China has been building helipads and trenches in Doklam but these are not a threat to India, Union Defence Minister Nirmala Sitharaman said on Monday.She said that China has been undertaking these construction activities to maintain its troops during the winter and that the troop strengths of both sides have been reduced after the two-and-half-month-long stand-off that ended in August 2017."Post disengagement from the face-off in 2017, troops of both the sides have re-deployed themselves away from their respective positions at the face-off site. The strengths of both the sides have been reduced," Sitharaman told the Rajya Sabha in a written reply."In order to maintain these troops during the winter, the People's Liberation Army (PLA) has undertaken construction of some infrastructure, including sentry posts, trenches and helipads," she added.She said the Indian government regularly takes up the issues pertaining to the Line of Actual Control (LAC) with the Chinese side through established mechanisms, including Border Personnel Meetings, Flag Meetings, meetings of Working Mechanism for Consultation and Coordination on India-China Border Affairs, as well as through diplomatic channels.In a separate reply, Minister of State for Defence Subhash Bhamre told the Upper House of Parliament that "situations arise on the ground" with PLA due to the varying perceptions of LAC by the two sides."There is no commonly delineated Line of Actual Control (LAC) in the border areas between India and China. From time to time, on account of differences in the perception of LAC, situations have arisen on the ground that could have been avoided if we had a common perception of LAC," Bhamre said.He added that India "consistently maintains" peace and tranquillity on the India-China border, an "important pre-requisite" for the smooth development of bilateral relations.