Par. 1. - All excavations shall so be protected, by sheet piling if necessary, by the persons causing the same to be made, that the adjoining soil shall not cave in by reason of its own weight. It shall be the duty of the owner of every building to furnish, or cause to be furnished, such support that his building shall not be endangered by any excavation; provided, that the owner of any building which is endangered by an excavation carried by an adjoining owner more than ten feet below the grade of the street may recover the expense so caused of supporting such building from the persons causing such excavation to be made. All permanent excavations shall be protected be retaining walls. In case of any failure to comply with the provisions of this section the commissioner may enter upon the premises and may furnish such support as the circumstances may require. Any expense so incurred may be recovered by the city from the persons required by law to furnish the support.