The compacted soil surface beneath a road, concrete slab, or foundation that everything else is built on top of.
The native or compacted soil surface upon which a pavement structure, foundation, or slab is constructed. The bearing capacity and stability of the subgrade directly influence the thickness and design of the overlying structure. Weak or unstable subgrades require stabilization, replacement, or the use of geosynthetics before paving or construction can proceed.
A CBR value of 3 was measured for the native subgrade, requiring 12 inches of crushed aggregate base to achieve adequate pavement support.
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