Yes this is right that they laying old rails in place of 2nd line construction on which track laying machine run and replace it with new rail. I said about new rails thrown beside already laid single line which I saw in pics.. So their was CTR sanctioned for some sections between Gadag Hotgi so due to that they might be going for track renewal of already GCed single line. Also now a days freight traffic is increasing in this section which might be sensed them to renew them..