For ampacity of cables in tunnels see
Power cables in tunnels by Birron M. Weedy University of Southampton England
Power Cables and Their Application, 3rd Edition by Lothar Heinhold/Reimer Stubbe (Editors) Part I chapter 18.5
In my opinion, DOHA CABLES fabricates Single Core Copper Conductor, XLPE insulated, Copper Wire Screen and HDPE Sheathed of 127 / 220 (245) kV according to IEC standards, starting from 400 sqr.mm [90.6 mm overall diameter]