As with any pavement structure, quality begins at the foundation level. These structures must have a uniform, stiff, durable foundation that will adequately support the premium materials placed above. A geotechnical investigation of the underlying soils is essential to establish the appropriate type and level of treatment needed to stabilize the foundation layers. Where adequate treatment of the subgrade is impractical, a high quality granular base, cement-treated base, or other engineered foundation should be used.