Seismic Performance and Design of Bridge Foundations in Liquefiable Ground with a Frozen Crust

INE/AUTC 12.3

Seasonally Frozen Soil Effects on the Seismic Performance of Highway Bridges

INE/AUTC 12.0

Thermal Design Considerations for a Seasonally Frozen Capillary Barrier Diversion Cover System

Soil covers on mining waste are typically designed for temperate climates and often rely on fine-grained soils to limit net percolation. Mine sites in cold regions, such as Northern Canada, have limited fine-grained materials and have climates that reduce the effectiveness of designs utilized in more temperate climates. A new cover system that harnesses the cold climate and available coarse textured materials has been proposed. The cover system, a seasonally frozen capillary barrier diversion cover system, relies on the ability of frozen soils with high levels of water saturation, to divert infiltrating meltwater downslope and away from the underlying mine waste. The thermal effects of flowing water on heat transfer in the frozen soil were studied in this research. The potential for early thaw due to the convection and conduction associated with water flow was examined through the use of a numerical model to simulate several case studies and cover geometries. Vertical forced convection was investigated through a case study of frozen column experiments. Lateral convection was investigated through a case study of a natural analogue at Wolf Creek, Yukon, while conduction was investigated through a case study of ponding water and increased conduction. Illustrative cover design models incorporated climate data and idealized materials from a representative mine site into several different geometries, each representing a potential thermal failure mode. These simulations reveal that no one thermal process dominates in frozen soil. Lateral convection can dominate in sloped high hydraulic conductivity soil, given enough water is available to generate large lateral water flows. Under low flow conditions, the influence of lateral convection drops. Vertical convection will result when large amounts of water percolate vertically, causing greater thaw rates throughout the slope than by conduction alone. Conduction will occur regardless of water flow, but increased rates of conductive heat transfer can occur when water ponds on the ground surface, which results in increased rates of thaw leading to preferential infiltration of water below ponded areas. In finer layers of low hydraulic conductivity, conduction will always dominate, as water cannot achieve the flow rates necessary for convection to dominate. This research has shown that the proposed cover design is a viable alternative to the current practice. Further modelling, laboratory and field studies are recommended for future research

Permafrost extension modeling in rock slope since the Last Glacial Maximum: application to the large Séchilienne landslide (French Alps).

12 pagesInternational audienceRecent dating performed on large landslides in the Alps reveal that the initiation of instability did not immediately follow deglaciation but occurred several thousand years after ice down-wastage in the valleys. This result indicates that debuttressing is not the immediate cause of landslide initiation. The period of slope destabilization appears to coincide with the wetter and warmer Holocene Climatic Optimum, indicating a climatic cause of landslide triggering, although the role of seismic activity cannot be ruled out. A phenomenon which may partly explain the delay between valley deglaciation and gravitational instability is the temporal persistence of thick permafrost layers developed in the Alps since the Last Glacial Maximum (LGM). This hypothesis was tested through 2D thermal numerical modeling of the large Séchilienne landslide (Romanche valley, French Alps) using plausible input parameter values. Simulation results suggest that permafrost vanished in the Séchilienne slope at 10 to 11 ka, 3,000 to 4,000 years following the total ice down-wastage of the Romanche valley at 14.3 ka. Permafrost persistence could have contributed to the failure delay by temporally strengthening the slope. Numerical simulations also show that the permafrost depth expansion approximately fits the thickness of ground affected by gravitational destabilization, as deduced from geophysical investigations. These results further suggest that permafrost development, associated with an ice segregation mechanism, damaged the rock slope and influenced the resulting landslide geometry

