Retaining Wall Design: Client Information and the Enquiry Process

Retaining wall design is more information-dependent than most domestic structural work. The height of retained earth, the soil type, the drainage arrangement, what is on top of the retained area, and whether the wall forms part of a building all significantly affect the design outcome.

This article explains what information PorthouseDean needs to get started and how the design process works.

What Retaining Walls Do

A retaining wall holds back a mass of soil (or other material) on one side while the other side is at a lower level. The wall must resist:

– Earth pressure — the horizontal force from the retained soil pushing against the wall
– Surcharge — any additional load on the surface of the retained area (vehicles, paving, a structure)
– Water pressure — if groundwater builds up behind the wall, the hydrostatic pressure can be greater than the earth pressure
– Overturning — the tendency of the earth pressure to tip the wall over
– Sliding — the tendency of the earth pressure to push the base of the wall forward

Information Needed for Design

To design a retaining wall, PorthouseDean needs:

1. Height of retained material
The vertical height from the top of the retained soil to the toe of the wall (the base of the retained face).

2. Soil type
Clay, sand, gravel, chalk, made ground? If a ground investigation report exists, provide it. If not, we will design for a conservative assumption — but soil type significantly affects wall and foundation sizing.

3. Drainage arrangement
Is there a granular drainage layer and drain at the base of the retained material? Is the retained area paved and essentially waterproofed, or is it open ground that will accumulate groundwater? Undrained conditions require significantly more robust walls.

4. Surcharge
Is there anything on the surface of the retained area? A car park, a building, a sloping garden, a terrace? All of these add to the lateral pressure the wall must resist.

5. Site access and constraints
What space is available for foundation construction? Is the wall adjacent to a boundary, existing structure, or service corridor?

6. Architectural intent
Is this a structural masonry wall, a reinforced concrete wall, a sheet pile wall, or a gabion structure? The structural form affects feasibility, aesthetics, and cost.

The Design Process

1. Enquiry: Client provides the above information, PorthouseDean assesses and quotes
2. Ground investigation: Trial pits or desk study to confirm soil parameters (client arranges, results provided to PorthouseDean)
3. Design: Stability check, foundation design, reinforcement or structural form specification
4. Drawings and calculations: Issued for Building Regulations submission (where required) and construction

When Retaining Walls Require Building Regulations

Retaining walls over 1 m in height typically require Building Regulations approval where they are within 1 m of a highway, or where failure could affect a building or public space. In all cases, designed walls over the BRE GBG 27 limits require submitted calculations.

Contact us to discuss your retaining wall project — we’ve designed retaining structures for garden terracing, basement walls, and boundary applications across thousands of projects.