Foundation Underpinning Pennsylvania
W.A. Building Movers has been underpinning foundations for more than 50 years in New Jersey, New York, Pennsylvania and Connecticut. Underpinning is a method used to increase the foundation depth. It is the process of modifying an existing foundation system by extending it to or into subsurface strata that is deeper and more stable than the near surface soil that supports the existing foundation system. This is done to provide vertical support that is not present in the existing design.
Methods of underpinning include the construction of footings, stem walls, driven piling or drilled piers.
Reasons for Underpinning
Underpinning may be necessary for many reasons:
- The original foundation is simply not strong or stable enough.
- The usage of the structure has changed and needs more support.
- The properties of the soil supporting the foundation may have changed or were miss characterized during design.
- The construction of nearby structures necessitates the excavation of soil supporting existing foundations.
- To increase the depth or load capacity of existing foundations to support the addition of another story to the building (above or below grade).
- It is more economical, due to land price or otherwise, to work on the present structure’s foundation than to build a new one.
- Earthquake, flood, drought or other natural causes have caused the structure to move, thereby requiring stabilization of foundation soils and/or footings.
Types of Underpinning
There are a number of different types of underpinning that are used depending on the circumstances. These include mass concrete underpinning, beam & base underpinning and mini-piled underpinning.
Mass Concrete underpinning is the most common method of underpinning. The ground below the existing building foundation is excavated in controlled stages (or pins). When strata suitable for bearing the weight of the building has been reached, the excavation is filled with concrete and left to cure before the next pin is excavated. Safe transfer of the building load to the new pin is achieved by ramming a dry sand cement packing mortar between new and old foundations.
Beam and Base
Beam and Base underpinning is a more technically advanced adaptation. A reinforced beam transfers the building load to mass concrete bases, the size and depth of which are dependent upon prevailing ground conditions and the applied loads of the building.
Mini-Piled underpinning is most suited to sites with variable ground conditions, restrictive access, or environmental pollution. It is used when foundation loads need to be transferred to stable soils at considerable depths.
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