2023
Permanent URI for this collectionhttps://hdl.handle.net/1807/126402
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Item Effect of plastic fine particles on shear strength at the critical state of sand-clay mixture(Canadian Science Publishing, 2024-09-10) Shan, Yi; Tan, Songming; Cui, Jie; Yuan, Jie; Li, Yadong; Huang, ZhentongA large number of engineering cases have shown that there is significant presence of the sand-clay mixtures during the engineering geological accidents. Static liquefaction or loss of bearing capacity is frequently observed due to the rise in pore water pressure from large deformation in such engineering geology. This study investigates the static behavior of sand-clay mixtures with varying fines contents and various plasticity indices of fines by means of the monotonic drained consolidation triaxial shear tests in conjunction with the binary packing model. Factors influencing the active fines content (b) of the sand-clay mixtures are examined based on the mixtures’ critical state. This study also discusses the reasons for variations in the critical friction angle (M) of the sand-clay mixtures using environmental scanning electron microscope tests. Results indicated that the changes of fines content and the plastic index of fines have a certain effect on the static behavior, active fines content (b), and the friction angle (M) of the sand-clay mixture. This study presents an equation with reliable predictive results. These findings hold considerable importance for a deeper understanding of the mechanical properties of the sand-clay mixture with and the influencing mechanisms of different plasticity index of fines.Item Reappraisal of reliability of a slope through hybridisation of regional and site-specific soil shear strength information(Canadian Science Publishing, 2024-11-11) Lo, Man Kong; Leung, Y.F.; Chan, C.L.; Sze, E.H.Y.Uncertainty in soil parameters is usually characterised by probability density functions (PDFs), with the influence on system performance represented through the probability of failure. Difficulties in selecting representative PDFs for a project often arise from scarcity of site-specific information, even with ample previous knowledge and test data of similar soil types in the region. This paper proposes an approach to rationally assimilate regional and site-specific information. A newly-compiled regional database of shear strength information for saprolitic soils in Hong Kong is presented, based on results of multi-stage consolidated-undrained triaxial tests. A hierarchical Bayesian model is fitted to the regional database, followed by a partial pooling model that produces posterior predictive distributions of shear strength parameters. The posterior estimates incorporate site-specific features into regional information, leading to profound impacts on the evaluation of failure probability for a slope case. To further illustrate the significance of data hybridisation, four semi-hypothetical scenarios are created using the same slope geometry, by assuming that distributions of shear strength parameters are completely known at the site. With the proposed approach, the estimated failure probability approaches the true value with increasing amount of site-specific data, and is more robust than adopting regional data or site data alone.Item Exploring the role of sample size on fracture growth mechanisms in intact rock: Insights from 3D DEM-DFN analysis(Canadian Science Publishing, 2024-11-11) Gao, Ge; Meguid, M.A.; Zhang, LuluThe effect of sample size on the deformation characteristic and fracture growth mechanism of intact rock subjected to unconfined compressive stress state is examined in this study via discrete element method coupled with discrete fracture network. Three-dimensional numerical models are first developed based on reported laboratory experiments and verified to realistically replicate the effect of sample size on the macro-mechanical response of the intact rock. This includes strength behavior, fracturing activities and energy budgets. Micromechanical analyses are then performed to understand the role of sample size on the deformational behavior and damage progression in intact rock. Emphasis is placed on the distributions of coordination number, evolutions of crack density and the degree of crack anisotropy with regard to invariants of crack tensors. Results reveal that deformability and strength of intact rock are vastly reliant on the sample size. Increasing sample size facilitate the accumulation of induced microcracks due to the increased probability of interparticle bond failure. It is found that the increase in sample size can result in more tensile openings with strong dilatancy. Finally, the monotonical increase in seismic b-values with the increase in sample size suggests an acceleration in the number of small-magnitude AE events.Item Kinematics of Post-Wildfire Debris Flow Initiation Mechanism: Impact of Hydrophobic Layer Spatial Variability and Particle Size(Canadian Science Publishing, 2024-10-30) Movasat, Mahta; Tomac, IngridPost-wildfire debris