In all cases where excavations are made entirely across a street, alley or sidewalk, street or alley crossings, or any other public grounds, whether paved or unpaved, a substantial walk or driveway bridge shall be maintained, as the case may be, across the trench or opening by the party making the excavation, such walk or driveway bridge at all times to be subject to the approval of the city. (Ord. 861 §1, 1998)