Knoxville (WVLT) - The evening rush is underway and a massive sink hole on Pellissippi Parkway is causing some major backups.

TDOT crews have been working non-stop since midnight Tuesday.

Shortly, they hope to start paving over the filled sink hole.

Crews first had to open the hole to 60 feet long, 20 feet wide, and 30 feet deep.

Then, they filled the sink hole with big boulders, poured concrete over that.

They covered that with big stones. Now they're topping it off with gravel.

TDOT crews are no stranger to sink holes in East Tennessee.

"Sometimes sinkholes happen in the middle of a field or on the side of the road or drainage. This time, it wanted to open up in the middle of Pellissippi Parkway," says TDOT spokesman Travis Brickey.

According to the TDOT website, repairs aren't expected to be completed until 7:00 p.m. tonight.

Knoxville (WVLT/AP) – If part of your evening commute takes you southbound on Pellissippi Parkway from Oak Ridge, expect serious delays. A sinkhole reported Monday evening is still being repaired, blocking all but the shoulder of the Parkway.

Tennessee Department of Transportation crews are working to repair a sinkhole in the middle of the southbound lane of Pellissippi Parkway.

The sinkhole opened Monday night about a quarter mile from State Route 62, just north of Solway.

TDOT spokesman Travis Brickey says the hole looked like an upside-down funnel and was about 25 feet deep. The opening was about eight feet across and the bottom opened up to about 25 feet.

Brickey says a crew has dug it out to about 40 feet across and made the hole wedge-shaped. Many truckloads of large rock are being dumped into it.

Engineers say the sinkhole was probably caused by water eroding away the limestone bedrock beneath the blacktop.

That leads to cracks, then cavities, then a collapse like this.

"Since we have ditches on both sides of the traffic land, that's a source of water that filtrates through the top surface, that's why they happen within our highway system because we have drainage systems which cause the water to go to the direct bedrock," says TDOT Engineer Saieb Haddad.

Both southbound lanes are blocked, but the shoulder is open for one lane of traffic.

There's no timetable for re-opening the southbound lanes of the parkway. The afternoon commute is heavier southbound.