2024 Onward

Permanent URI for this collectionhttps://hdl.handle.net/1807/137418

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Diaphragm wall lateral movement in deep excavations in Bangkok clays: impacts and influencing factors
(Canadian Science Publishing, 2024-05-29) Boonyarak, Thayanan; Aung, A. Y.; Kamchoom, Viroon; Aye, Zaw Zaw
Deep excavation in Bangkok clay layers involving diaphragm walls can cause ground movement, potentially affecting nearby structures. Understanding the magnitude and profile of this movement is crucial for assessing its impact on adjacent buildings. This study examines factors influencing the lateral displacement of rigid diaphragm walls in Bangkok's deep excavations, including construction methods, excavation duration, depth ratios, soft clay depth, and system stiffness. The research data were collected from 230 dataset of lateral movement in diaphragm walls with a thickness ranging from 0.60m to 1.50m. These walls had toe depths between 14m and 65m, across various excavation depths (He) from 6m to 35m. Maximum lateral wall displacements ranged from 0.10%He to 0.27%He for the top-down method, and from 0.20%He to 0.50%He for the bottom-up method. If the system stiffness is sufficient, variations in wall thickness and construction method have minimal impact on wall deflection. However, with the bottom-up method and 1.0m thick walls, long excavation times can lead to displacements up to 0.60%He. This is mainly due to consolidation and creep in the clay beneath the area where the base slab construction is delayed.
3D large deformation modeling of the 2020 Gjerdrum quick clay landslide
(Canadian Science Publishing, 2024-05-29) Tran, Quoc Anh; Rogstad, Agnete; Depina, Ivan; Fernández, Fabricio; Alene, Gebray Habtu; Grimstad, Gustav; Nordal, Steinar
A quick clay slide in Gjerdrum, Norway, occurred at 4 a.m. on 30th December 2020, killing ten people and destroying houses, roads, and other infrastructures. Approximately 1.35 million cubic meters of clay were released, a large volume liquefied, and debris was transported almost two kilometers downstream. An investigation following the slide determined that the slide was initialized in a 30-meter-high slope after 2-to-2,5-meter vertical erosion in a small creek running along the toe of the slope. After the initiation, the slide developed retrogressively in the order of 500 meters backward and sideways over a period of about 2 minutes. A conventional geotechnical slope stability analysis explains the initial slide. However, more advanced numerical tools are needed to simulate the retrogressive mechanism and the debris flow. The aim of the paper is to demonstrate a 3D Material Point Method model to capture some of the mechanisms involved from initiation until the debris comes to rest and how this method can be used to reproduce and study the processes involved in large deformation landslides.
An improved small-scale test setup for assessing backward erosion piping
(Canadian Science Publishing, 2024-08-06) Ramezanifouladi, Sina; Côté, Jean
Backward erosion piping is one of the erosion mechanisms that lead to embankment dam incidents, whereby foundation granular materials are transported to the downstream toe leaving a shallow pipe in place. Most previous studies have focused on secondary erosion as the responsible process for the pipe progression. On the other hand, a few experimental investigations have considered primary erosion by restricting the pipe pathway within a confined channel for easier monitoring of local gradients. This paper presents a modified small-scale setup with the hole-type exit configuration to capture local hydraulic conditions associated with the progression of the pipe in a realistic and unconstrained pathway. Horizontal compaction and a more accurate measurement and acquisition system are other improvements added to this setup. The test outcomes of the two fine sands have revealed that the scale factor of Sellmeijer’s model can be used to predict the critical global hydraulic gradient for the specific geometry of the small-scale setup with the hole-type exit. Moreover, the progression of the pipe remains unaffected by loading history. Results also confirm the previous findings regarding the mutual influence of local gradient and pipe tip progression.
Long-term Performance of Textured HDPE Geomembranes in Municipal Solid Waste Landfills
(Canadian Science Publishing, 2024-03-12) Rowe, R. Kerry; Ali, M. Mahmoud; Morsy, Mohamed S.