flow events have been more frequent due to climate change and increased wildfire adversity. Changes in non-cohesive soil hydrophobicity, burn, and vegetation removal during wildfires dramatically enhance slopes' vulnerability to rainfall-induced failure in the arid Southwest USA and similar areas worldwide. This paper contributes to a better understanding the hydrophobic sand slope failure mechanism using experiments and theory. In total, 36 indoor raining experiments use different configurations of fine, medium, and coarse hydrophobic sands subjected to various rain intensities on different slope inclinations. Specific findings contribute to understanding how the spatial variability of the post-wildfire hydrophobic layer, concerning depth and the sand grain size variations, affects the slope failure mechanisms. Clarifying slope failure mechanisms in different layouts is crucial for understanding the initiation and further spatiotemporal debris flow evolution. Results indicate that the surficial hydrophobic layer fails because erosion develops simultaneously from many small failure patches. Erosion pattern, time to failure, water, and sediment overflow temporal dynamics correlate to the dominant sand grain size. Furthermore, seepage-induced shallow infinite slope occurs when the hydrophobic sand layer develops below the surface. Finally, this study identifies the fine sand as the most vulnerable to failure in both configurations.Item Ultrasonic Interrogation of a Clayey Tailings During Sedimentation-Consolidation(Canadian Science Publishing, 2024-09-18) Peruga, Hirlatu; Khanlarian, Misagh; Cascante, Giovanni; Simms, PaulUltrasonic methods are used for non-destructive detection of changes of low-strain properties in concrete, soils, and other materials. This paper presents the use of ultrasonics to detect density and structure changes in a soft clayey tailings. Such tailings undergo sedimentation and consolidation following their deposition, which may occur simultaneously with flocculation and other fabric-altering processes, resulting in time-dependent consolidation characteristics. Here we attempt to measure structural changes in the clayey tailings using ultrasonics, which presents several challenges due to the material’s relative softness. Ultrasonics testing was attempted using a special 3D printed column with height and diameter of 540 mm and 110 mm, respectively. Specially fabricated sample holders were designed to repeatedly ensure proper connections of compression (P-wave) and shear (S-wave) wave transducers. The arrival time corresponding to the largest P-wave amplitude showed a strong correlation with density of the tailings, while a specific frequency bandwidth of the P-wave spectra indicates an increase in wave amplitude (signal energy) occurring subsequent to most of the volume change. Ultrasonic measurements appear to be a promising technique to monitor density and stiffness in soft clays, tailings, and similar soft sediments.Item A rapid segmentation and occlusion completion method for morphology analysis of packed granular particles considering uncertainty(Canadian Science Publishing, 2024-10-07) Zhang, Haoran; Yin, Zhen-Yu; Zhang, Ning; Wang, XiangOcclusions of granular particles in images significantly affect the accuracy of evaluating particle morphology for granular materials. In this study, a novel framework of SOLO-PCNet is proposed, which can automatically segment all the particles and predict the complete contours of the occluded particles in densely packed materials. Firstly, the instance segmentation model SOLOv2 is trained for the prediction of all the detectable particles. Then a self-supervised learning algorithm PCNet-M is introduced for the inference of the complete contours of the occluded particles so that the prediction of SOLOv2 can be directly input to PCNet-M for the subsequent completion. Thereafter, the particle morphology characteristics including elongation, equivalent mean size, convexity, and circularity are automatically calculated. Then, the evaluation metrics of the segmentation model and morphology characteristics are validated, and the results exhibit the strong generalization ability of the segmentation and completion tasks. Finally, the uncertainty of the completed contours with morphology properties is explored for reliable analysis. This study successfully acquires the complete contours for each particle and provides the foundation for evaluating the mechanical properties of the packed granular materials from individual particles.Item Non-isothermal Fractional Order Two-surface Viscoplastic Model for Stiff Clays(Canadian Science Publishing, 2024-09-18) Cheng, Wei; Yin, Zhen-Yu; Cui, Yujun; Peng, Mao-ZhuStiff clay exists widely in the world, but its significant time- and temperature-dependent mechanical features have not been fully modelled. In the context of fractional consistency viscoplasticity and bounding/subloading surface theory, this study proposes a novel non-isothermal fractional order two-surface viscoplastic model for stiff clays. First, with proposing a