Special foundations

Micropiles — deep foundations to strengthen existing structures

Q: Is a soil investigation needed before micropiles?

Yes. The geotechnical study (G2 then G3 missions under NF P 94-500) determines the depth of the bearing layer and the load on each micropile. After damage, the insurer usually requires it.

Q: What is the difference between a micropile and a pile?

A conventional pile exceeds 300 mm in diameter and needs heavy plant. A micropile is slimmer and is drilled with a small rig: it suits existing buildings and tight access.

Q: Are micropiles covered by ten-year liability insurance?

Yes. Our SMABTP ten-year (décennale) insurance covers special foundations, including micropiles and underpinning.

Drilled and grouted micropiles: underpinning, extensions and building on low-bearing ground.

A micropile carries a building’s loads down to a competent soil layer several metres deep, without heavy excavation. It can be installed outside or inside a building, including where access is difficult.

Request a quote

A small-diameter pile, drilled then grouted

What is a micropile?

A micropile is a drilled pile under 300 mm in diameter, most often around 150 mm, reinforced with a steel tube or bars and bonded to the ground with cement grout. It carries load through friction along its grouted length in the competent layer, so its length depends on how deep that layer is: often around ten metres for a detached house.

French practice distinguishes four types by grouting method: type I (cased borehole filled with mortar), type II (gravity grouting), type III (single global pressure grouting, IGU) and type IV (repeated selective grouting, IRS). The more thorough the grouting, the higher the friction mobilised. The design engineer chooses the type according to the ground and the load to be carried.

What defines a micropile

Typical figures for common projects; every project is designed by an engineering firm.

Drilling diameter

Under 300 mm, most often around 150 mm: a compact rig is enough.

Steel reinforcement

A tube, for instance 88.9 × 6.5 mm, or bars, over the full length of the micropile.

Cement grout

Injected from the bottom up, it bonds the reinforcement to the ground and protects it.

Load capacity

Calculated from soil tests, according to the grouted length and the type of ground.

Access

Garage, living room, cellar, conservatory, foot of a slope or narrow terrace.

Connection to the building

Reinforced concrete pads or ground beams cast against the existing foundations.

Our expertise

Know-how in special works

We install micropiles for underpinning and for new foundations, from drilling through to connection pads and verification tests.

Our key skills

Drilled micropiles grouted with cement
Underpinning of cracked houses
Connection pads and ground beams
Drilling indoors and in difficult access
Tension tests on micropiles

How a Sirianni Travaux project unfolds

Soil investigation

The geotechnical design study (G2 mission, French standard NF P 94-500) sets the anchoring layer and the allowable loads.

Layout plan

Number, length and position of the micropiles, based on the structural engineer’s load take-down.

Drilling and grouting

Each micropile is drilled, reinforced and grouted; geotechnical construction monitoring (G3 mission) records lengths and grout volumes.

Connection and testing

Connection pads or ground beams, then a verification test on one micropile.

Frequently asked questions

Is a soil investigation needed before micropiles?

Yes. The geotechnical study (G2 then G3 missions under NF P 94-500) determines the depth of the bearing layer and the load on each micropile. After damage, the insurer usually requires it.

How many micropiles does a house need?

It depends on wall loads and on the ground. For underpinning, micropiles are placed under the load-bearing walls: one at each corner and wall junction, then at regular intervals.

Can micropiles be installed inside a house?

Yes. Drilling goes through the slab of a garage, living room or cellar, with a compact rig and after the rooms have been protected.

What is the difference between a micropile and a pile?

A conventional pile exceeds 300 mm in diameter and needs heavy plant. A micropile is slimmer and is drilled with a small rig: it suits existing buildings and tight access.

Do micropiles fix cracks caused by drought?

Yes, when the foundations sit on clay prone to shrinking and swelling: micropiles transfer the loads below the zone whose moisture varies. Cracks are repaired once the structure is stable.

Are micropiles covered by ten-year liability insurance?

Yes. Our SMABTP ten-year (décennale) insurance covers special foundations, including micropiles and underpinning.

A consolidation or foundation project?

Describe the situation — cracks, settlement, a new build — and we will come back to you once we have analysed the structure and its surroundings.

Phone06 59 90 51 91 Emailcontact@sirianni-travaux.fr

Address113 Allée des Cigales, 06700 Saint-Laurent-du-Var