No part of any building or structure of any kind, and no cellar or other excavation, shall encroach upon or within any public street, sidewalk, land, easement or right-of-way, except by specific authority of Council as contained in a franchise, ordinance or resolution of Council duly noted in its journal or minutes; and any building or structure or part thereof and any cellar or other excavation which may exist at any time in violation of this section may be declared by Council to constitute a nuisance subject to abatement; provided, that nothing in this section shall apply to any excavation made pursuant to an excavation permit under the provisions of Article 909.