2023 - 2024
New Approaches for Evaluating the Seismic Performance of Slopes and Earth Dams
by Ellen M. Rathje, Ph.D., P.E., F.ASCE, Professor, Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin (UT). on Monday June 10th, 2024 at 1730
Seismic performance assessments for earth slopes and dams are based on evaluating the permanent displacements induced by earthquake shaking and more recently probabilistic approaches have been proposed to incorporate uncertainties into the analysis. This presentation will describe newly developed predictive models for earthquake-induced slope displacements based on finite element simulations. The models are developed using both classical regression techniques and artificial neural networks (ANN), and models for both the median displacement and its variability are provided. A missing part of most seismic performance assessments for slopes and dams is the translation of a displacement level into a damage state. This presentation will also outline a seismic fragility framework for earth dams and slopes that is modeled after the approaches used for other types of infrastructure, such as bridges. The framework uses an engineering demand model to predict the permanent displacement as a function of ground motion intensity, and a seismic capacity model to predict the probability of a damage state given the permanent settlement.
Debris flow mitigation with flexible barrier systems
by Andi Buechi, A.Sc.T., (Geobrugg North America, LLC) on Thursday April 25th, 2024 at 1730
Debris flow mitigation using flexible nets and barriers that have been installed in Western Canada over the past 20 years. Owners of highways, hydro dams, pipelines, railways and other infrastructure projects have increasingly relied upon and installed flexible mitigation systems to protect their assets. The systems require a very small footprint, both physically and environmentally, while providing a certified, adaptable, and engineered solution that can outperform more rigid engineered structures. There is an increased demand for these adaptable off the shelf systems to be installed after wildfires, due to increased frequency and intensity of rainstorms causing both debris flow and flood events.
Through the talk you will learn about how these mitigation systems were developed, how the systems are tested and certified, as well as the current state-of-the-art in this field of expertise. Case studies of different installations of early debris flow barriers protecting railways, towns, and highways through to more recent examples will also be presented. The case studies will cover recent post wildfire installations in the USA and Canada where the design and installation of the flexible barriers were conducted in environmentally sensitive areas. Slides will be shown of systems outlining some of the key sizing and design information such as the various heights, lengths, impact ratings and ground conditions. Designers, contractors and engineers will find tips and best practices for installing systems in different conditions such as soil, rock and talus.
Women in VGS: Inclusion in Action
The Vancouver Geotechnical Society was proud to host its first Women in VGS Event with a panel discussion on “Inclusion in Action” on Wednesday, April 10th, 2024. Seeing so many dynamic women (and allies!) coming together was inspiring!
Many thanks to the panel members for sharing their experience, which was inspiring, empowering, and most important - relatable!
Caroline Andrewes
María V. (Mavi) Sanín Blair
Susan Hollingshead
Carie-Ann Lau
Karen Savage
A thank you to our sponsors, BGC Engineering Inc., Ecora Engineering & Environmental, Klohn Crippen Berger, RAM, Stantec, Tetra Tech, Thurber Engineering Ltd., and WSP, for supporting this event.
UBC GeoRox Distinguished Lecture - WHY DAM FAILURES HAPPEN AND WHAT CAN WE DO ABOUT IT ?
by Dr. Violeta Martin, P.Eng. on Wednesday, 03rd April at ESB 1012, Earth Science Building, UBC
The safety of mining dams is being increasingly scrutinized by the public, investors, regulators, and engineering communities in the wake of recent catastrophic failures that resulted in loss of life and environmental damage. This talk will focus on dams and some of the hazards associated with dams. While it can be argued that a dam is a dam, and that every dam needs to satisfy the same safety criteria, specific considerations related to tailings dams are worthwhile discussing. Failure modes and mechanisms will be reviewed, along with recent advancements in evaluating the consequences of potential failures, which can be vastly different from failures of water dams. Understanding the consequences is critical because every life matters, the damage to the environment matters, and the loss of cultural and economic values matters. This knowledge can lead to design improvements and further advancements in risk mitigation measures, as well as the safe decommissioning of dams.
