AustraliaAS 4678:2002AS3600:2018 (Amdt 2)
Design L-type cantilever retaining walls to AS 4678:2002 and AS 3600:2018 (Amdt 2). Rankine active earth pressure, overturning, sliding, and bearing stability checks are followed by stem and base slab reinforcement design.
Method & scope
Calculation method
The L-Type Cantilever Retaining Wall calculator designs reinforced concrete L-shaped retaining walls to AS 4678:2002 (earth retaining structures) and AS 3600:2018 (Amendment 2). It checks global stability against overturning, sliding, and bearing failure, then designs the stem and base slab as cantilever structural members.Geometry and wall profile
The L-type wall geometry is defined by retained height (h_ret), stem height (h_stem), stem thickness (t_stem), base thickness (t_base), heel length (L_heel), toe length, and cover depth in front of the toe (d_cov). The L-type profile means the base extends primarily behind the stem on the heel side, relying on the weight of retained soil above the heel to provide stability.Lateral earth pressure, Rankine theory
Lateral earth pressure is computed using Rankine active theory. The active pressure coefficient is: Ka = tan²(45°, phi’/2) where phi’ is the effective friction angle of the retained soil. Water table depth is included, pore pressure is added to the soil lateral pressure below the water level. sigma_a(z) = Ka × gamma × z + u(z) For soil cover in front of the toe, passive resistance is included using: Kp = tan²(45° + phi’/2)Stability checks (AS 4678:2002)
Three global stability checks are performed per unit wall length. Overturning, moments are taken about the toe: utilization = M_overturning / M_resisting ≤ 1.0 (minimum factor of safety 1.5 per AS 4678) Sliding, passive resistance and base friction resist the total horizontal force: utilization = H_driving / H_resisting ≤ 1.0 (minimum factor of safety 1.5) Bearing, the maximum base pressure (trapezoidal distribution) is compared to the allowable bearing capacity q_a: utilization = q_max / q_a ≤ 1.0Stem design (AS 3600:2018, Cl 8.1 and 8.2)
The stem is treated as a vertical cantilever fixed at the base. The critical design moment at the stem base is computed from the triangular active pressure distribution plus any surcharge. Flexural reinforcement is sized for the ultimate moment demand: utilization = M / (phi × M_u) ≤ 1.0* One-way shear at the stem base is checked using the simplified method (Cl 8.2.4.3): utilization = V / (phi × V_u) ≤ 1.0*Base slab design (AS 3600:2018, Cl 8.1 and 8.2)
The base slab heel and toe are each designed as cantilevers. The heel is loaded upward by net soil and concrete weight minus downward bearing pressure; the toe is loaded upward by bearing pressure. Critical bending and shear sections are taken at the face of the stem: utilization = M / (phi × M_u) ≤ 1.0* (heel and toe separately) Minimum reinforcement per AS 3600:2018 Cl 8.1.6.1 is enforced for both stem and base elements.Assumptions
No shear key is included. The retained soil is granular only. Wind and seismic loads are excluded. Concrete detailing (bar laps, hooks, anchorage) is to be checked separately using AS 3600:2018 Cl 13. Shear uses the simplified method (Cl 8.2.4.3), valid for f’c up to 65 MPa.How to use it
1
Open the calculator
Open it from Run calc in the About this calculator panel above.
2
Enter your inputs
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3
Review the results and export
Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.
L-Type Cantilever Retaining Wall: Tutorial
L-Type Retaining Wall: Example
Common questions
What design standards does this calculator use?
What design standards does this calculator use?
The calculator applies AS 4678:2002 for earth retaining structure design and AS 3600:2018 (Amendment 2) for concrete member design. Rankine theory is used to determine lateral earth pressure, with retained soil assumed to be in the active state and soil cover in front of the toe in the passive state.
What are the key inputs?
What are the key inputs?
Key inputs include retained height and wall geometry (stem height and thickness, base length, heel and toe dimensions, base thickness), concrete compressive strength, reinforcement bar size and spacing for stem and base, soil unit weights and friction angles for retained and base soils, bearing capacity, water table depth, and surcharge load.
What checks and outputs does the calculator provide?
What checks and outputs does the calculator provide?
The calculator produces: overturning stability check (resisting moment / overturning moment), sliding stability check (resisting force / driving force), bearing pressure check against allowable capacity, stem flexural capacity and shear capacity (AS 3600:2018 Cl 8.1 and 8.2), base heel and toe bending and shear checks, and required reinforcement quantities for stem and base. Each check reports a utilization ratio.
Can it handle a water table behind the retaining wall?
Can it handle a water table behind the retaining wall?
Yes, a water table height behind the wall can be specified. The calculator accounts for hydrostatic pressure on the submerged retained height and uses saturated unit weight for the soil below the water table when computing lateral earth pressure and vertical loads.
What assumptions apply to this calculator?
What assumptions apply to this calculator?
The calculator assumes no shear key, no surcharge slope behind the wall, no wind or earthquake loads, granular retained soil only, and that concrete detailing requirements are checked separately. The simplified shear strength method (AS 3600:2018 Cl 8.2.4.3) applies, valid for f’c up to 65 MPa with no prestress, tension, or torsion.
How do outputs connect to other calculations in a project?
How do outputs connect to other calculations in a project?
Footing bearing reactions and reinforcement outputs can inform connected concrete development length checks using the Development Length calculator in the same project. Where the retaining wall is part of a broader structure, column loads above can also be linked into the base design automatically.
Next steps
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