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To prevent the Retaining wall from sliding.
The shear strength and stiffness of soil determines whether or not soil will be stable or how much it will deform. Knowledge of the strength is necessary to determine if a slope will be stable, if a building or bridge might settle too far into the ground, and the limiting pressures on a retaining wall. Soil is an assemblage of particles that have little to no cementation while rock (such as sandstone) may consist of an assembly of particles that are strongly cemented together by chemical bonds. The shear strength of soil is primarily due to interparticle friction and therefore, the shear resistance on a plane is approximately proportional to the effective normal stress on that plane
The main purpose of installation of shear keys is to increase the extra passive resistance
developed by the height of shear keys. However, active pressure developed by shear keys
also increases simultaneously. The success of shear keys lies in the fact that the increase of
passive pressure exceeds the increase in active pressure, resulting in a net improvement of
sliding resistance.
On the other hand, friction between the wall base and the foundation soils is normally
about a fraction of the angle of internal resistance (i.e. about0.8) where is the angle of
internal friction of foundation soil. When a shear key is installed at the base of the retaining
wall, the failure surface is changed from the wall base/soil horizontal plane to a plane
within foundation soil. Therefore, the friction angle mobilized in this case is instead of
0.8in the previous case and the sliding resistance can be enhanced.
In determining the external stability of retaining walls, failure modes like bearing failure, sliding and overturning are normally considered in design. In considering the criterion of sliding, the sliding resistance of retaining walls is derived from the base friction between the wall base and the foundation soils. To increase the sliding resistance of retaining walls, other than providing a large self-weight or a large retained soil mass, shear keys are to be installed at the wall base. The principle of shear keys is as follows:
The main purpose of installation of shear keys is to increase the extra passive resistance developed by the height of shear keys. However, active pressure developed by shear keys also increases simultaneously. Thesuccess of shear keys lies in the fact that the increase of passive pressure exceeds the increase in active pressure, resulting in a net improvement of sliding resistance.
On the other hand, friction between the wall base and the foundation soils is normally about a fraction of the angle of internal resistance (i.e. about0.8p ) where p is the angle of internal friction of foundation soil. When a shear key is installed at the base of the retaining wall, the failure surface is changed from the wall base/soil horizontal plane to a plane within foundation soil. Therefore, the friction angle mobilized in this case is p instead of0.8p in the previous case and the sliding resistance can be enhanced.
The main purpose of installation of shear keys is to increase the extra passive resistance developed by the height of shear keys. However, active pressure developed by shear keys also increases simultaneously. Thesuccess of shear keys lies in the fact that the increase of passive pressure exceeds the increase in active pressure, resulting in a net improvement of sliding resistance.
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