Geohazards from the november 2021 atmospheric river - learnings from indigenous and western science
by Carie-Ann Lau, M.Sc., P.Geo (BGC Engineering) and Rick McKamey (Willow Creek Environmental Services) , Thursday, March 14th, 2024 at 1730
The November 2021 atmospheric river caused more than 1,300 geohazards to be triggered in southern British Columbia. Many of these geohazards were sourced from watersheds that had experienced previous cumulative damages, such as wildfires, logging, and resource road construction. These geohazards were sources of sediment that entered mainstem rivers and contributed to flood and bank erosion damages to communities, infrastructure, and ecological systems. The geohazards and associated damages of the November 2021 atmospheric river are examples of cumulative watershed issues that Indigenous communities have long expressed concerns about. Watersheds draining into Leq’á:mel First Nation have been heavily logged and frequently produce sediment-laden flooding. During the November 2021 atmospheric river, Leq’á:mel experienced damages to critical ecological habitat, community infrastructure, and critical facilities. As we learn from the November 2021 atmospheric river and apply these learnings to resilient community planning, geotechnical practitioners can benefit from integrating Indigenous knowledge about geohazards and watershed management practices.
helical piles: efficient foundation for static, dynamic, and seismic applications
by Hesham El Naggar, Ph.D., P.Eng., FCAE, FEIC, FASCE - Professor at the University of Western Ontario, Monday, October 16, 2023 at 1730
Helical piles have become popular foundation option owing to their many advantages related to ease of installation and large load carrying capacity. They are typically manufactured of straight steel shafts fitted with one or more helices and are installed using mechanical torque. They can sustain static and dynamic loading and are increasingly used in applications that induce complex loading conditions on them. The behavior and design of single vertical helical piles subjected to static loading is well investigated. However, the dynamic and seismic behavior of single helical piles and their group behavior are of great importance in modern foundation engineering practice but not yet well understood. This presentation presents recent advances in evaluating the axial and lateral capacity and performance of single and grouped helical piles and their response to static, dynamic and seismic loads.
2022 - 2023
Tailings-Specific Liquefaction Assessment
by Mason Ghafghazi, Ph.D., Professor at the University of Toronto, Wednesday, May 17, 2023 at 1730
Tailings dams are man-made earth structures used for storing mining waste, comprised of water and fine minerals left behind from the extraction process. Tailings are usually non-plastic fine sand-and-silt-sizedsoils with angular particles that are often deposited in a loose state. The current practice mostly ignores the important differences among soils and how these differences influence CPT interpretation and calculation of residual shear strengths. Advances in CPT interpretation though still rely on CPT calibration chamber data on clean quartz sands. Case history based residual strength correlations do not account for differences among soils, how liquefaction was triggered, or system level differences.
Research done on various aspects of liquefaction assessment in tailings over the past few years at University of Toronto will be presented. This includes a new state parameter interpretation technique that provides soil-specific correlations by taking in Norsand’s parameters as input. It will be shown that this method estimates the in-situ state parameter more accurately than existing screening methods. Correlations between residual strength and state parameter are then presented based on laboratory tests on various gradations of tailings and natural soils. It will be shown that residual strength is soil-specific, and laboratory tests can be used in conjunction with case-histories
NEXT GENERATION LIQUEFACTION HAZARD ANALYSIS - DATA, ISSUES, AND MODEL DEVELOPMENT - Canadian geotechnical society cross Canada lecture tour (cclt) Spring 2023
by Dr. Steve Kramer, Professor Emeritus of the University of Washington, May 1, 2023 at 1730
The geotechnical engineering profession's understanding of soil liquefaction has advanced greatly since its effects were first widely observed following 1964 earthquakes in Niigata, Japan and Alaska. Both laboratory- and field case history-based approaches have illuminated liquefaction susceptibility, triggering, and consequences and developed useful tools for estimating each. Liquefaction models have historically been developed by small groups of researchers who have individually collected and interpreted laboratory and case history data. This has resulted in different models based on different data and different interpretations that can provide different results under conditions of interest in practice. The Next Generation Liquefaction (NGL) project was conceived of and designed to promote the development of liquefaction models based on consistent, publicly available, up-to-date field and laboratory data. This presentation will introduce the NGL project, discuss important issues relative to susceptibility, triggering, and consequences encountered in practice, and describe the innovative approaches taken to address them by the NGL modeling teams.
lESSONS LEARNED FROM THE SR-99 HIGHWAY TUNNEL PROJECT IN SEATTLE - OWNER’S PERSPECTIVE
by Gregg Korbin, Ph.D., Geotechnical Consultant on Thursday, April 13, 2023 at 1730.
The SR-99 highway tunnel under the city of Seattle was designed to replace the waterfront viaduct damaged by the Nisqually earthquake. At time of bid, the 17.5 m diameter EPBM manufactured by Hitachi was the world’s largest TBM. The speaker was a member of Washington State Department of Transportation’s (WSDOT’s) technical review board from design through construction (2009 to 2017). The project faced many technical challenges, and despite a difficult start up, it ended up setting a new standard for the soft ground tunneling industry in terms of ground control and monitoring methodologies. The technical presentation will be from the owner’s perspective. Topics include design and contract approach, TBM issues related to manufacturing, breakdown and rebuild, the management change, TBM performance and ground response from mining, and the court case, as well as the contribution of WSDOT’s technical review board.
