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Lateral resistance of pile group foundation based on large-scale field tests
Kyle M. Rollins, Professor, Brigham Young University 
Sept. 13, 2024

Pile group interaction during lateral loading reduces lateral resistance. Based on full-scale lateral pile group testing, the reduction is a function of pile spacing, row position and soil type. Lateral resistance within a given row did not generally show any consistent trends. P-multipliers provide a reasonable method to account for group interaction and equations are provided for pile groups in sand and in clay based on full-scale and centrifuge tests. Typically, group interaction effects decrease as pile spacing increases and become insignificant when piles are spaced more than 6 to 8 pile diameters center-to-center. P-multipliers for third and higher rows in a group tend to be relatively consistent. For a given pile load, the maximum bending moment is greater for trailing rows in a group than for a single pile at the same load because the surrounding soil is softened by group interaction effects. P-multipliers tend to be somewhat lower for piles in sand and increase as friction angle decreases, as for a clay. P-multipliers are equal to 1.0 for liquefied sand. Lateral statnamic tests indicate that damping ratios are about 30% for piles in clays.

About the speaker: Kyle Rollins received his B.S. from Brigham Young University and his Ph.D. from the University of California at Berkeley. After working as a geotechnical consultant, he joined the civil engineering faculty at BYU in 1987, following his father, who was previously a geotechnical professor. His research has involved deep foundation behavior, geotechnical earthquake engineering, soil improvement techniques, gravel liquefaction, bridge abutment resistance and collapsible soils. His work typically involves full-scale testing to evaluate and improve performance of bridges and buildings. In this effort, he pioneered the use of blast-induced liquefaction testing to evaluate ground improvement effectiveness and pile performance in full-scale tests. The American Society of Civil Engineers has recognized his work with the Huber research award, the Wellington prize, the Wallace Hayward Baker award and the H. Bolton Seed Medal. He was a Cross-Canada Geotechnical lecturer for the Canadian Geotechnical Society and he received the Osterberg award for innovation in foundation design from the Deep Foundation Institute.

Infrastructure Geotechnics in Gravelly Soils: Considerations in Characterization and Engineering Analysis
Jason T. DeJong, Ph.D. | Professor, University of California, Davis
Dec. 1, 2023 

Gravelly soils, both natural and anthropogenic, often are pervasive in large infrastructure projects such as dams and bridges, and yet the characterization and engineering analysis of those materials is both challenging and highly uncertain. This presentation will systematically consider the formation and characteristics of those materials, propose a systematic methodology for performing site investigation programs, cover gravel-specific techniques including the instrumented Becker Penetration Test (iBPT), and examine how engineering analyses may need to be modified for gravelly soils. More specifically, we will examine how the effects of the particle size and broad gradation of these gravelly soils may influence soil properties, engineering behavior, characterization methods and ultimately system behavior.

About the speaker: Jason T. DeJong, a professor at the University of California, Davis, is the director of the UC Davis Center for Geotechnical Modeling and the UC Davis lead for the NSF ERC Center for Bio-mediated and Bio-inspired Geotechnics. Professor DeJong’s major technical contributions have been in the areas of soil and site characterization, bio-mediated and bio-inspired geotechnics, earthquake engineering and geotechnical sustainability. He has developed several in situ and laboratory tools as well as associated analysis and interpretation techniques to characterize challenging soils — soft sediments, intermediate soils, tailings and gravelly soils. Results from his research program have been disseminated through 250 publications and he is chair of the ISSMGE TC102 In situ Testing committee. DeJong serves as a reviewer or technical advisor on several civil infrastructure projects, and methods he has developed have been implemented in practice.

Role of Bi-Directional Static Load Testing in Deep Foundation Projects
Jon Sinnreich, P.E., Load Test Consulting, Ltd.
Dec. 2, 2022

Deep foundation design and construction entails inherent uncertainties and risks, which are mitigated using full‑scale load testing. Standard top-down load testing requires an external reaction system. As test loads surpass 500 tons these reaction systems can become prohibitively expensive, and potentially unsafe. Bi-directional static load testing (BDSLT) is considered by many engineers to be the premier deep foundation element axial load test method. It requires no external reaction system, is inherently safe and typically can apply significantly more load to the test element. This presentation will provide an overview of the benefits of deep foundation testing in general. The relative advantages and disadvantages of BDSLT, as well as interpretation of test results and some of the technical challenges of implementing this test method will be discussed. 

About the speaker: Jon Sinnreich is a founder and the principal engineer of Load Test Consulting, Ltd. He earned a bachelor’s degree in civil engineering and a master’s degree in structural engineering at the University of Florida. He has participated in hundreds of international bi-directional load test projects and led R&D efforts on various technologies including ultrasonic shaft profiling. He is a registered professional engineer, current chair of ASTM Subcommittee D18.23 (Field Instrumentation) and the DFI Seismic and Lateral Loads committee and serves on the DFI Journal editorial board.

