Portland-Milwaukie Light Rail Bridge – 1 year milestone
December 22, 2011
Drilling for first of 12 shafts complete; rebar cage placed in shaft in advance of concrete pour Friday
One year ago, the Federal Transit Administration gave TriMet permission to authorize Kiewit Infrastructure West to begin design and construction of the Portland-Milwaukie Light Rail Bridge, the first bridge to be built over the Willamette River in more than 40 years. In that time, more than 1 million pages of calculations have gone into the engineering of the bridge, now being built in the river.
Other major milestones include:
- Securing 34 federal, state and local permits to begin construction
- All work completed in the 4-month, in-water construction window
- Drilling for the first shaft is complete; crews are placing the rebar cage (in two sections).
Today, crews placed the second rebar cage, 10' x 75', into the shaft in preparation for the concrete pour on Friday.
Drilling the shafts into the Troutdale Formation
Scientists have extensively studied the formation and geological makeup of the Portland region. Both upstream and downstream from Vancouver, Wash., at the edge of the "Portland Basin", there are exposures of Columbia River basalt. Within the basin itself, the basalt lies more than 1,000 feet below the surface. Over the course of the Miocene and Pliocene epochs 23 to 2.6 million years ago, the basin was filled by sediments of the ancestral Columbia River. Named the Troutdale Formation, these deposits can be divided into two general parts: a lower gravel section containing pebbles and cobbles, and an upper section that contains volcanic glass sands.
Deposition of the Troutdale Formation was followed by a period of volcanism 2.6 to 1.3 million years ago. This volcanic activity was associated with faulting and structural deformation of the Troutdale Formation and further depression of the Portland Basin. Over time, the upper layer of the Troutdale Formation has been "reworked" by river currents, weather and erosion. Beneath the reworked layer there may occur hardened portions of the formation that have been cemented or partially cemented by time and pressure. While these hardened portions are known to occur, where they occur and how large they are varies.
About the project
The 7.3-mile project is the region's sixth MAX line to be built and extends from the terminus of the MAX Green and Yellow lines at Portland State University to South Waterfront, Southeast Portland, Milwaukie and Park Avenue in Clackamas County. It will create about 14,000 jobs and generate $573 million in personal earnings. When it opens in September 2015, it will extend the MAX system to 60 miles.