"Our goal is to get this cleaned up as soon as possible," said NC Department of Transportation construction engineer Ted Adams.

The slide generated a miles of backup for hours on Interstate 40 on Friday night.

ASHEVILLE – A slide of rocks, dirt and trees will keep a 20-mile section of Interstate 40 in Western North Carolina closed for up to a week as crews remove debris and set up an alternate route.

The slide of about 20,000 cubic yards of material occurred around 7:30 p.m. Friday at mile marker 7.5, near the Harmon Den exit.

"We had a small slide with rocks falling from a pretty high elevation, and when they were hitting the road, they were bouncing into the eastbound lanes," said Ted Adams, construction engineer for NC Department of Transportation's District 14, on Saturday afternoon.

More:What we know about the I-40 rockslide closure: Details, timeline and detours

NCDOT closed I-40 westbound at exit 20 (U.S. 276) and eastbound lanes at the Tennessee state line. Both lanes were closed for the safety of both drivers and cleanup teams.

While crews on Saturday cut down trees on the slope, which sits right at the edge of the roadway on a curve, dirt, rocks and more would periodically slide down into the westbound lanes.

NCDOT crews will set up the eastbound lanes to allow for one lane in each direction for about 1,500-2,000 feet around the slide site. "Absolutely in a week we'll have traffic running out here," Adams said.

"Our goal is to get this cleaned up as soon as possible," he added. They will work 24 hours a day to get traffic flowing again.

But moving all the dirt, rocks and debris from the slope will take longer — about four to six weeks. "We hope we can do it quicker, but that's our preliminary estimate," he said.

Car damage and backed up traffic

When the slide started on Friday, nine cars were damaged, many getting flat tires from running over rocks in the road, Adams said. One car was hit on the side by a falling rock when as the vehicle stopped so it didn't hit debris in the road. No people were hurt.

The slide generated miles of backup for hours on Interstate 40, and NC State Highway Patrol helped clear the backup by turning cars around. This stretch of road carries an average of 26,000 cars daily.

Tractor-trailers were guided through the slide zone by crews watching the slope rather than backing them up to the rest area 2 miles away, as was the initial plan, Adams said.

In cleaning up the slide, the slope itself will be scaled back, taking the weight off, Adams said, to prevent future slides.

A small slide, by comparison

The last major slide in the area was in 2009.

"Most of our slides have been over 100,000 cubic yards, which is about a thousand dump truck loads of material. This one's closer to 20,000 cubic yards," Adams said.

Geotechnical engineers have "scoured this entire gorge" looking for other potential trouble areas. "We know where all the hot spots are. The problem is we just don't know when and where."

A rock excavation about three years was done just west of the site of the current to prevent a major slide from occurring, he said.

Harrison Construction has received an emergency contract to perform the work. Its crews were expected on site Saturday afternoon to begin work on the project.

Adams estimated the cost of the project to be around $750,000, which will be paid out of federal funds.

What is the DOT's I-40 detour?

DOT's detour is a long one but familiar one: It takes westbound traffic back to Asheville and sends drivers onto I-240 east to I-26 west into Tennessee. From I-26, drivers take I-81 south back to I-40. Eastbound traffic should follow in reverse: I-40 to I-81 to I-26 to I-40.

The detour, from exit 20 near Waynesville, is about 160 miles long.

Both Adams and NCDOT spokesman David Uchiyama urged drivers to stick to the posted detour rather than following GPS directions.

A history of slides

In February 2012, the interstate was shut for several days because of a slide just west of mile marker 7. At the same time, a slide had blocked the roadway on the Tennessee side at the state line.

But a much bigger slide occurred in 2009, closing the major trucking route for six months.

At that time, engineers installed 543 bolts into the rock face, designed to keep the rock wall from sheering off in the future. The 150-foot-tall rockslide closed the interstate near the Tennessee line on Oct. 25, 2009. Nearly 20,000 vehicles a day had used that stretch of interstate, at the time.

For updated traffic information,check NC DOT's traffic information site.