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In civil Engineering (Concrete structures), What is the function of shear keys in the design of retaining walls?

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Question added by Muhammad Shakeel , CAD Design Manager , M/S zeeruk Intl.
Date Posted: 2015/02/24
Suhas Jadhav
by Suhas Jadhav , Assistant General Manager- Structural Design , RNA Corp.

To prevent the Retaining wall from sliding.

Deleted user
by Deleted user

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 

Mohamed Galal Hussein Ahmed Mohamed
by Mohamed Galal Hussein Ahmed Mohamed , Technical Mnager , Fast Building Contracting Co.

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.

Ridha SAIDANI
by Ridha SAIDANI , Maintenance Manager , SOMIPHOS / Technical Direction

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.

Arun Kumar
by Arun Kumar , Junior Engineer , Govt.

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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