The active pressure caused by a cohesionless backfill on a smooth vertical retaining wall may be reduced by:

(i) compacting the backfill

(ii) providing a surcharge load on the backfill

(iii) saturating the backfill with water

Choose the correct option.

Explanation:

Active Pressure Reduction on Retaining Walls Active pressure on a retaining wall is the lateral pressure exerted by the soil onto the wall. For a smooth, vertical retaining wall with cohesionless backfill (e.g., sand or gravel), several factors can influence this pressure.

Analyzing the Given Options

1. Compacting the backfill. (Correct)

   • Compaction increases the density and internal friction angle of the soil, which can reduce the lateral pressure exerted on the wall.

2. Providing a surcharge load on the backfill. (Incorrect)

   • A surcharge load increases the vertical stress in the soil, which can translate into higher lateral pressure on the wall, not lower.

3. Saturating the backfill with water. (Incorrect)

   • Saturation of the backfill increases the pore water pressure, which can lead to higher lateral pressure due to the reduction of effective stress.