Excavation is more than moving dirt around with heavy machinery.
Before the foundation can even be laid for the commercial or residential structure, what is not needed on-site has to go.
Depending on the type of structure under construction and its function, any of four different Excavation processes may be used:

Trenching: the process of removing soil and rock to form a narrow underground trench that is wider than it is deep
Digging: the break-up and removal of soil and rock for off-site disposal to prepare for a level foundation to the structure
Dredging: the process of digging done underwater, where sediment and water are excavated together for off-site disposal
Site Development: Site Prep that directly relates to the site but indirectly to the building under construction (landscaping, excavating for walkways and sewer systems, crushing and recycling site debris, placing topsoil, forming a water retention basin, etc.)