Complex sentence: The ceiling of the mine is bordered on the whole surface by wooden balconies for the circulation of the authorized personnel during the periodical controlling of the stability of the surfaces of the superior zone of the mine construction.
Split into simpler sentences: The ceiling of the mine is bordered by wooden balconies on the whole perimeter. The balconies are used for the circulation of the authorized personnel during the periodical inspection of the stability of the surfaces of the superior zone of the mine construction.