Retaining wall safety against sliding: When the factor of safety is found < 1.5, the downward projection at the heel provided to mobilize passive resistance is called what?

Introduction / Context:
Retaining walls must be checked for overturning, sliding, and bearing. If the sliding check gives a factor of safety below the target (often 1.5 at working loads), additional measures are taken to increase resistance. One common detail is a shear key projecting downward from the base slab, typically under the heel, to mobilize passive earth pressure and increase the sliding capacity.

Given Data / Assumptions:

• Gravity or cantilever retaining wall with base slab (toe and heel).
• Sliding check shows FS < 1.5.
• Foundation soil can develop passive pressure in front of a key.

Concept / Approach:

A shear key increases resistance by engaging passive pressure on its front face, adding to frictional resistance at the base. It is distinct from a cut-off wall used primarily for seepage control and different from ribs used for stiffening thick members.

Step-by-Step Solution:

Verification / Alternative check:

Alternative measures include increasing base width, adding anchors, or roughening the base. The shear key is a practical detail when plan dimensions are constrained.

Why Other Options Are Wrong:

(b) A cut-off wall addresses seepage, not primarily sliding. (c) A rib is not the standard term or function for this purpose. (d) “All” is incorrect because functions differ.

Common Pitfalls:

Overestimating passive pressure without accounting for excavation/compaction; placing the key on the wrong side; ignoring global stability or bearing after adding the key.

Final Answer:

A key (shear key)