Services · Deep foundations · Underpinning
Underpinning: Strengthening Foundations Without Demolition
Underpinning strengthens the foundation of a building that is settling, or that will carry more load, without pulling it down. We do this with micropiles, jet grouting and grouting, chosen to suit the building and the ground.
Methods
Micropiles, jet grouting, grouting
Building
Usually stays in use
Process
Investigation, design, staged work, monitoring
Design and testing
With our partners
Control
Settlement and crack monitoring
Region
Türkiye and Central Asia
What is underpinning?
Underpinning makes the foundation of an existing building, or the ground beneath it, safer without demolishing the building. We add elements that carry the load down to a firm layer, improve weak ground or fill voids under the foundation. The building’s condition and the ground decide which of these it needs.
Underpinning on its own is not seismic retrofitting. If the building’s columns, beams and shear walls are weak, work on the foundation alone is not enough. That is why every job starts with a structural assessment of the building.
When do you need underpinning?
- Settlement cracks have appeared in the building and are growing
- The building is getting extra floors, or a change of use will raise the load
- An excavation on the next plot has affected the ground under the building
- A water leak has washed out the ground under the foundation
- A study has found a liquefaction risk in the ground
Underpinning methods
There are four main methods for existing buildings. On most projects we use two of them together.
| Method | What it does | When we choose it |
|---|---|---|
| Micropiles | Carry the load down to a firm layer | The firm layer is deep, or the load will rise |
| Jet grouting | Strengthens weak ground under the foundation | Loose sand and fill, liquefaction risk |
| Grouting | Fills voids and densifies the ground | Settlement caused by leaks and voids |
| Footing enlargement | Increases the bearing area of the footing | Ground is adequate but the footing is small; with a structural design |
When choosing the method, we also take the building’s use into account. For example, a low basement calls for compact rigs. Also, if the building cannot be emptied, we plan the work sequence with the occupants.
The underpinning process
We run an underpinning job in five steps. The first rule is simple: find the cause first, then propose a solution.
- Survey: We inspect the cracks and settlement on site and set up monitoring points.
- Site investigation: Our drilling partner carries out the site investigation.
- Structural assessment and design: With our design partner we assess the building and have the underpinning design prepared.
- Staged work: We follow the sequence in the design, so the building never loses support everywhere at once.
- Monitoring: We measure settlement during and after the work to check the result.
The most common mistake we see on site: applying a fix before finding the cause. For example, grouting before anyone repairs a water leak soon goes to waste. That is why every job starts with the cause.
Underpinning or demolition and rebuilding?
The building’s structural system decides this. If the structure is sound and the problem lies only in the ground, underpinning is an economical solution. If the building counts as a risky structure, however, or its structure is very weak, rebuilding comes into play.
For the rebuilding option, we explain urban regeneration and the flat-for-land model on our urban regeneration page. In both cases, the right time to decide is after a structural assessment.
Monitoring after underpinning
Measurements show whether the strengthening works. So before work starts, we set up settlement and crack monitoring points on the building.
| Check | What it shows | When |
|---|---|---|
| Settlement monitoring | Vertical movement of the building | Before, during and after |
| Crack gauges | Whether a crack is opening | During and after the work |
| Installation records | Pile, column and grouting details | For every element |
| Load test | Pile capacity | If the design calls for it |
What does the price of underpinning depend on?
The chosen method and the building’s condition set the cost. So nobody can give a sound price without a survey and a design. First we define the problem with you, then we quote from the quantities.
- Chosen method and quantities
- Working inside the building, ceiling height and access
- Staged work and keeping the building in use
- Site investigation, structural assessment and design
- Monitoring period
- Mobilisation
What to send for a quote
- The building’s architectural and structural drawings, and any foundation plan
- Photos of the cracks and problem areas
- Any site investigation and earlier assessments
- Basement dimensions, access width and address
Write to us even if you have no drawings. We carry out the first survey and plan the investigation and design with our partners.
Frequently asked questions about underpinning
We have grouped the questions we receive by who asks them. If yours is not here, call us or write through the quote form.
Building owners and managers
My building has cracks. Does it need underpinning?
Not every crack means a foundation problem. Settlement cracks are usually diagonal and often start at the corners of doors and windows. For a firm answer you need a site survey and a site investigation.
Can you underpin without emptying the building?
In most cases, yes. We work with compact rigs in the basement and around the building. However, the underpinning design makes this decision.
How long does underpinning take?
The method, the quantities and the working conditions inside the building set the duration. After the investigation and design, we give a programme based on the quantities.
Is underpinning enough to add a floor?
Adding a floor affects both the foundation and the structural system. So strengthening only the foundation may not be enough. Adding a floor also needs legal permits.
Is underpinning cheaper than rebuilding?
If the structure is sound and the problem lies only in the ground, underpinning is usually cheaper. If the building is unsafe, however, rebuilding may be the better choice. The structural assessment decides.
Contractors and project managers
An excavation next door has affected our building. What should we do?
First, monitor the movement and notify the contractor in writing. Then a survey of the ground and the building finds the cause, and an underpinning design follows if needed.
Who takes part in the work?
We run the site investigation with our drilling partner and the design with our design partner. Our own crews carry out the work on site.
Which rigs do you use inside buildings?
In basements and tight spaces we use compact micropiling rigs. The Casagrande C6 and Soilmec SM14 in our fleet suit this kind of work.
Structural and geotechnical designers
How do you transfer the load?
The new piles tie into the existing foundation through a cap, a beam or a steel connection. What matters is that the load passes from the old foundation into the new elements without a break.
Why do you work in stages?
Drilling or opening the existing foundation everywhere at once weakens the building. So the design defines the work sequence, and we follow it exactly on site.
Which method should we choose?
Micropiles lead when the firm layer is deep, jet grouting when the weak ground is loose, and grouting when there are voids. Many projects use two methods together.
Neighbours and urban regeneration
Underpinning is under way next door. Will my building be affected?
Well-planned underpinning does not harm the neighbours. Still, have your building’s condition recorded before work starts, and tell the contractor in writing if you see a problem.
Can a building designated as risky be underpinned?
For buildings officially designated as risky, a different legal process applies. In that case you need to follow the urban regeneration legislation (Law No. 6306).
Academics and students
How do you recognise settlement cracks?
Settlement cracks are usually diagonal and often start at the corners of doors and windows. The direction of the crack shows which side of the building has settled more.
Sources
Request a quote for underpinning
Send us your building’s drawings and photos of the cracks. Let us define the problem together and plan the investigation and design.