Services · Deep foundations · Micropiles
Micropiles: Underpinning and Deep Foundations in Tight Spaces
Micropiles are small-diameter piles: we drill a narrow hole, insert a steel tube or bar and fill it with cement grout. Our compact rigs work inside existing buildings, in basements and on narrow plots.
Drill diameter
Under 300 mm
Load-bearing steel
Steel tube or bar
Grouting
Cement grout, pressure grouting if needed
Direction
Vertical or raking
Working area
Basements, inside buildings, narrow plots
Region
Türkiye and Central Asia
What are micropiles?
A micropile is a drilled and grouted pile, usually with a drill diameter under 300 mm. The European standard EN 14199 uses the same limit. In Türkiye the method is known as mini kazık.
The steel inside carries most of the load. The cement grout around it protects the steel and passes the load into the ground. So a micropile is not simply a small bored pile; it works in a different way.
Micropiles also work in both compression and tension. Because we can drill them at an angle, they also help resist horizontal and seismic forces.
When do you need micropiles?
- The foundation of an existing building is no longer adequate, or the building is getting extra floors
- The work is in a basement or inside a building with a low ceiling
- The plot is narrow, the neighbour is attached and a large rig cannot get in
- The ground holds fill, boulders or rock that make drilling hard
- The structure has tension loads, for example uplift from groundwater
Micropiles or bored piles?
Both piles carry loads down to deeper layers. However, they carry the load in different ways, use different rigs and suit different places.
| Topic | Micropile | Bored pile |
|---|---|---|
| Diameter | Usually under 300 mm | Usually 60 cm and above |
| What carries the load | Mostly the steel tube or bar | The reinforced concrete section |
| Fill material | Cement grout | Concrete |
| Rig | Compact; fits into basements and buildings | Heavy; needs a wide working area |
| Direction | Vertical or raking | Mostly vertical |
| Load per pile | Relatively low; more piles share the load | High |
| Typical use | Underpinning, tight spaces | New foundations, retaining walls |
Jet grouting, by contrast, is not a pile but a ground improvement method. It mixes the soil with cement in place to form columns. On some strengthening jobs we use micropiles and jet grouting together.
Where do we use micropiles?
We use micropiles most often in existing structures. They are also useful for new ones.
Underpinning
Ties the foundation of a settling or more heavily loaded building to a firm layer.
Basements and interiors
Our compact rig works in low basements and inside factories.
Narrow plots
Builds new foundations on terraced plots that a large rig cannot reach.
Tension piles
Resist uplift from groundwater and overturning forces.
In an existing building, the most critical issue is how the load moves from the old footing into the new pile. The structural design sets this connection, and we build it on site to the design.
How do we install micropiles?
Each pile takes five steps. In an existing building we do not install all the piles at once but follow the sequence in the design.
- Coring and setting out: We mark the pile positions and core through the existing footing where there is one.
- Drilling: Depending on the ground, we use an auger, rotary drilling with rods or a down-the-hole hammer. If the hole could collapse, we advance with casing.
- Steel insert: We lower the steel tube or bar into the hole with centralisers. The centralisers keep an even layer of grout around the steel.
- Grouting: We pump cement grout from the bottom of the hole upwards. Where the design calls for it, we add a second stage of pressure grouting.
- Connection: We tie the pile head into the footing with a plate or a new pile cap.
The most common mistake we see on site: pouring grout in from the top of the hole. The grout then separates from water and mud, and the pile ends up with voids. That is why we always place grout from the base through a hose.
Micropile diameters and grout volume
Load, ground and rig together set the diameter, steel and length. On most projects the drill diameter falls between 15 and 30 cm. The structural design chooses the steel.
| Drill diameter | 1 m of pile, theoretical grout | 12 m pile, theoretical grout |
|---|---|---|
| Ø15 cm | 0.018 m³ | 0.21 m³ |
| Ø20 cm | 0.031 m³ | 0.38 m³ |
| Ø25 cm | 0.049 m³ | 0.59 m³ |
| Ø30 cm | 0.071 m³ | 0.85 m³ |
The table shows the theoretical hole volume without deducting the steel. On site, however, grout use comes out higher. This is because grout also travels into voids in loose fill and fractured rock.
Micropile quantity and grout calculator
You can work out the total drilled length and the theoretical grout volume for your project below. The result is for an early budget; the design sets the final quantities.
Optional: rough budget with your own unit rates
Rough budget: —
Theoretical geometric volume. Grout take on site is often clearly higher, depending on the ground. Steel, mobilisation and taxes are not included.
Quality control and load testing of micropiles
For every pile we record the drilled length, the layers, the steel details and the grout volume. If the supervising engineer wants grout samples, we help take them during grouting. When working in an existing building, we also recommend monitoring its settlement.
| Check | What it shows | What it does not show |
|---|---|---|
| Installation record | Drilled length, layers, steel and grout volume | The load the pile will carry |
| Grout samples | Grout strength | Grout continuity in the hole |
| Static load test | Movement and capacity in compression or tension | The quality of the other piles on its own |
The client or the specification usually asks for a load test. When asked, our testing partner carries it out. For micropiles, a tension test is also easier to set up than a compression test.
What does the price of micropiles depend on?
We usually price micropiles per metre. However, work in a basement and work on an open site cannot cost the same. That is why we do not publish rates and quote from the quantities instead.
