Over excavation
The term 'excavation' refers to the process of removing earth to form a cavity in the ground, typically to allow a below-ground structure to be constructed.
The term ‘over excavation’ refers to an excavation that goes beyond the depth required for the formation of a below-ground structure.
This might be necessary for example if the ground conditions at the level that the below-ground structure will be constructed do not have sufficient stability or load-bearing capacity to support that structure. In this case the excavation must be taken to a deeper, more stable level, the unsuitable material removed, the ground at the lower level may need to be treated to ensure it has suitable load-bearing capacity, then the excavation back-filled to the required level with suitable compacted fill.
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