2019 - 2020
Multi-hazard System reliability of distributed infrastructure
by Professor Paolo Zimmaro of the Universities of Calabria and California (LA), Friday, August 28, 2020
Natural and anthropogenic hazards, such as earthquakes, landslides, and flooding events, can strongly affect the built environment and the life of our communities. New risk factors such as climate change, sea-level rise, and the increasing rate of induced seismicity, define new challenges for current and future generations. Furthermore, in recent years, community vulnerability and exposure globally increased as a result of an unprecedented rate of the population growth and a new, largely unplanned, urbanization development. Engineering approaches can be effectively implemented to create future resilient communities. Such procedures are traditionally based on the evaluation of the performance of individual elements of the built environment (i.e. a levee cross section, a dam, a landslide, etc.). However, our society heavily relies on infrastructural systems distributed over large areas and urban networks with interconnected lifeline systems. As a result, modern engineering frameworks should assess multi-hazard risk of critical lifeline networks and distributed infrastructure. This presentation illustrates how multidisciplinary approaches linking geotechnical engineering, data analytics, and robust probabilistic frameworks can be the key to reduce future risks and ultimately improve the resilience of our society to natural and anthropogenic hazards. Main results presented here are related to system reliability of flood-control levees. The framework can be applied to other lifeline networks and distributed infrastructure. Outcomes of this research can effectively help public agencies and other stakeholders to make informative decisions related to infrastructural systems.
-Cancelled- Listening to Infrastructure: acoustic emission monitoring of geotechnical limit states
by Professor Neil Dixon and Dr. Alister Smith
There is an urgent need for improved and affordable approaches for health monitoring of geotechnical infrastructure systems to facilitate asset management (e.g. slopes, foundations, dams and buried pipes). A proportion of energy dissipated during deformation of soil, soil-structural interactions and seepage processes is converted to heat and sound. The high-frequency (>10kHz) component of this sound energy is called acoustic emission (AE). It has been established that detected AE rates are proportional to rates of soil deformation and can be used to provide early information on both serviceability and ultimate limit states.
AE instrumentation is now available for continuous and real-time geotechnical monitoring. This presentation will introduce AE generation mechanisms and monitoring approaches in geotechnical engineering and describe the development and use of AE sensors for landslide early warning. It will also detail on-going research to deliver AE monitoring solutions for a range of applications (e.g. buried pipelines and earth dams).
Response of soil sites during earthquakes - a 60 year perspective (55th Terzaghi Lecture)
by Professor Emeritus Izzat M. Idriss of UC (Davis), Wednesday, March 4, 2020
The talk will be focused on the following topics: importance for the site response analyses; recorded earthquake ground motion data; comparison with empirical earthquake ground motion models (GMMs); need for analytical procedures; historical perspective; currently available analytical procedures (equivalent linear and nonlinear); comparisons of calculated and recorded earthquake ground motions at selected sites; and finally concluding remarks and recommendations.
The earthquake ground motions at the Treasure Island site are calculated using two equivalent linear and two nonlinear procedures. The calculated values are compared to those recorded during the 1989 Loma Prieta earthquake at the Treasure Island site. These comparisons, and similar comparisons at other sites during the Loma Prieta and other earthquakes offer the means to assess the accuracy and usefulness of each procedure. Finally, a number of recommendations are offered.
The presentation slides are available here, and an earlier recording of the presentation at the 2019 Geo-Congress here.
Mitigating a fatal flaw in modern geomechanics: understanding uncertainty, applying model calibration, and defying the hubris of numerical modeling - CGS Colloquium lecture
by Kathy Kalenchuk, Thursday, February 27, 2020
This colloquium has been prepared to achieve two objectives. The first objective is to provide a discussion of the practical limitations of numerical modelling in the field of geomechanical engineering. Too many discussions of numerical methods in geomechanical engineering are centered on the impressive ability of numerical tools to conduct complex and sophisticated analyses with relative ease and efficiency. Practitioners need to have a grounded conversation of numerical modelling with the reality that geomechanical designs are often data limited, with high degrees of uncertainty. When data limits and uncertainty are overlooked geomechanical engineers are at risk of introducing unforeseen fatal flaws in our engineering design. The second objective is to provide ‘how to’ guidelines for model calibration using a variety of ground reaction data types. Model calibration is truly the only means to reduce numerical uncertainties. Formal training in numerical modelling is often focused on software utilization and sometimes computational methods, however there are few opportunities for formal training on how to calibrate a model for practical engineering applications. This colloquium provides workflow guidelines for calibration methods and procedures.
Managing Landslide Risk in the Rohingya Refugee Camps in Bangladesh
VGS-TAC Talk by Philip LeSueur, Tuesday, January 14, 2020
This meeting is being held in the Uber Room of Steamworks Pub next to Waterfront Station (375 Water Street). Doors at 5:30pm, talk begins at 6:15pm.
Hazard-consistent assessment of seismically-induced displacements
by Professor Jorge Macedo of Georgia Institute of Technology (Atlanta), Wednesday, November 20, 2019
This seminar will present performance-based procedures for the estimation of: 1) liquefaction-induced settlement of buildings with shallow foundations, and 2) seismically-induced slope displacement of earth/waste systems and natural slopes. The current standard-of-practice for seismic performance assessment is to develop an elastic acceleration response spectrum based on a defined hazard level (or return period), which is then used as an input to estimate engineering demand parameters. The issue with this approach is that it assumes that the hazard design level for an intensity measure (e.g. spectral acceleration) is consistent with the hazard design level for an engineering demand parameter (e.g. seismically-induced displacement), which may not always be the case. The procedures to be presented in this seminar provide seismically-induced displacement estimates that are hazard-consistent and can be readily used in engineering design. The seminar will also discuss the differences between performance-based procedures that provide hazard-consistent estimates and standard-of-practice procedures, in the context of the seismic performance-based assessment of geotechnical system. Finally, the seminar will present a new computational platform that enables the straightforward application of the presented performance-based procedures in engineering practice.
Geomechanics of trenchless pipe installation, repair and replacement - 2019 Fall Cross Canada Lecture
by Dr. Ian Moore of Queens University (Kingston), Thursday, November 7, 2019
Traditional pipe installation and replacement involves extensive excavation of trenches along the full length of the pipeline that are both expensive and disruptive. To minimize those costs, many different ‘trenchless technologies’ have been developed by contractors and manufacturers, to permit pipe installation, pipe repair and pipe replacement using minimal earthworks. The inventive individuals and organizations that develop these techniques generally focus on development of the construction tools, materials and procedures, rather than the geotechnical (and structural) consequences of these methods, and so a variety of Geomechanics investigations are needed to establish how ground conditions influence the success or failure of such projects.
