2018
Permanent URI for this collectionhttps://hdl.handle.net/1807/81039
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Item Open Access Probabilistic seismic slope stability analysis and design(Canadian Science Publishing, 2018-12-11) Burgess, Jesse; Fenton, Gordon A.; Griffiths, D.V.Deterministic seismic slope stability design charts for cohesive-frictional (c-Ď ) soils are used by geotechnical engineers to include the effects of earthquakes on slopes. These charts identify the critical seismic loading which brings the slope to a state of limit equilibrium. In this study, probabilistic seismic stability of slopes, modeled using a two-dimensional spatially random c-Ď soil, is studied for the first time using the Random Finite Element Method (RFEM). A series of slope stability design charts, which consider the influence of the spatial variability of soil, for seismic loading are provided for a mean friction angle of tan(20°). The charts may be used to perform the design of slopes subject to seismic loading, and to provide estimates of the probability of slope failure without requiring computer simulations. Application of the design charts is demonstrated with an example of slope remediation cost analysis and risk-based design.Item Open Access A novel vegetated three-layer landfill cover system using recycled construction wastes without geomembrane(Canadian Science Publishing, 2018-12-01) Ng, C.W.W.; Chen, Rui; Coo, Jason Lim; Liu, Jian; Ni, Junjun; Chen, Yun Min; Zhan, Tony Liang Tong; Guo, Hao Wen; Lu, Bang WenTo promote environmental protection and sustainability, the use of plants and recycled wastes in geotechnical constructions such as landfill covers are recommended. A landfill cover field test was conducted at the Shenzhen Xiaping landfill site, located in a humid climatic region of China. The main objective is to validate the field performance of a novel vegetated three-layer landfill cover system using recycled construction waste without the need of geomembrane. Unsieved completely decomposed granite and coarsely crushed concrete was used for the top and intermediate layer while sieved completely decomposed granite was used as the lowest layer. One section was transplanted with Bermuda grass while the other section was left bare. To assess the landfill cover performance, pore water pressure, volumetric water content, percolation and atmospheric parameters were measured for a period of 13 months under natural climatic conditions. The cumulative rainfall depth was about 2950 mm over the whole monitoring period. During rainfall, the presence of grass led to lower pore water pressure (or higher suction) and volumetric water content in the three-layer landfill cover system. At the end of monitoring, the cumulative percolation was about 27 mm and 20 mm for the bare and grass covered landfill cover, respectively. It is evident that the vegetated three-layer landfill cover system using recycled concrete without geomembrane can be effective in minimizing percolation at humid climates.Item Open Access Effect of interface transmissivity and hydraulic conductivity on contaminant migration through composite liners with wrinkles or failed seams(Canadian Science Publishing, 2018-12-01) Rowe, R. Kerry; AbdelRazek, Ahmed Y.The leakage and the peak chloride concentration in an aquifer for a single composite liner facility is modelled for: (i) a hole in a geomembrane wrinkle, and (ii) a failed seam. A method using a closed form solution to calculate leakage together with a l½D semi-analytic contaminant transport model is proposed and the results compared with those obtained from 2D finite element modelling (FEM). Leakage is shown to be highly dependent on the interaction between the interface transmissivity (θ) and hydraulic conductivity beneath the wrinkle (kb). Similar leakages arising from different combinations of transmissivity and hydraulic conductivity are shown to have significantly different impacts on an underlying aquifer. Contaminant transport modelling is needed to assess this effect for the likely range of uncertainty regarding interface transmissivity (θ) and hydraulic conductivity. The 2D FEM model is conceptually more comprehensive, however using conventional software only a very limited size of problem could be accurately modeled given the greatly different scales that must be modelled. In contrast, the semi-analytic 1⅟2D approach readily allowed consideration of the highly variable scales, and gave results at the downgradient edge sufficiently similar to the 2D.Item Open Access Mitigation of liquefaction hazard by dynamic compaction - a random field perspective(Canadian Science Publishing, 2018-12-25) Shen, Mengfen; Juang, C. Hsein; Chen, QiushiThis paper presents the findings of a case study to quantitatively assess the effect of dynamic compaction (DC) on mitigating liquefaction hazards from a random field perspective. DC is known to increase the density and strength of loose sand deposits, leading to a decrease in liquefaction potentials. Thus, by comparing the liquefaction