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Stepped footings

On flat building sites (or sites without slopes) a footing excavation can be made at a constant depth from the natural ground surface. Flat sites allow easy access and generally are simpler to excavate than sloping sites.

The base of the excavation is always horizontal and parallel to the natural ground surface.

Obtaining horizontal excavation bases on sloping sites presents problems. If the slope of the ground exceeds 1:10 fall (a 1 in 10 or 10% fall) it is unacceptable to excavate parallel to the natural ground surface.

Sloping footings can slide down an allotment due to gravity. For this reason the base of strip footings should be excavated horizontally, where possible.

This picture contains the following scene. Diagram of a step of 200 mm or less in the soil. The excavation for this is made parallel to the ground surface and the footing is shown as a diagonal band. Diagram of a step of 200 mm or less in the soil. The sloping middle section of the footing has a horizontal length of 1.5 D where D is the depth of the footing. Diagram of a step of 200 mm or less in the soil. The middle section of the excavation for the footing is shown as a step which is labelled as 1.5 D in width. Diagram of a step in the soil which greater than 200 mm but less than or equal to 2D in the soil. The middle section of the excavation for the footing is shown as a large step which is labeled as 1.5 D in width.