The construction of the first phase of a major metro project in Chennai, India, may be causing cracks in more than 200 buildings in the city, and the buildings’ owners are calling for a formal investigation.

Federal Minister for Urban Development Kamal Nath recently stated that as part of precautionary measures, strengthening and even temporary evacuation was being conducted for structurally weak buildings to ensure safety. “In the event of significant impact on any building, the repair works are undertaken based on the recommendations given by the experts from the Indian Institute of Technology (IIT), Chennai,” Nath said.

Some residents have speculated that the tunnel boring machines (TBM)s being used on the project could have caused the cracks. However, one structural engineer close to the project, who asked not to be identified due to the sensitive nature of the subject, told ENR that this has not been proven, given the fact that 70% of the buildings that developed the cracks were very old.

“The metro was built all over Delhi including close to very old heritage buildings, and there were no incidents…” On the other hand, he said, “It could have been a design failure. One cannot rule out negligence for not ensuring a minimum cone of influence.”

Cracks often occur when the soil is weak around the tunneling area with a settling foundation. “Incidents of cracks are largely unavoidable in such large scale construction particularly in congested areas where known methods of strengthening cannot be carried out”, S. R. Gandhi, Head of the Department, Civil Engineering, IIT, Chennai, was quoted saying to a local daily, The Hindu.

“It is certainly challenging to carry out tunneling in Chennai's soil conditions which is a coastal region with large variations and occasional soft marine clay layers,” Gandhi added.

The 90-km long, more than $3 billion metro project is being built by the Chennai Metro Rail Ltd. (CMRL), a joint venture between the government of India and the southern state of Tamil Nadu.

Delhi Metro Rail Corporation (DMRC), prime consultant for the first phase, will assist CMRL in an advisory role in the execution of the project.

The first phase to be completed by the first quarter of 2015, will have two corridors with a combined length of 45km, of which the underground section will be 24km with 19 stations.

One of the first to be awarded a tender for the design and construction on the 3.3 km twin tunnels that will include three stations, was Larsen and Toubro in joint venture with Shanghai Urban Construction Group.

On the two Tunnel Boring Machines (TBM) used, “all necessary precautions with regard to the plugging of old bore wells and utility diversions have been taken well in advance and all buildings en-route will be monitored round the clock when TBMs are in operation,” S. Krishnamoorthy, chief general manager on the project, had assured 14 months ago.

The TBMs are usually operated at a speed of 6-10 meters a day. The project brief was “based on a detailed evaluation, experience and internationally accepted practices,” according to CMRL.