Excavation begins on a construction project when digging commences on the site to remove earth, usually in preparation for foundation work. The extent of excavation is usually determined by the object's footprint as well as the depth of its basement.

In most cases excavation belongs to the site preparation phase of a structure, and not to actual construction because digging does not in itself build anything. However, excavation often occurs during or after foundation work - for example, a basement is often excavated after piles or caissons are built below the basement by drilling or pounding through the extra layer of soil.

The event concerns the first digging for the project even when foundation installation precedes it. A ceremonial groundbreaking can take place separately; loosening a symbolic shovelful does not establish that excavation work has started.