"Roadheaders can accurately operate in a wide range of rock formations. With careful planning and their advanced computer systems helping guide them, these machines use a rotating cutter head (the pineapple-shaped part on the front) with tungsten carbide teeth that can chew through incredibly hard rock. "

But this says it all.

"Compared to a tunnel boring machine (TBM), which is limited to excavating a space that is roughly equal to its own size, the pivoting arm of a roadheader allows for flexibility in the shape of the tunnels or caverns it excavates. "

https://www.metrolinx.com/en/discover/transforming-ontario-line-station-construction-with-roadheaders