I read a Viva 100 news that wrote DL E&C announces on the 15th that it is using the largest Tunnel Boring Machines (TBM) for Seoul's metropolitan area express railway (GTX)-A route.

A 11.6 meter diameter‘Gripper TBM’ isused for the 4265m section of downtown Seoul and a 8.2 meter diameter shield TBM is used  for the 1314m section of the lower part of the Han River.

https://www.viva100.com/main/view.php?lcode=&series=&key=20220715010003713