Question
What is function of shear keys in designing of retaining walls?

Answer
In formative external constancy of retaining walls, failure modes similar to bearing failure, sliding and overturning are usually considered in design. In considering criterion of sliding, sliding resistance of retaining walls is derived from base friction between wall base and foundation soils. To enlarge sliding conflict of retaining walls, rather than providing a large self-weight or a large retained soil mass, shear keys are to be installed at wall base. Opinion of shear keys is as follows-

Main purpose of installation of shear keys is to enhance an extra passive resistance industrial by height of shear keys. However, active pressure industrial by shear keys increases at the very same time. Success of shear keys lies in the information that enhance of passive pressure go over increase in active pressure, resulting in an improvement of sliding conflict.

On other hand, friction between wall base and foundation soils is usually about a fraction of an angle of interior resistance as in about 0.8φ where φ is an angle of inner friction of foundation soil. When a shear key is installed at base of the retaining wall, failure surface is changed from wall base or soil horizontal plane to a plane within foundation soil. Therefore, friction angle mobilized in this case is φ in its place of 0.8φ in earlier case and sliding resistance be capable of be enhanced.