I strongly suspect that the encasement of the 12kV conductors in a concrete raceway/conduit is to minimize the chance of mechanical damage from any potential cause, especially when trackwork, etc. is being performed. Additionally, the encasement provides mechanical support which lessens the potential wear from vibrations and greatly simplifies the task of replacing a failed cable. My employer from which I am retired has underground transmission at Voltages up to 345kV and most if not all of which is encased.
~Ken :: Fairmont ex-UP/MP C436 MT-14M1 ::
Black River Railroad Historical Trust :: [/url]
Black River Railroad Historical Trust :: [/url]