generalized plastic strain rate, the isotach viscosity is modified and extended to both over-consolidated and non-isothermal conditions that takes into consideration the effects of temperature and OCR on thermal accelerated creep. Then, two strain rate and temperature dependent yield surfaces are proposed with isotropic and progressive hardening rules to consider thermal collapse, strain rate effects, and smooth transition from elastic to viscoplastic behaviors. Next, the stress-fractional operator of the loading surface, according to the principle of the fractional consistency viscoplasticity, is introduced to describe the non-associativity of stiff clays. Finally, the predictive ability of the model is validated through simulating triaxial tests on Boom clay with various stress paths considering the temperature- and time-dependent features of stiff clays.Item Landslide life-loss risk quantification based on historical fatalities(Canadian Science Publishing, 2024-04-29) Strouth, Alexander; McDougall, Scott; Mark, Emily; LeSueur, Philip; Holm, KrisLife-loss risk estimates inform decisions that have dramatic impacts on individuals and communities in landslide hazard zones. Literature provides methods for making these estimates through multiplication of site-specific parameters. However, there is no method in the literature for calibrating those estimates, and regional context is needed to make efficient, fair, and affordable decisions. Therefore, we developed methods to quantify risk to individuals and groups based on regional historical fatality and hazard zone population data. The methods can be used to evaluate the accuracy of large sets of site-specific risk estimates, to assign quantitative risk values to buildings and hazard zones at a regional scale, to develop a long-term regional budget for landslide risk management, or to inform selection of a risk tolerance threshold that can inform where limited resources are invested in landslide mitigation. An example of the methods is provided for a case study of residential landslide risk in British Columbia, Canada. It estimates that there are between a few hundred and a few thousand people living with individual risk exceeding 100 micromorts (1 in 10,000) per year, and between 70 and 370 landslide hazard zones with annual probable life loss greater than 1E-3 (1 death in 1,000 years), based on a historical fatality rate of 0.4 to 1.4 deaths per year across the entire province.Item Effect of thermal cycles on sand-concrete interface under constant shear stress(Canadian Science Publishing, 2024-07-19) Rafai, Mouadh; Tang, Anh Minh; Badinier, Thibault; De Sauvage, Jean; Salciarini, DianaEnergy geostructures provide a profitable solution for structural support as well as the heating and cooling of buildings. However, their activation can produce in structure and its surrounding soil thermally-induced stresses and strains with a crucial role played by the soil-structure interface which is the thin layer that transmits the thermal and mechanical loads. In the present work, the thermo-mechanical behaviour of the soil–structure interface is investigated using a temperature-controlled direct shear box. Tests were conducted on loose and dense sands in contact with a concrete plate representing the structure's surface. After applying the normal stress (25, 50, or 100 kPa), a shear stress was increased up to 45% of the shear strength. This stress state was then maintained while 20 cycles of temperature varying between 13 °C and 34 °C at the soil-concrete interface were applied. The obtained experimental results reveal that temperature cycles lead to irreversible cumulative displacements in both normal and shear directions. These displacements were found to be more significant in loose sand compared to dense sand. Additionally, under higher stress levels, greater displacements were observed for both soil densities.Item Effect of spacing of grid PHD on performance of combined PHD-PVD vacuum preloading method for treatment of clayey slurry(Canadian Science Publishing, 2024-09-24) Pan, Yu; Song, Ding-Bao; Yin, Zhen-Yu; Yin, Jian-HuaA novel ground improvement method that combines grid prefabricated horizontal drains (PHDs) with prefabricated vertical drain (PVDs) assisted by vacuum preloading is proposed for the beneficial reuse of dredged clayey slurry for reclamation purpose. To assess the feasibility of this innovative method, physical model tests are designed and conducted using high-water content Hong Kong marine deposits (HKMD) as the clayey slurry material. Furthermore, the impact of the spacing configuration of the grid PHD on the effectiveness of the proposed method is investigated through a series of model tests. A test without the installation of PVD was set, and in this case, two phases of vacuum preloading are applied sequentially through the PHD layer installed in stage. The other three tests involve three phases, with the addition of a vacuum preloading stage through PVD and variations in arrangement pattern of grid PHD layer. Results show that this proposed approach yields a final