ICC Subscriptions

1806A.1 General.

Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning.

Retaining walls higher than 12 feet (3658 mm), as measured from the top of  the foundation, shall be designed to resist the additional earth pressure caused by seismic ground shaking.

The resultant of  the vertical loads and lateral pressures using load combinations of  Section 1605A.3 acting on the wall and its base shall pass through the middle half  of  the bottom of  the footing.

Retaining walls shall be restrained against sliding by friction of  the base against the earth, by passive resistance of  the soil or by a combination of  the two. When used, keys may be assumed to lower the plane of  frictional resistance and depth of  passive resistance to the level of  the bottom of  the key. Passive resistance pressures shall be assumed to act on a vertical plane located at the toe of  the footing. Overturning shall be computed about the bottom of  the spread footing. Passive resistance on the face of  the wall may be included in computing resistance to overturning. Frictional resistance on the face of  the wall may be included in computing resistance to overturning, except when lateral loads include seismic forces.

Gravity-type retaining walls utilizing precast concrete units may be used as an alternative to the conventional cantilever retaining systems only after they have been accepted by the enforcement agency.

1806A.2 Freestanding cantilever walls.

A stability check against the possibility of  overturning shall be performed for isolated spread footings which support freestanding cantilever walls. The stability check shall be made by dividing Rp used for the wall by 2.0. The allowable soil pressure may be doubled for this evaluation.

For overturning about the principal axis of  rectangular footings with symmetrical vertical loading and the design lateral force applied, a triangular or trapezoidal soil pressure distribution which covers the full width of  the footing will meet the stability requirement.