Special foundations

Underpinning — strengthening the foundations of an existing building

Q: When should underpinning be considered?

When cracks open or come back after repair, and a geotechnical diagnosis points to the foundations or the soil. Filling cracks without treating the cause only hides them.

Q: Which technique is used?

Most often drilled micropiles, connected to the walls by reinforced concrete pads or ground beams. The choice and design follow from the geotechnical study.

Q: How long do the works take?

From a few days to a few weeks depending on the number of micropiles and access. The sequencing keeps the building stable at every stage.

Q: Is the result lasting?

Yes: the loads rest on a deep layer, sheltered from the moisture changes that make surface clay move.

Underpinning with micropiles: cracked houses, settlement, drought damage on clay soils.

Underpinning transfers the loads of an existing building to stable, deeper ground when its foundations are no longer adequate: cracks opening up, settlement, clay weakened by drought. We work on houses, apartment buildings and older structures, alongside engineering firms and insurers’ loss adjusters.

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Giving a moving building sound footings again

What is underpinning?

Underpinning strengthens or deepens the foundations of a building without demolishing it. It is needed when cracks open and close with the seasons, when a corner of the house sinks, or when an extra storey would load foundations that were not designed for it.

In the Var and parts of the Alpes-Maritimes, the most frequent cause is shrink-swell clay: the ground shrinks in summer, swells in winter, and shallow foundations follow its movements. Poorly compacted fill, leaking pipes and sloping ground come next. Underpinning then means carrying the building on micropiles anchored below the moving zone, connected to the walls by reinforced concrete pads or ground beams.

Signs of a foundation problem

They call for a diagnosis before any crack repair.

Stepped or diagonal cracks

Along the joints of a block wall, or running from the corners of doors and windows.

Cracks that change with the seasons

Wider at the end of summer, finer in winter: a sign of clay soil.

Sticking doors and windows

Openings distort when part of the building sinks.

Terrace or extension pulling away

A gap opening between the house and a terrace, garage or conservatory.

Clay soil and drought

Municipality recognised as a drought natural disaster area, medium or high shrink-swell hazard.

Plans for an extra storey or extension

New loads on existing shallow foundations.

Our expertise

Know-how in special works

We carry out underpinning with micropiles on damaged buildings or buildings to be strengthened, working with the engineering firm and, after damage, with the insurer’s loss adjuster.

Our key skills

Underpinning with micropiles
Connection pads and ground beams
Drilling indoors, under a conservatory or in a garage
Drought damage and expert assessments
Sites with difficult access

How a Sirianni Travaux project unfolds

Diagnosis

A geotechnical diagnosis (G5 mission, French standard NF P 94-500) establishes the cause of the damage: soil, foundations, water.

Design

Geotechnical design (G2 mission) and micropile layout based on the building’s load take-down.

Works

Micropiles drilled and grouted along the walls, outside and inside, then connection pads cast against the existing foundations.

Monitoring and repairs

Construction monitoring (G3 mission), a verification test, then crack repair once the structure is stable.

Frequently asked questions

When should underpinning be considered?

When cracks open or come back after repair, and a geotechnical diagnosis points to the foundations or the soil. Filling cracks without treating the cause only hides them.

Do we have to move out during the works?

Usually not. Micropiles are drilled from outside; when some are needed indoors, the rooms concerned are cleared and protected for the duration of the works.

Can underpinning be covered by insurance?

Yes, if a drought natural disaster decree (catastrophe naturelle) covers the municipality and the period of the damage, or if the builder’s ten-year liability insurance applies. The claim must be filed with the insurer within 30 days of the decree’s publication; the insurer then appoints a loss adjuster.

Which technique is used?

Most often drilled micropiles, connected to the walls by reinforced concrete pads or ground beams. The choice and design follow from the geotechnical study.

How long do the works take?

From a few days to a few weeks depending on the number of micropiles and access. The sequencing keeps the building stable at every stage.

Is the result lasting?

Yes: the loads rest on a deep layer, sheltered from the moisture changes that make surface clay move.

Let’s talk about your project or structural issue

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