The effect of texturing (co-extrusion using a blowing agent) on the long-term performance of geomembranes immersed in synthetic municipal solid waste (MSW) leachate is examined over an approximately 8-year period. Antioxidant depletion of the textured part is shown to be much faster than that of the smooth edge. Likewise, the degradation in the tensile break properties at 85°C is faster for the textured part than for the smooth edge portion and smooth equivalent. The updated estimates for antioxidant depletion time based on data at four different temperatures (40, 55, 75, and 85°C) over 98 months of data collection are compared with predictions based on 34 months of data and the implications are discussed. Nominal failure was reached at 75°C, and this combined with data at 85°C allows prediction of the time between depletion of Std-OIT and nominal failure at lower temperatures. The effect of salt concentration in incubation fluid on the time to degradation is examined. Finally, the paper comments on the uses of textured versus smooth geomembrane.
Measurement of true tensile strength from Brazilian tensile strength laboratory tests
(Canadian Science Publishing, 2024-04-30) Packulak, Timothy Robert Micheal; Day, Jennifer J.; McDonald, Mark R; Jacksteit, Anya C.; Diederichs, Mark S
Brazilian tensile strength (BTS) testing in standard practice is a practical method to approximate tensile strength for rock core using the conversion of axial compressive vertical and diametral loading to horizontal tensile stress in the centre of the core disk. The method, however, routinely inflates tensile strength, using peak tensile stress calculated from the BTS, versus true tensile stress (TTS) from direct tensile strength (DTS) tests. This study presents a novel technique to measure TTS directly from the BTS test via the onset of nonlinearity in horizontal strain response. TTS is equivalent to the peak strength of a DTS test. While not yet standardized, the modification to achieve TTS measurements is to instrument the BTS specimen with a horizontal strain gauge on each flat side. Over 100 BTS specimens of varying lithologies were instrumented, tested, and analyzed to measure their TTS and compare to peak BTS. Results demonstrate the average measured TTS is 0.81BTS, 0.75BTS, 0.85BTS for granitoid, carbonate, and metamorphic rocks, respectively. This concurs with previous studies, validating the proposed novel TTS measurement method. We recommend measurement of TTS be adopted into standard practice for BTS laboratory testing to improve accuracy of tensile strength data in rock engineering design.
Quantification and practical solution for bottom boundary condition effects on long-term permafrost models
(Canadian Science Publishing, 2024-08-03) Ross, Cameron; Beddoe, Ryley; Siemens, Gregory A.
Permafrost models are commonly used to simulate future ground temperatures under the influence of climate change and/or proposed infrastructure. Most, if not all model input decisions are made based on limited subsurface knowledge. Shallow model domains offer more efficient run-times especially with gridded 1D schemes as well as 2D and 3D simulations over longer time periods. Recent focus has been on the development of surface boundaries; however, less attention is given to the bottom boundary condition. In this paper, first we quantify the effect of model domain depth and bottom boundary condition type on long-term ground temperature evolution in transient model simulations. Model domains less than 100 m deep with the bottom boundary condition set to both geothermal gradient and a perfectly insulated base (q=0) show significant overwarming and overestimate thawing in cold permafrost. Guidance is provided to interrogate model results to avoid bottom boundary condition effects. For cases where further models are needed, a practical solution to this challenge is developed to obtain model depth-independent results. This solution allows for reduced computational requirements while maintaining consistent results for century-scale transient simulations considering climate change effects on thawing permafrost.
Effective thermal conductivity of granular soils: a review of influencing factors and prediction models towards an investigation framework through multiscale characters
(Canadian Science Publishing, 2024-03-20) Chen, Tairu; Fei, Wenbin; Narsilio, Guillermo
The effective thermal conductivity of soil is important to geo-engineering applications, and it is controlled by factors across different length scales. Through a comprehensive review of these factors, we found that while other more traditional factors have been well studied, there is still a lack of characterisation of soil microscale and mesoscale structures and their influence on effective thermal conductivity. In addition, after reviewing the models available in the literature for soil effective thermal conductivity prediction, it was found that compared with empirical and theoretical models, machine learning models can account for the influence of multi-scale factors, however, research into them is scarce. To overcome the limitations of previous research, we proposed a framework that can investigate the factors influencing soil effective thermal conductivity at multiple scale. It includes the impact of soil structural factors at micro to mesoscale, and this impact is integrated with the influence from other factors for accurate thermal conductivity prediction.