SHEAR WAVE-VELOCITY OF LIQUEFIED SOIL: AN UPDATE
by Robert Kayen, Ph.D., Professor from UC Berkeley on Thursday, March 23, 2023 at 1730.
The shear-wave velocity (Vs) offers a means to determine soil's seismic resistance to liquefaction by a fundamental soil property. This talk will present the results of a decades-long international project to gather Vs site data and develop probabilistic correlations for seismic soil liquefaction triggering using shear wave velocity. The first correlation, published in 2013, analyzed 121 sites from the literature and 310 test sites we investigated in China, Japan, Taiwan, Greece, and the United States.
We are updating the initial correlation and have expanded the data set to approximately 650 sites, mainly through new testing of the M9.0 2011 Tohoku Earthquake, Japan, and the 2011 Christchurch and 2010 Darfield Earthquakes, New Zealand. Of critical importance, these new case histories occupy locations previously investigated by penetration testing. Bayesian regression and structural reliability methods facilitate a probabilistic treatment of the Vs catalog for performance-based engineering applications. Analysis of the uncertainties of the variables comprising both the seismic demand and the soil capacity is integral to the study and allows for the reduction of overall model error.
MINING, SUSTAINABILITY, AND MINE DESIGN CRITERIA IN THE CONTEXT OF A CHANGING SOCIETY
by Dr. Anthony Hodge, P.Eng., Professor from UBC on Tuesday, March 28, 2023 at 1800.
During the last half century, mining practices have been increasingly examined through the lens of their short and long-term impacts to human and ecological well-being. The result has often been tension, as today’s insights and values challenge those of the past. This tension touches not only on the technical content of decisions but also the nature of how decisions are made. And it continues at a time when society’s need for mined materials continues to increase, particularly in support of the world’s transition to a low-carbon economy. This lecture discusses some of the major changes that the mining industry has experienced, and how a quest for fairness is central to effective mine design and implementation and reduction of the trust-deficit that exists between mining and society.
Field Trials of microbially induced desaturation for earthquake liquefaction mitigation in portland, oregon
by Diane Moug, Ph.D., Assistant Professor from Portland State University on Thursday, February 23, 2023 at 1730.
Earthquake liquefaction hazards in silty soils are a critical problem in Portland, Oregon and other areas around the world. This is a particular problem for existing facilities founded upon silty liquefiable soil, for which there exists no cost-effective mitigation solution at the present time. Recent studies suggest that liquefaction mitigation using microbially-induced desaturation (MID) may provide the capability to do this. MID treatment can be performed by injecting a treatment solution into liquefaction-prone soils. The treatment solution stimulates growth of native bacteria that produce nitrogen gas as a biproduct. The objective of MID is to reduce earthquake-induced excess pore water pressure generation compared to saturated soil, and thereby reduce the potential for triggering liquefaction. This presentation will describe two field trials of MID for liquefaction mitigation performed in Portland, OR in summer 2019. Low-plasticity, liquefiable silts were treated with MID by injecting a treatment solution to stimulate native bacteria for a duration of four weeks. Migration of the treatment solution and saturation ratios were monitored with a range of methods, including: crosshole pressurewave velocity measurements, a vertical array of embedded sensors that measure water content and bulk electrical conductivity, pre- and post-treatment seismic cone penetration tests, and direct soil sampling of the treated soils. Monitoring at both sites indicated that liquefiable silts were successfully desaturated and that desaturation has sustained for over 3 years.
bridges to prosperity - 2022 cyarera bridge project - joint event with the tunnelling association of canada (TAC)
by Heather Hughes-Adams, from McMillen Jacobs on January 24, 2023 at 1700.
Sustainable practices for geotechnical engineering - canadian geotechnical society cross canada leCture tour (cclt) fall 2022
by Catherine Mulligan, PhD - Professor, from Concordia University on November 29, 2022 at 1730.
Due to depletion of natural resources, increased natural disasters, waste, greenhouse gas emissions, pollutant generation, and environmental deterioration, and loss of biodiversity, geotechnical engineers are facing new challenges. While it is generally believed that the concepts of sustainable development must be followed for protecting future generations, it is much easier said than implemented. Therefore, the focus of this talk will be to focus on the application of the principles of sustainable geoengineering to projects and processes. Some tools and frameworks for evaluating and implementing sustainable practices will be presented. The use of environmental, social and economic indicators for measuring and comparing design options will be demonstrated. Best practices in carrying out Indigenous engagement and consultation will be highlighted. Finally, case studies and examples of sustainable practices in design in addition to the challenges and needs for the future will be included. The role of geotechnical engineers in sustainable development has been undervalued but is critical for future generations.
Changes in Seismic site response analysis approach to be consistent with the 6th generation seismic hazard model of canada
by Chris Weech, M.A.Sc., P.Eng from Thurber Engineering on November 16, 2022 at 1730.