The presenter has worked for the last twenty years exploring the Geomechanics and soil-pipe interactions associated with trenchless technologies, and this lecture presents an overview of some of the associated research problems and their solutions. After introducing three of the commonest trenchless technologies, examples are presented illustrating how computational and experimental projects are being used to explain and quantify the underlying Geomechanics phenomena. First, pipe installation using horizontal directional drilling is introduced, and the Geomechanics research illustrated considering studies of mud transportation from the borehole as a result of blowout or hydrofracture. Next, pipe repair using liners is introduced, with description of research investigations of soil-pipe-liner interaction under earth loads. Finally, pipe replacement using static pipe bursting is explained, where studies have explained how cavity expansion and soil dilation lead to uplift at the ground surface and damage to overlying infrastructure.
Tailings- Specific Liquefaction Assessment
by Professor Mason Ghafghazi of University of Toronto, Thursday, October 17, 2019
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-sized soils with angular particles that are often deposited in a loose state. The geotechnical engineering practice currently relies on an empirical case-history-based approach for predicting the susceptibility of non-plastic granular soils to cyclic liquefaction due to earthquake loading. These case-histories are dominated by natural soils at shallow depth, in flat or gently sloped ground, whereas tailings dams involve manmade deposits, often tens of metres deep, and near steep dam slopes. Empirical correlations also dominate static liquefaction assessment through the state parameter. These empirical correlations are largely based on CPT calibration chamber data on clean quartz sands, which are also inherently different from most tailings.
Research done over the past few years at University of Toronto investigating the dependency of critical state parameters, cyclic resistance, and residual strength on fines content and fabric of tailings will be presented. The influence of these parameters on the relation between the state parameter and CPT measurements is discussed. It is shown that while empirical methods are generally adequate in estimating properties of natural sands, they have significant shortcomings in estimating in-situ properties of tailings. Other ongoing and future research including calibration chamber testing and analysis of tailings liquefaction case histories with Norsand will be discussed.
Liquefaction: lessons, challenges, and opportunities and VGS Annual General Meeting
by Professor Ross Boulanger of University of California (Davis), Thursday, September 26, 2019
Liquefaction during earthquakes has been the subject of extensive study for over half a century and is now routinely addressed in engineering practice using a wide range of technical approaches that depend on the project size and importance. These past studies have produced major advances in our scientific understanding of liquefaction phenomena and the engineering practices used to address liquefaction hazards, but there remain numerous situations where knowledge gaps and engineering practice limitations hinder the efficient mitigation of earthquake-induced liquefaction damages to our infrastructure and communities. This presentation examines a number of lessons, challenges, and opportunities regarding the evaluation and mitigation of liquefaction hazards, including aspects of site characterization, engineering analysis methods, challenging soil types, remediation methods, performance-based engineering procedures, and risk management approaches.
The presentation is available here.
2018 - 2019
Membrane Behavior and Chemico-Osmosis in Clays - 2019 Spring Cross Canada Lecture
by Dr. Charles Shackelford, Thursday, June 6, 2019
Semipermeable membrane behavior refers to the ability of a porous medium to restrict the migration of dissolved, aqueous-phase chemicals (solutes). Solute restriction occurs in a porous medium when the sizes of the pores available for solute migration are smaller than the sizes of the migrating solutes. The existence of membrane behavior in porous media also results in chemico-osmosis, or the flow of water from a region of lower solute concentration to a region of higher solute concentration. In Geotechnical Engineering, chemico-osmosis resulting from membrane behavior in clays has been shown to influence volume change behavior, cause apparent deviations from Darcy's law, and generate anomalous pore-water pressures in low-permeability geologic formations (e.g., shales). The existence of membrane behavior in high activity clays, such as sodium bentonites, also has been studied extensively from the viewpoint that solute restriction in bentonites can improve the containment function of such bentonites used for chemical containment barriers (e.g., geosynthetic clay liners, compacted sand-bentonite liners, soil-bentonite vertical cutoff walls, and bentonite buffers for high level radioactive waste disposal). This presentation will (1) illustrate the fundamental concepts of membrane behavior and chemico-osmosis in porous media, (2) describe the basis for membrane behavior in clays, (3) review the historical relevance of membrane behavior in clays with respect to consolidation, non-Darcian flow, and anomalous pore-water pressures in geologic formations, and (4) summarize the presenter's 20 years of experience in determining the existence and magnitude of membrane behavior in bentonites used as engineered barriers for chemical containment applications (e.g., municipal and hazardous waste landfills, tailings impoundments, lagoons, low and high level radioactive wastes, etc.).ty geologic formations (e.g., shales). The existence of membrane behavior in high activity clays, such as sodium bentonites, also has been studied extensively from the viewpoint that solute restriction in bentonites can improve the containment function of such bentonites used for chemical containment barriers (e.g., geosynthetic clay liners, compacted sand-bentonite liners, soil-bentonite vertical cutoff walls, and bentonite buffers for high level radioactive waste disposal). This presentation will (1) illustrate the fundamental concepts of membrane behavior and chemico-osmosis in porous media, (2) describe the basis for membrane behavior in clays, (3) review the historical relevance of membrane behavior in clays with respect to consolidation, non-Darcian flow, and anomalous pore-water pressures in geologic formations, and (4) summarize the presenter's 20 years of experience in determining the existence and magnitude of membrane behavior in bentonites used as engineered barriers for chemical containment applications (e.g., municipal and hazardous waste landfills, tailings impoundments, lagoons, low and high level radioactive wastes, etc.).
Leveraging Three-Dimensional Remote Sensing in Geotechnical Engineering
by Dr. Matthew Lato, Wednesday, May 8, 2019
Robust and effective geotechnical outcomes emerge when the design is based on a thorough understanding of the geology and the environment, and the interaction of these systems over time. Traditionally, a significant challenge faced by geotechnical professionals is our ability to observe, interpret, and understand the physical environment, particularly as it applies to changes over time, and the effect of those changes. Examples of such changes include the displacement of a highway crossing a landslide, the effect on a pipeline crossing under a meandering river with shifting sediments, a dam deforming due to reservoir filling, or movement of a foundation due to permafrost degradation. State-of-the-art 3-dimensional (3D) data collection and analysis techniques are expanding our mapping and monitoring abilities, opening doors to solving problems with confidence previously not possible.
