Structure: Approved Document A

O N L I N E V E R S I O N A1/2 Section 2E: Foundations of plain concrete Conditions relating to the ground Diagram 21 Elevation of stepped 2E1 There should not be: foundation a. non-engineered fill (as described in BRE See paras 2E2d and e Digest 427) or wide variation in ground conditions within the loaded area; nor b. weaker or more compressible ground at such a depth below the foundation as could impair the stability of the structure. Design provisions 2E2 The following design provisions relate to foundations: a. the foundations should be situated centrally under the wall; b. for foundations in chemically aggressive soil conditions guidance in BS 8500-1 and BRE Special Digest 1 should be followed. In non-aggressive soils, concrete should be composed of Portland cement to BS EN 197-1 and -2 and fine and coarse aggregate conforming to BS EN 12620 and the mix should comply with one of the following Diagram 22 Piers and chimneys recommendations: i. in proportion of 50kg of Portland cement See para 2E2f to not more than 200kg (0.1m3) of fine aggregate and 400kg (0.2m3) of coarse aggregate; or ii. grade ST2 or grade GEN I concrete to BS 8500-2; c. minimum thickness T of concrete foundation should be 150mm or P, whichever is the greater, where P is derived using Table 10 and Diagram 23. Trench fill foundations may be used as an acceptable alternative to strip foundations; d. foundations stepped on elevation should overlap by twice the height of the step, by Diagram 23 Foundation dimensions the thickness of the foundation, or 300mm, whichever is greater (see Diagram 21). See para 2E2c For trench fill foundations the overlap should be twice the height of the step or 1m, whichever is greater; e. steps in foundations should not be of greater height than the thickness of the foundation (see Diagram 21); f. foundations for piers, buttresses and chimneys should project as indicated in Diagram 22 and the projection X should never be less than the value of P where there is no local thickening of the wall. Minimum width of strip foundations 2E3 The recommended minimum widths of foundations given in Table 10 may be used. Structure Approved Document A 36 O N L I N E V E R S I O N