Physical model case study: treatment effect of soft ground by vacuum preloading combined with liquid bag pressurization method
(Canadian Science Publishing, 2024-05-30) Feng, Shuangxi; Xing, Daorun; Lei, Huayang; Jia, Rui; Li, Jiankai; Codjia, Coffi Edgard; Bao, Yilin
Vacuum preloading and composite ground reinforcement are commonly used methods for reinforcing soft soil, but there is a lack of integrated design method for vacuum preloading combined with composite ground. This case study introduces an innovative approach that combines vacuum preloading with liquid bag pressurization to achieve the integrated design of consolidation drainage method and composite ground reinforcement, which is different from the reported air bag pressurization. To illustrate the effectiveness of this method. Model tests were carried out to analyze the variation of water discharge, pore water pressure, ground settlement, and average consolidation degree in the process of vacuum consolidation. The study investigated the water content, undrained shear strength and ground bearing capacity of composite ground after ground treatment. A correlation between average undrained shear strength and characteristic value of ground-bearing capacity was established to evaluate and predict the treatment effect of composite ground. Research shows that compared with traditional vacuum preloading, the undrained shear strength can be increased by 13.78%~65.08%, and the characteristic value of bearing capacity for the composite ground can be enlarged by 2.3-4 times. These results indicate that the vacuum preloading combined with liquid bag pressurization can significantly improve reinforcement effect on soft ground.
Reflection coefficient of a natural sodium bentonite in aqueous mixed electrolyte solutions: positive and negative anomalous osmosis
(Canadian Science Publishing, 2024-07-24) Guarena, Nicolò; Dominijanni, Andrea; Manassero, Mario
A natural sodium bentonite was tested in the laboratory to measure its reflection coefficient, ω, in equilibrium with mixed aqueous solutions of sodium chloride (NaCl) and potassium chloride (KCl), with the aim of assessing the relative contribution of chemico-osmosis and diffusion induced electro-osmosis to the non-hydraulic component of the liquid flux in the presence of two cationic species, which diffuse at different rates in the pore solution. The former chemico-osmotic contribution is only related to the ionic partition effect in the bentonite pores, and causes ω to vary in the 0 to 1 range, whereas the latter electro-osmotic contribution is controlled by the diffusion potential, which spontaneously builds up across the bentonite layer in response to the different aqueous-phase diffusion coefficients of the ionic species. The theoretical interpretation of the obtained test results demonstrated that chemico-osmosis was the major contribution to ω when the testing solutions only comprised KCl. However, significant deviations in the values of ω from those expected for pure chemico-osmosis were observed for mixtures of NaCl and KCl, with both negative (ω = - 1.234) and positive (ω = 1.040) anomalous values of the reflection coefficient, resulting from the enhanced influence of diffusion induced electro-osmosis.
Modelling the impact of deep fractures on groundwater flow and slope stability in post-glacial marine clays (Quebec, Canada)
(Canadian Science Publishing, 2024-02-26) Ospina Llano, Julián Andrés; Young, Nathan Lee; Lemieux, Jean-Michel; Molson, John; Locat, A.; Locat, Pascal
It is usually assumed that post-glacial marine clay deposits, such as those found in Quebec, are generally intact below a shallow fractured crust (3 to 5-m depth). However, recent work has shown the presence of hydraulically-active fractures to depths of down to 16-m. In light of this finding, the potential impacts of these fractures on groundwater flow dynamics and slope stability are explored by comparing field data with the results of transient and steady-state groundwater models with and without fractures. Two slope geometries that exhibit contrasting groundwater flow directions and different fracture scenarios were considered. The results of the hydrogeological modelling were then imported into a slope stability model to determine how the hydraulic effects of these fractures impact slope stability. Results show that fractures increase hydraulic head when they act as preferential pathways for infiltration, but can also reduce hydraulic head by acting as pathways for water to more quickly exit the formation within the slope face. Therefore, from a hydrogeological perspective, fractures could improve or reduce slope stability depending on the groundwater flow system. As this study only addressed the hydrogeological impact of the fractures, future work should focus on the coupled hydromechanical impacts of these features.
