Retaining walls in highway works: typical proportions for dry rubble masonry A retaining wall built of dry rubble stone is commonly designed with a top width of about 60 cm. What is the usual front batter (face batter) adopted for such walls to ensure stability and drainage on the backfill side?

Introduction / Context:
Dry rubble masonry retaining walls are frequently used along roads and in small civil works to hold back earth on cut slopes. Without mortar, stability comes from weight, proper batter, and good drainage. The face batter is a simple but critical geometric parameter that controls the wall’s self-stability and how it resists earth pressure.

Given Data / Assumptions:

• Construction type: dry rubble masonry (without mortar).
• Typical top width: 60 cm (light retaining duty along road shoulders).
• Question: customary front batter ratio for the exposed face.

Concept / Approach:
For gravity walls made with irregular stones, a moderate batter helps keep the resultant of weight and earth pressure within the middle third of the base and improves apparent stability. Empirical practice for dry rubble walls supporting ordinary heights uses a front batter around 1 vertical in 4 horizontal (1:4) to 1:6. With a relatively slim 60 cm top, a 1:4 batter is a widely accepted typical value.

Step-by-Step Solution:
Recognize the wall as a gravity wall relying on mass and battered geometry.Dry construction needs more conservative geometry than mortared masonry.Select a standard face batter used in practice with 60 cm top width → about 1:4.Therefore, the suitable answer is 1 : 4 front batter.

Verification / Alternative check:
Design handbooks commonly illustrate typical dry rubble retaining walls with face batters in the 1:4 to 1:6 range; smaller ratios (steeper faces) are usually reserved for mortared or reinforced walls.

Why Other Options Are Wrong:

• 1 : 2 and 1 : 3: faces are too steep for dry rubble; less conservative.
• 1 : 5: feasible in some cases, but 1 : 4 is the commonly quoted “typical” proportion with 60 cm top width.

Common Pitfalls:
Ignoring drainage and weep holes; relying only on batter without checking base width and bearing; assuming mortared wall rules apply to dry rubble.

Final Answer:
1 : 4 front batter