3 years is too ambitious by any standard if you have so much underground work. Anyway .. best wishes for this project.
Bangladesh has no real experience even to build the surface rail road. Now, this country is talking about all these fancy underground and surface constructions to be completed in only 3 yrs. This is an impossible task in such a short period.
It will take more than 3 yrs to prepare even a master plan. In order to finalize a master plan, the following works must be done:
1) Selection of route, 2) Overground survey works that include not only Theodolite Transit and Levelling surveys but also the survey of all the existing facilities along the proposed route, 3) Standard Penetration Tests (SPT) to know about the Sub-surface soil conditions, and 4) Many other miscellaneous works.
Only after completion of the above works, the Structural Analysis works can be started, then the Design Drawings, and then the Construction Drawings. Construction works may start only after all these works have been completed. So, a 3 year plan is too short.
I guess, a total of 8 years will be needed to construct even a 10 km stretch of rail track laying works. However, if three teams work separately, then there can be 30 km construction during this same period.
All depends upon the thinking of people at the high level. PM certainly has little knowledge about this type of construction. She was telling after the election that BD will produce electricity from HAOR and BAOR. In Bangla the translation of hydro-elctricity is PANI-BIDDYUT. PANI is water, and BIDDYUT is electricity. Haor and Baor have water, therefore, she thought that power can be produced from those waters.
Either the govt people do not understand the gigantic task of building a train track inside a busy city, or they are making fool of the public to keep their popularity intact. This is what my honest personal opinion is about the proposed construction of a hi-fi railway system in a country, which never added 1 km of rail road after the British left and no steel factory has ever produced 1 metre length of steel rail line. Sorry to shatter some people's sweet dreams.
Perhaps, Indian design and construction companies are much able to do such a job, but their participation will certainly be politicized. I have seen photographs of a tunnel and part of a rail track in Tripura. I would say, these seemed to me perfect. In some other thread in the PDF, I have also seen how the Indian engineering companies themselves are building a long multi-span bridge over the sea. Why not give them some contract, then learn from them and do other similar jobs by ourselves!