Underpinning represents the process of providing temporary or permanent support to an existing foundation. Underpinning may be accomplished by extending the foundation in depth or in breadth so it either rests on a soil layer with an increased bearing capacity or distributes its load across a greater area. The main reasons for underpinning are the following:

• Avoid overloading subgrade;
• Weak foundation soil;
• Compressible layer underlies bearing material;
• Additional floors or basement;
• Adjacent excavation (settlement);
• Pile driving vibration (consolidation of loose soil);
• Groundwater pumping (settlement).

Common methods in underpinning are the use of micro-piles and jet grouting, but it can be achieved also by means of steel wales, struts braces and also timber. Due to the fact that even the most cautiously installed underpinning suffers minor settlements, these settlements must be designed to be uniformly distributed.