Nonlinear one-dimensional site-specific response analysis, historical perspective and current practice
Youssef Hashash, Ph.D., P.E.
Nov. 19, 2021

Observations from earthquakes over the past several decades highlight the influence of site-specific ground conditions on recorded surface motion. One-dimensional equivalent linear-site response analysis was introduced to provide engineers with tools to evaluate the changes ground motions as they propagate in a soil column. Over the last 20-30 years, supported by measurements during strong ground shaking, there has been increasing recognition of the importance of explicit representation of nonlinear soil behavior in 1-D site response. This presentation will provide an overview of key developments in 1-D nonlinear site response analysis, including issues related to viscous damping, controlling for soil strength in addition to modulus reduction and damping curve definitions, numerical efficiency and representation of uncertainty. The presentation will discuss site investigation, including geotechnical and geophysical survey needs to conduction such analyses. Examples of site responses analysis results versus generic site factors will also be presented.

About the speaker: Youssef Hashash is a professor of civil and environmental engineering at the University of Illinois at Urbana-Champaign with an extensive background in the field of geotechnical, earthquake and tunnel engineering. His expertise includes underground structures, deep excavations, numerical modeling, earthquake engineering and static and dynamic soil-structure interaction analysis, visualization and application of information technology, deep learning and artificial intelligence to geotechnical engineering. He co-led or was a member of post-disaster reconnaissance teams documenting built infrastructure response to earthquakes, floods and explosions. Prior to joining UIUC, he worked in engineering practice for about 5.5 years. He is a licensed professional engineer in California. He has continued his involvement with challenging civil engineering projects as an advisor or peer reviewer. Hashash holds a B.S., M.S. and Ph.D. in civil engineering from the Massachusetts Institute of Technology. 

Standard of Practice Update, AASHTO Subsurface Characterization, Geotechnical Engineering Circular #5
Robert C. Bachus, Ph.D., P.E., D.GE
Geosyntec Consultants, Kennesaw, Georgia
Sept. 18, 2020

The AASHTO Manual was published by the American Association of State Highways Transportation Officials (AASHTO) in 1988 and, since that time, has been the “go-to” reference guide regarding the standard of practice for subsurface investigations, particularly those focused on the transportation community. Over the past 30 years, subsurface geotechnical conditions may not have changed dramatically, but the techniques used by transportation agencies and their consultants for geotechnical investigation and interpretation have advanced significantly due to improvements and reliance upon technology advancements. A similar recognition was made by the Federal Highway Administration (FHWA) with regard to its 2002 edition of Geotechnical Engineering Circular (GEC) No. 5 regarding soil and rock properties. Geosyntec Consultants was commissioned by the National Academies to prepare the revised AASHTO Manual and authored the original GEC#5. Updates to these seminal reference documents will be highlighted and discussed during the presentation.

About the speaker: Robert Bachus is a civil engineer with more than 40 years of experience, with an expertise in geotechnical and geoenvironmental engineering. He started his career as a member of the faculty at the Georgia Institute of Technology, where he taught for 11 years before joining Geosyntec Consultants in 1990, where he is a senior principal. The firm specializes in geotechnical, environmental and water resource engineering, with more than 1,200 employees in its 75 offices in the U.S., Canada and Europe. His research and project activities cover a wide range of topics, including dams and levees, landslide assessment, landfill design and performance, soil/rock properties, geosynthetics and forensic engineering. He has worked extensively on the properties and beneficial use of coal combustion residuals and geotechnical data management and visualization. He is currently an adjunct professor at Georgia Tech and chairman of the Transportation Research Board’s Standing Committee on Soil and Rock Properties.

Estimating Liquefaction-Induced Building Settlement
Johnathan Bray, Ph.D, P.E., NAE Faculty Chair in Earthquake Engineering Excellence
Nov. 22, 2019

Significant settlement and damage may occur due to liquefaction of soils beneath shallow-founded buildings. The primary mechanisms of liquefaction-induced building settlement are shear-induced, volumetric-induced and ejecta-induced ground deformation. Volumetric-induced, free-field ground deformation may be estimated with available empirical procedures. Although challenging to estimate, ground failure indices and experience can be used to estimate roughly ejecta-induced building settlement. Nonlinear dynamic soil-structure interaction (SSI) effective stress analyses are required to estimate shear-induced ground deformation. Results from over 1,300 analyses identified earthquake, site and building characteristics that largely control liquefaction-induced building settlement during strong shaking. A simplified procedure was developed based on the results of these analyses to estimate the shear-induced component of liquefaction building settlement. The standardized cumulative absolute velocity and 5%-damped spectral acceleration at 1 s period capture the ground shaking. The liquefaction building settlement (LBS) index, which is based on the shear strain potential of the site, captures in situ ground conditions. Building contact pressure and width capture the building characteristics. Field case histories and centrifuge test results validate the proposed simplified procedure. Recommendations and an example for evaluating building performance at liquefiable sites are shared.

About the speaker: Jonathan Bray is the faculty chair in Earthquake Engineering Excellence at the University of California, Berkeley. He is a registered professional civil engineer and has served as a consultant on important engineering projects and peer review panels. He has authored more than 350 research publications on topics that include liquefaction and its effects on structures, seismic performance of earth structures, earthquake ground motions and earthquake fault rupture propagation. He created and led the Geotechnical Extreme Events Reconnaissance (GEER) Association. Bray is a member of the U.S. National Academy of Engineering and has received several honors, including the Terzaghi Award, Ishihara Lecture, Peck Award, Joyner Lecture, Middlebrooks Award and Huber Research Prize.