Any contractor offering to do any new concrete work on the streets, alleys or sidewalks of the city, by public or private contract, shall first notify the engineer of such intention and the location of such proposed work. Upon such notice, the city engineer shall, as soon as is possible, set the necessary line and grade stakes, giving what instructions may be needed for such work, which work shall in all cases be done by a strict compliance with these specifications. (Prior code § 27-47)