Bridge could remain intact after longwall passage

</element><element id="paragraph-1" type="body"><![CDATA[Late last week American Coal Company's longwall mining system passed under Harco Road in an area of about 1,000 feet between Netty Green Road and Johnston City Road.

The area between those roads is closed due to insecurity over the stability of a bridge that passes over the Middle Fork of the Saline River.

The passage of the machine had been long-anticipated and the Saline County Highway Department was planning to close that section of the road until the effect of the mining on the road was evident. In the past the passage of the longwall 350 feet under the ground meant a drop of elevation about 4 feet. That was what happened last year in a section east of the current passage when the logwall went under Netty Green Road. The highway dropped and the road was closed for temporary repairs.

Unique about the latest pass of the longwall was the fact it mined under the bridge that spans the Middle Fork of the Saline River. The road runs north and sound and the longwall runs west to east. The ground drops in a gradual west to east wave that can place extraordinary pressure on a bridge until the ground stabilizes. In the past bridges and guardrails have twisted and popped bolts. The bridge will be closed until the amount of damage can be determined.

"The bridge on Netty Green Road, subsidence tore it all to pieces," Saline County Highway Engineer Jeff Jones said.

The Saline County Highway Department, engineers from Brown and Roberts, Galatia Township officials and other interested parties have been checking on the bridge to determine its stability. As of Monday afternoon there were no extraordinary signs of damage.

"The bridge has tilted east to west, but there is no obvious structural damage. But this time tomorrow I'll feel a whole lot better about it," Jones said.

A structural engineer from Brown and Roberts is to inspect the bridge Saturday. Someone from the Illinois Department of Transportation Bureau of Bridges and Structures may also be called for a determination. If there are no problems the road may be opened back up, Jones said. Whatever the case, there will be a new bridge built to replace the current one that was built in 1938 as per an agreement with American Coal Company.

"In the meantime it's a hassle," Jones said.

"It's part of the cost of mining jobs."

Currently, the west side of the bridge is about a foot lower than the east side.

Because the Middle Fork west of the bridge over the weekend sunk lower than that east of the bridge the water is ponding in the low spot.

"It was 2 feet deep and now it's 6 feet deep," Jones said.

Eventually the drainage should stabilize and continue flowing into the Saline River and to the Ohio, Jones said. The area of subsidence will cause the creek to be deeper in parts.

Wildlife has been active in the deeper section. Snakes and turtles swam about in the deeper pool beneath the bridge. Whether they are reacting to the shifting of the creek bottom is unknown.

The longwall is affecting about a 1,000 foot section of the road. Normally a longwall's path will be about 200 feet away from the previous path and that difference in road height is evident on Harco Road. Last year's path dips about 4 feet, raises back up about 200 feet and now the asphalt south of that 200 feet is cracking as the base subsides into the gulf left by the recent longwalling about 350 feet below the ground.

Initially the highway department planned to install a temporary one-lane bridge to ensure Harco Road would remain passable if the bridge sustained heavy damage. The longwall was ahead of schedule by about a month and the department was unable to build the temporary bridge in time.

If the subsidence remains fairly constant across the bridge's surface there may be no need to keep the bridge closed, Jones said.

"I think 24 hours from now we'll be pretty much out of the woods and after three days whatever is going to be done will be done," Jones said Monday afternoon.

There were 4-inch gaps between the bridge corners and the earth. The guardrails clanged softly, likely in response to changes in pressure. Cracks in the bank were visible evidence the ground was changing beneath the bridge and cracks in the asphalt about 4-inches wide were the most dramatic signs of subsidence. There was some cracking on the concrete pier cap on the bridge, but Jones said there were cracks there already.

Jones looked beneath the bridge and saw nothing out of the ordinary there, either.

"All the bolts seem to be in place," Jones said.