In NBC 2015, amplification factors, F(T), were provided which varied based on seismic site class and the site-specific probabilistic PGA for a Site Class C reference ground condition (PGAref) at the specified hazard level. In the 6th Generation Seismic Hazard Model of Canada (SHMC-6) adopted for NBC 2020, multiple ground motion models (GMMs) are used to calculate hazard values at ground surface which include site amplification effects calculated internally using site terms specific to each GMM. Linear amplification effects are calculated based on Vs30. Non-linear amplification effects are calculated using site terms that vary as a function of the median prediction of ground motion intensity associated with each event scenario considered in the hazard model. The amplified ground motion values for each event scenario are then aggregated to generate the probabilistic hazard values for a particular site location and Vs30.
This presentation will discuss the fundamental differences in the way that amplification is treated in NBC 2015 and SHMC-6. The results of a study that was carried out to implement SSRA-based amplification functions within SHMC-6 will be presented. The probabilistic UHRS generated using the rigorous method will be compared to SSRA-based UHRS generated using the NBC 2015-compatible SSRA methodology as well as a modified procedure for carrying out SSRA in a manner that is consistent with the way that non-linear amplification is treated in SHMC-6.
2021 - 2022
characterizing rock slope failure mechanisms using combined remote sensing and numerical modelling - 2022 spring Cross Canada Lecture
by Doug Stead, Ph.D Emeritus Professor from Simon Fraser University on June 20, 2022 at 1730.
Slope failure mechanisms vary in complexity from simple translational slides to complex multi-block/multi-slip mechanisms. Developments in remote sensing and slope analysis techniques have seen a rapid transition from air photograph interpretation and simple limit equilibrium analyses to increasingly sophisticated and readily available ground and airborne/satellite sensing methods and 2D/3D numerical models. A focus of this talk will be on improving our understanding of complex rock slope failure mechanism through remote sensing characterization and monitoring constrained against numerical models. Using case studies of natural and engineered slopes from North America, Europe and Africa the importance of structural geology, kinematics and slope damage will be demonstrated. With the continued advent of innovative technology, the need to fully optimize available data is emphasized, along with the need to ensure that the limitations of these techniques are considered and that the key role of conventional engineering geological and engineering geomorphological investigations recognized.
The January 28, 2021 highway 1 embankment failure at rat creek, bug sur, California & lessons learned
by Dr. Dimitrios Zekkos from University of California Berkeley on June 8, 2022 at 1730.
On January 28, 2021, a portion of scenic Highway 1 failed at Mile Marker 30 known as Rat Creek, in Big Sur, California. The failure resulted in complete closure of the highway at that location and a detour of 255 km for residents. The surface flow-induced erosion washed both lanes and some of the surrounding embankment material into the Pacific Ocean. An investigation under the Auspices of the Embankments, Dams, and Slopes (EDS) Technical Committee of the ASCE Geo-Institute (GI) was conducted and the findings of this investigation and subsequent studies will be presented. The failure was caused by overtopping and subsequent erosion of the roadway embankment that occurred after a debris flow triggered upstream and reached the embankment. The debris flow was triggered due to the destructive synergy of the Nolan wildfire that occurred a few months earlier, an atmospheric river that caused significant precipitation and the collapse of a natural debris-tree dam. The investigation involved on-the-ground field deployment that included UAVs, terrestrial lidar and geologic characterization as well as subsequent analyses. In addition, system-level analyses were conducted to understand exactly why the failure occurred specifically at Rat Creek and not somewhere else along the long stretch of Highway 1. The presentation will conclude with lessons learned from this failure and recommendations for enhanced system-level resiliency.
Liquefaction-induced downdrag on piles: centrifuge and numerical modeling, and design procedures
by Sumeet Kumar Sinha, PhD., Post Doctoral Scholar at University of California Berkeley on April 27, 2022 at 1730.
Pile foundations are designed to transfer superstructure loads through positive skin friction and tip resistance while undergoing acceptable settlements. For sites with liquefiable soil, estimating drag load (from soil reconsolidation) and pile settlement (from seismic loads, reduced pile capacity from excess pore pressures, and downdrag) becomes an important design consideration. Most of the challenges related to the liquefaction-induced downdrag phenomenon are the incomplete understanding of the different mechanisms that affect drag load and pile settlement leading to over-conservative or unsafely designed piles. A series of centrifuge model tests were performed on liquefiable soil deposits to assess liquefaction-induced drag load and pile settlement, understand the mechanisms of pore pressure generation/dissipation, and soil/pile settlement during and after a shaking event. A numerical modeling approach, dynamic TzQzLiq analysis, was developed incorporating the observed mechanism and validated with centrifuge test results. It consisted of the existing TzLiq and a new QzLiq material (implemented in OpenSees), which accounted for the changes in the pile’s shaft and the tip capacity as free-field excess pore pressures develop/dissipate in soil, initial drag load on piles, and sequencing of excess pore pressure and soil settlement. Results provided time-history of axially loading distribution and settlement of piles during an asking event. Finally, a displacement-based procedure was proposed for industry using a simplified pseudo-static (four-step) TzQzLiq analysis for designing axially loaded piles subject to seismic loading and liquefaction-induced downdrag. The redistribution of high pore pressures from liquefiable to adjacent non-liquefiable deposits also impacted pile performance significantly. Therefore, an analytical procedure was also developed to estimate excess pore pressure redistribution in liquefiable and non-liquefiable layers.
