ABSTRACT
A subgrade depth for obtaining samples depends on factors such as the type of formation, loading, and pavement type. The subgrade depth of testing varies depending on whether the tests are conducted as part of a site investigation or for construction quality testing. Each phase of a project has its own definition of a subgrade. This often leads to industry confusion as to the required depth for testing of a subgrade. Various approaches, such as finite element and Hertzian contact mechanics, are used to show how this subgrade testing depth requirement varies. There is no singular criterion when proof roll tests are used for subgrade assessment, and no visible movement applies only for very specific cases with high modulus values. Even then the proof roll pressures at subgrade level are significantly above the operational pressures, a subgrade experiences below a pavement. Heavy loads (one-off) represent a unique design consideration which relies on bearing capacity assessments. A case study of a subgrade assessment for a heavy load is described.
