- Loads are determined. This includes all the dead loads from soil weight and self weight of wall, live loads, surcharge load from above, any possible earthquake loads, impact loads, lateral earth pressure, water stream flow pressure if any etc… Then, we choose how do we insert these loads into load combinations, which are provided in applicable codes.
- Failure surface of the soil (line defining the “wedge”) behind the wall is determined.
- Earth pressure distribution behind the wall is determined. This also includes the lateral pressure from surcharge loads behind the wall for instance.
- Now that we know what loads will act on our wall, we can draw a free body diagram of our wall. From this free body diagram, we can now find reaction forces, to counter the loads acting on the wall. These reaction forces include the anchor forces that will hold the wall in place, and the passive resistance from the soil below the wall. see figure below.
retaining walls 4
From this, we can also find the shear force and bending moment that will act on the wall on all its sections, with similar logic to the example when we drew the shear and moment diagrams for the beam we solved under structural basics: forces and stresses section.
- So now since we know what forces will act on our wall and the tendons, we can design anchor lengths, wall thickness, soldier beams that will hold the wall in place and so on. If, after first round of design, which is called preliminary design, at least some values are not found to be ok, we return back, resize our members or geometry or redefine members, and then, repeat our design steps, until we can confirm that everything checks out.
In the next post of this series, we will discuss “Mechanically stabilized earth walls”