Will it stay or will it go?: use of lidar to assess slope instabilty
by Ben Leshchinsky, PhD., Associate Professor at Oregon State University on March 30, 2022 at 1730.
Lidar is a promising tool for evaluating the hazard and behavior of unstable slopes due to its resolution, accuracy, and the ability to process away visual obstacles, such as vegetation. Elevation models processed from lidar are particularly useful as they enable quantitative and enhanced qualitative interpretation of landslide features, and in the case of repeat data collection, evaluation of kinematics and changes that are not easily discernable by eye. Most of all, when integrated with principles of slope stability analysis, lidar data serves as a robust foundation for understanding landslide behavior at multiple scales. This presentation will discuss (1) use of lidar for deriving first-order estimates of landslide volumes and strength from forensic analysis of inventories, (2) use of digital elevation models and slope stability analyses towards creating landslide susceptibility maps for seismic and precipitation disturbance under a variety of remotely-sensed antecedent moisture conditions, and (3) interpretation of lidar to reveal drivers and change for landslides in Oregon’s coastal environment. The increasing availability of lidar presents us with a unique opportunity to better assess the risk stemming from geohazards, enhance asset management, and understand geomorphic and geologic processes at a more refined level.
efficiency of ground motion intensity measures with earthquake-induced earth dam deformations
by Richard J Armstrong, PhD., P.E., Associate Professor at California State University on February 23, 2022 at 1730.
Earthquake ground shaking characteristics have profound and varying impacts on civil engineering infrastructure. Traditional descriptors of earthquake shaking, such as peak ground acceleration and pseudo-spectral acceleration, have a strong history of use in seismic hazard assessment and post-earthquake damage prediction. More recently, however, other earthquake ground shaking characteristics (often called ground motion intensity measures, or IMs), which may be able to better characterize the relationship between ground shaking and civil infrastructure response, have gained traction in research and practice. This presentation will focus on the results and conclusions of a multi-year research project that involved evaluating the best ground motion intensity measures for embankment dam response. In this work, data from strong ground motion recordings during the 1989 Loma Prieta earthquake were used to evaluate the reasonableness of nonlinear deformation analysis (NDA) models of Lenihan and Anderson dams. These models were subsequently used to assess the efficiency of ground motion IMs with embankment dam deformations. A suite of 342 recorded ground motions was used with these NDA models to assess the relationship between ground motion characteristics and embankment dam deformations. The article begins with a summary of the NDA of Lenihan and Anderson dams during the 1989 Loma Prieta earthquake. Subsequently, the ground motion database used in the analysis is described, followed by the presentation of the results in the context of the efficiency of each IM.
Mallkuchusi suspended bridge project
A joint talk from the Tunneling Association of Canada (TAC) and VGS presented by Natalia Skomorowski (BGC Engineering) on January 18, 2022 at 1730.
During the summer of 2019, Notre Dame Students Empowering through Engineering Development (NDSEED), a student chapter of Engineers in Action (EIA), constructed a suspended footbridge in the rural community of Mallkuchusi, Bolivia. As part of the bridge design, they partnered with BGC to consult on the geotechnical conditions of the bridge site.
NDSEED began the Mallkuchusi Bridge Project in the spring of 2018. Upon arrival to site during the 2018 Build Season, the team realized that excavations of the in-situ rock would be exceedingly difficult and posed significant design and construction challenges. Due to the remote site conditions and limited ability to communicate with stateside resources, the team was unable to redesign the bridge abutments to reduce the excavations in during the 2018 Build Season. They proceeded to excavate a standard gravity abutment on the right side of the bridge, which took six weeks with the help of a local Bolivian miner utilizing both dynamite and manual excavations.
