Career after completion of M Tech in Tunnel engineering is Good because  the infrastructure development in India or surrounding Asiatic Countries will increase in 5 years time. so we need tunnels for building of pipelines and other infrastructure needs. There are nearly about many tunnel projects which are worth in thousands of crores  and thus there is a demand for skilled /fresher worker in this feild.

Also underground transportation will be the future of many placs with scarcity of land transport.

So summing up you shhould have interest in this industry and be ready to face challenges because they will demand you to work in many togh terrains and areas with more productivity.

All the best!!!