ADJACENT FOOTINGS.

Normally, adjacent footings should be placed at the same level. However, when adjacent footings are to be constructed at different levels, the distance between the edges of the footings shall be such as to prevent undesirable overlapping of stresses in soil and disturbance of the soil under the higher footing due to the excavation of the lower footing. The difficuty can be avoided by keeping the difference in footing elevations
(a) not greater than one half the clear distance (b) between the footings. However, when footing are founded on rock, b should not excedd a.

FIG. 3.36 ADJACENT FOOTINGS AT DIFFERENT LEVELS.

In clayey soils, the line (AB) drawn between the lower adjacent edge of the super upper footing and upper adjacent edge of the lower footing should not have a steeper slope than n1 (horiontal) : 1 (vertical), where n1 is equal to 2.

In granular soils, the line (AB1) drawn between the lower adjacent edges of adjacent footings should not have steeper slope than n2 (horizontal) : 1 (vertical), where n2 is equal to 2.