Having more time and resources during the 2018-2019 Academic year, the team proposed a new bridge abutment design, utilizing nonstandard rock anchors to reduce the necessary excavations from 65 m3 to 10 m3. As the abutment design relied upon the strength of the in-situ bedrock, NDSEED partnered with BGC to analyze the site’s geotechnical conditions. BGC engineers consulted for the team on a variety of issues, from safe abutment location to excavation feasibility and construction safety and monitoring practices. In January 2019, two BGC engineers conducted a site assessment trip to Mallkuchusi with one of the 2019 NDSEED team members to collect geotechnical data and assess the rock conditions exposed by the completed excavations on the right side, as well as to assess the rock stability on the left side. BGC provided NDSEED with the geotechnical information that was vital to redesign the bridge’s rock-anchored abutments.
During the 2019 build season, NDSEED was able to construct the non-standard anchor and the rest of the bridge superstructure with the assistance of the local community. The completed pedestrian bridge has a span of 96.2 meters. The bridge now serves the 63 people of Mallkuchusi as well as the 80 people of Cobre Villa and Janco Marca. They now have access to schools, groceries, and a community centre without having to cross the river on foot.
THE EFFECTS OF SOIL GRADATION ON THE LIQUEFACTION TRIGGERING AND DEFORMATION RESPONSE OF EMBANKMENTS
by Trevor Carey, Assistant Professor at the University of British Columbia on December 8, 2021 at 1730.
The liquefaction case-history database was primarily established from observations at sites consisting of relatively clean, poorly graded sands. These case histories serve as the basis for design practices but do not represent all liquefiable soil gradations found in the built environment. This has led to the use of poorly graded sand-based analysis procedures during the design and retrofit of embankments, which are typically constructed with well-graded soils. A poorly graded sand-based design procedure ignores the lower void ratios and higher peak strengths of well-graded soils. There is also an implicit assumption that the pre-and-post-liquefaction triggering behaviors of well-graded soils are the same as poorly graded sands.
Described in this presentation is a centrifuge test program undertaken to investigate how sand gradation affects the system-level performance of embankments subjected to strong shaking. The experiment design consisted of two identically instrumented submerged 10-degree embankments positioned side-by-sidein the same model container. One of the embankments was constructed with poorly graded sand, representative of the sand in the case-history database, and the other with well-graded sand. The embankments were dry pluviated to the same relative density, but the absolute densities of the sands were different. Results showed that embankments constructed at equal relative densities would both liquefy (i.e., the excess porewater pressure ratio (ru) reach 1.0). However, the post-triggering consequences were less severe for the embankment constructed of well-graded sand. Greater resistance to the generation and faster dissipation of excess porewater pressures coupled with stronger dilatancy of the well-graded sand increased stability, curtailing deformations. This work demonstrates that soil gradation properties should be accounted for in the liquefaction evaluation procedures to improve the accuracy of deformation predictions, required for performance-based design
Shared experience of value engineering case studies from middle eastern major projects
by Benoît Latapie, ing, Eur. Ing., Msc., on Tuesday, November 16, 2021; 1730 to 1830 PST
The goal of this presentation is to illustrate, via multiple examples from the speaker’s experience, the positive impact that the integration of the geotechnical engineer to multidisciplinary engineering teams has on the success of major construction projects in terms of cost, schedule and quality. Case studies, such as, significant optimization of foundations design for several skyscrapers in Dubai (UAE) and the reduction of temporary supports for the underground construction of the Doha Metro (Qatar) and Riyadh Metro (Kingdom of Saudi Arabia) projects were possible due to the integration of geotechnical engineering in the design stages, which will be presented. The value-add of embedding the geotechnical discipline into the design process is demonstrated in different markets (transportation, infrastructure, and property) and with different clients (P3 Contractors and property developers). The importance of investing in geotechnical field investigations, scoped to support advanced geostructural analyses, is highlighted and the value-add of soil-structure interaction modelling is integral to the presentation.
2020 - 2021
UNDERSTANDING SPREADS IN CANADIAN SENSITIVE CLAYS
by Ariane Locat, ing, Ph.D., on Thursday, May 20, 2021; 1730 to 1830 PST
Spreads are one type of large landslides occurring in Canadian sensitive clays. They are characterized by the rapid lateral spreading of a series of clay blocks, having horst and graben shapes, moving on an almost horizontal layer of remoulded clay. Spreads cover large areas (> 1 ha), develop rapidly with no warning signs, and conventional stability analysis do not apply, as they give too large factor of safety when back calculating entire spread. This leaves geotechnical engineers without tools in order to evaluate the risk regarding spreads. For the past decades, Université Laval, Ministère des transports du Québec and Ministère de la sécurité publique du Québec have worked together in order to answer the following question: what are the geotechnical and morphological parameters controlling initiation, propagation and extent of spreads in sensitive clays? This presentation portrays the latest advancement of the research program put in place with the goal to answer this question by integrating detailed field investigation, advanced laboratory testing and analysis and numerical modelling. It therefore presents the state of the art of our understanding of spreads in Canadian sensitive clays, focusing on three aspects: (i) synthesis of spreads in Eastern Canada, (ii) laboratory shear strength characterisation of sensitive clays, and (iii) application of progressive failure to spreads. Although it focuses on sensitive clays, the work presented has important applications to other materials presenting a strain-softening behaviour, such as rock, soft rocks, and snow, for example.
