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. ODOT elected to begin decommissioning of the site by removing the concrete girders only, and leaving the abutments and earthwork intact. This decision was made for several reasons:
1. Due to end abutment settlement the concrete girders were experiencing stresses that were causing structural stability issues, and resulting in impacts to railroad clearance.
2. In order to maximize further relevant geotechnical exploration and monitoring it was determined that the existing abutments and earthwork were the most beneficial elements to monitor as a “case study”. Bent 2 continues to show no sign of settlement so continued analysis of this bent would benefit any potential future solution.
3. By minimizing the removal work we could extend the funding to make short term improvements to the Wickiup Junction area that could help mitigate safety concerns that were the initial nexus for the project.
4. All of the potential solutions identified assume utilization of the new alignment. Under these scenarios some of the embankment would still be forward compatible.
The additional geotechnical monitoring and analysis will allow us to further refine the feasibility study completed in October of 2017. That feasibility study had to make long term predictions and assumptions based on 1 year of data. As a result all solutions contained significant risk based on the information at that time. It was determined by our Geotechnical Team, which included FHWA participation, that additional monitoring and analysis would help us remove assumptions and more clearly identify risks associated with the 6 options analyzed as part of the feasibility study. The additional geotechnical monitoring and analysis includes settlement measurements, piezometer monitoring, abutment inclinometer monitoring, etc.
It is our goal at the end of the analysis period, scheduled to be in the Fall of 2024, to outline a long term solution that has manageable risk. At that point we would estimate a cost for the long term solution and work with stakeholders do determine if the cost of the project provides the value intended to correct the at grade railroad crossing and the other intersection safety issues at Burgess and Rosland Roads. This decision point will most certainly involve FHWA and would also include potential further decommissioning discussions if the proposed solution is not feasible.
Project design - 2014-2015
Initial construction - 2016-2017
Post-construction activities - Bridge girders were removed in the Fall of 2018