4.2.2.2 requires them to be based on a mobilisation factor M of between 2 and 3. Where earth pressures in a cohesive soil are estimated on the basis of undrained shear strength, BS8002 Cl. The bearing pressure on the soil under the toe of the wall should not exceed the allowable bearing pressure recommended by BS8004, taking into account soil conditions, groundwater level and also foundation depth and breadth. The coefficient K p for passive pressure based on Rankine theory (smooth wall face, level soil surface) is tabulated below.
K a = cos²(Φ' - α)_Ĭos²α ²Ĭoefficients for Rankine active pressure are tabulated below The values of K a in the tables are for the horizontal component of the active pressure and are calculated from the formula Values are tabulated for δ = 0, δ = 20 º (the maximum value for a smooth wall surface) and also for tanδ = 0.75tan Φ', which is the maximum permitted by BS8002 for a rough wall surface. This gives very similar answers to the charts in BS8002 but the tables have been extended to cover walls with sloping backs. Maximum values of δ based on this limit are tabulated below.Ĭoefficients for the horizontal component of active earth pressure based on Coulomb’s theory (as extended by Mayniel and Muller & Breslau) are tabulated below. The design wall friction δ depends on the wall surface and the situation being considered but tanδ must not exceed 0.75 × design tan Φ'. For convenience, design values of Φ' for M =1.2 are tabulated below. In BS8002, the design shear strength of the soil is based on the tangent of the friction angle reduced by a mobilisation factor M. NOTES FOR EARTH RETAINING WALL DESIGN TO BS8002
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