Stability of Reinforoed-Concrete Retaining Wall

STABILITY OF REINFOROED-CONCRETE RETAINING WALL.

The preceding empirical rules for the thickness of a retaining wall are applicable primarily to stone-block masonry, and could be safely used for plain-concrete retaining walls; but are not applicable to reinforced-concrete walls, and there has not yet been sufficient ex perience with this form of construction to establish similar empirical rules. The stability of a reinforced-concrete wall may be determined in either of two ways, viz.: (1) by using a theoretical formula for the thrust of the earth; or (2) by making the stability against rotation equal to that of a solid wall that is known to be safe.

By Theoretical Formula for Barth Pressure.

The thrust of the earth against the back of the wall may be computed by any of the theoretical formuals, the direction being taken in accordance with the theory, and the force being applied at § of the height of the wall. For example, if Coulomb's formula for a level earth surface and a vertical back to the wall (equation 4, page 493) be used, the pressure is assumed to be horizontal and to be applied at of the height from the top of the footing. Knowing the amount,

direction, and point of application of the earth thrust, the dimensions of the wall can then be obtained as will be explained later (see 1038-43).

Instead of computing the resultant earth pressure as above, the coefficient of h' in the several formulas for earth pressure may be regarded as the weight per cubic unit of a liquid giving an equal lateral pressure; and the wall may be designed to support this liquid pressure. For example, Coulomb's formula (equation 4, page 493) gives a pressure equivalent to that of a liquid weighing 25 to 28 lb. per cu. ft., according to the weight of the earth and the angle of repose assumed.

By Comparison with a Solid Wall.

The overturning resist ance of the lightest wall which experience has shown to be safe, may be regarded as the maximum overturning moment - of the earth; and a reinforced-concrete wall, or other new form of construction for which experience has not established safe dimensions, may be de signed to have an equal stability. For an example of this method, see 1051.