Traditional methods of identifying and mapping change on geotechnical projects have been limited to point-based systems, such as survey prisms, that require significant time, effort and cost to establish, monitor and interpret. These systems involve sparsely distributed nodes physically mounted to the ground surface that cannot be used easily to understand the 3D mechanics of large-scale movement, nor can they be used to map change over large areas or long periods of time with unknown rates of movement. Traditional methods also rely on a priori knowledge of where change, movement or deformation is likely to occur, in order to optimize the placement of monitoring instruments. New methods were needed.
In the mid-2000s, the application of Light Detection and Ranging (LiDAR) -based technologies for evaluating natural and constructed environments started gaining the attention of geotechnical researchers. LiDAR is a 3D remote imaging technique that can generate high-resolution (up to thousands of points per square metre) surface models (topology). LiDAR data can be collected from tripods at static locations, and from moving cars, boats, unmanned aerial vehicles (UAVs), helicopters and airplanes. LiDAR opened the possibility to monitor sites and to conduct detailed analysis topographical change not reasonably practical with earlier stationary instruments.
Researchers’ sustained efforts on 3D remote sensing technologies and methods, their adoption by practitioners, and the evolution of data quality and processing capabilities in the past 20 years have generated revolutionary methods for detecting change in natural and constructed environments with unprecedented levels of accuracy and spatial extents. High resolution 3D topological data are transforming how we map natural terrain and understand movement over time across spatially extensive regions. Current research to push processing techniques further and exploit new data collection and computational processing capabilities is changing the foundation of geotechnical and geoscience topographical monitoring. Moreover, accuracy is expected to improve over time, and the costs of acquisition, processing and interpretation are expected to decrease. The current challenges faced when selecting and applying 3D remote sensing technologies are the need to keep up with their rapid advancement and expanding capabilities. Collaborative efforts between researchers and practitioners are needed to close this gap and provide the necessary information to those applying the techniques in practice.
As 3D data collection technologies and analysis methodologies continue to evolve, it is critical that we understand the capability of these tools to solve existing problems, and work with researchers to solve new ones. As we shift to designs with performance-based metrics, knowing how to accurately monitor and assess change will be pivotal to the success of future projects. LiDAR is routinely applied in some industries but only sparingly in others; this is likely to change as these new tools find routine use in the geotechnical profession.
A NEW AND UNIFIED APPROACH TO IMPROVED SCALABILITY AND VOLUMETRIC INTENSITY QUANTIFICATION FOR GSI AND ROCKMASS STRENGTH AND DEFORMABILITY ESTIMATION
by Dr. Paul Schlotfeldt, Wednesday, April 17, 2019
Several investigators have attempted to quantify the Geological Strength Index (GSI) chart, with the latest modification of the chart (2013) utilizing RQD as a measure of blockiness. This approach has limitation in where discontinuity spacing is wide (typically greater than 0.3 m) and RQD alone cannot adequately characterize the degree of blockiness, since it remains static at 100%. This talk introduces a new approach to quantifying widely spaced jointed rockmasses that is not dependent on RQD alone. At the core of the approach is a bias free volumetric fracture count (VFC) parameter (fractures/m3), that is integrated into the newly defined GSI chart as an aid to alleviate scalability and bias concerns related to the use of RQD in the quantification process. While the new GSI chart builds on the work of many, it is unique in the sense that not only is it fully quantifiable for a full range of block sizes including block sizes much larger that possible with RQD alone, but it provides a unique approach linking the VFC parameter with P32, a parameter frequently used in DFN modelling. The correlation of VFC with P32 in particular, is possible because the VFC parameter has no constraints of a limited number and/or assumed orthogonality of discontinuity sets or rectilinear block shapes or the need for black shape correction factors. The new chart also includes correlated scales on both the vertical and horizontal axis using both the RMR and the Q-systems, providing a unified approach that is both scalable and easily quantifiable and allows for the use of all three major rock mass classification systems along with P32 within one chart, something not attempted before. Data from a dam foundation rockmass in the Lesotho Highlands are introduced and are used to validate the quantification process for the overall GSI ratings for the foundation rock mass. These ratings have been used to estimate strength and deformability parameters for the foundation rock mass using the Hoek-Brown empirical failure criteria equations and then they were compared to the large-scale in-situ test results to validate the use of the V-GSI chart and system as a new tool for use in rock engineering.
TAILINGS DAMS – WHAT MIGHT THE FUTURE HOLD? – THE UBC GEOLOGICAL ENGINEERING 2019 DISTINGUISHED LECTURE
by Dr. Angela Kupper, Thursday, March 14, 2019
This year the selected topic is “tailings dams.” These are difficult times for the mining industry and for tailings dam engineering in particular, given the recent failures that caused loss of life and damage to the environment. This talk will discuss in general terms the current situation and where the industry could be going from here. Challenges and opportunities in design, construction and operation of tailings facilities that affect risk management will be discussed.
Simplified Procedure for Estimating Liquefaction-Induced Building Settlement – 6th Ishihara Lecture
by Dr. Jonathan Bray, Thursday, March 7, 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.
SEISMIC LANDSLIDE ASSESSMENTS: BRIDGING THE GAP BETWEEN ENGINEERS and EARTH SCIENTISTS - 2018 WilliaM B. Joyner Lecture
by Dr. Ellen Rathje, Monday, February 11, 2019
Earthquake-induced landslides represent a significant seismic hazard, as evidenced by recent earthquakes in Kaikoura, New Zealand and Gorkha, Nepal, and proper planning/mitigation requires accurate evaluation of the potential for seismic landslides. Engineers often tackle this problem through a detailed evaluation of individual slopes and more recently have introduced performance-based engineering (PBE) concepts into the analysis. Recognizing the compounding effects of multiple landslides across an area, earth scientists often evaluate seismic landslides at a regional scale. This approach sacrifices details, but provides a broader assessment of the impacts of earthquake induced landslides. This presentation will describe the integration of performance-based engineering concepts into regional-scale seismic landslide assessments. The basic PBE framework for seismic landslides will be introduced along with the modifications required to apply it at a regional scale. The application of the approach for a seismic landslide hazard map will be presented. The use of seismic landslide inventories to validate regional landslide assessments will be discussed, along with advancements in developing seismic landslide inventories using remote sensing techniques. Finally, research needs required to further advance regional seismic landslide assessments will be presented.
