L-Type Cantilever Retaining Wall

How it calculates

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 ≤ 1.0

Stem 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.