Actual pile capacity will depend on:
- The pile diameter
- The installed pile depth
- The ground conditions
- The achieved driving resistance
- The concrete and reinforcement design
- The loads imposed by the proposed structure
- The arrangement and spacing of the piles
A capacity figure should not be applied universally. Each foundation scheme must be designed for the individual project.
What Pile Diameters Can Be Installed?
The Grundomat sizes commonly used by Dawson Foundation Engineering are associated with:
- 100mm diameter piles installed using a 95mm Grundomat
- 150mm diameter piles installed using a 130mm Grundomat
These smaller diameters are particularly suited to lightweight structures and restricted-access domestic work.
Dawson Foundation Engineering also installs larger bottom-driven steel-cased piles using other compact driving equipment. Available bottom-driven pile diameters include:
- 100mm
- 150mm
- 168mm
- 220mm
- 273mm
- 323mm
The selected diameter will depend on the structural loading, pile capacity, ground conditions and equipment that can reach the site.
Do Grundomat Piles Create Spoil?
Grundomat piles do not create bored spoil during pile installation.
The steel casing is driven into the ground, displacing the surrounding soil rather than removing it with an auger.
This can be beneficial on residential and confined sites because it reduces:
- The amount of material requiring removal
- Storage requirements within a small working area
- Mud and spoil handling around an occupied property
- Potential disposal costs
- Disruption associated with transporting excavated material through narrow access routes
Excavated material may still be generated when forming ground beams, pile caps, floor slabs or other associated foundation works.
Are Grundomat Piles Low Vibration?
Grundomat piling is a driven method, so it does generate some noise and vibration.
However, the pneumatic hammer uses repeated high-frequency, low-impact blows and can produce lower vibration than some larger driven piling systems.
This can make the method suitable for projects close to:
- Existing houses
- Neighbouring properties
- Sensitive structures
- Internal walls and foundations
- Buildings requiring underpinning
Site-specific conditions must still be considered. The likely effect of the installation will depend on the ground, pile diameter, distance from neighbouring structures and condition of the surrounding buildings.
Where driven installation is not appropriate, a bored method such as Sectional Flight Auger piling may be considered.
Can Grundomat Piles Be Used for Underpinning?
Grundomat piles may be considered for underpinning where compact equipment and restricted-access installation are required.
The system can be useful inside existing buildings or close to walls where a conventional piling rig cannot operate.
The piles must be incorporated into a properly designed underpinning arrangement, which may include:
- Reinforced-concrete beams
- Cantilever beams
- Knuckle piles
- Internal piled rafts
- Connections to existing foundations
The suitability of the method will depend on the condition of the structure, ground conditions, access and required load transfer.
What Ground Conditions Are Suitable?
Ground conditions determine whether a Grundomat pile can reach the required depth and driving resistance.
The assessment should consider:
- Soil type, strength and consistency
- The depth of weak or unsuitable material
- The depth of suitable bearing strata
- Made ground or variable fill
- Groundwater conditions
- Buried concrete, old foundations or masonry
- Cobbles, boulders or other obstructions
Because the casing is driven rather than drilled, substantial buried obstructions can prevent the pile from advancing to the required depth.
Where the ground contains significant concrete, boulders, dense overburden or rock, an alternative method may be more appropriate.
Read more about why site investigation is important for pile design and the challenges associated with piling in made ground.
Does Grundomat Piling Require Site Preparation?
Grundomat systems generally require less access preparation than tracked piling rigs because the equipment is smaller and can be transported manually.
However, every project still requires a safe, stable and adequately prepared working area.
The site may need to accommodate:
- The hammer and associated compressed-air equipment
- Steel casing storage
- Welding operations
- Concrete or grout deliveries
- Reinforcement handling
- Foundation excavations
- Safe movement of operatives
A formal stone working platform may not be required for every Grundomat project, but the ground and excavations must still be suitable for the equipment and proposed activities.
Read our guide to working platforms for piling equipment.