VGS-TAC NEW YEAR'S TALK - Delivery of Safe Drinking Water in Bangladesh
by Mark Bolton, M.Sc., P.Geo., Tuesday, January 15, 2019
This meeting is being held in the Uber Lounge of Steamworks Pub next to Waterfront Station (375 Water Street). Doors at 5:30pm, talk begins at 6:15pm.
Bangladesh is one of the poorest and most densely populated countries in the world. Due to its low-lying topography and tropical location in the Bay of Bengal, the country is vulnerable to droughts and flooding, resulting in freshwater shortages and bacterial contamination of water supplies. Since the 1970s, tubewells have been installed across the country to provide access to groundwater and lower the disease burden from drinking surface water; however, in the 1990s, health officials began noting symptoms of arsenic-related diseases. Subsequent water quality surveys uncovered widespread naturally occurring arsenic contamination in groundwater, resulting in what has been referred to as the worst mass poisoning of a population in history. UNICEF, the United Nations organization that is responsible for improving the lives of the most vulnerable and disadvantaged children in the world, is working with the Government of Bangladesh and sector partners to tackle these challenges and increase access to safe drinking water and improved sanitation.
In this presentation Mark will share his experiences serving with UNICEF and contributing to the sector in Bangladesh. He will describe the unique geological setting in the Bengal Basin that has resulted in elevated concentrations of arsenic in groundwater and other factors that affect drinking water quality. These technical aspects will be discussed in the context of the physical, economic, political and social setting that has a profound impact on water supply and sanitation in Bangladesh. He will then present the innovative approaches that UNICEF and its partners are implementing to provide drinking water that is arsenic safe and resilient to the impacts of climate change. These approaches, which blend technical, social and financial tools, are successfully mobilizing and empowering vulnerable communities to access, operate and maintain safe water sources.
Passive Seismic Methods for Site Assessment and Microzonation Mapping in Greater Vancouver
by Sheri Molnar, Thursday, November 8, 2018
Passive seismic techniques that record Earth’s background seismic noise wavefield have gained significant popularity in the last few decades. Passive seismic methods are non-invasive and non-disruptive to the site and therefore provide environmentally-sensitive methodology to infer subsurface geology. The use of passive seismic methods in current geotechnical engineering practice is rare but will increase in future. This presentation will include the basic theory of passive seismic methodology, why these passive methods are best combined with active-source seismic methods, and present case-study examples from nearly 20 years of experience in developing and applying passive seismic methods across Canada, Chile and in Nepal.
Both active- and passive-source seismic methods are utilized to map subsurface ground conditions across western communities of Metro Vancouver related to a multi-year seismic microzonation mapping project, including shaking, liquefaction and slope stability hazards. The project is supported by Emergency Management British Columbia and the Institute for Catastrophic Loss Reduction. Key tasks have involved developing a 3D geodatabase from previously collected geological, geophysical and geotechnical datasets, and performing seismic testing for subsurface site characterization which began this past summer 2018. In addition, all available recordings from 7 moderate earthquakes of magnitude > 4.3 between 1976 and 2015 are utilized to provide a comprehensive assessment of observed site amplification in Greater Vancouver. This presentation will include a status update of the Metro Vancouver microzonation mapping including preliminary non-invasive seismic testing results and comment on challenges in development of the underlying datasets.
Lessons Learned from Geotechnical Failures - 2018 Fall Cross Canada Lecture and VGS Annual General Meeting
by Alex Sy, Thursday, October 18, 2018
Despite advances in geotechnical engineering, failures do occasionally occur because of unknowns, uncertainties, inexperience, miscommunications, etc. However, failures do provide valuable lessons for the profession that can be learned to minimize future failures. This lecture will present three examples of geotechnical failures in British Columbia, in which the author was engaged to carry out forensic engineering. Pertinent details of the geotechnical failures and their causes are described for the following three case histories: (1) the dyke breach at the Stanley Street Pump Station located on the North Arm of the Fraser River in New Westminster; (2) the excessive foundation settlement at the Queensborough Middle School using stone column foundations in very soft soils at the east end of Lulu Island, and (3) the damaging ground movements at the Panorama/Ridgeview Subdivision located on an old landslide or “earthflow” in Chilliwack. Subsequent remedial solutions and lessons learned are also discussed.
2017 - 2018
Lessons Learned for Ground Movements and Soil Stabilization from The Boston Central Artery - 2018 Spring Cross Canada Lecture
by Thomas O'Rourke, Tuesday, May 22, 2018
The Boston Central Artery and Tunnel (CA/T) was the largest and most complex U.S. construction project in the last 25 years for which new technologies were developed and applied at an unprecedented scale. One of these technologies involves mass stabilization of weak clay by systematic deep mixing with cementitious products. On the CA/T, over 500,000 m3 of marine clay and organics were stabilized with the deep mixing method (DMM). The method was used under difficult conditions that included reinforcement of basal clay at an ongoing, unstable excavation and widespread application on a crowded site with especially deep, low-strength clays and many surrounding facilities.
Professor O’Rourke will provide an overview of the CA/T, including its cost and contributions to the urban regeneration of Boston. His presentation includes a case history covering ten years’ experience with ground stabilization on the CA/T. Topics addressed include water pressure distribution behind DMM walls, statistical characterization of soil-cement properties, quality control/quality assurance procedures, comparison of measured and numerically simulated deformation in clay stabilized with various configurations of soil-cement elements, and shear modulus degradation characteristics of in situ soil-cement. Recommendations are made for soil-cement properties, installation procedures, analytical modeling, design, and inspection.
Mountain Permafrost Engineering and Mining
by Lukas Arenson, Wednesday, May 2, 2018
Many mineral resources are in polar regions or at high elevations attracting mining companies from around the world. In Northern BC, or the South American Andes, such deposits are typically in remote mountainous locations and often at high elevations characterized by its challenging glacial and periglacial environments. Climate change is currently changing these mountainous regions rapidly, creating new landscapes and forming major changes to geo-hazards that affect the design of
infrastructure. In the dry Andes, periglacial landforms such as rock glaciers, protalus ramparts, gelifluction slopes, pattern ground and ice wedges dominate over glaciers and glaciarets. And despite the dry conditions, excess ground ice is frequently found resulting in challenges for infrastructure design.
