By: Javier Encinas, PE | January 15, 2017

A retaining wall is a structure exposed to lateral pressures from the retained soil plus any other surcharges and external loads. All overall stability failure modes must be thoroughly checked, but cantilever walls may be particularly sensitive to overturning problems. This article discusses the overturning calculations in either concrete or masonry cantilever retaining walls. Our software *ASDIP RETAIN* will be used to support the discussion.

A typical retaining wall is composed of four main components: the *Stem*, the *Toe* at the front of the wall, the *Heel* at the backfill side, and the *Shear Key*. The images below show the geometry of a typical cantilever retaining wall.

**What are the typical loads on a retaining wall?**

In addition to the retained backfill, retaining walls may be subject to surcharge loads at the top of retained mass. A surcharge may be a strip load. The stem may also have concentrated loads at the top.

When the stem extends above backfill the retaining wall may be exposed to wind load. When retaining walls are located in seismic zones the seismic effects are considered by utilizing *Mononobe-Okabe* approach. *ASDIP RETAIN* is structural engineering software for engineering professionals to quickly model retaining wall loads. The image below depicts typical external loads on retaining wall.

Each applied load has a particular effect on the wall. The backfill exerts a triangular lateral pressure calculated per the corresponding earth pressure theory. The surcharge produces a uniform rectangular pressure on the wall. The seismic pressure is trapezoidal, with the higher pressure at the top.

For a more in-depth discussion of the theories and overall stability modes please read my post Cantilever Retaining Walls: An Overview of the Design Process (Part 1). The picture below shows schematically the lateral pressure diagrams on a typical retaining wall.

**How do you check the overturning failure mode?**

The horizontal pressures on the backfill side will push the wall outward, which will tend to overturn around the end of the toe, as shown at the right. The overturning moment from the applied forces must be resisted by an opposite moment produced by the vertical forces, including the wall selfweight and the weight of the backfill over the heel.

The factor of safety against overturning is defined as the resisting moment divided by the overturning moment, and the minimum value should be 1.50.

As an example, the picture below shows the *ASDIP RETAIN* overturning calculations. Note that the load combinations are based on service loads, since the wall stability is being checked. In this example the safety factor is greater than 1.5 for the load combination shown.

You may be interested also in the post How to Design Cantilever Retaining Walls Using ASDIP RETAIN.

Detailed information is available about this structural engineering software by visiting ASDIP RETAIN. You are invited to download a Free 15-Day Software Trial or go ahead and Place Your Order.

Best regards,

Javier Encinas, PE

ASDIP Structural Software

debasis mallickJanuary 19, 2017 at 2:38 amI prefer using line diagram analysis for fixing length of toe and heel from outer surface of wall the error thus caused is nominal (2.5-1.8) t/m^3. Two simple equations with two unknowns get formed and are needed to be solved for various load combinations. The largest of both with appropriate thickness required from design considerations are inserted to cross check which finalises the work.

Muhammad AbbasJanuary 19, 2017 at 4:56 amThank you to much sir, it’s very valuable increment in my knowledge.I hop you will continuously propagation these valuable awareness about constructional engineering.

M S A MihrajJanuary 29, 2017 at 5:50 amTall cantilever retaining wall stability issue overturning / sliding are critical.

Additional base pressure if ground supported & shear also critical leads to uneconomical design.

Better consider counter fort retaining wall or reinforced earth -suppose to be most cost effective options than vertical cantilever design.

Javier Encinas, PEJanuary 29, 2017 at 12:47 pmCantilever retaining walls are cost effective up to about 15 feet (3 m) high. In some cases it’s the only option if there are existing structures on top of the backfill, where neither counter fort nor reinforced earth are possible. Counter fort walls do help to reduce the bending on the stem, but the stability requirements remain. A well designed cantilever wall may be more cost effective than a similar counter fort wall due to the additional forming, material, and labor. What type of wall to use will depend on the particular circumstances of each project.