No person shall make any excavation in any street or in any manner interfere with any permanent improvement thereon except by permission of the city manager or other competent authority, and any excavation so made shall be so backfilled that the earth therein shall be securely tamped while the earth is being filled into the same or water shall be so used, such that the same shall at all times be above the dirt being thrown in, and any permanent improvement or sidewalk shall be re-laid in as good condition as the same was before the same was taken up, and said street and said improvements shall be maintained in good and safe condition for a period of six months after the time when said excavation was made at the cost of the person making said excavation, to be recovered upon his bond as herein provided.