Soil pressure on a retaining wall increases with the depth of the soil it is holding back. Walls typically fail in three ways - by bending, by sliding, or by toppling. When engineering a wall, the lateral thrust, reaction forces and friction must all be analyzed to account for these three failure modes.

The greater the depth of the wall, the greater the total lateral force of the soil. This exerts an overturning force that is -resisted by the weight of the soil over the footing and the weight of the wall itself. Friction at the base of the footing keeps the wall from sliding.
The greater the depth of the wall, the greater the total lateral force of the soil. This exerts an overturning force that is -resisted by the weight of the soil over the footing and the weight of the wall itself. Friction at the base of the footing keeps the wall from sliding.

To learn more about retaining walls, visit the JLC Field Guide - an online construction reference and training resource.