How to Build a Retaining Wall Foundation

Getting a super-looking landscape starts with first learning how to build a retaining wall. Retaining walls are walls built to restrain the soil on an unnatural slope. The walls are built to withstand the lateral pressure that results from a change in the ground that exceeds the soil’s angle of repose. The retaining wall requires a strong foundation to help the wall withstand the continuous pressure from the soil it is restraining. Here is how to go about it.

How to Build a Retaining Wall Foundation

First of all, you need to prepare the site where you want to build the retaining wall.

Draw a string at the point where the front of your projected wall will be. Mark the ground with spray paint along the line. Remove the string and dig a trench 60cm wide. The excavation should have an appropriate depth to hold the foundation, say 12 inches. Ensure that about 105{9d9681e4c6dc2bcc365b21c2d56e28b5b32bbb1e70b651a9b83f3bf689c16ca7} of the wall’s height is beneath the surface. Install a geotextile at the base of the trench to prevent contamination of the drainage system by the foundation. Ensure you leave some part of the geotextile on the ground which will you will use to cover the stones/wall once the backfilling is done. You may decide that hiring an expert would save you time and effort so if you want to enlist the help of the professionals, we recommend Australia’s retaining wall experts, Amber Tiles.


The strength of the wall will depend on the material you use. Gravel is a good option. You can also use compacted earth. Dig up to one foot deep and ensure the gravel is well placed. The larger pieces of the gravel should be at the bottom followed by the bigger pieces. Set it evenly to ensure it is level without dents. This will make the foundation support the walls well.

Strengthening the base

Besides the foundation material, add paving rock poles, flagstone rock, and molded concrete units to strengthen the wall structure. Ensure that if there are drainage pipes underneath, the foundation is not interfering with them.


The foundation design for cantilevered walls is normally strong. The wall is well equipped to handle the retained material under gravity pull. For a cantilevered wall, the foundation needs to be concreted. Before applying the concrete, install steel stem underneath which will reinforce the foundation. In this design, all the pressure is directed underneath the surface. In addition, the horizontal pressure on the top is converted into vertical pressure.

Types of foundations and when they are necessary

Gravity Type Foundation

This is necessary for a simple wall built by stacking rocks or slabs. Dig below the soil, line the base with gravel and mortar it roughly. You may also use concrete rods to reinforce the base.

Sheet Pile Foundation

This is necessary if the soil in that area is loose. Insert wood planks up to 2/3 in the soil. The upper 1/3 on the surface ensures good resistance of pressure especially where there are frequent rains.

The foundation will mainly be influenced by the area where you are building the wall. Once you determine the kind of wall you need, the topography of the area and the type of soil, build your wall foundation as illustrated above.