BRIDGE CONSTRUCTION INCLUDES SEISMIC TESTS

There appears to be little to no activity occurring on a platform situated in the middle of the Mississippi River.

However, a handful of workers are performing highly-complicated tests to ensure the Bill Emerson Memorial Bridge doesn't fall down if an earthquake ever occurs.

"It may look like all you can see is that drill turning around and around, but actually, they're doing all the work about 100 feet below that," said Randy Hitt, area engineer for Missouri's Department of Transportation.

Since mid-July, a 15-member crew has performed jet-grouting work to repair mud fissures in a section of bedrock in the middle of the river.

The fissures, caused by centuries of erosion, must be found and filled before bridge piers are built because of the bridge's seismic design.

"With that seismic design, if the earth gets to tilting, the bridge loading goes to about four times as much, so the support's got to be there," Hitt said. "We're most concerned about the corner edges."

The jet grouting process involves drilling some 200 holes in the bedrock that are eight inches in diameter and 50-feet deep. Pipe is laid in the holes, from which mud is pushed out with a high-pressure mixture of air and water.

As the mud is pushed out, the space is filled with grouting cement. Crews are able to drill and cement a maximum of two holes each day.

The process has added an additional $5 million to the cost to build the 4,000-foot-long cable-stay bridge. Other costs associated with the delay are not included in that figure.

"It's a slow process," said MoDOT engineer Jeff Grancolas. "We have to slow (the drill) down or speed it up depending on what we're working in."

Beyond the actual jet grouting process, repair work also is slowed by environmental and safety concerns, Hitt said. All of the mud and other material blasted from the holes must be loaded onto a special barge. The debris is taken to the Cape Girardeau Port Authority for disposal.

Hitt said workers also must abandon the project whenever the river height rises above flood stage. Special procedures also are required if river levels drop too low.

"We're always fighting the river," he said. "I can't believe less than two months ago we were fighter the water because it got so high, and now we're moving stuff because it's so low."

Hitt said the jet grouting should be completed by February, after which crews will begin building a foundation in the center of the river.