potentials before and after DC at a given site, the effectiveness of DC in mitigating liquefaction hazards can be quantified. In practice, however, a direct one-to-one comparison is challenging due to limited availability of in situ test data and the fact that the number and location of these data before and after DC are typically different. To overcome these challenges, a random field-based approach is proposed in this study to visualize and quantitatively evaluate the effectiveness of DC across the entire project site. This approach is proven effective in assessing the effects of DC and is validated with liquefaction observations from the 1999 Chi-Chi earthquake.Item Open Access Ground response to tunnelling incorporating a soil reinforcement system(Canadian Science Publishing, 2018-12-05) Le, Binh Thanh; Taylor, R N.The forepole umbrella system (FUS) uses steel pipes installed from within a tunnel to provide a canopy above the tunnel heading that both increases stability and reduces tunnelling-induced ground movements. Although the system is known to be beneficial and has been used in a number of projects, there is little information on how key parameters including length and forepole stiffness combine to produce effective support. To investigate this, centrifuge tests incorporating the three-dimensional (3D) geometry of a tunnel heading in clay and the model FUS have been undertaken. The tunnel heading was supported by a pressurized rubber bag lining with excavation being simulated by a reduction in air support pressure. Image analysis was used to obtain subsurface ground movements and a newly developed 3D imaging system was used to measure the soil surface deformations accurately. The performance of the FUS and the influences of key FUS parameters were quantified via the settlement reduction factor. The results showed that the FUS, arranged in various settings, reduced the maximum surface settlement by 35%–75%. The effects of the FUS parameters on the reinforcing effectiveness are dependent on the ratio of cover depth to tunnel diameter. An optimum design arrangement of the FUS is suggested.Item Open Access Using neutron spectroscopy to measure soil-water retention at high suction ranges(Canadian Science Publishing, 2018-09-13) Carnero-Guzman, Genaro Gonzalo; Gates, Will P.; Bouazza, Abdelmalek; Aldridge, Laurie P.; Bordallo, Heloisa N.Laboratory determination of water retention curves for geosynthetic clay liners (GCLs) and their bentonite components are time-consuming, especially for high suction ranges. This paper explores the potential use of neutron spectroscopy as a useful method to assess the water retention properties of montmorillonite at suction levels >10 MPa for GCL studies. The results from neutron spectroscopy are in good agreement with traditional methods when assessing the water retention of bentonite and GCLs. Additionally, the primary advantage of neutron scattering is that, contrary to conventional methods, water populations within the clay matrix, such as bulk-like water, confined water, and structure OH, are observed and can be quantified independently.Item Open Access Cyclic and post-cycling anchor response in geocell-reinforced sand(Canadian Science Publishing, 2018-12-01) Moghaddas Tafreshi, Seyed Naser; Rahimi, Mohammadyar; Dawson, Andrew; Leshchinsky, BenPlate anchors are commonly used to resist static, cyclic, and monotonic post-cyclic uplift loads. Under cyclic loading, progressive sudden failure may occur, characterized by accumulated displacement — even under loads significantly less than the static capacity. Despite extensive usage of geocell materials for increasing cyclic resilience, the influence of geocell reinforcements on cyclic uplift capacity is not well understood. In this study, a series of near-full-scale experimental tests, with and without geocell, are presented. Results show that the unreinforced system fails cyclically under a load that is almost 70% of its ultimate uplift capacity (Pu), but use of geocell enables stable cyclic resistance of over 100% Pu. For the given soil and configurations, a cyclic displacement rate that reaches less than 0.05 mm/cycle tends to highlight a likely stable response. Evaluation of the soil’s response to cyclic loading demonstrates that, with increasing loading cycles, the loading is increasingly transmitted through the soil close to the anchor in the unreinforced case, but that the reinforced case is less prone to this phenomenon. The monotonic post-cycling capacity of both reinforced and unreinforced anchors decreases after application of cyclic loading; however, the unreinforced scenario demonstrates larger decreases in capacity, particularly in the residual capacity.Item Open Access Coupled hydromechanical (H-M) performance of in situ shaft sealing components for nuclear waste disposal(Canadian Science Publishing, 2018-11-16) Kim, Chang Seok; Alfaro, Marolo; Blatz, James; Graham, JamesDecommissioning and closure of Canada’s Underground Research Laboratory (URL) involved installing a full-scale 5 m diameter by 