I81UPDATED: VDOT says an I-81 detour between Dixie Caverns and Christiansburg has now been lifted, after remaing in place during this morning’s commute. The 14-mile southbound stretch of interstate was shut down yesterday when construction crews discovered an “unstable rock slope”.  VDOT says even the most thoroughly-planned highway construction project can bring such surprises. WFIR’s Evan Jones has the story.