Stepped Strip Foundation
Sloping construction sites have implications for the design of foundations. For example, if trenches for a strip foundation were excavated on a steeply sloping site by digging down to a depth of 1000mm at the low end of the site, by the time excavation to the same depth was finished at the high end of the site, the trenches could be many metres deep. Obviously, excessive or unnecessary excavation is expensive and time-consuming so it is minimized on sloping sites by stepping the foundation up the slope (see Fig 41), at the same time maintaining the required amount of ground cover.
At each step, the upper level of a stepped foundation overlaps the lower level by twice the thickness of the foundation or by 300mm, whichever is the greater. In addition, the height of the step must not exceed the thickness of the foundation. From a practical point of view and for convenience, the height of the steps is often purposely constructed to be a multiple of 75mm, to match the gauge of the brickwork and to avoid the need for any ‘split courses’. Finally, it should be noted that the horizontal DPC of free-standing walls constructed on sloping sites will
step down (see Fig 41), in order to follow generally the line of finished ground level.