Direction-dependent failure envelopes of sand-structure interfaces with snakeskin-inspired surfaces
(Canadian Science Publishing, 2024-03-04) O'Hara, Kyle Blake; Martinez, Alejandro
Snakeskin-inspired surfaces generate direction-dependent interface strengths, with shearing in the cranial direction generating greater strength than in the caudal one. This directionality is enabled by the transfer of load in friction and passive resistances. It is unclear if failure of these interfaces can be captured by models used for purely frictional interfaces. Interface shear tests complemented with Particle Image Velocimetry (PIV) analyses were performed on snakeskin-inspired surfaces with different asperity geometries and on reference rough and smooth surfaces. The results of experiments performed at different initial effective stresses under Constant Normal Stiffness (CNS) boundary conditions show significant dilation-induced increases in effective stress. These increases were greater during cranial than caudal shearing, producing greater cranial strengths. These surfaces yielded non-linear failure envelopes, with greater shear to effective stress ratios at smaller effective stresses, while the rough and smooth surfaces mobilized linear failure envelopes. The PIV analyses indicate that the snakeskin-inspired surfaces induce localized strains in the vicinity of the asperities, leading to wavy failure planes. The average shear strains are correlated with the mobilized shear strengths, with increases in effective stress leading to decreases in both strains and stress ratio.
Observed soil arching-induced ground deformation and stress redistribution behind braced excavation
(Canadian Science Publishing, 2024-02-05) Liu, Muchun; Meng, Fanyan; Liu, Zhen; Chen, Renpeng
This paper presents observed arching-induced ground deformation and stress redistribution behind braced excavation using the top-down construction method. The soil properties around the excavation were determined by laboratory and field tests. The ground deformation, soil displacement vector, strain path, principal strain, maximum shear strain, lateral earth pressure, pore water pressure, and effective stress path are presented based on the measured data. The majority of soil behind the wall is under volumetric expansion, indicating consolidation, creep behavior, or a combination of both. Besides, two periods of increases in pore pressure are observed, due to stress transfer from the lower to the upper parts (i.e. soil arching effect). The deep inward movement of the wall and the nearby soil accounts for the distribution of lateral earth pressure acting on the wall. The soil located behind the area of maximum wall deformation and adjacent to the wall, as well as the soil below the excavation base intersected by the shear plane, is in an active stress state. The lateral earth pressure at 5 m from the left excavation wall showed minimal changes, due to the combined effects of soil arching from lateral excavation and shield tunneling.
Role of Substrate Roughness in Soil Desiccation Cracking
(Canadian Science Publishing, 2024-02-19) Yang, Yuhan; Zhang, Chao; Gou, Lingyun; Dong, Yi; Chen, Renpeng
Soil desiccation crack is ubiquitous in nature, yet the physics of its initiation and propagation remain under debate, as it involves complex interactions across multiple fields of mechanics, hydraulics, and thermals. Here, an experimental attempt is made to uncover the role of substrate roughness on the soil desiccation process. The substrate roughness is deliberately fabricated by 3D printing, whereas the thickness of sample and environmental humidity are controlled to eliminate the effect of large hydraulic gradient. Four types of soils with varying expansibilities were desiccated on substrates with varying roughness. It reveals that: (1) soil desiccation crack evolution can be conceived as a competing process between the shear failure of soil-substrate interface, i.e., slippage of interface, and the tensile failure of soil, i.e., crack initiation, in minimizing the total energy of drying soil; (2) substrate roughness alters the failure mode and shear strength of soil-substrate interface and its sensitivity to moisture, thereby it regulates the pattern of how soil crack propagates upon drying; (3) soil expansibility is recognized as a key factor governing the crack-initiation point in addition to the widely recognized air-entry, and flaws in soil are the sources for the 120° crack angle and bimodal crack angle distribution.
Analytical solution to non-isothermal pore-pressure evolution in hydrating minefill
(Canadian Science Publishing, 2024-03-02) Lu, G.D.; Selvadurai, Patrick; Meguid, M.A.
