Prepare the Wall Base and Drainage

because now there's nothing behind that push holding it what's happening is here's a great example wide open there's nothing back here pulling this one to that one and the soil behind it is pushing it out even bolder retaining walls need to be engineered when they're over four feet although typically you can build a gravity based retaining wall much taller with boulders than you can with a modular block Boulder retaining walls also will need a certain amount of drainage and base material depending on the subsoil conditions but if your soils are soft and compression of all you're going to want to fortify that base by laying something down before you put the boulders in place we're gonna talk about filtered fabric right now we're gonna dispel some of the myths boulder retaining walls in certain applications will require filter fabric and at other times you will not want to use filter fabric yada-yada-yada you have very sandy soils with very little clay binder behind it it is mandatory that you put filter fabric it or the soils will wash through the face of the boulder retaining wall but if you have a high clay content soil with a lot of silt within it beware that when you put filter fabric behind that Boulder retaining wall that fabric is going to plug up plain and simple and