The cut's relationship with trench cut SU410 is unclear on the S end. Either SU410 was cut first, then SU400, which left SU400's wall thin to the point that it degraded, or SU400 was cut first, then SU410, which led to the same cut wall destruction. Cut for posthole, on axis and in series with posthole cut SU402, in line with trench SU410.