Grundomat Piles vs Other Restricted-Access Methods
| Method | How It Is Installed | Typical Consideration |
|---|---|---|
| Grundomat piles | A compact pneumatic hammer drives small-diameter steel casings into the ground. | Particularly suited to modest domestic loads and very restricted access. |
| Rig-installed bottom-driven piles | A compact tracked rig or internal drop weight drives larger steel casings. | Can accommodate larger pile diameters and capacities where access allows. |
| Sectional Flight Auger piles | Short auger sections bore into the ground before concrete and reinforcement are installed. | Low-vibration alternative where a driven system is not suitable. |
| Screw piles | Steel shafts with helical plates are rotated into the ground. | Rapid installation and minimal excavation where the ground suits the method. |
The most appropriate method will depend on the structural loads, ground conditions, access, noise and vibration constraints and foundation design.
Learn more in our guide to the different types of mini piling.
Grundomat Piles and Ground Beams
Grundomat piles installed for a house extension are commonly connected using reinforced-concrete ground beams.
The ground beams transfer loads from the proposed walls and structure into the individual piles.
A complete foundation package may include:
- Pile and ground-beam design
- Setting out
- Foundation excavation
- Grundomat pile installation
- Reinforcement
- Formwork
- Concrete placement
- Floor slabs or pile caps
Dawson Foundation Engineering can undertake the piling alone or provide the associated reinforced-concrete foundation works.
Example of Grundomat Piling on a Restricted-Access Site
Dawson Foundation Engineering used a Grundomat displacement hammer for a residential extension project in Camden.
The working area was approximately 30 metres from the road and one storey below street level, making conventional piling-rig access impractical.
The team installed nine 150mm diameter bottom-driven piles to depths of up to 6 metres using the compact Grundomat system.
View the full case study: Bottom-Driven Piling Works for a Residential Extension in Camden.
When Might Grundomat Piling Not Be Suitable?
A Grundomat system will not be the correct solution for every residential piling project.
An alternative method may be required where:
- The structural loads exceed the practical capacity of the proposed pile diameter
- Substantial buried obstructions prevent the casing from advancing
- The ground conditions do not provide the required pile performance
- Noise or vibration restrictions prevent driven installation
- A larger pile diameter is required
- There is insufficient room to handle and weld the casing sections safely
- The proposed foundation arrangement requires a different pile system
Ground investigation information, structural loads and an assessment of the site access are required before the method can be confirmed.
Frequently Asked Questions
Is a Grundomat a piling rig?
A Grundomat is a compact pneumatic hammer rather than a conventional tracked piling rig. It operates inside the steel pile casing and drives it into the ground using repeated impacts.
What size piles can a Grundomat install?
Dawson Foundation Engineering commonly uses 95mm and 130mm Grundomat hammers to install 100mm and 150mm diameter piles respectively.
How deep can Grundomat piles go?
There is no single standard depth. Dawson Foundation Engineering has used the system to install 150mm piles to a depth of 10 metres. The required and achievable depth depends on the ground conditions, driving resistance and foundation design.
Are Grundomat piles suitable for house extensions?
Yes, where the loads and ground conditions suit the system. Their compact equipment and restricted-access capability make them particularly useful for rear and side extensions.
Do Grundomat piles create spoil?
No bored spoil is created during pile installation because the steel casing displaces the soil rather than excavating it.
Are Grundomat piles vibration-free?
No. Grundomat piling is a driven process and therefore generates some vibration. However, its high-frequency, low-impact operation can produce lower vibration than some other driven piling techniques.
Can Grundomat piles be installed inside a building?
They may be installed internally where there is sufficient space for the casing, hammer, compressed-air equipment, welding, concrete and reinforcement operations.
Do Grundomat piles need ground beams?
Many domestic schemes use reinforced-concrete ground beams to connect the piles and support the structure. The required connection will depend on the foundation design.
Are Grundomat Piles Suitable for Your Project?
Grundomat piles can provide a compact and cost-effective foundation solution for house extensions, underpinning works and other restricted-access domestic projects.
The method is particularly useful where small equipment is required, spoil removal would be difficult and the structural loads are suitable for small-diameter bottom-driven piles.
The final decision must be based on the ground conditions, structural design, access, nearby structures and the required pile capacity.
To discuss your project, call 0333 224 5196 or contact our team to arrange a free site visit and no-obligation quotation.