average undrained shear strength of soil of approximately 30 kPa, meanwhile reducing the average water content to around 50%. Furthermore, it is observed that decreasing the vertical spacing of grid PHDs results in growing final settlement. Reducing the horizontal spacing has less impact on the final settlement.Item Study on in-situ measurement and analysis method of rock pores based on borehole camera technology(Canadian Science Publishing, 2024-08-23) Wang, Chao; Han, Zengqiang; Wang, Yiteng; Wang, JinchaoIn-situ measurement and analysis of pores are helpful to understand the properties of rocks. However, continuous quantitative analysis of pores in whole borehole is still difficult. Borehole camera technology can capture the borehole wall image of the whole well section by going deep into the borehole, which provides technical conditions for the measurement and analysis of pores. In this paper, a continuous measurement method of rock pores based on borehole camera technology is introduced. According to the characteristics of the optical image of borehole wall, a method of pore recognition and analysis is proposed. Specifically, the influence of redundant information on pore recognition is eliminated, and then the pores are accurately recognized by binarization and morphological operation. Based on the results of pore recognition and the coordinate information provided by borehole wall image, the calculation methods of surface porosity and line porosity are proposed, and the statistical analysis of pore distribution is realized according to the calculation results. In addition, the morphological characteristics of pores are also discussed. This method realizes the accurate recognition and quantitative calculation of pore structure based on borehole wall image, and provides a new method for continuous analysis of pore structure in the whole well.Item Contrast Experiments on Breaching Characteristics of Landslide Dams and Debris-flow Dams(Canadian Science Publishing, 2024-08-19) Chen, Huayong; Li, Xiao; Chen, Xiaoqing; Ruan, Hechun; Wang, TaoAbstract: The difference in soil properties determines the different breaching characteristics exhibited by landslide dams (LD) and debris-flow dams (DFD). In this study, two types of soil were prepared by controlling the initial water content and the mixing time of the soil to construct the LD and DFD. Based on observations of breach in dams with six different grain size distributions: 1) the erosion resistance within the soil leads to a slower failure speed for DFD under the same grain size distribution and particle density. However, both types of dams exhibit a non-uniform downcutting process in the longitudinal direction, induced by uneven velocities. 2) Laterally, DFD are characterized by the creep slide of the breach bank, distinct from the intermittent slide observed in LD. 3) For the range of conditions tested, the peak discharge of LD significantly exceeds that of DFD. Additionally, the flood curve of LD exhibits a bimodal characteristic, attributed to the slide of the bank slope and the non-uniform distribution of particles within the dam. Finally, a prediction formula for the downcutting coefficient of the breach was established and validated by past studies. This study provides a basis for predicting outburst floods of LD and DFD.Item Landslide life-loss risk quantification based on historical fatalities(Canadian Science Publishing, 2024-04-29) Strouth, Alexander; McDougall, Scott; Mark, Emily; LeSueur, Philip; Holm, KrisLife-loss risk estimates inform decisions that have dramatic impacts on individuals and communities in landslide hazard zones. Literature provides methods for making these estimates through multiplication of site-specific parameters. However, there is no method in the literature for calibrating those estimates, and regional context is needed to make efficient, fair, and affordable decisions. Therefore, we developed methods to quantify risk to individuals and groups based on regional historical fatality and hazard zone population data. The methods can be used to evaluate the accuracy of large sets of site-specific risk estimates, to assign quantitative risk values to buildings and hazard zones at a regional scale, to develop a long-term regional budget for landslide risk management, or to inform selection of a risk tolerance threshold that can inform where limited resources are invested in landslide mitigation. An example of the methods is provided for a case study of residential landslide risk in British Columbia, Canada. It estimates that there are between a few hundred and a few thousand people living with individual risk exceeding 100 micromorts (1 in 10,000) per year, and between 70 and 370 landslide hazard zones with annual probable life loss greater than 1E-3 (1 death in 1,000 years), based on a historical fatality rate of 0.4 to 1.4 deaths per year across the entire province.Item Cyclic response of pre-failed and re-installed single-helix piles in sand(Canadian Science Publishing, 2024-09-02) Schiavon, José Antonio; Neme Gamarra, Mariano; Tsuha, Cristina