Weep holes in retaining and breast walls Typical spacing of weep holes provided to relieve hydrostatic pressure behind retaining/breast walls is:

Introduction / Context:
Weep holes allow trapped water behind retaining and breast walls to escape, reducing pore water pressure and preventing uplift or sliding. Proper spacing ensures adequate drainage and durability.

Given Data / Assumptions:

• Masonry or reinforced concrete retaining/breast wall on granular backfill.
• Standard small-diameter weep holes (e.g., 75–100 mm).
• Moderate rainfall and drainage blanket assumed.

Concept / Approach:
Practical guidance often calls for approximately 1 m × 1 m spacing as a baseline, adjustable with wall height, backfill permeability, and presence of drainage layers or filter media.

Step-by-Step Solution:

Verification / Alternative check:
Site-specific designs refine spacing based on hydrogeology and wall height; however, 1 m × 1 m is a common rule-of-thumb in many standard drawings.

Why Other Options Are Wrong:
50 cm × 50 cm is often unnecessary; 100 × 120 or 120 × 100 are asymmetric and may under-drain in one direction unless justified.

Common Pitfalls:
Omitting filters; placing holes too high; failing to provide a drainage layer behind the wall.

Final Answer:
100 cm vertically and 100 cm centre-to-centre horizontally