When the wall retains medium or low permeability (fine) soils, then the wall must be designed for a water level above formation level. In other words, dw < H, where dw is the depth to the water table and H the height of the wall.

Eurocode 7 states that, without reliable drainage, the water level must be taken at the surface of the retained material, i.e. dw = 0 on the left-hand side of Figure 11.5. If, however, a reliable drainage system is provided, then the water level may be assumed to occur below the top of the wall, i.e. dw > 0 on the right-hand side of Figure 11.5. In addition, a maintenance programme for the drainage system must be specified (in the Geotechnical Design Report -see Chapter 16) or the drains must be capable of operating adequately without maintenance. [EN 1997-1 ยง9.4.2(1)Pand 9.6(3)P]

Current British practice3 takes the distance dw, when drainage is absent, as:

0 0

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