DESIGN OF PILE-SUPPORTED WHARVES SUBJECTED TO INERTIAL LOADS AND LIQUEFACTION-INDUCED GROUND DEFORMATIONS
by Arash Khosravifar, Ph.D, P.E., on Thursday, April 22, 2021; 1730 to 1830 PST
Five dynamic, large-scale centrifuge tests on pile-supported wharves were used to investigate the time- and depth-dependent nature of kinematic and inertial demands on the deep foundations during earthquake loading. The wharf structures in the physical experiments were subjected to a suite of recorded ground motions and imposed superstructure inertial demands on the piles. Partial to full liquefaction in loose sand resulted in slope deformations of varying magnitudes that imposed kinematic demands on the piles. It was found that the wharf inertia and soil displacements were always in-phase during the critical cycle when bending moments were at their maximum values. The test results were analyzed to provide the relative contributions of peak inertial loads and peak soil displacements during critical cycles, and the data revealed the depth-dependency of these factors. The centrifuge tests data were also used to develop an equivalent static analysis (ESA) procedure to combine inertial and kinematic loads during earthquakes. The accuracy of the ESA procedure is evaluated against measurements from the centrifuge tests. It is shown that large bending moments at depths greater than 10 pile diameters are primarily induced by kinematic demands and can be estimated by applying soil displacements only (i.e., 100% kinematic). In contrast, the large bending moments at the pile head are primarily induced by wharf deck inertia and can be estimated by applying superstructure inertial loads at the pile head only (i.e., 100% inertial). The large bending moments at depths shallower than 10 pile diameters are affected by both inertial and kinematic loads; therefore, the evaluation of pile performance should include soil displacements and a portion of the peak inertial load at the pile head that coincides with the peak kinematic loads. Proposed ranges for inertial and kinematic load combinations in uncoupled analyses are provided.
risk management of rock slope instability - ubc georox distinguished lecture
by Duncan Wyllie, PhD on Thursday, March 18, 2021; 1800 to 1930 PST
The presentation discusses projects where risk management, involving the hazard and consequence of rock slope instability, were taken into account in the selection and design of stabilization measures. The first step in this work is to select the appropriate stabilization measure (or measures) for the site, with the options being removal of unstable rock, or reinforcement of in-place rock, or protection against rock falls. Risk management can be qualitative where assessments of hazard and consequence are taken into account, or quantitative where probability distributions are calculated so that a specific level of reliability can be incorporated in design.
geotechnical investigation of coastal sediments with regards to geomorphodynamcis
by Nina Stark, PhD on Monday, March 8, 2021; 1200 to 1300
Geotechnical sediment properties in coastal and marine environments vary with local sediment dynamics, and vice versa affect sediment erodibility and depositional behavior. Thus, geotechnical properties are directly related to geomorphodynamics, including shoreline change in response to extreme events and sea level rise. Changes of geotechnical properties in coastal and marine environments resulting from sediment dynamics also potentially affects the integrity of coastal structures, engineering actions, naval activities, and/or habitats. It follows that there is a need for geotechnical investigations of coastal sediments with regards to active geomorphodynamics and its implications on above listed issues. Research towards filling this gap in knowledge requires the development of novel methods suitable for geotechnical site investigation in energetic coastal and marine environments, as well as a better understanding of the complex interaction between geotechnical properties and coastal processes. This presentation includes examples of latest efforts of method developments for the geotechnical investigation of coastal environments, as well as examples of geotechnical field data collections in areas affected by a variety of coastal processes and conditions. The presentation concludes with an outlook towards next steps and opportunities.
The 6th generation seismic hazard model of canada and proposed provisions for the 2020 edition of the national building code of canada
by Tuna Onur, PhD & Michal Kolaj on Wednesday, February 24, 2021; 1730 to 1830
The latest hazard assessment, the 6th Generation Seismic Hazard Model of Canada (CanadaSHM6), was released in 2020 and is currently proposed to be the basis for the seismic design values for the 2020 edition of the National Building Code (NBC) of Canada. NBC 2020 is expected to be released in late 2021. The new model includes recent advancements in our understanding of: recurrence of great subduction earthquakes; revisions in the geometry of deep inslab earthquakes; inclusion of newly-discovered potentially active faults; and the adoption of new ground motion models. Seismic hazard values are now also computed directly for various site conditions and provided to the end-user for their specific Vs30 (time-averaged shear wave velocity in the top 30 meters) and/or Site Class. This approach removes the need for separate site factor look-up tables in the building code, expands the applicability of the results, and simplifies the way end-users will determine seismic design spectrum. This presentation will summarize the key new model changes for CanadaSMH6, their impacts and present the proposed changes to the site properties provisions of the NBC 2020.
