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Lake Oswego, OR, United States

Strahler A.W.,Oregon State University | Walters J.J.,Shannon and Wilson | Stuedlein A.W.,Oregon State University
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2016

Frictional resistance between soil and steel reinforcements develops as a result of relative displacement at the soil-reinforcement interface and is typically characterized using interface shear or reinforcement pullout tests. The soil-reinforcement interaction between uniformly-graded soils and metal reinforcements has been well-characterized. However, the interface response of well-graded gravelly soils and ribbed steel strips is primarily based on lower-bound estimates of pullout resistance using databases of single isolated reinforcement pullout tests. Increases in horizontal stresses that develop in tall mechanically stabilized earth (MSE) walls are often accounted for in design by reducing the reinforcement spacing; however, the effect of possible frictional interference between closely spaced inextensible reinforcements has not been explored. Two reinforcement pullout apparatuses have been developed to study the soil-reinforcement interaction and effect of reinforcement proximity in a well-graded sandy gravel. A single strip pullout apparatus was developed to establish the baseline frictional resistance, comparable to typically-conducted pullout tests. The assessment of reinforcement strip interaction effects possible in closely spaced reinforcements was evaluated using a multistrip pullout apparatus. The effects of passive resistance at the front facing that alters the load-displacement response and contribute to epistemic uncertainty were mitigated using a well-characterized, soft boundary condition. Generally, the available resistance was observed to increase with increases in the localized stiffness, whereas the secant stiffness of the resistance-displacement response reduced with increases in localized stiffness. Current pullout resistance factor models are shown to be conservative and biased, and recently proposed calibrated exponential models more accurately capture the measured responses. Fitted isolated and confined strip models presented in this paper should help practitioners estimate the frictional resistance of ribbed steel strips in sandy gravel soils and incorporate increases resulting from closely spaced reinforcements into design methodologies and numerical simulations. © 2016 American Society of Civil Engineers. Source

Pradel D.,Shannon and Wilson | Pradel D.,University of California at Los Angeles | Wartman J.,University of Washington | Tiwari B.,California State University, Fullerton
Association of State Dam Safety Officials, Dam Safety 2015 | Year: 2015

In the Kanto plains north of Tokyo, Japan, the Magnitude 9.0 (Mw) Tohoku earthquake caused widespread liquefaction, lateral spreading, seismically induced settlement, slope instabilities and, importantly, resulted in 920 river levee failures. Along the Tone, Nakagawa, Fuji Rivers and its tributaries, failures affected more than 40 miles (65 km) of levees. Since the damaged levees were located at an epicentral distance of over 200 miles (320 km), failures of such magnitude surprised many engineers. In April 2011, the authors conducted post-earthquake engineering field reconnaissance as part of an ASCE-sponsored investigation of the Tohoku earthquake. A major portion of the observed levee damage was associated with liquefaction and associated lateral spreading. Importantly, our investigation revealed that much of the liquefaction was associated with anthropogenic (man-made) changes and in particular with fluvial transportation improvements implemented between the 16th and 20th centuries. These findings have important implications for river levees in seismically active areas, such as the Sacramento and American Rivers in California and the Mississipi River near the New Madrid seismic zone. © Copyright 2015 Association of State Dam Safety Officials, Inc. All Rights Reserved. Source

Benson C.H.,University of Wisconsin - Madison | Kucukkirca I.E.,Shannon and Wilson | Scalia J.,University of Wisconsin - Madison
Geotextiles and Geomembranes | Year: 2010

Samples of geocomposite drain (GCD), geomembrane (GM), and geosynthetic clay liner (GCL) were exhumed from a final cover at a solid waste landfill to assess their condition after 4.7-5.8 yr of service. Permittivity of the GCD diminished by a factor of 3.9, but the transmissivity was higher than published by the manufacturer. Ply adhesion of the GCD diminished by a factor of 2.0. Geonet ribs in the geocomposite drain (GCD) contained a light coating of fines and plant roots, but there was no evidence of significant clogging. The geotextile on the upper surface of the GCD met the commonly used criterion for filtration (AOS < 0.6 mm for adjacent soil with <50% fines), indicating that this filtration criterion was satisfactory. Tensile yield strength of the GM diminished by a factor of 1.2, but the melt flow index was unchanged and the oxidation induction time exceeded the manufacturer's specification. GCD-geomembrane interface strength appeared unchanged. Four GCL samples had hydraulic conductivities 1000-10,000 times higher than the hydraulic conductivity measured during construction, whereas hydraulic conductivity of the other seven samples was practically unchanged. Based on these observations, the following reduction factors are suggested for installation damage and near-term service conditions (<6 yr) for the geosynthetics used at this site: GCD permittivity or transmissivity - 4.0, GCD ply adhesion - 2.0, geomembrane tensile strength - 1.5, and GCD-geomembrane interface friction - 1.0. No recommendation is made regarding a factor for the hydraulic conductivity of GCLs. © 2010 Elsevier Ltd. Source

Vessely M.,Shannon and Wilson
Geotechnical Special Publication | Year: 2013

The purpose of transportation asset management is to meet life-cycle performance goals through the management of physical assets in the most costeffective manner. The performance goals can include safety, mobility, preservation, economics, and environmental aspects. Example geotechnical features that can be incorporated into the broader practice of transportation asset management include engineered and native slopes, embankments, tunnels, and earth retaining structures. Currently, many agencies address geotechnical features on the basis of "worst-first" conditions, reacting to failures and often incurring significant safety, mobility, environmental, and intangible costs. The goal of risk based methods for management of geotechnical features is to implement project planning, selection, and maintenance on the basis of "most-at-risk", by identifying and managing the features with the greatest probability of failure and consequence. When analyzing risk, it is important to recognize the process will only be successful when all features that create risk are included. Further, the use of multi-tier risk based assessment approaches can identify geotechnical features with the greatest risk to transportation performance goals. The concepts presented in this paper can be used to implement risk based management of geotechnical features. © 2013 American Society of Civil Engineers. Source

Murphy K.D.,Shannon and Wilson | McCartney J.S.,University of Colorado at Boulder
Geotechnical Testing Journal | Year: 2014

This paper presents the details of a new modified borehole shear device that has the capability of measuring the impact of temperature on the in situ shear stress-displacement curves for soil-concrete interfaces. The thermal borehole shear device incorporates concrete shoes with embedded heaters, a pneumatic loading device for application of horizontal normal stresses, and an automated loading system with local vertical displacement and load measurement systems that permits either displacement-control or load-control testing. A methodology for measurement of the soil-concrete shear stress-displacement curves and for evaluation of the drained interface shear strength failure envelopes at different temperatures is presented in this study. Typical results from proof-of-concept tests performed in a clay layer compacted in a laboratory tank in a borehole in a silty sand deposit in the field are presented in this paper. The results are synthesized to show how the impacts of temperature and normal stress on the normalized shear stress-displacement curves can be evaluated. These normalized curves can be measured on a site-specific basis for the calibration of thermo-mechanical load transfer analyses or finite element analyses, which are often used to design and evaluate soil-structure interaction in drilled shaft foundations with geothermal heat exchangers (energy foundations). Copyright © 2014 by ASTM International Source

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