No area wall or enclosure shall be erected under the sidewalk of any street less than sixteen inches in thickness, and the travel upon such sidewalk shall not be wholly obstructed during the time when any excavation for any area purposes is being made, nor while the wall thereof is being constructed, and the same care and caution shall be exercised to insure the safety of persons traveling upon said streets while said area is in course of construction, as is provided for in Section 17.04.010 when buildings are being constructed.  Should any person violate or fail to observe any of the regulations imposed in this section in constructing such area or walls thereof, he shall be subject to the fine in this chapter specified and the city manager may and shall order any excavation made for area purposes to be filled up at the cost of the person so offending.