subgrade undercutting
Subgrade stabilization refers to the action of excavating for and installing a more suitable material in place of the old unsuitable material that was removed, primarily in subgrade locations that exist under pavement . The most common soil deemed unsuitable as a subgrade are clayey or silty soils as they are cohesive and retain water more readily, creating a more frost-heave vulnerable base.
Non-cohesive, granular, or coarse grained soils which are sand or gravel ridden tend to be considered more suitable as pavement base subgrades, and are likely to be more drainable in terms of surface water.
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The material used for stabilization typically consists of aggregate stone at different gradations depending on the planned pavement or structure above. Larger stone aggregate is typical for stabilization underneath footers and foundations, as is controlled density fill which is a sand/water/cement mixture of psi ranges from 500 to 2000. Medium stone aggregate is typically acceptable for stabilization under most pavement areas. Subgrade stabilization fabric is also common between the exposed subgrade and the newly placed stabilization material.