Foundation underpinning strengthens the foundation of an existing structure. Underpinning may be necessary for several reasons:
- The original foundation is weak or unstable
- Soil conditions supporting the foundation have changed
- Soil conditions were misdiagnosed prior to construction
- New construction nearby required excavation
- Flood, drought or landslides have caused the structure to move
One approach to underpinning is extending the depth or breadth of the foundation. The goal is to extend the foundation to rest on more supportive soil or to distribute the load more evenly across a greater area. Other underpinning techniques include micropiles and jet grouting. Grouting involves injecting an expandable resin into the soil to compact and strengthen the soil. Minipiles are a viable option when ground conditions are inconsistent. They’re also ideal in tight quarters where maneuverability is limited. Underpinning minipiles are often reinforced with anchoring or tie backs and may be combined with grouting.
Other underpinning methods include beam and base underpinning, pile and beam underpinning, piled raft underpinning and screw pile and bracket underpinning. The right technique for your project is dictated by soil condition, foundation condition and other factors.