An overview of the behavior of pile foundations in liquefiable and non-liquefiable soils during earthquake excitation

Biography

W. D. Liam Finn graduated from the National University of Ireland in 1954 with a B.Eng. in Civil Engineering. He got his M.Sc. and Ph.D. from the University of Washington in Seattle in 1957 and 1960 respectively. After the 1964 Niigata Earthquake, he began to specialize in Geotechnical Earthquake Engineering and started the first program in Canada at the University of British Columbia (UBC) in Vancouver. He was Head of Civil Engineering and Dean of Applied Science at UBC. In 1999, he was appointed as the first Anabuki Professor of Foundation Geodynamics at Kagawa University, Takamatsu, Japan. Liam Finn is also president of Pan-American Engineering and Computing Services Ltd. in Vancouver. He is an Honorary International Member of the Japanese Geotechnical Society and the Chinese Society of Soil Dynamics, PRC. He is also an Honorary Professor of the Metallurgical Institute in Beijing.

Abstract

The seismic response of a pile foundation is usually analyzed by approximate methods in practice. These methods typically neglect one or more of the important factors that affect seismic response such as inertial interaction, kinematic interaction, seismic pore water pressures, soil nonlinearity, cross stiffness coupling and dynamic pile to pile interaction. A nonlinear 3-D analysis is used to show how all these factors affect pile response, to demonstrate some of the consequences of using various approximate methods and to provide a comprehensive overview of how pile foundations behave during earthquakes in liquefiable and non-liquefiable soils.

https://doi.org/10.1016/j.soildyn.2014.09.009

SPT- and CPT-based relationships for the residual shear strength of liquefied soils

Biography

I.M. Idriss, a UC Davis professor emeritus of geotechnical engineering, was on the second floor of a San Francisco high-rise when the 6.9 magnitude Loma Prieta earthquake struck on Oct. 17, 1989. As colleagues dove for cover beneath a conference table, Idriss stood in a doorway … where he had a perfect view of buildings swaying in response to the forces he had studied throughout his career.

“Each earthquake tells us a story,” Idriss explained, during an interview given on the 20th anniversary of this catastrophe. “Sometimes it confirms something we know, or sometimes it tells us something we didn’t know.”

Izzat M. IdrissIn the wake of the Loma Prieta quake, Idriss was one of eight people named to Gov. George Deukmejian’s Board of Inquiry; the panel was assigned to find out why the Cypress section of I-880 and a section of the San Francisco-Oakland Bay Bridge had failed … and how the state could prevent this from happening again. Idriss and his fellow panel members eventually recommended that all of the state’s approximately 24,000 bridges be inspected for quake-worthiness and — if necessary — retrofitted.

Following this inquiry, Idriss and several other UC researchers continued to work with Caltrans, serving on the state’s Seismic Advisory Board and on peer advisory panels for all the Bay Area toll bridge retrofit projects.

Idriss has spent half a century studying how soils react to the shaking that occurs during an earthquake. During that time, his geotechnical advice has been sought by government agencies and advisory panels around the world. He has been involved with the follow-up analysis of every major earthquake since the 1964 Alaska quake, including those at San Fernando, Mexico City, Northridge and Kobe; he has been part of the team of engineers that descends on a region in the aftermath of a major quake, to analyze damage and determine causes of structural collapse.

Loma Prieta was, however, the only quake he experienced in person.

His research on soil mechanics and foundation engineering has influenced the construction of dams, nuclear power plants, seaports, office buildings, residences, hospitals, railways and bridges around the world.

In 1999, Idriss received a UC Davis Distinguished Public Service Award, an honor that recognizes faculty members who have made public service contributions to the community, state, nation and world throughout their professional careers. This followed his 1989 election to the National Academy of Engineering, and the many high honors he has received from the American Society of Civil Engineers.

Recognizing the value of such awards, Idriss subsequently established one himself: the UC Davis Prize for Excellence in Geotechnical Engineering — now known as the Idriss Award — which recognizes a graduate student’s achievements in outstanding scholarship, leadership and fellowship.

Abstract

An evaluation of post-earthquake stability of earth embankments or slopes that contain, or are founded on, soils that may liquefy requires estimating the liquefied soil׳s residual shear strength, Sr. Decisions regarding the need for expensive mitigation efforts, including ground improvement work, often hinge on the selected Sr values. This paper presents recommended SPT- and CPT-based relationships for estimating the residual shear strength ratio, Sr/, of liquefied nonplastic soils in the field based on a review of prior case history studies, laboratory testing studies, and recent findings regarding void redistribution mechanisms. The recommended relationships provide guidance regarding the unavoidable task in practice of having to extrapolate beyond the available case history data. Limitations in the state of knowledge are discussed.

https://doi.org/10.1016/j.soildyn.2014.09.010

Summarizing geotechnical activities after the 2011 Tohoku earthquake of Japan

Biography

Abstract

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 1300 analyses identified earthquake, site, and building characteristics that largely control liquefaction-induced building settlement during strong shaking. A simplified procedure is 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 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.

https://doi.org/10.1016/j.soildyn.2017.08.026

An investigation into why liquefaction charts work: A necessary step toward integrating the states of art and practice

