6.5.3 Sliding resistance

(1)P Where the loading is not normal to the foundation base, foundations shall be checked against failure by sliding on the base.

(2)P The following inequality shall be satisfied:

Hd ≤ Rd + Rp;d
(6.2)

(3)P Hd shall include the design values of any active earth forces imposed on the foundation.

(4)P Rd shall be calculated according to 2.4.

(5) The values of Rd and Rp;d should be related to the scale of movement anticipated under the limit state of loading considered. For large movements, the possible relevance of post-peak behaviour should be considered. The value of Rp;d selected should reflect the anticipated life of the structure.

(6)P For foundations bearing within the zone of seasonal movements of clay soils, the possibility that the clay could shrink away from the vertical faces of foundations shall be considered.

(7)P The possibility that the soil in front of the foundation may be removed by erosion or human activity shall be considered.

(8)P For drained conditions, the design shear resistance, Rd, shall be calculated either by factoring the ground properties or the ground resistance as follows;

Rd = V'd tan δd
(6.3a)

or

Rd = (V'd tan δk)/γR;h
(6.3b)

NOTE In design procedures where the effects of actions are factored, the partial factor for the actions (γF) is 1,0 and V'd = V'k in equation (6.3b).

(9)P In determining V'd, account shall be taken of whether Hd and V'd are dependent or independent actions.

(10) The design friction angle δd may be assumed equal to the design value of the effective critical state angle of shearing resistance, φ'cv;d, for cast-in-situ concrete foundations and equal to 2/3 φ'cv;d for smooth precast foundations. Any effective cohesion c' should be neglected.

(11)P For undrained conditions, the design shearing resistance, Rd, shall be calculated either by factoring the ground properties or the ground resistance as follows:

Rd = (Accu;k)/γR;h
(6.4a)

or

Rd = Accu;d
(6.4b)

(12)P If it is possible for water or air to reach the interface between a foundation and an undrained clay subgrade, the following check shall be made:

Rd ≤ 0,4Vd
(6.5)

(13) Requirement (6.5) may only be disregarded if the formation of a gap between the foundation and the ground will be prevented by suction in areas where there is no positive bearing pressure.

6.5.4 Loads with large eccentricities

(1)P Special precautions shall be taken where the eccentricity of loading exceeds 1/3 of the width of a rectangular footing or 0,6 of the radius of a circular footing.

Such precautions include:

— careful review of the design values of actions in accordance with 2.4.2;

— designing the location of the foundation edge by taking into account the magnitude of construction tolerances.

(2) Unless special care is taken during the works, tolerances up to 0,10 m should be considered.

6.5.5 Structural failure due to foundation movement

(1)P Differential vertical and horizontal foundation displacements shall be considered to ensure that they do not lead to an ultimate limit state occurring in the supported structure.

(2) A presumed bearing pressure may be adopted (see 2.5) provided displacements will not cause an ultimate limit state in the structure.

(3)P In ground that may swell, the potential differential heave shall be assessed and the foundations and structure designed to resist or accommodate it.

Eurocode 7 Geotechnical design Part 1 : General rules