The presentation focuses on engineering as well as environmental challenges that exist on developing and operating large mining projects in such mountainous environments. Results from complex site investigations recently carried out using advanced geophysical analysis techniques, as well as experience from the first sonic drill carried out in a South American in a rock glacier are
presented. Finally, challenges in communicating complex processes as well as how public perception affects large controversial projects are discussed.
Protecting Society from landslide hazard and risk – The UBC Geological Engineering 2018 Distinguished Lecture
by Suzanne Lacasse, Thursday, March 15, 2018
Risk is all around us: landslides, earthquakes, floods, storms and tsunamis are some of the daily natural hazards increasing risk to society. Quantitative risk assessment and risk management is needed because the future is not simply a projection of the present. This lecture will present the basic concepts of reliability‐based design and the principles for managing risk and achieving robust geotechnical designs. Case studies involving slope failures and landslide risk management will be used to provide illustrative examples. It will be demonstrated that our role is not only to act as experts providing judgment on factors of safety, but has evolved to providing input in the evaluation of hazard, vulnerability and risk associated with landslides. The conclusion is that our profession should be increasingly perceived as reducing risk and protecting communities.
The presentation slides are available here.
RobERTS bANK TERMINAL 2 SITE INVESTIGATION CASE HISTORY
by Jamie Sharp, Wednesday, February 21, 2018
ConeTec completed a large and comprehensive nearshore geotechnical site investigation in the summer and fall of 2016 on behalf of the Port of Vancouver. This case history covers the preparation, execution, and initial data analysis aspects of the site investigation. The proposed Roberts Bank Terminal 2 Project will be a new three-berth container terminal at Roberts Bank in Delta, BC. The site will be located on reclaimed land immediately NW of the existing terminal, with water depths ranging from 4 m to 25 m. The field investigation included deep CPTu and SCPTu testing, downhole seismic testing, electric Vane Shear Tests, and sonic/mud-rotary boreholes with disturbed and undisturbed sampling. Concurrent with the field work, a comprehensive laboratory program was conducted by others. This presentation will cover innovations made and challenges faced while performing a nearshore site investigation for a major port terminal in a high-risk seismic environment.
Study of Current State-of-Practice on Tailings Management Technologies
by Kate Patterson, Wednesday, January 24, 2018
KCB completed a study examining and comparing dewatering technologies (e.g., thickened, paste and filtered tailings) to conventional slurry for the management of tailings (e.g., thickened, paste and filtered tailings) currently used in Canada. The strengths, limitations, and physical and environmental risks of these alternative technologies were compared to those of conventional slurry. Strengths, limitations and physical and chemical risks were considered across the entire life cycle of tailings facilities, from design and construction through to long-term post-closure.
The study applied the following approach:
Conduct a survey to identify the current state-of-practice, and projects that use alternative technologies in Canada.
Evaluate the alternatives, comparing tailings management technologies and costs using the information obtained in 1., along with case study information provided by select Canadian and international mine sites.
Review advantages and disadvantages of the technologies, assess applicability to Canadian mines, and identify knowledge gaps.
The main conclusion from the study is that there is NO one-size-fits-all technology or management strategy and no technology should replace best practices in design, operations and closure of a tailings facility. This presentation will give high-level review of the study and present a snapshot of the current state-of-practice in the Canadian mining industry and key conclusions.
The presentation slides are available here.
vgs-tac new year's Talk - Landslide Risk Reduction in guatemala for homeowners in under-privileged areas
by Lauren Hutchinson, Tuesday, January 9, 2018
This meeting is being held in the Uber Room of the Steamworks Pub next to Waterfront Station (375 Water Street). Doors at 1730, talk begins at 1815.
BGC teamed up with two grad students to go to Guatemala and teach the local communities about rainfall induced landslides. Simple classification techniques (adding up some points to get a risk level) and mitigation options were taught to local NGOs and communities to assess the area. A short article about the work can be found here.
Probability Approach for Ground and Structure Response to GSC 2015 Seismic Hazard Including Crustal and Subduction Earthquake Sources
by Guoxi Wu, Tuesday, November 14, 2017
This presentation will provide an overview on how to make use of crustal, in-slab, and interface subduction hazard values from the 2015 GSC Model for the 13148 grid points (10 km by 10 km) in southwestern Canada (southern BC and western Alberta). USH spectra for crustal/in-slab earthquakes and USH spectra for Cascadia subduction interface earthquake can be derived at a couple of probability levels. Structure performance assessment can then be determined separately for the two main earthquake sources at a couple of probability levels. The overall probability at a given performance level (displacement, liquefaction or others) can then be determined by adding the probabilities from each of the two individual performance hazard curves. The overall performance (displacement, liquefaction or others) at a target probability level (e.g., 2%/50 years) is then determined from the overall combined performance hazard curve. Examples for determining seismic slope displacements from empirical equations (Bray and Travasarou 2007, Macedo et al. 2017) and for assessing site response and liquefaction using nonlinear finite element time history analyses (VERSAT, Wutec 2016) will be shown to illustrate the proposed procedure.
The presentation slides are available here.
Advances in Dam Design - 2017 Fall Cross Canada Lecture
by Jean-Marie Konrad, Wednesday, October 25, 2017
Embankment dam performance and life span are closely related to the hydric, thermal and mechanical behaviour of materials used during its construction. The apparent simplicity of embankment dams hides complex and often poorly known behaviours resulting from thermo-hydro-mechanical coupling phenomena. Understanding the different behaviours as well as their interrelationships is of paramount importance to optimize the life cycle of these structures.
Hydro-Québec Production obtained the necessary approvals to build a 1,550-MW hydroelectric complex on the Rivière Romaine, north of the municipality of Havre-Saint-Pierre on the north shore of the St. Lawrence. The complex will consist of four hydropower generating stations with average annual output of 8.0 TWh.
Construction of the Romaine-2 development began in 2009. Romaine-2 was commissioned in 2014 and the Romaine-1 development was commissioned in 2015. Work on the Romaine-3 and Romaine-4 developments, which will be operational in 2017 and 2020, respectively is underway.
Since 2009, the NSERC/HQ industrial research chair in Life Cycle Optimization for Embankment Dams contributed to the advancement of various aspects in dam design. Major developments for seepage induced erosion are presented. The use of centrifuge testing for predicting deformation of Romaine 2 are discussed. Rockfill properties are viewed from a fractal perspective.
