Assessing the external stability of retaining walls involves scrutinizing potential failure modes, notably bearing failure, sliding, and overturning. When focusing on sliding resistance, the friction between the wall’s base and the underlying soil is crucial.
To augment this resistance, aside from increasing the wall’s self-weight or the retained soil mass, engineers often employ shear keys at the wall base. The fundamental principle behind shear keys is to enhance passive resistance through their height. However, this also results in increased active pressure. The effectiveness of shear keys hinges on the increase in passive resistance outweighing the rise in active pressure, thus yielding a net improvement in sliding resistance.
Normally, the friction between the wall base and soil is approximately a fraction (around 0.8) of the soil’s internal friction angle (φ). With a shear key, the failure surface shifts from the horizontal wall base/soil interface to a plane within the foundation soil. This change mobilizes the full friction angle (φ), amplifying the sliding resistance compared to the original scenario.
In conclusion, shear keys are a valuable tool for enhancing the stability of retaining walls, particularly in cases where increasing self-weight or retained soil mass is impractical. Their effectiveness relies on strategic placement and design to maximize the increase in passive resistance while minimizing the corresponding increase in active pressure.