Anomalous rises in minefill pressure during deposition shutdown have been increasingly reported in recent field investigations, raising growing concerns over contemporary underground tailings disposal. While constrained backfill expansion during hydration-heat release has been invoked to rationalize such perplexing observations, a benchmark for understanding the complex minefill response to thermal loading is still lacking. A novel analytical procedure is thus proposed in this study to characterize the non-isothermal evolution of pore pressure in cemented backfill hydrating in undrained adiabatic settings. By constructing a suitable variable system and selecting a proper auxiliary parameter for calculation, the proposed strategy based on canonical thermo-poroelasticity could enable straightforward implementation and has shown excellent compliance with computational and experimental results. The analytical results suggest that because higher temperature could stimulate cement hydration while enhancing simultaneously fluid expansivity, the pore pressure would decline initially with the rising curing temperature and then revert to increase after a critical threshold. Moreover, our investigation has shown that increasing binder usage is not always conducive to pore-pressure dissipation, as the payoff can be also hinged strongly upon the initial thermal condition. These findings could better elucidate the intriguing control of coupled multiphysics processes on backfill behaviour, and can also serve benchmarking purposes for sophisticated computational procedures.
Real-time Fusion of Multi-Source Monitoring Data with Geotechnical Numerical Model Results using Data-driven and Physics-informed Sparse Dictionary Learning
(Canadian Science Publishing, 2024-02-13) Tian, Huaming; Wang, Yu; Phoon, Kok-Kwang
Development of digital twins is emerging rapidly in geotechnical engineering, and it often requires real-time updating of numerical models (e.g., finite element model, FEM) using multiple sources of monitoring data (e.g., settlement and pore water pressure data). Conventional model updating, or calibration, often involves repeated executions of the numerical model, using monitoring data from a specific source or at limited spatial locations only. This leads to a critical research need of real-time model updating and predictions using a numerical model improved continuously by multi-source monitoring data. To address this need, a physics-informed machine learning method called multi-source sparse dictionary learning (MS-SDL) is proposed in this study. Originated from signal decomposition and compression, MS-SDL utilizes results from a suite of numerical models as basis functions, or dictionary atoms, and employs multi-source monitoring data to select a limited number of important atoms for predicting multiple, spatiotemporally varying geotechnical responses. As monitoring data are collected sequentially, no repeated evaluations of computational numerical models are needed, and an automatic and real-time model calibration is achieved for continuously improving model predictions. A real project in Hong Kong is presented to illustrate the proposed approach. Effect of monitoring data from different sources is also investigated.
Temporal effective stress response of soil elements below the base of an excavation in sensitive clay
(Canadian Science Publishing, 2024-02-15) Tornborg, Johannes; Karlsson, Mats; Dijkstra, Jelke
Investigations into the temporally evolving stress state below the base of excavations and underground structures are very scarce, in contrast to studies of horizontal earth pressures during the construction stage. Therefore in this work, the measured temporal response in terms of vertical and horizontal effective stresses and displacements below a tunnel slab at the base of an excavation located in a deep sensitive clay deposit is reported. In addition to the measured unloading response over time, the completeness of the site description and complementary measurements enables future benchmarking of numerical models at boundary and element level. Instrument clusters of earth pressure cells and piezometers were installed at three locations in one cross-section. The monitoring data allows the interpretation of effective stress paths and stress ratios, K=σ'h/σ'v, at soil element level covering the construction and the serviceability stages. The in situ stress ratios enable a unique comparison to prior laboratory studies of K during unloading. The data presented herein on the evolution of K corroborate, although approximately, previous studies at laboratory scale. Furthermore, at system level, the monitoring data reveal the intricate interplay between deformations resulting from excavation and pile driving.
A thermo-mechanical model for saturated and unsaturated soil-structure interfaces
(Canadian Science Publishing, 2024-02-19) Cui, Sheqiang; Zhou, Chao
Shear behaviour of soil-structure interfaces greatly affects the performance of geotechnical structures. The soil-structure interfaces in geothermal structures (e.g., energy pile and energy wall) are often subjected to varying temperature and suction conditions. However, there is no constitutive model to simulate the coupled effects of suction and temperature on the shear behaviour of soil-structure interfaces. In this study, a thermo-mechanical model was newly developed based on the bounding surface plasticity framework to predict the thermo-mechanical behaviour of saturated and unsaturated interfaces. A power function was used to calculate the degree of saturation at the interface and improve the evaluation of suction effects on interface shear strength. A linear relationship between temperature and interface critical state friction angle was proposed to incorporate thermal effects. New equations were also proposed to describe the critical state lines (CSLs) in the void ratio versus stress plane (e-ln⁡σ_n^* ) and to model the shearing-induced deformation at various temperatures and suctions. The experimental data from different interfaces in the literature were used to evaluate the model capability. Comparisons between measured and computed results suggest that this model can well capture the coupled effects of temperature, suction and net normal stress on the shear behaviour of interfaces.
