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.