Construction Of New Foundation Near Old Structures:
When new foundations are to be constructed near old existing structures, the stability of the existing structures is likely to be affected due to vibrations and undermining effects.
The depth of new foundations and its distance from the old structure control the extent of harmful effect which may occur to the old structure. In order to eliminate the chances of any damage to the old structure, following precautions should be taken:
1. The clear horizontal distance between adjacent faces of old and new foundations should be at least to the larger of the widths of foundations.
2. If the foundation of new structure is to be laid touching the old structure, its foundation should not be carried to the depth greater than the depth of old foundation.
If however, new foundation has to be carried for large depth, the old structure should be adequately protected by giving lateral support to it and also by giving suitable support of the foundation.
3. For deciding the depth of new foundation up to which it can be excavated without affecting the old structure, draw an inclined line from outer bottom-most edge of old foundation.
The depth of new foundation should not cut this line. Inclination of this line with horizontal for soft soils is kept 30° and for average soils 45°.