(The following story by Tim Potter appeared on The Wichita Eagle website on October 26.)
WICHITA, Kan. — Emery Goad is a private investigator, not an engineer. But from his office along Wichita’s recently opened Downtown Rail Corridor, he says he saw what looked like a train wreck about to happen.
To him, it appeared that sand was leaking from a temporary, wire-and-reinforced-fabric wall bracing ton after ton of sand on the east side of the 2-mile, raised bed. He also noticed what looked like patch repairs. Now that trains have started rolling over the 25-foot-high track, Goad wondered how the wall could hold up.
But Goad and others who might wonder about the temporary wall don’t need to worry, says Mike Jacobs, the city engineer overseeing the $105 million rail project.
The east wall is not leaking sand. What Goad is seeing is leftover material, spilled during construction, Jacobs said. What looks like patches are places where the temporary wall has been bolstered as an extra precaution.
The temporary wall is designed to hold up two trains at once, even though it will have to support only one train at a time, he said. The wall gets much of its stability from an internal structure observers can’t see.
Inspectors have been closely monitoring the temporary wall, partly because it’s a newer design for train traffic, Jacobs said.
Satellites and surveying equipment have been used to watch for the slightest shifting.
“This wall is not moving,” he said.
At first, inspectors monitored the wall three times a day. That has been scaled back to once a day because the wall has performed as expected, Jacobs said.
Steve Forsberg, a BNSF Railway spokesman, said: “We would not have gone ahead with operating trains if we didn’t think it was safe to do so.”
On the Wichita route, BNSF trains weigh up to roughly 15,000 tons, spread over more than a mile. The heaviest single piece — a locomotive –weighs more than 400,000 pounds.
Since Oct. 16, about 30 trains a day have been using the new raised rails, said Jon Wolverton, a lead engineer with TranSystems, a project consultant.
The railway company has been monitoring the construction and has relied on independent inspections to confirm that the structure is safe, Forsberg said.
When BNSF trains started using the new bed, the first train was restricted to 10 mph as a precaution and to test the new structure. Since then, trains have been able to increase their speed to 30 mph, Forsberg said.
The opening of the raised corridor has been hailed as a major benefit for commuters and emergency crews who previously had to stop for trains. Now, vehicles can pass under trains at bridges along the corridor.
The west side of the raised bed has a permanent, concrete outer wall connected to an interior honeycomb of reinforced concrete and compacted sand.
By the end of the year, crews will begin installing the same kind of permanent wall and support network on the east side.
The east-side work is expected to be completed about a year from now, Jacobs said.
Because of logistics and railroad operations, crews couldn’t erect a permanent east wall at the same time they built the permanent west wall.
By the spring of 2009, a second track is expected to be installed atop the raised bed, after the permanent wall is built.
The design provides a margin of safety, Jacobs said. The finished structure — carrying two trains at a time — will be able to safely support three trains. The design would allow for a third track to be added eventually.
The temporary wall slopes in slightly as it reaches the top, like a layer cake.
Each layer of sand is encased by three layers of reinforced fabric and wire. The engineered fabric on the wall extends 4 feet deep into the sand fill.
As a precaution, a subcontracting firm has installed, at its expense, 7-foot-long anchor bolts to bolster sections in a few places where crews didn’t properly align the wall during construction, Jacobs said.
Years ago, crews built raised railroad beds with massive amounts of concrete. The Wichita structure employs far less concrete. But a special process increased its density for extra strength, Jacobs said.
“It’s just as strong or stronger,” he said.
The sand that fills spaces between the concrete structure underwent tests at three laboratories to make sure it had the proper friction to provide stability.
To stabilize the base of the corridor, crews drilled 8,000 holes into the ground and filled them with compacted rock.
At first glance, the walls appear to be vertical, but are slightly sloped in. Even if they were vertical, they would have been strong enough; the sloping adds stability, Jacobs said.
Building with a wider base would have raised costs “and disrupted and moved many businesses,” he said.
Wichitans will be looking at the structure for a long time.
Engineers designed it to last 75 years.