UPDATED--Both lanes of southbound Interstate 81 between mile markers 120 and 125 near Blacksburg, Va., remain closed due to an unstable slope. As a safety precaution, traffic is being detoured until enough unstable material can be brought down to stabilize the slope, according to the Virginia DOT.

Since Tuesday, southbound I-81 traffic has been detoured off the interstate and onto Route 11/460 at mile marker 132 and then back onto I-81 at exit 118. The detour could remain in place as long as ten days.

A blast that took place at 9:30 a.m. today did not remove enough material to stabilize the slope. Throughout the day crews have used heavy equipment to remove material. If another blast is necessary, the date and time will be announced.

Crews have been blasting as part of work to repair an unstable slope near mile marker 124 on a project to construct a truck-climbing lane between mile markers 120 and 125. During a scheduled blast on Monday an existing crack in the unstable slope increased from approximately 50 feet to 120 feet in length.  Geotechnical specialists reviewed the slope, and the state DOT in the interest of public safety decided to close southbound Interstate 81. 

Signs and message boards are in place to alert drivers.

For traffic information and updates, visit www.511Virginia.org.

Update adds post-blast information.

Beginning at 4:30 p.m. Tuesday, both lanes of southbound Interstate 81 in Montgomery County near Blacksburg, Va., will close starting at mile marker 132 due to an unstable slope. A detour will be in place.

Traffic will be detoured at exit 132 (Dixie Caverns) onto Route 11/460 and back onto I-81 at exit 118 (Christiansburg). The detour will remain in place for at least one day but could remain as long as ten days. As a safety precaution, traffic will be detoured until the unstable material on the slope can be brought down. It is unknown at this time exactly how long it will take to stabilize the slope.

Crews have been blasting as part of work to repair an unstable slope near mile marker 124 on a project to construct a truck climbing lane in Montgomery County between mile markers 120 and 125. During a scheduled blast on Monday, Aug. 26, an existing crack in the unstable slope increased from approximately 50 feet to 120 feet in length. Geotechnical specialists spent Tuesday reviewing the slope, and VDOT in the interest of public safety has decided to close southbound Interstate 81.

The next blast is scheduled for Wednesday, Aug. 28, at 9:30 a.m. Once this blast is complete, a more definite time frame for how long the detour will be in place may be available.

During the blast on Wednesday, Aug. 28, State Police will slow traffic on northbound I-81 beginning at mile marker 114 to keep the area near the blast clear of traffic. Once the blast has occurred, traffic will be released to travel at a normal speed. Drivers should expect delays. During blasting, the on-ramps will be restricted onto northbound Interstate 81 at exit 118 (Christiansburg). Flaggers will control traffic on Route 636 (Seneca Hollow Road and Friendship Road) during blasting.

Signs and message boards will be in place to alert drivers.

Work on the truck climbing lane project is expected to be completed in November 2013.  For traffic information and updates, visit www.511Virginia.org.