Multi-Scale Modelling of Cold Regions Hydrology

Numerical computer simulations are increasingly important tools required to address both research and operational water resource issues related to the hydrological cycle. Cold region hydrological models have requirements to calculate phase change in water via consideration of the energy balance which has high spatial variability. This motivates the inclusion of explicit spatial heterogeneity and field-testable process representations in such models. However, standard techniques for spatial representation such as raster discretization can lead to prohibitively large computational costs and increased uncertainty due to increased degrees of freedom. As well, semi-distributed approaches may not sufficiently represent all the spatial variability. Further, there is uncertainty regarding which process conceptualizations are used and the degree of required complexity, motivating modelling approaches that allow testing multiple working hypotheses. This thesis considers two themes. In the first, the development of improved modelling techniques to efficiently include spatial heterogeneity, investigate warranted model complexity, and appropriate process representation in cold region models is addressed. In the second, the issues of non-linear process cascades, emergence, and compensatory behaviours in cold regions hydrological process representations is addressed. To address these themes, a new modelling framework, the Canadian Hydrological Model (CHM), is presented. Key design goals for CHM include the ability to: capture spatial heterogeneity in an efficient manner, include multiple process representations, be able to change, remove, and decouple hydrological process algorithms, work both at point and spatially distributed scales, reduce computational overhead to facilitate uncertainty analysis, scale over multiple spatial extents, and utilize a variety of boundary and initial conditions. To enable multi-scale modelling in CHM, a novel multi-objective unstructured mesh generation software *mesher* is presented. Mesher represents the landscape using a multi-scale, variable resolution surface mesh. It was found that this explicitly captured the spatial heterogeneity important for emergent behaviours and cold regions processes, and reduced the total number of computational elements by 50\% to 90\% from that of a uniform mesh. Four energy balance snowpack models of varying complexity and degree of coupling of the energy and mass budget were used to simulate SWE in a forest clearing in the Canadian Rocky Mountains. It was found that 1) a compensatory response was present in the fully coupled models’ energy and mass balance that reduced their sensitivity to errors in meteorology and albedo and 2) the weakly coupled models produced less accurate simulations and were more sensitive to errors in forcing meteorology and albedo. The results suggest that the inclusion of a fully coupled mass and energy budget improves prediction of snow accumulation and ablation, but there was little advantage by introducing a multi-layered snowpack scheme. This helps define warranted complexity model decisions for this region. Lastly, a 3-D advection-diffusion blowing snow transport and sublimation model using a finite volume method discretization via a variable resolution unstructured mesh was developed. This found that the blowing snow calculation was able to represent the spatial redistribution of SWE over a sub-arctic mountain basin when compared to detailed snow surveys and the use of the unstructured mesh provided a 62\% reduction in computational elements. Without the inclusion of blowing snow, unrealistic homogeneous snow covers were simulated which would lead to incorrect melt rates and runoff contributions. This thesis shows that there is a need to: use fully coupled energy and mass balance models in mountains terrain, capture snow-drift resolving scales in next-generation hydrological models, employ variable resolution unstructured meshes as a way to reduce computational time, and consider cascading process interactions

Numerical studies of thermal-mechanical responses of embankments under a changing climate in two first nation communities, Saskatchewan, Canada

Records show that ongoing global warming has changed the thermal condition of the ground in seasonally frozen areas of Canada, causing widespread ground surface settlement and harm to infrastructure, particularly embankments. In the current study, finite element numerical analysis is conducted to evaluate how climate change may influence the thermal-mechanical (TM) regimes in road embankments that are under climate conditions in two Indigenous communities in Saskatchewan, Canada, namely Yellow Quill and James Smith. This evaluation includes the analysis of embankment on the climate data from 1975 till 2100, where the data is divided into different time periods of Historical (1975-2000), Future-1 (2023-2048), Future-2 (2049-2074) and Future-3 (2075-2100. From each period, 5 representing years including extreme cold, extreme hot, expected hot, expected cold, expected mean years are considered to simulate the TM regimes with and without traffic loads. The relation for temperature-dependent thermal expansion coefficients of soils is derived and included in the modeling based on the ice content and a mixture theory. Temperature dependent mechanical properties are also involved to account for freeze-thaw induced stress redistribution and the related potential plastic deformation. According to the coupled thermal-mechanical study, which takes into account the Linear Drucker-Prager yield criterion for the stress analysis at critical location of embankments, cases with an extreme cold climate indicates the worst effect on the embankment foundation. It is reflected by the more significant temperature variations causing larger plastic zones in the toe of the embankment when compared with other climate scenarios. The extreme hot cases tend to generate more displacement on the road surface as the climate is getting warmer. The present study only sheds light on the thermal-mechanical aspect, and it does not include pore water flow behavior due to frost actions. Therefore, the result on the heave or settlement of embankment surface is not significant. Nevertheless, the inclusion of temperature-dependent thermal expansion coefficients considering the ice contents provides a better estimation of thermal-mechanical responses

Numerical Modeling in Civil and Mining Geotechnical Engineering

This Special Issue (SI) collects fourteen articles published by leading scholars of numerical modeling in civil and mining geotechnical engineering. There is a good balance in the number of published articles, with seven in civil engineering and seven in mining engineering. The software used in the numerical modeling of these article varies from numerical codes based on continuum mechanics to those based on distinct element methods or mesh-free methods. The studied materials vary from rock, soil, and backfill to tailings. The investigations vary from mechanical behavior to hydraulic and thermal responses of infrastructures varying from pile foundations to tailings dams and underground openings. The SI thus collected a diversity of articles, reflecting the state-of-the-art of numerical modeling applied in civil and mining geotechnical engineering

Physical modelling of arctic coastlines-progress and limitations

Permafrost coastlines represent a large portion of the world's coastal area and these areas have become increasingly vulnerable in the face of climate change. The predominant mechanism of coastal erosion in these areas has been identified through several observational studies as thermomechanical erosion-a joint removal of sediment through the melting of interstitial ice (thermal energy) and abrasion from incoming waves (mechanical energy). However, further developments are needed looking how common design parameters in coastal engineering (such as wave height, period, sediment size, etc.) contribute to the process. This paper presents the current state of the art with the objective of establishing the necessary research background to develop a process-based approach to predicting permafrost erosion. To that end, an overarching framework is presented that includes all major, erosion-relevant processes, while delineating means to accomplish permafrost modelling in experimental studies. Preliminary modelling of generations zero and one models, within this novel framework, was also performed to allow for early conclusions as to how well permafrost erosion can currently be modelled without more sophisticated setups. © 2020 by the authors