Session: 06-03-02 Ground Monitoring

Paper Number: 133253

133253 - Fels Glacier Valley Slope Deformation Analysis and Geohazard Assessment for the Trans Alaska Pipeline System (TAPS) 

Abstract: 

Alyeska Pipeline Service Company (Alyeska) conducts ongoing pipeline integrity monitoring of the Trans Alaska Pipeline System (TAPS), including sites prone to slope instability and potential future landslides. Fels Glacier valley is an eastern tributary of the upper Delta River valley in the glaciated, rugged east-central Alaska Range. Located about three miles east of the Richardson Highway and the TAPS pipeline, Fels Glacier valley is drained by Lower Miller Creek, which crosses the TAPS pipeline at TAPS milepost MP 587.8. The south‐facing slope of Fels Glacier valley is a site of active slope movement. Several university researchers have postulated that a long‐runout rock avalanche or a sequence of events involving catastrophic failure of the deforming slope, damming of the drainage from Fels Glacier, and subsequent outburst flooding with entrained floodplain debris, could impact the Richardson Highway and nearby TAPS oil pipeline. However, this conclusion was reached without a structured geohazard assessment to estimate the probability of occurrence of this sequence of events and vulnerability of the TAPS pipeline to such an occurrence. In 2016, Alyeska convened a Technical Advisory Team to review work conducted in the Fels Glacier valley, and to advise on matters related to the observed slope instability. Desktop analysis of LiDAR data using a novel image analysis technique to estimate 3D displacement vectors was an important aspect of the assessment to establish the pattern of ground displacement. This information was supplemented by review of literature and satellite monitoring conducted by others to develop a geologic model of the site. Field reconnaissance visits were conducted in July 2016 to confirm various aspects of the geologic model, and in July 2018 in conjunction with a collaborative radar monitoring effort by the University of Alaska Fairbanks (UAF) and Simon Fraser University (SFU). Empirical screening calculations were supplemented by landslide runout modeling and hydrotechnical assessment by others. Outcomes of the various studies were used as the basis for a screening‐level geohazard assessment using the quantitative approach documented in an ASME book on pipeline geohazards (Rizkalla and Read, eds., 2019). This paper provides an overview of the screening-level geohazard assessment and details of the LiDAR image analysis used to develop the geologic model used for the analysis. The findings illustrate the utility of comparative image analysis using repeat LiDAR surveys and orthophotos to estimate a true 3D displacement field as part of quantitative geohazard assessment.

Presenting Author: Rodney Read RSRead Consulting Inc.

Presenting Author Biography: Dr. Rodney Read is a Professional Engineer and Geoscientist with almost 40 years of professional practice experience. He is President and Principal Consultant of RSRead Consulting Inc., a Canadian engineering consulting firm based in Okotoks, AB, specializing in Geological / Geotechnical Engineering and Applied Rock Mechanics. He is co-editor and a contributing author to the 2019 ASME book "Pipeline Geohazards: Planning, Design, Construction and Operations".

Authors:

Rodney Read RSRead Consulting Inc.
Richard Reger Reger's Geologic Consulting
Geoffrey Preston Merrick & Company
Frank Wuttig Alyeska Pipeline Service Company