AEG OR Chapter November 19, 2019 Meeting
Glaciolacustrine Earthflow Slides on US95
PURCHASE OF TICKETS USING BROWN PAPER TICKETS: Ticket sales stops by Noon on Monday November 18th.
(At the door payments in Cash or Checks only.)
6:00 Social Hour
6:45 Dinner (Salad and Pizza)
Speakers: Collin McCormick, P.E.
Failure of a cut slope along US 95 just south of Bonners Ferry, Idaho impacted traffic along a major highway linking commerce between the US and Canada in March 2017. Initial field reconnaissance revealed groundwater seeps emanating from thin sand layers within glaciolacustrine silt deposits. Piping occurred in the seepage areas, resulting in flow slides and slumping of destabilized portions of the cut slope. Liquefied slide debris traveled down the cut slope over long runout distances, flowed into the ditch, and then onto the highway and across to the opposite side. This highly-fluid earthflow was difficult to contain. Concrete barriers placed along the edge of pavement were pushed by the leading edge of the advancing earthflow. Retrogression of the head scarp caused additional slumping and subsequent lobes of earthflow debris posed a continuing hazard to traffic.
Temporary mitigation measures were developed to address the immediate earthflow hazards. A temporary debris retention barrier was rapidly constructed using readily available materials to contain liquefied slide debris.
Supplemental temporary mitigation measures were necessary to maintain highway safety through winter. In late summer 2017, the slope was laid back in the headscarp area to improve local stability and a network of French drains were installed in the slide debris perched on the cut slope to reduce water runoff and groundwater pressures.
SPEAKER BIO: Collin McCormick, P.E.
Collin McCormick has worked as a geotechnical engineer at Landslide Technology in Portland, Oregon since 2013. He obtained is masters degree from the University of Washington and his bachelors from Oregon State University. Collins experience in geotechnical consulting has been focused on rockfall and landslide mitigation projects, embankment dam and levee evaluations, and geotechnical earthquake engineering.
Old Market Pub (View)
6959 SW Multnomah Blvd.
Portland, OR 97223
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