Biography

Abstract

This paper is a systematic effort to clarify why field liquefaction charts based on Seed and Idriss[U+05F3] Simplified Procedure work so well. This is a necessary step toward integrating the states of the art (SOA) and practice (SOP) for evaluating liquefaction and its effects. The SOA relies mostly on laboratory measurements and correlations with void ratio and relative density of the sand. The SOP is based on field measurements of penetration resistance and shear wave velocity coupled with empirical or semi-empirical correlations. This gap slows down further progress in both SOP and SOA. The paper accomplishes its objective through: a literature review of relevant aspects of the SOA including factors influencing threshold shear strain and pore pressure buildup during cyclic strain-controlled tests; a discussion of factors influencing field penetration resistance and shear wave velocity; and a discussion of the meaning of the curves in the liquefaction charts separating liquefaction from no liquefaction, helped by recent full-scale and centrifuge results. It is concluded that the charts are curves of constant cyclic strain at the lower end (Vs1<160m/s), with this strain being about 0.03-0.05% for earthquake magnitude, Mw≈7. It is also concluded, in a more speculative way, that the curves at the upper end probably correspond to a variable increasing cyclic strain and Ko, with this upper end controlled by overconsolidated and preshaken sands, and with cyclic strains needed to cause liquefaction being as high as 0.1-0.3%. These conclusions are validated by application to case histories corresponding to Mw≈7, mostly in the San Francisco Bay Area of California during the 1989 Loma Prieta earthquake.

https://doi.org/10.1016/j.soildyn.2014.09.011

Soil-Foundation-Structure Systems Beyond Conventional Seismic Failure Thresholds

Biography

George Gazetas has been Professor of Geotechnical Engineering at the National Technical University of Athens for 30 years, following an academic career in the US, where he taught at SUNY-Buffalo, Rensselaer (RPI), and Case Western Reserve University. His main research interests have focused on the dynamic response of footings, piles and caissons; the seismic response of earth dams and quay-walls; soil amplification of seismic waves; and soil–structure interaction problems. Much of his research has been inspired by observations after destructive earthquakes. An active writer and teacher, he has been a consultant on a variety of (mainly dynamic) geotechnical problems. The recipient of prestigious awards for his research contributions, he has given the Coulomb (2009) and Ishihara (2013) Lectures, and received the Excellence in University Teaching Award in Greece (2015).

Abstract

A new paradigm has now emerged in performance–based seismic design of soilfoundationstructure systems. Instead of imposing strict safety limits on forces and moments transmitted from the foundation onto the soil (aiming at avoiding pseudo-static failure), the new dynamic approach “invites” the creation of two simultaneous “failure” mechanisms: substantial foundation uplifting and ultimate-bearing-capacity slippage, while ensuring that peak and residual deformations are acceptable. The paper shows that allowing the foundation to work at such extreme conditions not only may not lead to system collapse, but it would help protect (save) the structure from seismic damage. A potential price to pay: residual settlement and rotation, which could be abated with a number of foundation and soil improvements. Numerical studies and experiments demonstrate that the consequences of such daring foundation design would likely be quite beneficial to bridge piers and building frames. It is shown that system collapse could be avoided even under seismic shaking far beyond the design ground motion.

https://doi.org/10.1016/j.soildyn.2014.09.012

Liquefaction Research by Laboratory Tests versus In Situ Behavior

Biography

Dr Takaji Kokusho is a Registered Engineer based in Japan. Since 2015, he has been the Professor Emeritus at Chuo University. Prior to this, he was a Professor in the Civil & Environmental Engineering Department, Faculty of Science and Engineering at Chuo University. Dr Kokusho specializes in dynamic soil properties and their evaluation, dynamic response of ground, liquefaction of sand/gravelly fines containing sands and earthquake induced slope failure. His awards include the Research paper Award from the Japanese Geotechnical Society (2014) and the Research paper Award from Japan Society for Civil Engineers (2005).

Abstract

Major advances in liquefaction research in the laboratory to understand the basic mechanisms in comparison with in situ behavior during previous earthquakes are reviewed. Then, several issues related to liquefaction triggering and post-liquefaction deformation are selected for further discussion in the author’s perspective. These include effects of fines associated with aging, effects of gravels, effects of initial shear stress and lateral spreading and lateral flow due to void redistribution. It has been disclosed that a quite a few issues still remain to be settled in evaluating liquefaction onset and post-liquefaction deformations for improving engineering design, particularly for Performance-Based Design (PBD).

https://doi.org/10.1016/j.soildyn.2016.07.024

Simplified procedure for estimating liquefaction-induced building settlement

Biography

Jonathan Bray is the Faculty Chair in Earthquake Engineering Excellence at the University of California, Berkeley. He earned engineering degrees from West Point, Stanford, and Berkeley. Dr. Bray is a registered professional civil engineer and has served as a consultant on several important engineering projects and peer review panels. He has authored more than 350 research publications. His expertise includes the seismic performance of earth structures, seismic site response, liquefaction and ground failure and its effects on structures, earthquake fault rupture propagation, and post-event reconnaissance. Dr. Bray was elected into the US National Academy of Engineering and is a Fellow in ASCE. He has received several other honors, including the Terzaghi Award, Ishihara Lecture, Peck Award, Joyner Lecture, Prakash Award, Huber Research Prize, Packard Foundation Fellowship, and NSF Presidential Young Investigator Award.

Abstract

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 1300 analyses identified earthquake, site, and building characteristics that largely control liquefaction-induced building settlement during strong shaking. A simplified procedure is 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 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.

https://doi.org/10.1016/j.soildyn.2017.08.026

Simplified procedure for estimating liquefaction-induced building settlement

Biography

Abstract

After the 2011 Tohoku earthquake in Japan, I as the Vice President and then as the President of the Japanese Geotechnical Society took initiatives in damage reconnaissance, developing new safety criterion for liquefaction-prone residential areas, quantitative evaluation of ageing effects in liquefaction resistance of sand, investigation on damage mechanism of river levees, recovery from the tsunami incidence of Fukushima No.1 Nuclear Power Plant and ground improvement in existing residential area. Some of them were conducted urgently within several months after the earthquake, while others encountered many difficulties from the view point of public agreement. This paper summarizes the post-earthquake activities of geotechnical engineering in restoration of the community.