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RETAINING WALL DESIGN

The variables, unknowns and constraints involved in retaining wall design are many, making it a complex and challenging task. A retaining wall design has to account for a number of factors, foremost being the stability of the wall itself. A thorough analysis of the geotechnical investigation report, project requirements, construction sequence, type of proposed structure and other factors is initially performed by design engineers.

This analysis, coupled with the experience of the designers, generates the first input for computer software (such as ReWaRDŽ from Geocentrix and STAAD.proŽ from Bentley) to further analyze the complex loads and perform the calculations. Typically a retaining wall designer has to consider the following:

Pressure

Earth and water pressures that are expected to act on the wall.

External Stability

The overall external stability of the retaining wall acting as one whole body (sliding and overturning). Sliding instability is caused by horizontal forces while overturning is caused by the moments generated from these forces.

Bearing Stability

Overturning increases stresses at the wall toe and decreases them at the heel; thus the bearing capacity of the foundation soil has to be considered to ensure that wall settlements are kept within acceptable levels.

Global stability

Even when external and bearing stabilities are acceptable, retaining walls may still be susceptible to an overall rotational type failure. This type of failure originates well below the retaining wall itself due to weaker soil zones.

Structural Integrity

After a satisfactory stability design, structural calculations are made on the wall itself to determine the proper sizing of longitudinal and shear reinforcement.

Retaining Wall Support

Designers have to also consider if the retaining wall itself requires further support (such as anchoring or bracing).

Safety Factors

An appropriate factor of safety is incorporated into the design calculations for each element of the design criteria.