Underpinning to Walls

To prevent fracture, damage or settlement of the wall(s) being underpinned the work should always be carried out in short lengths called legs or bays. The length of these bays will depend upon the following factors:

1. Total length of wall to be underpinned.
2. Wall loading.
3. General state of repair and stability of wall and foundation to be underpinned.
4. Nature of subsoil beneath existing foundation.
5. Estimated spanning ability of existing foundation.

Generally suitable bay lengths are:

1000 to 1500 for mass concrete strip foundations supportingwalls of traditional construction.
1500 to 3000 for reinforced concrete strip foundations supporting walls of moderate loading.
In all the cases the total sum of the unsupported lengths of wall should not exceed 25% of the total wall length.
The sequence of bays should be arranged so that working in adjoining bays is avoided until one leg of underpinning has been completed, pinned and cured sufficiently to support the wall above.