How to prepare the ground before laying concrete
You definitely shouldn't pour concrete over mud. Also, I guess your local can get quite cold during the winter, thus you need to dig the soil, at least, down to the frost depth to avoid differential settlement due to heave. The soil is considered &quot;competent&quot; if it can support the weight above without significant settlement. You can get the information from the local building code, a engineer, or an experienced contractor. Below is the suggested details.