Numerical modelling of pile jacking in highly sensitive clays
(Canadian Science Publishing, 2024-01-06) Karmaker, Ripon; Hawlader, Bipul C.; Perret, Didier; Dey, Rajib
This paper presents large deformation finite element (FE) modelling of penetration of solid cylindrical piles into highly sensitive soft clay. The simulations are performed using a Coupled Eulerian-Lagrangian (CEL) FE modeling technique. The pile is penetrated at a constant rate, and the analyses are performed for undrained conditions to simulate the response during penetration. The soil model considers the effects of strain softening and strain rate on the undrained shear strength. The FE calculated results are compared with available analytical and numerical solutions for idealized soil profiles. Simulations are also performed for two instrumented piles previously installed into highly sensitive clay at Saint-Alban in Québec, Canada. The installation-induced changes in stresses, degradation of undrained shear strength, and tip resistance obtained from FE analyses are consistent with the field test results. Large plastic shear strains develop near the pile, which can significantly remould the soil near the pile shaft. A parametric study shows that a quicker post-peak degradation of undrained shear strength of highly sensitive clay creates a smaller zone of high plastic shear strain near the pile, while the plastic zone is wider for low- to non-sensitive clays.
A viscoplastic constitutive model for plastic silts and clays for static slope stability applications
(Canadian Science Publishing, 2024-01-20) Oathes, Tyler J; Boulanger, Ross W.; Ziotopoulou, Katerina
A viscoplastic model for representing plastic silts and clays in geotechnical static slope stability applications is presented. The PM4SiltR model builds on the stress ratio-controlled, critical state-based, bounding surface plasticity model PM4Silt and is coded as a dynamic link library for use in the finite difference program FLAC 8.1. PM4SiltR incorporates strain rate-dependent shear strength, stress relaxation, and creep using a consistency approach combined with an internal strain rate and auto-decay process. The model does not include a cap, and as such cannot simulate strain rate-dependent consolidation under increasing overburden stress. Six parameters control the viscous response for PM4SiltR while the parameters controlling the nonviscous components of the response are the same as for PM4Silt. Single element simulations are presented to illustrate the influence of viscoplasticity on the constitutive response in direct simple shear loading and undrained creep. Single element responses are shown to be consistent with observed experimental results. Simulations of a hypothetical tailings dam constructed using the upstream method are performed to illustrate use of PM4SiltR at field scale. Results of field scale simulations show PM4SiltR can model undrained creep and progressive failure leading to delayed slope instability after relatively minor changes in loading conditions at field scale.
Estimating relative density from shallow depth CPTs in normally consolidated and overconsolidated siliceous sand
(Canadian Science Publishing, 2024-07-04) Jensen, Mathias Rolf
Current interpretation of relative density (Dr) based on CPT end resistance (qc) data in sand relies on empirical expressions established from calibration chamber studies for which a deep failure penetration mechanism is attained. These expressions are mainly based on stress normalised qc data. Previous studies have highlighted the importance of performing the normalisation procedure with respect to the mean effective stress (p') in overconsolidated (OC) sand deposits instead of the vertical effective stress (σ'v) that has been used in normally consolidated (NC) deposits. Due to a large variation in the coefficient of earth pressure at rest (K0), on which p' depends, in the uppermost (3-5) m of OC sand, a recent study has demonstrated a rigorous unified approach for estimating a varying K0 with depth. However, the surficial shallow failure penetration effects are not accounted for, and consequently, interpretation of the upper (0.5-1.5) m of sand is still erroneous. This depth range is very important for low stress geotechnical applications such as offshore flowlines and mudmats. With a reinterpretation of previously published data, a new global model is presented that enables estimation of Dr from shallow CPTs in siliceous sand by taking into account both the shallow failure penetration effects (important in the uppermost 0.5-1.5 m) as well as the varying K0 with depth for OC sand (important in the uppermost 3-5 m).

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