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.


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.


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.


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.