‘Ancient lake’ soil forces ODOT to tear out Wickiup Jct. project

(Update: Comments from ODOT, area residents)

Soft soil in an unforeseen ancient lake bed will prompt dismantling of the mostly complete $17 million Wickiup Junction railroad overcrossing, ODOT told La Pine officials and residents Wednesday evening. The remaining money will be used to come up with a new design option.

Crews suspended construction in May after tests showed the ramps leading to the bridge were settling at an unusual pace. ODOT hired a third-party engineering firm to study the settlement problem, and make a recommendation on how to proceed.

Experts found silica skeletons from algae known as diatoms that used to live in an ancient volcanic lake. These diatoms were causing the settlement issue.

ODOT Region 4 Manager Bob Bryant and other officials provided the update to a packed La Pine City Council work session Monday evening.

“We did our normal, subsurface investigation as part of this project that we would do for any type of project of this kind,” Bryant said. “What we didn’t anticipate was the subsurface condition that exists here at Wickiup Junction.”

Diatomaceous soil is rare, ODOT officials said, with few studies done on it. That means agency engineers cannot be sure how the material would hold a bridge’s weight.

Bryant told councilors the project was 80 percent complete in the spring, on track for expected completion by the end of the year. It was supposed to provide a safe way for cars to cross the railroad tracks.

Although the future of the overpass is unknown, ODOT did say they will continue to look for new options to improve safety at the crossing for travelers and area residents.

“I’m a fireman here in La Pine, and it makes it a lot simpler for us because a lot of times we get called and when we are heading down 97, a train comes across,” said resident Ted Sommers. “We have to sit there with an ambulance, waiting for a patient that’s dying.”

Construction on the $17 million project began in 2016 and was put on hold twice in just under a year. Safety still remains a primary concern.

Bryant said, “We have buses, school buses, hazardous material loads that have to stop there legally at a railroad crossing. Right now, their only option is to stop on Highway 97.”

Engineers concluded there are alternatives to allow continuing the current project, but they are costly, and the unusual nature of the soil means there is no certainty it could hold the original bridge design.

Most councilors told the agency they want ODOT to find other options to proceed as soon as possible. And there was, perhaps inevitably, frustration, even anger among some in the City Hall audience.

“They should have done their homework first before they went this far with it,” said resident Chuck Lee.

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Here’s the ODOT news release issued late Monday afternoon, detailing what was found and what happens now.

Engineers for the Oregon Department of Transportation have developed a recommendation for the next steps of the stalled US97 Wickiup Junction – BNSF Overcrossing project.

The $17 million overpass safety project was proposed to eliminate the last “at grade” highway crossing of railroad tracks in Central Oregon.

Crews suspended construction in May after tests showed that the earthen ramps leading to the bridge structure were settling at an unusual pace. Crews removed some of the earthen embankment to stabilize the settlement until further analysis could be completed under the surface.

ODOT’s Region Manager Bob Bryant brought in geotechnical experts from the Federal Highway administration and contracted with an outside firm, Cornforth Consultants, to conduct a comprehensive subsurface soil study at the project site.

Technicians drilled additional boreholes and removed soil samples from as deep as 280 feet below the surface. That investigation revealed the contents of an ancient lake below the project, thought to have been formed when lava flows from the nearby Newberry Volcano dammed the Deschutes River.

At its deep base, under layers of volcanic ash, pumice, sand and silt deposits, experts found silica skeletons from microscopic algae known as diatoms which lived in the lake and sank, forming a thick bed on the lake bottom thousands of years ago. Under the weight of the project, the diatoms began to crush and reorient, causing unpredictable settlement.

Cornforth concluded that the normal practice for soil testing and geotechnical analysis would not have found this unique geologic condition.

“Our standard of practice for this work does not typically include the use of a scanning electron microscope and x-ray diffraction,” Bryant said.

Cornforth Consultants employed those advanced techniques to determine that diatoms were present in the soil deep underground. Bryant added, “We have encountered an extremely unique subsurface condition here in Central Oregon.”

The geotechnical engineering team decided that increasing settlement from the earthen ramps would cause further displacement of the bridge girders. The girders placed over the railroad tracks are the beams that would have supported the bridges’ deck. (The falling of two large beams had prompted an earlier suspension of the project.)

The department has decided that the next step for the project should be the removal of those girders. ODOT engineers will also recommend to the Oregon Transportation Commission removing the rest of the bridge and ramps, and use the remaining funding to evaluate alternatives for achieving the original goal for the project. The Commission will take up the matter at their October meeting.

In addition, ODOT Director Matthew Garrett will convene a panel of experts through the Federal Highway Administration’s Resource Center to enhance the department’s geotechnical design process and ability to analyze problem soils in other locations in Oregon.

“I think it is incumbent upon us to take the information that Cornforth has identified and build upon it,” said Garrett. “We are bringing in a panel of outside independent eyes to review what we have in hand, but more importantly to review the processes and protocols that we have surrounding our geotechnical discipline.”

To see more on the original plans: http://www.oregon.gov/odot/projects/pages/project-details.aspx?project=09679