Not sure where you got such wrong information by tunnel boring machines. They are widely used and are cheap (don't believe 1 billion$ per mile some businessman sells you). Both Delhi and Mumbai have used tunnel boring machines. Indian metro cost 30-100 million dollars per mile based on property prices, number of stations, and ratio of underground/overground. Don't know the breakdown, but have read that the major costs are stations. Tbm themselves are expendable. That is why Delhi and Mumbai ordered 19 and 17 tbm for a single phase and a single line.
>>Not sure where you got such wrong information by tunnel boring machines.
I'm not saying they don't use it. I'm saying they don't buy it. They lease it. Bangalore Metro's snail pace is largely due to inability to afford renting more TBM's.
TBM's are not cheap. Not for the budget projects like Bangalore(and other cities get) metro gets. Delhi and Mumbai are a different deal, as government spends money through a fire hose there. In fact South India pays most of the taxes and gets little in return, compared to North, which gets >1 rupee for every rupee it contributes to the exchequer.
South Indian cities are not that lucky.
One of the feedbacks that went into further phases for Bangalore Metro was to get more TBMs. They only used like 4 for the first phase, and even there one broke down and it took like months to get it fixed.
http://delhimetrorail.com/press_reldetails.aspx?id=aIUb8nwzH...
https://indianexpress.com/article/cities/mumbai/mumbai-metro...