more-in After experiencing several road cave-ins in phase I, Chennai Metro Rail has decided to be cautious in phase II of the project that is likely to begin soon. According to officials of the Chennai Metro Rail Limited (CMRL), they have decided to make some changes in the alignment according to soil conditions. “But these changes will be only minor ones. We have planned to do it as we had issues of roads caving-in in some areas in phase I because of loose soil and want to avoid them in this phase,” an official said. This will be significant as a major portion of phase II runs underground, unlike the phase I. The CMRL decided to resort to this plan because an underground network will not need as much land as an elevated track would. Phase II will criss-cross the city for nearly 108km with 116 stations; of this, about 81km and 88 stations will be underground while the elevated track will be 27 km long with 28 stations. But since this is a massive project it will be taken up in sections; at first, the CMRL will construct a 52 km stretch — from Madhavaram to CMBT and Madhavaram to Sholinganallur. Now, a crucial step for the project — soil testing — has begun at Madhavaram and will go on for a few months. “This is when we will know how the soil conditions are and how we can carry out tunnelling work for nearly 81 km without affecting the residents or buildings located along this alignment. Based on the results, we will make some changes in the alignment,” he added. Design consultants Simultaneously, they are in the process of appointing detailed design consultants, who will prepare a study for phase II. This detailed design will have every aspect of the project covered — from the precise location of the station, the exact areas the alignment will traverse through, land required for each station and how construction will be carried out. This work is likely to be completed in about 6-8 months. But experts say it may be challenging to make changes in the alignment according to the soil conditions. An engineering expert from IIT-Madras said mixed soil conditions prevail in many of the areas. “If the soil condition is rocky, it is not too difficult to handle it; it is the loose and clayey soil which is likely to cause problems, such as cave-ins,” he added. An expert from IIT-Madras said the CMRL drilled holes to identify soil type underground, but there are more sophisticated methods which can help in knowing the conditions accurately. “They can do geophysical testing of soil which will give them continuous profiling of soil conditions. But above all this, instead of making changes in the alignment, they can safely carry out tunnelling with ‘soil stabilisation’ — a process of altering soil properties to better its strength,” he added.

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