Davidson said the alternative to the nine-day closure would have been carrying out the work over 30 weekends, adding that would have been “much more disruptive”.
Buses will replace services between Gravesend and Dartford towards Crayford, Barnehurst, and Slade Green.
Services will run as normal into London along the Sidcup, Bexleyheath and Woolwich routes.
Preparatory work will take place on 7 and 8 February, and follow-up work is scheduled for 1 March and 5 April, with closures also planned on those dates.