Shimla, September 23 (UNI) The Himachal Pradesh unit of the Communist Party of India (Marxist) has expressed serious concern over cracks appearing in buildings in Shanti Vihar ward, Bhattakufar and adjoining areas of Shimla allegedly due to the construction of twin tunnels between Chalounti and Bhattakufar under the National Highways Authority of India (NHAI) four-lane project.