Sleeper Retaining Wall

How it calculates

The Sleeper Retaining Wall calculator designs a post-and-sleeper retaining wall in which vertical steel posts, embedded as piles, resist lateral earth pressure and any wind load from a fence above. Horizontal timber sleepers spanning between the posts are designed separately in a linked beam module. The calculation covers earth pressure, fence wind load, pile embedment strength, pile deflection, and steel post capacity.

Earth pressure and loads

Lateral earth pressure is estimated with the Rankine-Bell method per AS 4678:2002 (Figure E2), for granular or cohesive retained soil. The wall is conservatively assumed to be vertical. Pressure is built from the unit weight, angle of internal friction, and, where selected, the effective cohesion of the retained soil, plus any groundwater height and surcharge. Horizontal forces are resolved separately for strength (with the applied load factor) and serviceability analysis.

Wind loads on the fence

Where a fence sits above the wall, wind pressure on the fence is derived from the AS 4055:2012 wind classification, the fence height and length, and the solidity ratio of the fence structure. The resulting horizontal force is added to the demand on each post over its tributary width.

Pile strength design - cohesive foundation soil (Broms method)

For cohesive foundation soil, the required embedment of the short free-head pile is designed by the Broms method, using the undrained shear strength (undrained cohesion) of the foundation soil. Material uncertainty factors from AS 2159:2009 are applied according to the retained and foundation soil condition selected.

Pile strength design - cohesionless foundation soil (IBC method)

For cohesionless foundation soil, the embedment is designed using the method of IBC 2018 Section 1807.3.2.1, based on the foundation soil classification and the coefficient of horizontal subgrade reaction.

Pile deflection (Broms method)

Deflection at the top of the embedded post is calculated by the Broms method from the coefficient of horizontal subgrade reaction and, optionally, the pile rotation. The tip deflection is compared against the maximum allowed absolute deflection and the length-to-deflection ratio limit.

Steel post capacity (AS 4100:2020)

The embedded steel post is checked to AS 4100:2020 for the governing horizontal forces. The calculator reports shear capacity, moment section capacity, and the shear-moment interaction, and it evaluates the deflection of the steel post. Posts are assumed oriented so the major axis resists the soil loads.

Assumptions

The maximum retaining wall height is 3 m and earthquake loads and liquefaction are not considered. The concrete pile is assumed not to crack or fail in bending, which holds where the steel post is embedded to full depth; the user should verify this. Group effects for embedded piles are ignored, and the sleeper is designed in a separate, linkable beam module.