Stones used for the construction of retaining walls must be
🧱 Understanding the Function of a Retaining Wall
A retaining wall is a structure designed to "retain" or hold back a mass of soil. Its primary job is to resist the lateral (sideways) pressure exerted by the soil behind it. A "gravity" retaining wall is the most common type, and it achieves this resistance primarily through its own mass.
🔬 Detailed Analysis of the Required Properties
D. Heavy
This is the correct and most important property. A gravity retaining wall relies on its own weight to provide stability against the two main failure modes: overturning and sliding.
- Resisting Overturning: The weight of the wall creates a large stabilizing moment that counteracts the overturning moment from the soil pressure. A heavier wall is much harder to tip over.
- Resisting Sliding: The friction between the base of the wall and the soil beneath it prevents the wall from sliding forward. This frictional force is directly proportional to the weight of the wall. More weight means more friction and more resistance to sliding.
B. Hard
While hardness is a desirable quality for durability (resisting wear and weathering), it is a secondary requirement compared to weight. A stone can be very hard but also relatively light (low density), which would make it unsuitable for a gravity retaining wall. The primary need is mass to resist the soil pressure.
C. Light
This is the opposite of what is required. A light retaining wall would have very little stability. It would offer minimal resistance to the overturning and sliding forces from the soil and would fail easily.
A. Soft
Soft stones are completely unsuitable for retaining walls. They lack the necessary compressive strength to handle the internal stresses and are not durable enough to withstand the constant contact with moist soil and weathering forces.
📊 Summary: Property vs. Application for Retaining Walls
| Property | Relevance to Retaining Walls | Verdict |
|---|---|---|
| Heavy | Provides stability against sliding and overturning. | Essential |
| Hard | Provides durability and strength. | Desirable, but secondary to weight. |
| Light | Reduces stability and resistance to soil pressure. | Unsuitable |
| Soft | Lacks strength and durability. | Unsuitable |
💡 Study Tips
- Retaining Wall = Resists Pushing: The main job is to fight the push from the soil.
- Weight Wins the Fight: The best way to resist a push is to be very heavy and hard to move. Think of a sumo wrestler versus a lightweight boxer.
- Gravity Wall = Uses Gravity: The name itself is a clue. A gravity retaining wall uses the force of gravity (its own weight) to do its job. Therefore, it must be heavy.