It shall be unlawful for any person to make an excavation in any street or streets for any purpose whatsoever unless a written permit is issued by the City Council authorizing such excavation. Excavation in streets and alleys shall be made in such a manner as to impede travel as little as possible. Warning lights shall be maintained on all unfinished work, at night from dark until sunrise, and sufficient barricades shall be in place at all times until the work is completed, to prevent any persons from injury in coming upon or crossing such work. After completion of any job or work, all surplus material must be removed at once from the streets and alleys.