Flexible cantilevered walls must be designed to resist the maximum anticipated water pressure. For a horizontal static groundwater table, the total hydrostatic water pressure can be determined from the hydrostatic head by the traditional method. For differing groundwater levels on opposite sides of the wall, the water pressure and seepage forces can be determined by net flow procedures or other methods. Seepage can be controlled by installation of a drainage medium. Preformed drainage panels, sand or gravel drains, or wick drains can be placed behind the facing with outlets at the base of the wall. It is important that drainage panels maintain their function under design earth pressures and surcharge loadings. AASHTO requires that they extend from the base of the wall to a level 1 ft (300 mm) below the top of the wall.
Where thin drainage panels are used behind walls, saturated or moist soil behind the panels may be subject to freezing and expansion. In such cases, insulation can be provided on the walls to prevent soil freezing or the wall can be designed for the pressures that may be exerted on it by frozen soil.
