No person shall excavate any sewer or trench within the corporate limits of the City to a greater depth than five feet unless the sides of such trench or sewer excavated are supported by proper cribbing strong enough to prevent the earth from caving or falling in.
In all contracts on behalf of the City for the construction of sewers or trenches, it shall be stipulated that excavations to a greater depth than five feet must be supported by proper cribbing. (1963 Code §901.05)