12 m long seal in the main access shaft. The seal consisted of clay and concrete components spanning a major water-bearing fracture zone (FZ2) located at a depth of around 275 m that isolates two hydrogeochemical regimes. This paper presents results of coupled hydromechanical (H-M) numerical modelling that simulated measured performance of the seal. Parameters for the H-M modeling were determined from previously measured laboratory test data. Results from the modelling were compared with field data for water uptake and total pressures in the system. They show that hydration of the clay seal was dominated by the groundwater flow from FZ2. The simulations showed good agreement with field readings and provide an improved understanding of various interrelated physical processes that take place during hydration.Item Open Access Observed performance of three adjacent 48-m depth concrete diaphragm wall panels in silty soils(Canadian Science Publishing, 2018-12-11) Liu, Wei; Shi, Peixin; Li, Haiguang; Wang, FeiThe performance of three adjacent 48 m depth concrete diaphragm wall panels in silty soils is measured throughout the complete process of the wall installation including trench excavation, trench concreting, and concrete hardening. The analysis of the field measurement data shows that the ground movement induced by the wall installation is a function of construction activities. The maximum lateral movement occurs during the trench excavation. The trench concreting reduces the lateral movement. Field measurement at the end of wall installation may not catch the value of the maximum lateral movement. The ground settlement continues to increase during the complete process of panel installation, but with a decreasing rate. Roughly 90% of the settlement occurs during the trench excavation. The ground movement is also closely related to the properties of subsurface strata. The weak superficial fill materials sustain high disturbance, which consequently results in relatively large ground movement. With current engineering means and methods and good construction workmanship, the ground movement can be well controlled. In the current project, the maximum lateral ground movement was controlled within 2.0 cm and the maximum settlement was controlled within 0.05% of trench depth.Item Open Access Ultimate seismic bearing capacities and failure mechanisms for strip footings placed adjacent to slopes(Canadian Science Publishing, 2018-12-01) Zhou, Haizuo; Zheng, Gang; Yang, Xinyu; Li, Tao; Yang, PengboThe assessment of the ultimate bearing capacity of foundations adjacent to slopes is complex as it is highly dependent on the slope geometry and soil properties. Seismic loading may impact both the critical failure mechanism and its associated bearing capacity. The existing approaches for analyzing the seismic bearing capacity of footings near slopes typically employ coefficients developed to fit the conventions of Terzaghiâ s bearing capacity equation, herein referred to as the â superposition methodâ . In this study, a rigorous assessment of the seismic bearing capacity is performed using an upper-bound limit state plasticity framework known as discontinuity layout optimization (DLO), which makes few prior assumptions concerning the failure geometry. The results show that soil properties, slope configuration, and pseudostatic seismic loading all influence the realized failure mechanism and associated bearing capacity. The use of bearing capacity coefficients that fit within the conventional superposition method may underestimate limit loads when the underlying soil provides a relative increase in resistance but may greatly overestimate bearing capacity when the self-weight of the soil is destabilizing in nature. A set of design charts using direct computational methods for a variety of geometric, geotechnical and seismic conditions is provided.Item Open Access Determination of efficient sampling locations in geotechnical site characterization using information entropy and Bayesian compressive sampling(Canadian Science Publishing, 2018-11-28) Zhao, Tengyuan; Wang, YuSite characterization is indispensable in geotechnical practice, and measurements on soil properties are performed through in-situ tests, laboratory tests, or other methods. However, due to time or budget limit, technical or access constraints etc., the measurements are usually taken at a limited number of locations. This leads to a question of how to select the efficient locations for measurements/sampling such that as much as possible information on the spatial variability of soil properties can be obtained from a given number of measurements. In addition, site characterization is a multi-stage process, and additional measurements might be required at a later stage of site characterization. In this case, how to efficiently select the additional sampling locations such that the pre-existing measurements obtained from the preliminary stages of site characterization can be best used and as much as possible information on soil properties can be further