Hollanda Cavalcanti; Thorel, LucHelical piles can be re-screwed at greater depths after failure and put back into service again as long as their integrity is preserved. However, reports on the lifetime performance after re-installation are completely missing in the literature. This work compares the tensile cyclic response of single helix piles in dry and saturated sand after experiencing failure due to monotonic uplift and after re-installation, using centrifuge model testing. Tensile cyclic tests were conducted on three model piles with different helix-to-shaft diameter ratios, under two different conditions: (1) cyclic loading after monotonic pile failure, and (2) cyclic loading on a pile that has been re-installed deeper into the soil after experiencing a monotonic failure. The experiments revealed that the preceding monotonic failure causes significant influence on the post-failure cyclic performance, in which few tens of cycles are enough to lead to a critical accumulated displacement. The cyclic tests on the re-installed helical pile at a depth of 2D (D = helix diameter) below the initial helix depth showed that the cyclic performance can be partially to fully recovered depending on the loading amplitude.Item Quantifying Uncertainty of In-Situ Horizontal Stress and Geotechnical Parameters Using a Bayesian Inference Approach for Pressuremeter Tests(Canadian Science Publishing, 2024-07-29) Zheng, Dongming; Zhang, Bo; Chalaturnyk, RickUnderstanding in-situ horizontal stress is crucial for various applications in deep ground, including oil drilling, hydraulic fracturing, and nuclear waste repository design. The pressuremeter has gained increasing attention as a tool for characterizing in-situ stress fields and engineering properties of soil and rock. However, quantifying the uncertainties associated with in-situ horizontal stress and geotechnical parameters remains a challenge task. In this study, we propose a Bayesian inference approach formulated by an objective function that calculates the logarithm of the probability density function using observed and predicted data to address this problem. This approach integrates the analytical solution and the finite difference numerical model into the Bayesian model. The Bayesian inference approach consists of two phases: (1) using the maximum a posteriori method for point estimation, and (2) employing Markov Chain Monte Carlo sampling to obtain parameter statistics from posterior distributions. Compared to frequentist statistical methods, the Bayesian inference approach provides a natural way to incorporate prior knowledge, update our beliefs by conditioning on the observed data, and facilitate exploratory analysis of Bayesian models with various diagnostic tools. This provides a robust and adaptable framework for addressing uncertainty in the study of in-situ stress fields and geotechnical parameters using the pressuremeter.Item Soil-Pile Interaction of Laterally Loaded Fixed-Head Piles and Pile Groups in Unsaturated Sand(Canadian Science Publishing, 2024-08-23) Komolafe, Oladayo; Ghayoomi, MajidThis study investigates the lateral behavior of piles in unsaturated cohesionless sandy soil using centrifuge modelling. The lateral loading was conducted on a single fixed-head pile and 2×2 fixed-head pile groups with 3D and 5D spacings. The results showed that the single fixed-head pile demonstrated greater magnitudes of lateral resistance response compared to the leading and trailing piles of the pile groups. Moreover, the piles experienced greater lateral loads when the water table was about a quarter of the embedded pile depth in the soil layer for the single fixed-head pile and leading piles in the group. The group efficiencies of the pile increased as the water table reduced up to half of the embedded pile length for the 3D pile spacing. However, this effect was negligible for 5D pile spacing. Considering the mixed unsaturated-saturated ground condition can lead to a more resilient foundation design under climate-induced and seasonal fluctuations of water table level and also pave the path for the inclusion of future climatic scenarios.Item Strength and Dilatancy of Crushable Soils With Different Gradings(Canadian Science Publishing, 2024-07-19) Dong, Zong-Lei; Tong, Chenxi; Zhang, Sheng; Cheng, Yi Pik; Sheng, DaichaoPeak strength and dilatancy of granular materials generally decrease with increasing mean effective stress, and such a decrease will be enhanced due to the occurrence of particle breakage. This paper presents a simple empirical approach to modify Bolton’s original strength and dilatancy equation for crushable soils with different crushability. The proposed approach is based on data of a series of drained triaxial tests on carbonate soils with five different particle size distributions (PSDs) and three initial relative densities. It is also validated against other published experimental data on various crushable soils, including carbonate soils, limestones, coarse aggregates, and silica sands. The modified relation retains a similar form to Bolton’s equation with only