Simplified calculation method for retaining wall design

Density of backfill (ɣ) in kN/m3
Height, measured vertically (H1) in m
Surcharge (P) in kPa
Angle of internal friction of backfill (ɣ) in degrees
Distance between geosynthetic layers (T) in m
Friction coefficient between geosynthetic / soil
Safety factor over all (F), without dimension
Safety factor installation damage F(installation), without dimension
Safety factor durability F(durability), without dimension
Safety factor against creep F(creep), without dimension
Required strength of geosynthetic in kN/m
Anchoring length of geosynthetic is backfill in m

Calculation method

Until the development of reinforced soil, vertical retaining walls worked following the principle of designed resistance to overturning moments caused by the retaining soil mass and water pressure. In a wall, reinforced with geosynthetics, the traditional functioning is reversed, leading to the soil holding up both itself and the wall. The simplified calculation method divides the acting forces into (1) pull-out forces and (2) frictional anchor forces. The assumption is made that the fill is free draining, so that water pressures does not need to be taken into account. Surcharge is calculated into a virtual equivalent thickness of soil. The necessary length of the anchoring is calculated for pull out, as well as for the internal stability of the wall (+1m extra).

Function of the geosynthetic

The frictional anchor forces are result of the friction angle between the geosynthetic layers in contact with the backfill and the weight of the soil above. Safety factors have to be introduced, special attention should be given to the creep properties of the geosynthetic.