This article is on the strengthening of the foundation of buildings. We will be discussing the method of improving the footing. Foundation strengthening shall be done after a detailed study of the soil condition, loadings on the foundation, behavior of the superstructure, etc.
Why we need Foundation Strengthening
The following can be identified as the main reasons for the strengthening of footings.
- Excessive Settlement of Foundation
Footing could settle due to the weak ground condition. The low bearing capacity of the foundation that of considered for the design of the footing could lead to the foundation settlement.
In addition, an incorrect estimation of the bearing capacity of the soil could also lead to the settlement of the footing.
- Foundation Failures
Foundation could fail due to inadequate capacity. If we notice the failure of the foundation, in such instances, foundation improvement is doubtful. However, before the loading, if we notice that the foundation thickness is not adequate, improvement of the foundation can be done.
Durability issues also could lead to the failure of the foundation. Aggressive chemicals such as chloride, sulfate, etc., and construction issues such as low cover to the reinforcement could lead to corrosion of reinforcement.
This will lead to the failure of the foundation in the load run. After careful studying, foundation improvement could be done properly. On some occasions, it may be required to replace the foundation or repair it partially.
The article underpinning the art of foundation improvement could be referred to for further information.
- Increase in the load on the Foundation
On some occasions, it could be required to increase the number of floors. This could happen after the construction of the house or during the construction.
In these instances, an increase in the column load could be assessed. Once the assessment is made, the required area of the footing can be done. Then we can do the strengthening the foundation.
More importantly, it shall check the column capacity also to make sure they can carry the increased load.
What are the Available Methods to strengthen Foundation
There are two methods for foundation improvements. Namely, they are,
- Increase the Area of the Footing
By this, the pressure under the foundation can be reduced or maintained the same with the increased load.
If we are doing the foundation improvement due to a settlement, with the increase in the foundation area, the pressure under the footing will be reduced.
- Increase the Thickness of the Footing
When the structural capacity is not adequate, an increase in the thickness of the footing can be done.
What are the Steps to be Following in Foundation Strengthening
The following steps could be followed in the foundation-strengthening process.
- Based on the cause of foundation improvement, calculate the required area of the footing and required thickness of the footing.
- Calculate the reinforcement requirement and prepare a construction drawing based on the existing drawings.
- Carrying out the excavation
- Verify the size of the foundation with the actual conditions. If required, the foundation design could be adjusted.
- Clean the concrete surface adequately.
- Chip the concrete surface
- Place screed concrete around the footing to the extent we need to increase the footing area.
- Insert the dowel bar as per the structural drawing
- Dowels shall be chemically anchored into the existing concrete. The anchorage length could be maintained in the range of 150-300mm.
- Tie the reinforcement as required.
- Apply the bonding agent to the concrete surface
- Do the concreting.