obtained? This paper aims to address these two problems using information entropy and Bayesian compressive sampling (BCS). Real cone penetration test data along vertical and horizontal directions are used to illustrate and validate the proposed methods. The results show that the proposed methods are very effective and robust in selecting efficient sampling locations for geotechnical site characterization.Item Open Access An experimental study on the lateral pile–soil interaction of offshore tetrapod piled jacket foundations in sand(Canadian Science Publishing, 2018-12-01) Zhu, Bin; Wen, Kai; Li, Tao; Wang, Lujun; Kong, DeqiongRecently, tetrapod piled jacket (TPJ) foundations have shown considerable promise in offshore developments, due to the increases in power capacity and water depth for offshore wind turbines. This paper presents a set of centrifuge tests to look into the lateral loading behaviour of TPJ foundations in sand, with the overall load–displacement responses of the foundation as well as the soil resistance and internal forces on or within individual piles being examined carefully. Test results show that the back-row piles are more likely to be pulled out when the TPJ foundation is loaded laterally along the diagonal direction compared to when loaded along the orthogonal direction. The lateral soil resistance per unit length on the back-row pile(s) is approximately 60% of that on the front-row one(s) in the orthogonal loading case, and only about 40% in the diagonal loading case. Moreover, although the TPJ foundation is in its form a special case of pile groups, it is highlighted in the present study that the former case exhibits distinct loading behaviour from the latter case due to the typically large overturning moment encountered by the foundations for offshore wind turbines. Finally, the p-multipliers of the piles are demonstrated to be dependent on pile deflections, but independent on soil depths, and as a result, a modified pm model is proposed to provide guidance for the design of TPJ foundations in sand.Item Open Access Equivalent number of uniform cycles versus earthquake magnitude relationships for fine-grained soils(Canadian Science Publishing, 2018-11-21) Verma, Priyesh; Seidalinova, Ainur; Wijewickreme, DharmaIn current geotechnical seismic design practice, the empirical correlation between equivalent number of uniform cycles (Neq) of shaking and earthquake magnitude (Mw) forms an integral part of liquefaction potential evaluation. This relationship, in turn, is used to derive the magnitude scaling factors that are commonly used in field-based liquefaction evaluation procedures. The Neq versus Mw relationship for liquefaction assessment was examined for fine-grained soils using time-histories in the range 5 < Mw ≤ 9, especially including strong ground motion time-histories from the latest subduction zone earthquakes with Mw > 8.0. The experimental database available from cyclic direct simple shear tests conducted on natural fine-grained soils retrieved from undisturbed soil sampling was used to obtain the cyclic shear resistance weighting curves for the study. The work presented herein has contributed to further improving the current models used to represent magnitude scaling factor (MSF) values for large earthquake magnitudes and the functional dependency of this parameter on soil type. The MSF–Mw curve derived for low-plastic Fraser River Delta silt lies in-between the MSF curves derived for clean sand and clay, resonating with the inferences that have been made that the silt behavior can neither be considered sand-like nor clay-like.Item Open Access An optimization strategy for evaluating modified Cam clay parameters using self-boring pressuremeter test data(Canadian Science Publishing, 2018-10-04) Gaone, Fillippo Mario; Doherty, James; Gourvenec, SusanThis paper presents an efficient, practical, and automated strategy for deriving modified Cam clay parameters from undrained self-boring pressuremeter (SBPM) data. A mixed approach involving a parametric sweep and numerical optimization is used, with a focus on parameter groups that dominate the modified Cam clay response in undrained cavity expansion. The proposed technique is illustrated using data from SBPM tests carried out in soft estuarine clay. The resulting parameters are used to back-analyse large-scale foundation load tests and are shown to provide an excellent match to the measured foundation response.Item Open Access HYDROMECHANICAL BEHAVIOUR OF OVERCONSOLIDATED UNSATURATED SOIL IN UNDRAINED CONDITIONS(Canadian Science Publishing, 2018-11-16) Wu, Shengshen; Zhou, Annan; Li, Jie; Kodikara, Jayantha; Cheng, Wen-ChiehHydromechanical behaviour of an unsaturated silt with various suctions and different overconsolidated ratios (OCRs) was investigated through a series of undrained triaxial tests (constant water contents, CW). All the samples were prepared from the slurry state. Different OCRs (= 1, 2, 4, and 8 in net stress) were achieved by unloading the samples to 400, 200, 100, and 50 kPa from an initial