A wall system is designed to resist the lateral earth pressures

A wall system is designed to resist the lateral earth pressures.

18/gen/2016 13:28:53 hollowbar Contatta l'autore

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A wall system is designed to resist the lateral earth pressures and water pressures that develop behind the wall. Earth pressures develop primarily as a result of loads induced by weight of the retained soil, earthquake ground motions, and various surcharge loads. For purposes of anchored wall system design, three different lateral earth pressure conditions are considered:

(1) active earth pressure;

(2) passive earth pressure;

(3) at-rest earth pressure.

The distinction between actual ground behavior and conventional design assumptions is particularly important when considering earth pressures. The simple linear assumptions about active and passive pressures based on theoretical analyses are a considerable simplification of some very complex processes which depend on the following factors:

(1) the mode of wall movement (rotation, translation);

(2) wall flexibility;

(3) soil stiffness and strength properties;

(4) horizontal prestress in the ground; 

(5) and wall/soil interface friction. For anchored wall systems with flexible wall elements, semi-empirical “apparent earth pressure envelopes” are commonly used.

 Active and Passive Earth Pressure Active and passive horizontal earth pressures may be considered in terms of limiting horizontal stresses within the soil mass, and, for purposes of this discussion, a smooth (i.e., zero wall friction) wall retaining ground with a horizontal backslope is considered (figure 14); this case defines Rankine conditions. Consider an element of soil in the ground under a vertical effective stress, σv′ (figure 15).

In considering the potential movements of a retaining wall, the element may be brought to failure in two distinct ways that are fundamentally important in the context of retaining wall design. The horizontal soil stress may be increased until the soil element fails at B, when the stress reaches its maximum value c’h (max).

This scenario will occur when significant outward movement of the wall increases the lateral earth pressure in the soil at the base of the wall (see figure 14). Similarly, the horizontal stress may be reduced until failure at A, when the stress reaches its minimum value c’h (min). This scenario models the outward movement which reduces the lateral earth pressures behind the wall (see figure 14).


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