We organize many interesting events throughout the year.
Presentation: A new probabilistic common-origin approach to level-ground liquefaction susceptibility and triggering in all CPT-compatible soils using DQ and its application in engineering design Scott M. Olson, PhD, PE
Scott M. Olson, PhD, PE and Kevin W. Franke, PhD, PE
Zoom Link: https://us06web.zoom.us/j/88612944518
Based on a comprehensive database involving 401 cases of observed liquefaction (or no liquefaction), the authors developed a new probabilistic procedure to simultaneously assess liquefaction susceptibility and triggering for nearly all CPT-compatible soils ranging from non-sensitive clays to clean sands. This procedure has several advantages, including (1) it eliminates the need for a fines content adjustment; (2) it identifies a threshold for fine-grained soils that are not susceptible to liquefaction and large strength loss; and (3) it differentiates the liquefaction resistance of clean sands with differing mineralogy and compressibility, as reflected in CPT parameters. At the same time, based in part on conversations with numerous practitioners, the authors have identified two troubling trends in probabilistic liquefaction triggering analyses. Firstly, many engineers employ only model uncertainty in probabilistic liquefaction triggering analyses, which may significantly underestimate the total uncertainty involved in an analysis. Secondly, many engineers apply a factor of safety “buffer” to deterministic liquefaction triggering curves defined from probabilistic studies. This combination may result in significant (over)conservativism in a triggering analysis. When considered jointly with all the conditional probabilities associated with unacceptable liquefaction hazard (e.g., ground motions, triggering, and consequences), it appears that we, as a profession, often over-predict the actual risks from liquefaction-related effects.
SCOTT M. OLSON, PhD, PE
Scott M. Olson, PhD, PE is a Professor and Faculty Excellence Scholar in the CEE Department at the University of Illinois, where he joined the faculty in 2004. Prior to joining Illinois, Scott worked in practice for Woodward-Clyde Consultants and URS Corporation. Prof. Olson has researched static and seismic liquefaction for over 25 years, and has been involved in dozens of research and consulting projects involving geotechnical earthquake engineering; tailings dam engineering; in situ, laboratory, and centrifuge testing, soil-foundation-structure interaction; and paleoliquefaction and geohazards analysis. From these activities, Scott has published nearly 150 journal papers, conference articles, and reports, and has received numerous awards, including the ASCE Walter L. Huber Civil Engineering Research Prize and the Canadian Geotechnical Society R.M. Quigley Award. Prof. Olson serves in various capacities for the Geo-Institute, USUCGER, EERI, and the Transportation Research Board (TRB). And recently, he became a founding member of the U.S.-based Tailings and Industrial Waste Engineering (TAILENG) Center.
KEVIN W. FRANKE, PhD, PE
Kevin W. Franke, PhD, PE is an Associate Professor in the Department of Civil and Environmental Engineering at Brigham Young University, where he joined the faculty in 2012. Kevin’s principal research focus relates to geotechnical/earthquake engineering, performance-based methods for dealing with soil liquefaction and its associated hazards, and autonomous applications of unmanned aerial vehicles (UAVs) in monitoring infrastructure and performing post-disaster reconnaissance. He serves as a Co-Principal Investigator in the NSF-sponsored Center for Unmanned Aircraft Systems (CUAS), a Steering Committee member of the Geotechnical Extreme Events Reconnaissance Association (GEER), Vice Chair of the Earthquake Engineering and Soil Dynamics Committee of the ASCE Geo-Institute, and member of the U.S.-based Tailings and Industrial Waste Engineering (TAILENG) Center. Since 2012, Kevin has published more than 70 peer-reviewed journal papers and conference articles. Prior to his current academic position, Kevin worked for 6 years as a professional engineer for Kleinfelder, Inc. and URS Corporation.
Presentation: An End Bearing Method for Evaluating Instrumented Becker Penetration Test Data Khaled Chowdhury, PhD, PE, GE ABSTRACT Becker Penetration Tests (BPT) with instrumentation are regularly performed to characterize the density of
Khaled Chowdhury, PhD, PE, GE
Becker Penetration Tests (BPT) with instrumentation are regularly performed to characterize the density of embankment dams and foundations that consist of sandy gravel, gravelly soils or rockfill, where other methods such as the Standard Penetration Test (SPT) and the Cone Penetration Test (CPT) are difficult to perform. An embankment dam constructed in the 1950s was recently evaluated using instrumented BPT and sonic borings, as well as earlier large diameter in-situ ring density tests and BPTs, original construction records, and observations and in-situ testing as part of a dam modification project. Three commonly used BPT methods for conversion of BPT blow counts to equivalent SPT N60 values were evaluated. Wide differences in the resulting equivalent SPT N60 values between (1) the Harder and Seed (1986) BPT method and the instrumented BPT-based methods of (2) Sy and Campanella (1994) and (3) DeJong et al. (2017) and Ghafghazi et al. (2017) were observed in this project. This finding is consistent with several other projects that were reviewed. These different equivalent SPT N60 blow counts from different methods would result in significantly different estimates of expected seismic performance of an embankment dam or other structures.
Based on an evaluation of the origins and development of the three BPT and instrumented BPT interpretation methods listed above, and further analyses of available data, an alternative “end bearing” method was developed to determine site-specific equivalent SPT N60 values from BPT. This proposed method systematically and transparently analyzes the collected BPT instrumentation data and provides equivalent SPT N60 values considering in-situ soil characteristics; a significant improvement to commonly used procedures. The end bearing method is based on transparently separating the shaft friction and residual force of the BPT piles by using CAPWAP-RSA and CASE methods to accurately determine the end bearing capacity of soil. In addition to site characterization for seismic analyses, this method can be used for deep foundation design and capacity verification.
Khaled Chowdhury is a Senior Geotechnical Engineer at the USACE South Pacific Division Dam Safety Production Center in Sacramento, California and the USACE HQ National Earthquake Program Policy Advisor. Khaled has over 22 years of experience in evaluation, design, and construction of infrastructure projects. He currently provides technical leadership on several major dams and levees evaluation and design projects nationwide, addressing static and seismic potential failure modes. Khaled contributed or is currently contributing to development of several USACE and California DWR guidance and regulatory documents on dams and levees. He received his BS in Civil Engineering from Bangladesh University of Engineering and Technology and ME in Civil Engineering (Geotechnical) from Texas A&M University. Khaled earned his PhD from the University of California, Berkeley under supervision of Professor Ray Seed. Khaled’s research and practice areas include site characterization, soil liquefaction, residual strength, seismic deformation analyses, seepage cutoff walls, and levee and dam design and construction. Khaled co-teaches numerical methods in geotechnical engineering course at UCLA with Dr. Ethan Dawson. Khaled is the lead instructor for USACE Prospect Course on seismic stability of embankment dams. Khaled can be reached at Khaled.Chowdhury [at] usace.army.mil.