From Mapquest:
Note to I-40 Travelers in the vicinity of Asheville, NC: Both directions of I-40 are closed between Exit 20, West of Asheville in North Carolina, and Exit 421 (I-81 Interchange) East of Knoxville in Tennessee due to a rock slide at mile marker 2.6 on I-40 in North Carolina. The road is not expected to reopen for several months. You can drag your route to avoid this section of highway or use the official NCDOT Detour: Motorists traveling on I-40 West are advised to take Exit 53B, I-240 West. Follow I-240 West to Exit 4A, I-26 West. Follow I-26 West (a North Carolina Scenic Highway) to I-81 South. Take I-81 South and follow back to I-40, Mile Marker 421, in Tennessee. This route is 53 miles longer than I-40. We also recommend visiting the NCDOT Travel site for additional information. For your safety, always obey local construction and detour signs.