This code of practice outlines the design principles for various types of retaining walls, including gravity, cantilever, and counterfort walls. It details the methods for calculating earth pressures (Rankine and Coulomb theories), checking stability against overturning, sliding, and bearing capacity failure, and provides specific guidance on drainage and seismic design considerations.
Provides guidelines for the design and construction of various types of retaining walls, including gravity, cantilever, and counterfort walls.
Quick Reference Values
Minimum Factor of Safety against Overturning (Static)1.5
Minimum Factor of Safety against Sliding (Static)1.5
Minimum Factor of Safety against Overturning (Seismic)1.2
Minimum Factor of Safety against Sliding (Seismic)1.2
Minimum Factor of Safety against Bearing Capacity Failure2.5
Minimum diameter of weep holes75 mm
Maximum spacing of weep holes2 m c/c horizontally and vertically
Key Formulas
Ka = (1 - sin φ) / (1 + sin φ) — Rankine's active earth pressure coefficient
Kp = (1 + sin φ) / (1 - sin φ) — Rankine's passive earth pressure coefficient
F.S. (Overturning) = Σ(Resisting Moments) / Σ(Overturning Moments)
F.S. (Sliding) = Σ(Resisting Horizontal Forces) / Σ(Driving Horizontal Forces)
Practical Notes
The majority of retaining wall failures are caused by inadequate drainage leading to hydrostatic pressure build-up. Ensure drainage provisions like weep holes and a granular backfill zone are properly designed and implemented.
The assumptions of earth pressure theories (e.g., wall movement, backfill condition) must be understood. Actual site conditions may require modifications to theoretical pressures.
Proper compaction of the backfill material in layers is as critical to the wall's performance as the structural design of the wall itself.