Prove the Structural Edge/Retaining Wall for Lateral Force

We are working on a project, where the planting area will be edged with 18" high aluminum profiles. For having a better understanding of the situation, see an image attached from similar bedding. The depth of the soil is approx. 18", and we need to prove that the structure remains upright while standing on the 8" side, and the min/max distance between the reinforce panels (perpendicular to the profile), to keep the profile in shape. Inputs: - 5052 Grade Aluminum - Thickness 1/8" (3mm) - Determining the horizontal force, please apply the worst-case scenario, like apply the properties of saturated sand, instead of soil. Questions: a.) Prove that the structure standing on the 8" side remains upright, and not tilts. b.) What is the maximum distance between the reinforcing panels to keep the profile's shape? Tolerance: +/- 1/16". In other words: What is the maximum length of a unit, if there is only one panel welded on in the middle. c.) Call the minimal friction between the edge units and the crushed stone bedding which prevents slide effects. Thanks, Gabe