Evergreen LINE RAPID TRANSIT: dEEP FOUNDATION AND GROUND IMPROVEMENT SOLUTIONS - aND ANNUAL GENERAL MEETING
by Ali Azizian, September 20, 2017
The 11 km long alignment of the Evergreen Line Rapid Transit (ELRT) project through Burnaby, Coquitlam and Port Moody consists of elevated and at-grade guideway sections as well as cut-and-cover and bored tunnels. Because of the high seismicity of the region, liquefiable and soft soils posed the main challenges for the design of structures. A performance-based design approach with varying levels of performance requirements were specified for the project. Several deep foundation and ground improvement solutions were used to meet the design objectives, while satisfying cost, schedule and site constraints. Foundation types included drilled shafts and driven steel pipe piles. Ground improvement solutions included Cement Deep Soil Mixing (CDSM) and driven timber piles. The presentation will provide an overview of the subsurface ground conditions along the alignment, seismic analyses (e.g. FLAC modelling), selected foundation or ground improvement types for each section, and some of the challenges faced during construction.
2016 - 2017
SANICLAY and SANISAND plasticity models: recent advances and applications
by Mahdi Taiebat of the Univeristy of British Columbia, Tuesday, May 16, 2017
Simplicity of structure and presentation versus sophistication of performance are the characteristics of constitutive models that must be properly balanced in order to achieve eventually being useful in practice. This can be accomplished without sacrificing the igor of correct mechanics, and one of the simplest ways, is to present first the main building blocks of a model from the perspective of great simplicity. SANICLAY and SANISAND are families of Simple ANIsotropic CLAY and SAND plasticity models, developed over the last several years for application in geotechnical and earthquake engineering. They are within the useful framework of critical state soil mechanics, formulated based on bounding surface plasticity, and built on familiar foundations of Modified Cam-Clay and Drucker-Prager, respectively. The models in both class include anisotropy as one of their important ingredients for addressing monotonic and cyclic loading, and include multiaxial tensorial formulation. The contributions on these models over the years include various constitutive ingredients in the form of simple add-ons features that can be activated depending on the availability of data and needs of application. This presentation includes a general introduction to the basic features of these two families of soil plasticity models, and briefly reviews selected add-on features. Some examples of model validation and application will also be presented and discussed.
Risk Assessment in geotechnical Engineering - 2017 Spring CROSS CANADA LECTURE
by Dr. Vaughan Griffiths of the Colorado School of Mines, Wednesday April 12, 2017
Geotechnical engineering has seen a rapid growth of interest in risk assessment methodologies. This seems a logical evolution since soils and rocks are among the most variable of all engineering materials and geotechnical engineers must often make do with materials they are dealt with at any particular site. A probabilistic analysis may lead to a “probability of failure”, as opposed to the traditional “factor of safety”, representing a fundamental shift in the way engineers need to think about the suitability of their designs. The seminar will review some of the benefits and potential pitfalls of these different approaches and describe some introductory methods of probabilistic analysis.
Importance of Geology and Rock Mechanics in the Siting and Construction of Dams – The UBC Geological Engineering 2017 Distinguished Lecture
by Richard Goodman, Professor Emeritus, University of California (Berkeley), Thursday, March 23, 2017, Earth Sciences Building 1013, UBC
The serious difficulties with dam foundations containing soluble limestones and evaporates are well known and appreciated. But important problems can also develop with dam foundations on non-soluble rock formations by virtue of geologic structural features. This lecture will describe a number of relevant and instructive case histories of dam safety reviews and the measures that were taken to assure foundation safety. These cases illustrate the importance of fully respecting and interpreting geologic and rock mechanics details in the siting and construction of dams.
Refreshments and mingling will run from 1730 to 1830. The lecture will being at 1830.
Challenging Rock Slope Excavation and Remediation
by Charles Hunt, Wednesday, February 22, 2017
The technical issues associated with rock slope engineering are generally well known and understood. However, challenging, heterogeneous rock slopes require tailored solutions specific to controlling the rock fall hazard identified. The presentation will focus on overviewing such tailored solutions on a number of rock slopes with different hazards created by unique geological, slope and catchment characteristics. To categorize the examples they will be split into solutions with minimal catchment, solutions which required urgent time critical procurement of materials, and finally some innovative examples of remediation techniques where both the nature of the hazard and time/budget constraints necessitated creative thinking.
A Screening Tool for Impact Hammer Selection for Installation, Testing and Damage Mitigation for Open-Toe Steel Pipe and H-Piles
by David Tara, Thursday, February 2, 2017
In this talk David will share his experience in a presentation that will build on those given at GeoVancouver in October 2016. The presentation will cover some of the considerations involved in impact hammer selection for installation and high‑strain dynamic testing of open-toe, steel pipe and H‑piles:
minimum, suggested and maximum hammer size required for pile installation
minimum, suggested and maximum hammer size required for high-strain dynamic testing
maximum driving stresses
damage susceptibility relative to pile cross section dimensions
damage mitigation
The latter half of the talk will focus on the application of the screening tool to published case histories and data in David’s files. The applicability of the screening tool for impact hammer selection will be assessed and, with the aid of advanced pile driving simulation and signal matching software, to also show how pile damage could have been predicted.
VGS-TAC NEW YEAR'S PARTY
by Ross Varin, Tuesday, January 10, 2017
Engineers Without Borders will be giving a presentation on a project they are working on in Panama.
RECENT TRENDS IN THE SAFETY ASSESSMENTS FOR TAILINGS DAMS
by Bryan Watts, Tuesday, November 29, 2016
This talk will be an encore presentation of this Keynote address on “Recent Trends in the Safety Assessments for Tailings Dams” given at the recent CDA conference in Halifax in mid-October. Four case histories of tailings dam failures: Omai, Los Frailes, Mt. Polley, and Fundao are described together with their impact on tailings dam stewardship. This is followed by a discussion of current trends in tailings dam management structures, the continuing malaise in data organization at tailings dam sites, and the value of tying acceptable Factor of Safety guidelines to the ability to monitor the failure mode of interest.
LIQUEFACTION AND SPATIAL VARIABILITY - 2016 FALL CROSS CANADA LECTURE
by Ross W. Boulanger, of the University of California Davis, Thursday, October 27, 2016
The development and application of engineering procedures for evaluating soil liquefaction during earthquakes rely heavily on case histories and their interpretations. Our ability to correctly interpret and utilize case history observations requires a sound understanding of the underlying physics, as is often derived from a synthesis of experimental and theoretical findings. In this regard, understanding the effects of spatial variability on liquefaction phenomena is essential for facilitating interpretation of case histories and application of liquefaction evaluation procedures.