- Diameter, length, number and total quantity
- Ground and rock: rock drilling and the need for casing
- Type and amount of load-bearing steel
- Grout use and pressure grouting
- Coring and connection work at the existing footing
- Working height, site access and the tests you need
What to send for a quote
- Site investigation report and borehole logs
- Pile plan, a list of diameters, lengths and numbers, and the steel detail
- For existing buildings, the strengthening design and the foundation plan
- Basement ceiling height, access width and photos
Write to us even if some documents are missing. We make an initial assessment from what you have and fill the gaps together. Also, if you need a site investigation, we can arrange it with our drilling partner.
Frequently asked questions about micropiles
We have grouped the questions we receive by who asks them. If yours is not here, call us or write through the quote form.
Buying and cost
How much do micropiles cost per metre?
We do not publish a fixed rate, because the price depends on the ground, the steel and the site. Send the pile list and the site investigation and we will quote from the quantities. Our quote shows drilling, steel, grout and connection work on separate lines.
Who supplies the steel tube?
We agree at quote stage who buys the steel and state it clearly in the quote. In every case we also check the steel type and length against the structural design.
Are micropiles cheaper than bored piles?
On open sites with heavy loads, bored piles are often cheaper, because one bored pile carries the load of several micropiles. In a basement or on a narrow plot, however, a bored piling rig cannot get in. There, micropiles may be the only option.
Why do quotes from different firms differ so much?
Usually the scope differs. For example, one quote may leave out coring, casing, pressure grouting or the load test. Line up the items first, then compare the unit rates.
Project managers and contractors
How long does micropiling take?
The number of piles, their length, the ground and the working conditions set the duration. Also, in an existing building we install the piles in stages, so the programme differs from an open site. With the quote we provide a programme based on the quantities.
Can you work while the building is in use?
In most cases, yes. However, the strengthening design makes this decision. So we separate the work area for noise, dust and safety, and agree a schedule with the occupants.
Will micropiling damage the building?
We work by drilling, so vibration stays low. Still, coring the footing and removing soil call for care. That is why we follow the pile sequence in the design and recommend monitoring the building’s settlement.
How much headroom does the rig need?
That depends on the rig and the rod length. So send us the ceiling height and the access width, and we will plan the rig and rods around them. For example, under a low ceiling we work with short rods joined one by one.
Do you work outside Türkiye?
Yes. We work in every province of Türkiye and have also worked in Uzbekistan. For distant sites we fix the rig and crew plan before work starts.
Site engineers
What do we need to prepare for work in a basement?
Check the access route for the rig, the ceiling height and the load capacity of the slab. You will also need space for the grout mixer and pump, plus water and power. We set up the system for collecting drilling water and mud together with you.
How do you drill through the existing footing?
We core through the reinforced concrete footing with a core drill. Before coring, we check the design for reinforcement and service positions. If a pile needs moving, we only do it with the designer’s approval.
What happens if we hit water while drilling?
Water does not stop micropiling. If the hole starts to collapse, we advance with casing. Because we place grout from the base, the grout pushes the water up and out.
How do you drill raking piles?
We set the rig mast to the angle in the design and drill along that line. We also check the angle on every pile and note it in the record.
Supervising engineers and inspectors
What records do you keep for each pile?
We record the pile number, drilled length, angle, layers passed, steel details and grout volume. If we pressure grout, we also note the pressure and volume. These records form the basis for payment and for reading load test results.
What does high grout consumption mean?
Loose fill, voids or fractured rock absorb grout. So high consumption is not a fault on its own. If it is very high, however, we look for the cause together and inform the designer.
Which standard do you work to?
For construction we follow EN 14199 (execution of micropiles), which Türkiye adopts as TS EN 14199. Designers use TBDY 2018 and Eurocode 7. On public works we also follow the client’s technical specification.
Structural and geotechnical designers
What limits micropile capacity?
Two things limit capacity: the strength of the steel and the bond between grout and ground. In weak ground, steel buckling also needs a check. The designer does the design; we build the diameter, length and steel it specifies.
What does pressure grouting add?
Pressure grouting helps the grout grip the ground better in the bond zone. As a result, a pile of the same length can carry more load. The design should therefore state which grouting method to use.
How do you connect the pile to the existing footing?
The structural design sets the connection. For example, we fit a steel plate on the pile head or embed the pile in a new reinforced concrete cap. What matters is that the load passes from the old footing into the pile without a break.
Building owners and managers
My building is settling. Can micropiles help?
They can, but first you need to find the cause. We cannot decide without a site investigation and a structural assessment of the building. If the strengthening design calls for micropiles, we install them on site.
Do I need micropiles to add a floor?
An extra floor increases the load on the foundation. So if the existing foundation cannot carry that load, micropile underpinning is one option. The structural design decides, and adding a floor also needs legal permits.
Are micropiles earthquake resistant?
Well-designed micropiles help carry seismic forces, and raking piles work well against horizontal loads. A pile alone, however, does not make a building earthquake resistant. The building’s structural system also needs its own assessment.
Academics and students
Are mini piles and micropiles the same thing?
Yes. Mini pile, micro pile and micropile all describe the same system. They share a small drilled hole, load-bearing steel and cement grout. EN 14199 puts piles with a drill diameter under 300 mm in this class.
What are the grouting types?
The FHWA classification has four types. In Type A the grout goes in under its own weight; in Type B it goes in under pressure as the casing comes out. In Types C and D a second stage of pressure grouting follows the first grout.
Why does buckling matter?
A micropile is a very slender element. In very soft ground or across a void, lateral support drops and the steel can buckle. For this reason the section needs its own check in weak layers.
Sources
Request a quote for your micropiles
Send us your site investigation and strengthening design. Add the basement dimensions and photos, and we will settle the rig and a quantity-based quote together.