UDATE: ODOT removed the bridge girders in Fall 2018 and returned the site to a more stable condition. A Refinement Plan is also underway to examine further opportunities to enhance safety and improve traffic flow from 1st Street in La Pine to Drafter Road.
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 brought in geotechnical experts from the Federal Highway Administration and contracted with 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.
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 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.
Project design - 2014-2015
Initial construction - 2016-2017
Post-construction activities - Bridge girders will be removed in Fall 2018