Selection of stones for retaining walls — which property is most important for stability against earth pressure? Pick the most appropriate attribute.

Introduction / Context:
Retaining walls resist lateral earth pressure through a combination of weight, geometry, and structural action. When using masonry or random rubble, the self-weight of the stones plays a critical role in preventing sliding and overturning.

Given Data / Assumptions:

• Traditional gravity or semi-gravity retaining wall using stone masonry.
• Primary concern is global stability under lateral soil loads.
• Material choices influence unit weight and durability.

Concept / Approach:
For gravity action, higher unit weight provides larger stabilizing moments and frictional resistance. While hardness relates to durability and abrasion resistance, “heavy” directly targets the wall's self-weight, which is the main stabilizing factor against overturning and sliding in gravity-type walls.

Step-by-Step Solution:

Verification / Alternative check:
Design handbooks emphasize unit weight for gravity walls, often using dense stones or concrete to attain needed resisting moments.

Why Other Options Are Wrong:

• Soft: Suggests lower strength/durability; not preferred.
• Hard: Desirable for durability but secondary to unit weight for stability in this context.
• Light: Reduces self-weight; unfavorable.

Common Pitfalls:
Equating surface hardness with structural stability; forgetting that gravity walls primarily rely on mass.

Final Answer:
Heavy