Stepped Foundations

These are usually considered in the context of strip foundations and are used mainly on sloping sites to reduce the amount of excavation and materials required to produce an adequate foundation.

Foundations - Calculated Sizing

Typical procedure (for guidance only)

Therefore a foundation width of 500 mm is adequate. Note: This example assumes the site is sheltered. If it is necessary to make allowance for wind loading, reference should be made to BS 6399-2: Code of practice for wind loads.

Foundations - Basic Sizing

Basic Sizing ~ the size of a foundation is basically dependent on two factors

1. Load being transmitted, max 70 kN/m (dwellings up to 3 storeys).
2. Bearing capacity of subsoil under proposed foundation.

Bearing capacities for different types of subsoils may be obtained from tables such as those in BS 8004: Code of practice for foundations and BS 8103-1: Structural design of low rise buildings. Also, directly from soil investigation results.

The above widths may not provide adequate working space within the excavation and can be increased to give required space.

Foundation Beds - Typical Example

Bed - A concrete slab resting on and supported by the subsoil, usually forming the ground floor surface. Beds (sometimes called oversite concrete) are usually cast on a layer of hardcore which is used to make up the reduced level excavation and thus raise the level of the concrete bed to a position above ground level.

Foundation Types

TRADITIONAL STRIP

DEEP STRIP OR TRENCH FILL

SOLID SLAB RAFT

BEAM AND SLAB RAFT

ISOLATED PAD

COMBINED PAD