Wednesday, May 21, 2008

Sinkhole - USA (Arkansas) MAY

THEBACHA/FORT SMITH - A crater-sized sinkhole on Highway 5 disrupted traffic for a short time last week.


A sinkhole encroaches onto Highway 5 about 150 kilometres west of Fort Smith on the evening of May 11

Although the collapsed portion of highway 150-kilometres west of Fort Smith didn't close the road completely, traffic was reduced to one lane and vehicle restrictions were applied as crews worked to repair the damage.

Rob Billard, the regional manager for the South Slave with the Department of Transportation, said it measured about 11 metres long and eight metres wide, and was about seven metres deep.

"It seemed like this one moved fairly quickly," Billard said.

At its largest, the sinkhole was about halfway into the east lane of the highway.

Billard said both lanes of the highway were excavated, one lane at a time, until solid ground was reached.

"Slowly and surely, it was filled in and compacted," he said.

During repair work on Monday traffic could pass by in one lane or on small detours on each side of the road. The road was never closed to light trucks and cars, but was closed to commercial trucks from 9 p.m. on May 11 to 11 a.m. on May 12.

By the evening of May 12, both lanes were open.

Billard said the sinkhole started in a ditch and grew until it encroached upon the road.

Located at Nyarling River, the hazard was first spotted by passing motorists on May 11.

One of the first to see it was John Evans, who was heading home to Fort Smith at about 6 p.m.

Evans was stopped by a motorist who warned of the sinkhole and placed branches on the road as a warning to other travellers.

Evans said when he got to the sinkhole, it was broken through right up to the edge of the hard driving surface of the unpaved road.

Evans said he walked towards the edge of the sinkhole to see how deep it was, but he could hear things falling in and didn't go right to the edge.

"The whole thing could have caved in," he said. "I really didn't know."

Evans found a box, stuck a branch into it, and left it on the side of the road as a warning to other motorists.

When he returned to Fort Smith, Evans contacted his brother Earl, a highways maintenance supervisor with the Department of Transportation, who rushed out to put warning signs around the sinkhole.

The department also stationed a watchman at the site throughout the night.

Billard said the sinkhole was about a couple of hundred metres west of the underground Nyarling River.

The area features karst geological formations, meaning underground limestone and other soft rock has been dissolved by water, which can lead to sinkholes.

As for the underground river, Billard said, "Whether that was associated with the sinkhole or not is impossible to tell. There was no water in the sinkhole."

Billard said the Department of Transportation is looking at options for surveying the subsurface strata of the highway to determine if other sinkholes might develop.

An engineering survey was previously done on the highway, he said. "It didn't identify any problems at that time."

While the area is within Wood Buffalo National Park, the road is maintained by the territorial government.

Fort Smith Mayor Peter Martselos said the community is concerned about the sinkhole.

"Thank God no accident took place," he said, adding someone driving at night could run into such a hole.

"It's very, very dangerous," he said.

"Nobody can predict what can happen when a river is running underground."

Evans said the sinkhole doesn't make him worry about travelling Highway 5.

"There are sinkholes all over the place," he said. "But you don't expect them in the road." - Source

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