Underpinning foundation methods
Underpinning refers to the process of providing support to the structure whereas setting up new foundations or executing repairs and modifications devoid of affecting the strength of prevailing structures.
Underpinning is done in the following situations :-
- If a building with deep foundation should have been developed adjacent to a building on shallow footings. In this case, the shallow footing should be initially reinforced.
- To safeguard a prevailing structure against the risk of extreme or differential settlement of foundation.
- To enhance the bearing strength of the foundation with the purpose of withstanding higher loads for which deepening or broadening of foundation is performed.
- To arrange a basement for a prevailing structure.
Some useful preventive measures :-
Prior to employing proper underpinning measures, the following vital points should be taken into consideration.
- All weak masonry work like joints, cracks, plastering should be corrected well in advance.
- Essential shoring and struting should be accomplished to maintain the safety of the prevailing structure.
- Critical repairing works like grouting of cracks, addition of rod among walls etc. should be executed prior to starting underpinning.
- Proper and ample care should be taken so that no movement of structure happens for which levels should be pointed.
The following methods of underpinning are mostly recognized :-
- Pit method
- Pile method
- Chemical method
- Other methods (cement grouting, freezing, vibrofloatation etc.)