动土 is a separable verb (离合词) that literally means 'to move earth' and is used in the context of starting construction — the ceremonial 'breaking ground' or the actual beginning of digging for a building project. The verb 动 and the object 土 can split: you can say 动了土 ('broke ground'), 动过土 ('have broken ground'), or 动一次土 ('break ground once'). It is formal and often associated with traditional rituals performed before a construction project begins.