On the outset District Collector will not take any action to remove the illegal encroachments. Hence after 15 days or one month, file an online petition to CM's Special Cell as a Public grievance quoting your previous petition details. http://cmcell.tn.gov.in/login.php
From CM's office, your grievance will be forwarded to the District Collector for his action/reply. Please donot get disappointed, if the illegal encroachment is not removed.
For sure, the District Collector will not take any action on your petitions to remove the illegal encroachments, untill and unless he is instructed by a Court Order.
In the meantime, thru' RTI Act 2005, get all the details about this 70 ft road from DRDA / PWD / Coimbatore Corporation authorities, to file a PIL before the honorable High Court.