How do we strengthen an existing foundation of an old building?

Generally, strengthening of the foundations might be needed due to the alterations in serviceability of the buildings. One method of strengthening can be carried out by constructing a concrete jacket to the existing footings.

Strengthening foundations by installing jackets can be achieved either without increase in bearing area at the base or increasing it, whenever the soil has inadequate bearing capacity. Below mentioned procedure is for soil with adequate bearing capacity.
Steps to be followed:
Step1 – Excavate the surcharge soil around the footing.

Step2 – Roughen the top surface of the base slab for proper bond between the poured concrete and existing one.

Step3 – Drilling holes in the existing concrete of footing to install dowels.
Step4 – Fastening the new steel bars with the dowels using steel wires. The diameter and number of steel bars should be according to the design.

Step5 – Coating the external footing surface for proper bond between new concrete and old concrete.
Step6 – Completing the Jacketing of the footing by pouring new concrete in the steel cage.

Note: The new jacket should be properly anchored to the existing footing and column neck in order to guarantee proper transfer of loads.

Other methods which can be carried out for strengthening:
1. Strengthening by Underpinning and Enlarging the base of the foundations – By underpinning with additional structural elements below the existing foundations in form of solid concrete slabs.
2. Strengthening of the Foundations by Converting the Type of Them – That is converting a set of isolated footings to strip footings.
3. Strengthening of the Foundations by Piles

Images Source: Google and Quora

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