The Chennai Metro Rail Limited has deployed 2 specialised tunnel boring machines for carrying out underground tunnel works in Chennai to make headway in the rocky terrain in the stretch between Royapettah and Taramani. The works would be part of a 45.8-km stretch of Corridor-3 in the phase-2 project from Madhavaram to SIPCOT. Till Taramani the stretch would be underground and from there up to SIPCOT the stretch would be elevated.
From Madhavaram to Kellys the soil conditions can be managed well, but from Kellys to Royapettah, the soil conditions start changing gradually from sandy to marine clay to rocky strata. After Royapettah, the presence of rock underneath would become pronounced and at Taramani it would be rock hard below. The tunneling works would be facing issues as it would be tough to be carried out. Two special TBMS would be utilized for drilling the hard rocks underneath and it must be considered that normally TBMs would bore nearly 10m in a day but due to the presence of hard rock the TBMs would be able to drill just 3 to 4m per day. From Kellys to Taramani alone, as many as 8 TBMs would be used to drill tunnels.
In totality, 23 TBMs would be used for drilling works in Chennai and for a depth of 18m to 20m, metro stations are being constructed in the metro phase-2 is known. The stations go to a depth of 25m also in places like Mylapore and Taramani. The presence of a rock at a depth of 13 to 14m in Taramani would pose a huge issue for CMRL. Phase-2 metro rail construction work at a cost of ₹61,843 crores is one of the biggest ongoing construction works in Chennai.