In this presentation, nonlinear dynamic analyses of liquefaction in spatially variable (stochastic) deposits are used to draw insights on how spatial variability may affect the system performance and be appropriately accounted for in other types of analysis procedures. Results and insights are summarized for different types of problems: dynamic response and pore pressure generation as observed at the Wildlife liquefaction array; lateral spreading and surface settlements in gently sloping ground underlain by alluvium with different depositional structures; and deformations of an embankment dam underlain by a liquefiable alluvial layer. The practical lessons drawn from these simulations illustrate the complementary roles of theoretical, experimental, and case history based findings for advancing our ability to address liquefaction problems in engineering practice.
GROUND IMPROVEMENT AND LIQUEFACTION MITIGATION USING DRIVEN TIMBER PILES - AND ANNUAL GENERAL MEETING
by Armin W. Stuedlein of Oregon State University, Wednesday, September 14, 2016
Conventional driven timber pile ground improvement can provide a cost-effective liquefaction mitigation method, as it provides densification and reinforcement to an improved subgrade. The potential for drained timber piles to improve densification and potentially reduce in-earthquake pore pressures could allow densification, reinforcement, and drainage in one mitigation method. However, the soil densification possible with timber pile ground improvement is rarely incorporated into stability analyses of supported geostructures because of the current lack of understanding of the amount of densification possible. This study focuses on a field trial of driven conventional and drained timber piles to investigate the effect of pile spacing, time-since- installation, and drainage on the amount of soil densification. The test site consisted of clean to silty sands with a relative density ranging from 40 to 50 percent prior to installation. Following installation of the timber piles spaced at two, three, four, and five pile diameters, cone penetration tests were conducted to evaluate the degree of densification. These tests were performed at approximately 10, 50, 120, and 250 days following installation to evaluate the effect of time and to understand the role of fines content on the degree of densification. In general, the relative density of the soils improved to approximately 60 to 100 percent depending on the pile spacing and the presence of drainage elements. A controlled blasting test plan was also conducted at an un- improved control zone and in the improved timber pile test area to evaluate the effectiveness of this ground improvement alternative to reduce the excess pore-water pressures and mitigate liquefaction. The treated zones were shown to mitigate liquefaction by reducing the peak residual r u values 10 to 25 percent and lowering the soil settlements by approximately 75 percent compared to the un-improved zone.
The presentation slides are available here.
2015 - 2016
Progressive failure in overconsolidated brittle clay. lessons from the failure of a tailings dam - 2016 spring CROSS CANADA LECTURE
by Dr. Antonio Gens of the Technical University of Catalonia (Barcelona), Thursday, May 5, 2016
Progressive failure of brittle materials exhibit two very undesirable characteristics: i) they usually occur without warning, and ii) consequences are often catastrophic. Brittle low-permeability materials also involve significant challenges for design such as the selection of the operational strength and the slow dissipation of pore pressures. All those issues are examined in the context of the failure of a tailings dam that caused an important environmental disaster affecting a very large area. The lecture describes in detail the features of the case, the failure event and the subsequent investigation. The forensic investigation led to the unambiguous identification of the mechanism of failure that is consistent with the observations before, during and immediately after the failure.
It was conclusively shown that the main causes underlying the failure were the occurrence of progressive failure in the brittle foundation clay and the presence of very high pore water pressures in the foundation. The mechanism of the failure also explains the large post-failure movements (more than 50 m) that were responsible for the large spill of tailings. The study of the failure was supported by numerical analyses of increasing degree of complexity that provided additional insights into the problem.
The lecture concludes with some general lessons that can be extracted from the case and applied to other problems involving the potential failure of brittle stiff clays.
19 July 1985 Stava tailings dam failure: what can we learn from it?
by Luca Zorzi, Wednesday, April 13, 2016
On 19 July 1985 the failure of two tailings dams located just upstream from the village of Stava in the municipality of Tesero (Eastern Alps, Italy) triggering a vast mudflow that flowed down-channel through Stava, a small village of 20 buildings. The mudflow rapidly traveled over 4.2 km along the Stava Valley and passed through Tesero, before flowing into the Avisio River. The flowing mass had an initial volume of 180,000 m3 of mud and water which spilled out of the tailings dams plus nearly 50,000 m3 of additional material resulting from soil erosion, destruction of buildings, and uprooting of trees. The total area affected by the mudflow was about 435,000 m2 along the total stretch of 4.2 km. Along it’s run out path, the flowing mass destroyed 53 houses, 3 hotels, 6 industrial buildings and 8 bridges; 9 buildings seriously damaged; and caused erosional processes over an area of 27,000 m2. 268 people lost their lives, including 59 boys and girls less than 18 years old, 89 men, and 120 women.
In recent years, the Stava 1985 Onlus Foundation has been established aiming to keep the memory of the disaster alive. The duty of the Foundation is to keep alive the historical memory of the Stava Valley and strengthen the culture of prevention, correct territorial management, and safety since shortcomings in these fields were the cause of these and other man-induced disasters. The Foundation is principally active in the field of education and information directed at high school and university students, graduates, technicians and administrators who are in charge of the management of tailings dams and geotechnical structures throughout the explanation of genesis, causes, and responsibilities of this catastrophe.
In this presentation, an overview of the principal causes and conditions that led to the disaster, along with the responsibilities will be presented aiming to highlight what has been learnt and what we still have to learn from this tragedy.
DEBRIS FLOW HAZARD AND RISK ASSESSMENT & LESSONS FOR LIFE AS YOU HEAD INTO PRACTICE: A PERSPECTIVE ON GROUNDWATER MODELS - THE GEOLOGICAL ENGINEERING 2016 DISTINGUISHED LECTURES
by Dr. Oldrich Hungr and Dr. Leslie Smith, Tuesday, March 22, 2016
Dr. Oldrich Hungr: Debris Flow Hazard and Risk Assessment.
The Topic: A brief review will be given of a practical approach towards characterizing debris flow hazards in a watershed, estimating risks and selecting remedial measures. The presentation will focus on debris flow hazards typical of coastal B.C. and will be illustrated by some examples.
The presentation slides for Dr. Hungr are available here, and Dr. Smith here.
Dr. Leslie Smith: Lessons for Life as You Head into Practice: A Perspective on Groundwater Models
The Topic: Over the past decade there has been a substantial increase in the level of detail built into groundwater models submitted in support of environmental assessments and permitting for mining projects. A synthesis of recent case histories suggests: (i) poor choices can still be encountered in defining conceptual models; (ii) powerful modeling tools can create the illusion of knowledge; (iii) models are viewed by some as defining a decision rather than a decision support tool. This presentation suggests some simple guiding principles to consider when developing groundwater models in an environment of rising expectations.
