Whenever any city officer shall let any work or improvement which shall require the digging up, use or occupancy of any street, alley, highway or public ground of the city, there shall be inserted in the contract for the same, substantial covenants requiring such contractor, during the nighttime, to put up and maintain such barriers and lights as will effectually prevent the happening of any accident in consequence of such digging up, use or occupancy of any such street, alley, highway or public grounds, for which the city might be liable, and also such other covenants and conditions as experience may prove necessary to save the city harmless from damages. And also to provide in such contract that the party contracting with the city shall be liable for all damages occasioned by the digging up, use or occupancy of such street, alley, highway or public grounds, or which may result therefrom or which may result from the carelessness of such contractor, his agents, employees or workmen. (R.O. 1959, Ch. 36, Art. 5, Sec. 10)