M 2021

202103mar5:15 pmASCE Oregon Section March Virtual Meeting

Event Details

The ASCE Oregon Section Geotechnical Group has shared an invitation for their March virtual meeting.  The meeting will include a presentation by Armin Stuedlein (Oregon State University)  titled, “Blast-Liquefaction Tests to Evaluate the Deep, In Situ, Nonlinear-Inelastic Dynamic Response of Medium Dense Sands at PDX.”

Meeting Registration here.

Abstract

As part of its long-term resilience goals, the Port of Portland has determined that one of its two runways must be hardened against the vertical and lateral deformations anticipated following rupture of the Cascadia Subduction Zone and the nearby Portland Hills fault. Both runways lie in close proximity to the Columbia River, which has been dredged to maintain shipping channels to depths as great as 20 m. Lateral spreading has been determined to pose a significant risk to the runways, given that the subsurface consists of dredge sand fill, medium stiff silt, and a deep deposit of medium dense sand. Deep (25 m), in-situ, blast-liquefaction experiments were conducted to provide a means to understand the seismic performance of these soils without the possible effects of sample disturbance, small sample-size effects, and artificial drainage conditions to support design efforts at the Port. This presentation describes the experimental approach, blast-induced ground motions, and quantification and evaluation of dynamic constitutive soil properties from the linear-elastic to the nonlinear-inelastic regime with loading that produced direct simple shear-equivalent shear strains larger than 1%. Shear waves generated due to near- and far-field unloading of the initial compression wave were found to control the soil response, and were associated with frequencies common in earthquake ground motions. Constitutive soil properties including the threshold shear strains to trigger soil nonlinearity and residual excess pore pressure, ue,r, as well as changes in constitutive responses as a result of alterations in the soil fabric and geostatic stress state are described. Field drainage during the experiments was observed to exert a significant influence on large-strain shear modulus, and its effects distinguishes the in-situ response from those observed in cyclic, fully-undrained or constant-volume laboratory tests. The significantly reduced geostatic stress state inferred from shear wave velocity and settlement measurements following the second and largest blast experiment facilitated comparison of the shear strain-excess pore pressure relationship for vertical effective stresses ranging from approximately 0.5 to 2.5 atmospheres of overburden pressure, and confirms that such relationships are highly pressure-dependent as inferred from other centrifuge and low-stress field experiments. The technique developed and deployed in this study can be used to determine fundamental dynamic soil properties in any soil and at any depth.

Bio

Armin is a licensed professional engineer and Professor of Geotechnical Engineering in the School of Civil and Construction Engineering at Oregon State University. He received his MS and PhD in geotechnical engineering from Syracuse University (2003) and the University of Washington (2008), respectively. He joined the faculty at OSU in 2009 after consulting for Seattle-based firms, where he specialized in port and harbor engineering with an emphasis on foundation and earthquake engineering. His research has been published in over 100 peer-reviewed technical publications, and focuses on ground improvement and liquefaction mitigation, in-situ and laboratory-based testing for liquefaction and cyclic softening, experimental and numerical investigations of soil-structure interaction, and probabilistic geotechnical analyses. His research is funded by departments of transportation, the National Science Foundation, and industry partners. Armin serves as the Vice Chair of the ICSMGE Technical Committee 304 Engineering Practice of Risk Assessment and Management, the Vice Chair for the Soil Improvement Committee (ASCE G-I), an Editor at the ASCE Journal of Geotechnical and Geoenvironmental Engineering and the Journal of the Deep Foundations Institute, and Editorial Board member for Georisk and the Canadian Geotechnical Journal. Among other honors, Armin received the 2013 Deep Foundations Institute Young Professor Award, the 2015 Associate Editor of the Year Award for JGGE, and the 2017 ASTM Award for Outstanding Article on the Practice of Geotechnical Testing.

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