one additional parameter introduced. As a result, the crushing strength-related parameter in the original relation is modified to incorporate the impacts of particle shape, gradings, and mineralogy on particle breakage. This modified parameter tends to increase as soil crushability decreases, which keeps a similar physical meaning to Bolton’s crushing strength-related parameter, and is suitable for a wider range of crushable soils with different gradings. The proposed strength and dilatancy equation for crushable soils yields to Bolton’s equation for strong soil particles where particle breakage is negligible.Item Assessment of piles’ resistance driven sequentially in fine-grained soils using pile load tests(Canadian Science Publishing, 2024-07-24) Bilgin, Ömer; Alzahrani, Saeed; Narsavage, Peter; Nusairat, Jamal; Dettloff, Alexander; Merklin, ChristopherThis paper presents a field pile load test program conducted on four 0.36 m closed-end steel pipe (CEP) piles with lengths ranging between 11 to 13 m installed in fine-grained soils. Subsurface investigations with standard penetration tests (SPT) and cone penetration tests (CPT) with pore pressure measurements were performed at the site. Three pushed-in piezometers at incremental offsets from the piles were also installed to monitor pore water pressure changes during and after the installation of piles. Several dynamic load tests (DLT) were performed at different times to observe the change in pile resistance. A static load test (SLT) was also performed on one of the piles. Some load test results showed an unexpected decrease in the resistances of some piles with time. The study showed that construction activities, e.g. installation of other piles, disturbs the soil and groundwater conditions which can significantly affect the pile resistance measured during load tests. This investigation revealed that pile driving and restrikes should be scheduled such that the effect of construction activities on load tests results will be avoided or minimized.Item Development of a Scaling Function to Estimate Unsaturated Mechanical Soil Behavior from a Soil-Water Characteristic Curve(Canadian Science Publishing, 2024-07-07) Acheampong, Lucas; Bryson, L. SebastianThe small-strain shear modulus and shear strength are mechanical parameters crucial in the design of geotechnical structures and in the analyses of soil-structure interactions. This paper proposes a new approach for estimating these mechanical parameters. The proposed approach is predicated on the proportional inverse relationship of mechanical soil properties to the soil-water characteristic curve (SWCC). The proposed equations supporting the approach incorporate a scaling function, alongside the initial saturated mechanical property. The performance of the proposed equations was demonstrated across a variety of soil textures, utilizing literature soils subjected to varying net normal stresses, and across a wide range of matric suction up to the residual suction zone. It was established that a correlation existed between the scaling function and air-entry value for both small-strain shear modulus and shear strength of unsaturated soils. In addition, the behavior of the scaling function under potential hysteretic effects was demonstrated and recommendations were provided on how to apply the proposed model under such conditions. Finally, the modified equations including the correlation for the scaling function were used to predict additional literature soils.Item Estimating Thaw Settlement of Coarse-Grained Permafrost Sediments(Canadian Science Publishing, 2024-06-10) Mohammadi, Seyedeh Zakieh; Hayley, Jocelyn L.Thaw settlement, a frequently reported issue for infrastructure built on permafrost, contributes to high maintenance costs, reduced life cycles, and compromised serviceability of infrastructure. This paper presents a new method to estimate the thaw settlement in coarse-grained permafrost sediments, crucial for northern infrastructure planning. Utilizing available test results from the Canadian Arctic, an overview of the existing data for coarse-grained permafrost sediments is presented. The proposed method uses input parameters derived from particle size distribution to estimate the minimum void ratio of thawed sediments. The minimum void ratio is then used to infer the thawed void ratio, enabling the calculation of thaw strain. The effectiveness of the approach is confirmed by validating predicted thaw strains against measured values for over 60 permafrost samples. A comparison with existing empirical methods shows improved accuracy and reduced bias, further supporting the applicability of the approach. Additionally, an average thawed void ratio assigned to seven groups of granular soils proved valuable for predicting thaw strain when only visual descriptions of sediments are available. Tailored for granular materials and utilizing easily obtainable index properties, this approach provides a reliable and cost-effective method for predicting thaw settlement, benefiting engineers and planners in infrastructure development.