DEVELOPMENT OF ROCK STRENGTH PARAMETERS FOR NUMERICAL MODELLING
by Dariusz Wanatowski, Wednesday, February 3, 2016
European collieries suffer from severe floor and side deformation due to depth, tectonic stress and the soft strata within and beneath the seams which are also vulnerable to degradation over time, particularly when wet. This seminar will summarise findings from the recently completed research project ‘GEOSOFT’ funded by European Commission’s Research Fund for Coal and Steel. The project developed and applied improved means of measuring, representing and analysing this behaviour and its interaction with mine support, both in the laboratory and in the field. Its objectives were to improve our understanding of the phenomena and develop enhanced design and construction solutions utilising stress control, shotcrete, improved reinforcement and/or closed support structural sections. The research partners have come from the UK, Spain and Poland and included industry representatives, consultants and research bodies.
UNDERSTANDING SLOPE STABILITY THROUGH REMOTE SENSING
by Matthew Lato, Wednesday, January 20, 2016
An engineer’s ability to understand the conditions and mechanics of the environment they work in is critical to developing practical solutions. This ability becomes increasingly complicated when working on problems such as landslides where information is traditionally limited to sporadic (and costly) borehole mapping and instrumentation data, discrete surface measurements and observations, and interpolated geophysical data. Over the past ten years, advances in remote sensing technologies have enabled engineers to observe, interpret, and understand the physical environment and its evolution through time, at previously unimaginable levels of detail. This talk will cover the development of remote sensing tools, case studies, and state-of-the-art research and development. Three case studies from BC and Alberta will be presented:
i. understanding the movement of Fountain Slide between 2006 and 2015 through airborne lidar data and how this information is assisting in developing stability options for the site;
ii. identification of pre-failure rock block deformation from a natural slope along the CN railway line in the Fraser Canyon using high resolution ground based lidar data;
iii. mapping potential rock fall source zones and assessing preventative measures for a 150 metre high vertical rock face along a railway line in the Robson Valley using helicopter photogrammetry.
The presentation slides are available here.
VGS-TAC HOLIDAY PARTY
Presentation by Tim Smith, Tuesday December 8, 2015 @ Steamworks (Gastown)
The presentation will draw on Tim's personal experience of surviving the April 2015, Gorka Earthquake in Nepal. It is a unique perspective of what it is like for someone who normally deals with post natural disaster issues, when they are thrown in the middle of a natural disaster. Tim will discuss the earthquake events from a seismic perspective, what it actually feels like from a personal perspective to be in the middle of such a large disaster and the lessons we could learn from this disaster at a personal level as well as at a larger-scale as a community in a seismically vulnerable zone.
Doors at 1730, presentation at 1830. $10 for VGS/TAC members, $15 for non-members. Cover includes one drink and appetizers.
CANADA'S 5TH GENERATION SEISMIC HAZARD MODEL FOR THE 2015 NATIONAL BUILDING CODE
by Trevor Allen, Wednesday, November 25, 2015
Canada’s 5th Generation seismic hazard model has been developed to generate seismic design values for the 2015 National Building Code of Canada (NBCC2015). The model updates the earthquake catalogue, consistently expresses earthquake magnitudes in terms of moment magnitude, revises earthquake source zones, and includes probabilistic treatment of Cascadia and other fault sources, so as to estimate mean ground shaking at the 2%/50-year probability level. Hence it takes advantage of newer knowledge and replaces the 4th Generation 'robust' combination of alternative models used for NBCC2010 by a fully probabilistic model. The ground-motion models (Atkinson and Adams, 2013, Can. J.Civil Eng.) use a “reference suite” approach and represent a major advance over those used for the 4th Generation model. Seismic design values (mean-hazard on Soil Class C at VS30=450 m/s) for PGA, PGV and for Sa(T) for T = 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 s will be used in NBCC2015. The NBCC2015 specifies new period-dependent soil factors F(T) (replacing amplification factors Fa and Fv) related to a region-dependent PGA on reference rock.
The presentation slides are available here.
RUSKIN DAM UPGRADE
by Nathan Sweeny and Li Yan, Wednesday October 21, 2015
Ruskin Dam is located near Mission, British Columbia and is one of three BC Hydro facilities in the Alouette Stave Ruskin Hydroelectric System. The dam was constructed between 1929 and 1930 and is a concrete gravity structure founded primarily on bedrock. At the right abutment, which consists mainly of glacially deposited sands and silts, the dam connects to a cut-off system consisting of sloping concrete slabs, founded on retaining walls and sheet piles, which extend upstream of the dam. Significant seepage and piping issues occurred at the right abutment after first filling of the reservoir in 1930, and a number of remedial actions were carried out in an attempt to address the problems. Through extensive investigations it was determined that the reoccurring abutment seepage and piping issues, as well as the low seismic withstand of the concrete slab cut-off, posed significant dam safety risks to the facility. A seepage control upgrade project was initiated to address the deficiencies, which resulted in the construction of a new seepage cut-off wall with a special tie-in to the concrete dam, and a reverse filter blanket and drainage system on the downstream slope to collect and measure seepage. Analyses were carried out to evaluate the performance of the proposed upgrade during the design earthquake and to model the seepage regime.
The presentation slides are available here.
Reliability-Based Geotechnical Design: Link between Theory and Practice - 2015 Fall Cross Canada Lecture and annual general meeting
by Dr. Gordon Fenton of Dalhousie University, Thursday, October 1, 2015
Geotechnical design codes are increasingly migrating towards reliability-based design concepts. What this means is that geotechnical designs are starting to be specifically targeted at a failure probability that is societally acceptable and that depends on the severity of failure consequences. For example, the foundation of a hydro-electric dam, whose failure may result in significant downstream damage and potential life-loss, must be designed to have a lower failure probability than the foundation of a storage shed.
In order to properly employ reliability-based design concepts, a basic understanding of the probability concepts, as well as the link between site and model understanding and failure probability, is required. This lecture explains the basic ideas of probability theory and how they are used in modern geotechnical design concepts. Questions, such as "How are standard site investigation results used to estimate the probability of failure of a designed geotechnical system?” are addressed and illustrated using a number of examples.
The presentation slides are available here.