Gravity Retaining Walls

A retaining wall that relies solely on its own weight to stand up is called a gravity wall. Allan Block combines the basic engineering principles of setback, leverage and total unit mass with simple mechanics to make highly stable gravity walls.

Every retaining wall supports a “wedge” of soil. The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the retaining wall site, and can be calculated once the soil friction angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall.
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Video: How Does a Retaining Wall Work

Sliding Wedge Comparison

Leverage and Total Unit Mass

As the setback of a gravity wall increases, the leverage from course to course increases. This added leverage allows you to build taller retaining walls before reinforcement is needed.

With the hollow core design, Allan Block comes to the job site weighing less than solid, heavy block. Once the cores are filled, the Allan Block units develop the same unit mass as solid blocks. This mass combines with the setback to determine the maximum gravity wall heights. See the Gravity Wall Chart below for details.
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Allan Block’s 12° (Ref) system can achieve wall heights up to 5.5 ft. (1.7 m) without reinforcement in good soils with a level slope above.

Gravity Wall Heights

Use the chart below to find the maximum height that your retaining wall can be built before reinforcement is required. The gravity wall heights shown do not account for seismic loading. Check with a local engineer for assistance if you are in a seismic area.
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Gravity Wall Analysis

Before you analyze any retaining wall make sure you have an accurate picture of the jobsite conditions. Every retaining wall must be engineered to withstand the pressure from the soils and other loads behind and above them. Standard gravity wall analysis considers sliding, bearing and overturning forces. On sites with slopes or surcharges, a global stability check will also be necessary.

Sliding

Ability of the retaining wall structure to overcome the horizontal force applied to the wall.

Factor of safety = 1.5

Bearing Capacity

Ability of the retaining wall structure to overcome the horizontal force applied to the wall.

Factor of safety = 1.5

Overturning

Ability of the retaining wall structure to overcome the overturning moment created by the rotational forces applied to the wall.

Factor of safety = 1.5

Global Stability

Ability of the internal strength of the soil to support the complete soil mass. Contact local design specialist for help in evaluating your site.
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