bio-cementation soil improvement for the mitigation of earthquake-incuded soil liquefaction
by Michael G. Gomez, PhD (University of Washington) on Wednesday, February 10, 2021; 1730 to 1830
Recent advances in bio-mediated soil improvement technologies have highlighted the potential of natural biological/chemical reactions in the soil subsurface to enable mitigation of infrastructure damage resulting from natural hazards such as earthquakes. Bio-mediated geotechnical solutions leverage the capabilities of microorganisms already existing in the geotechnical subsurface to generate a diverse range of “products”, which can dramatically improve the engineering behavior of soils. One such technology, Microbially Induced Calcite Precipitation (MICP), is an environmentally conscious soil improvement technique that can improve the geotechnical properties of granular soils through the precipitation of calcite. The biogeochemical process offers an environmentally-conscious alternative to traditional brute-force mechanical and Portland cement based ground improvement methods, by utilizing natural microbial enzymatic activity to induce calcite precipitation on soil particle surfaces and at particle contacts. The resulting bio-cementation affords improvements in soil shear strength, initial shear stiffness, and liquefaction resistance, while reducing soil hydraulic conductivity and porosity. Although MICP has been demonstrated extensively at the laboratory scale, critical gaps remain in our understanding of this technology with respect to up-scaling the process to field-scale, understanding the engineering behavior of (bio-)cemented geomaterials, and evaluating material permanence. This presentation will provide a brief introduction to MICP and highlight results from several recent experiments completed at centimeter- and meter- scales aimed at: (1) developing the MICP process for field-scale deployment including techniques for the stimulation of indigenous microorganisms, management of ammonium by-products, and improvement of cementation spatial uniformity and extent, (2) characterizing the liquefaction resistance of bio-cemented geomaterials including triggering and post-triggering responses, and (3) systematically exploring the effect of treatment conditions and environmental factors on resulting material mineralogy and long-term permanence.
PERFORMANCE OF LEVEES: LEARNING FROM THE PAST - LOOKING TO THE FUTURE
by Dr. Adda Athanasopoulos-Zekkos, PhD (UC Berkeley) on Tuesday, January 12, 2021; 1730 to 1830
Most river cities, now growing at increasing rates, are protected from flooding by earthen levees. Natural disasters like Hurricane Katrina have provided warnings regarding the need to maintain and upgrade our aging and deteriorating flood protection systems. Furthermore, for seismic regions like California, the combined seismic and non-seismic risks are creating a new class of engineering problems, with regard to safe levee design, that need to be addressed. This presentation will include key findings from the investigation of the levee failures in New Orleans, and ongoing efforts to improve flood management nationwide. Furthermore, preliminary results from ongoing efforts to improve the health monitoring and inspection of levee systems. Specifically, work on data fusion of spatially resolved data of the surface and subsurface “signature” along the levee systems by leveraging UAVs equipped with optical cameras, LIDAR and infrared cameras for surface mapping and seismic geophysics and electromagnetic sensors for subsurface mapping, will be discussed.
evaluation of flow liquefaction and liquefied strength using cpt - an update
and VGS Annual General Meeting
by Peter Robertson on Wednesday, November 4, 2020; AGM 1700 to 1730, Lecture 1730 to 1830
Flow liquefaction can occur in any saturated or near saturated meta-stable soil, such as very loose sands and silts as well as sensitive clays and is a major design issue for large soil structures such as mine tailings impoundments and earth dams. Robertson (2010) outlined a method to evaluate the liquefied undrained shear strength of soils using the CPT that applies primarily to sand-like soils. This presentation will describe a recommended update to the Robertson (2010) method to include a transition from sand-like to clay-like soils. The proposed update acknowledges that soil behaviour can vary from sand-like to clay-like and that CPT interpretation to estimate the large strain liquefied or residual undrained shear strength changes due to the changing drainage conditions during the CPT. In sand-like soils the CPT penetration process is essentially drained and the correlation to large strain liquefied undrained strength is carried out through an intermediate parameter, such as state parameter. In clay-like soils the CPT penetration process is essentially undrained and the correlation to large strain residual undrained shear strength can be carried out more directly using the CPT sleeve friction, fs. The correlations to estimate the large strain undrained shear strength of soils based on CPT measurements are updated and extended to cover both sand-like and clay-like soils. The presentation will also discuss risk evaluation related to flow liquefaction.