All persons causing any excavations to be made for sidewalks shall have the place of excavation properly graded and protected, and shall properly barricade such place for the protection of the public. Whenever necessary, they shall, at their own expense, properly erect masonry or steel construction or a sufficient retaining wall to properly support the adjoining earth. Such retaining wall shall be properly coped or provided with an iron railing to guarantee safety to the public. (1976 Code Sec. 17-16)