confining net pressure of 400 kPa. Then the samples were dried to various suctions (0, 100, 200, 300, and 400 kPa). Unsaturated samples with different OCRs then were sheared at constant water content conditions following the conventional triaxial compression (CTC) paths. Full hydromechanical responses including the changes on deviator stress, stress ratio, volumetric strain, suction and degree of saturation with axial strain were monitored and presented in this paper. Some key findings include: (1) the critical state for unsaturated soils with different OCRs can be well defined by Bishopâ s effective stress; (2) the peak strength in Bishopâ s effective stress increases with increase of OCR but decreases with increase of suction in the undrained condition; and (3) the volume change of unsaturated soils in undrained conditions is related to OCRs and the volume of pore air.Item Open Access Mechanical behavior of an unsaturated clayey silt: an experimental and constitutive modelling study(Canadian Science Publishing, 2018-08-04) Romero, E.; Sanchez, Marcelo; Gai, Xuerui; Barrera, Mauricio; Lloret, Antonio AThis paper reports an experimental study and subsequent constitutive modelling focused on the stress-strain and volumetric responses during deviatoric stress application of a partially saturated clayey silt. The material was statically and isotropically compacted at constant water content towards a pre-defined pre-consolidation stress. A series of strain-controlled triaxial compression tests on a state of the art device and isotropic experiments are presented and discussed. The triaxial tests started at the same stress state (i.e., identical matric suction and mean net stress) and were conducted at the same constant suction. Several stress paths under isotropic conditions (i.e., drying–wetting, loading–unloading, and wetting–drying) were followed to induce different overconsolidated states before shearing the specimens. The test results are initially interpreted using the elastoplastic Barcelona Basic Model (BBM). Independent tests were selected to determine the model parameters associated with the volumetric behavior of the soil. The BBM was not able to capture the dilatant behavior observed during shearing. An enhancement of the BBM is proposed in this work, which includes both, a more general hardening law and sub-loading concepts. The main capabilities and limitations of the original BBM and the enhanced model are discussed and compared. The modified BBM was able to handle the dilatancy observed in the experiments and provided a more realistic description of the experimental stress-strain response.Item Open Access Delayed response of excavations in structured clays(Canadian Science Publishing, 2018-11-21) Bertoldo, Fabiano; Callisto, LuigiIn this paper, the behaviour of an idealised excavation carried out in a clay sensitive to destructuration is studied through a series of finite-element analyses, employing an advanced bounding surface model developed for structured clays. Several cases are examined, in order to investigate the influence of factors including the velocity of destructuration, the damage produced by the wall construction to the soil-wall contact, the width-to-height ratio of the excavation. The case of a soil deposit insensitive to microstructural damage is also studied for comparison. The results of the numerical analyses show that the progressive dissipation of the excess pore water pressures generated during the excavation stage can damage the clay microstructure severely enough to trigger an instability phenomenon. If the clay structure deteriorates rapidly, the instability is concurrent with the dissipation of the excess pore water pressures. However, for a clay less sensitive to microstructural damage, the instability can occur towards the end of the consolidation process, or even be preceded by a deceptively stable time interval, during which small redistributions of the pore water pressure can trigger an important destructuration and the collapse of the excavation. In a final part of the paper the results of the numerical analyses are used to provide indications about the most appropriate quantities to monitor in order to provide an effective early warning of the instability phenomenon.Item Open Access Stochastic modeling of kaolinite transport through a sand filter(Canadian Science Publishing, 2018-11-06) Won, Jongmuk; Burns, S.E.Accurately modeling the transport of clay particles through coarse-grained porous media is essential to engineering applications ranging from filtration and drainage, groundwater flow modeling, to contaminant transport. However, predicting the retention and clogging behavior of clay particles within a coarse-grained soil matrix is extremely challenging because clay particles can aggregate and form clusters with a variety of fabrics depending on the prevailing geochemistry of the pore fluid (i.e., pH and ionic strength). The work performed in this study developed a stochastic model to investigate the uncertainty of clay particle transport in porous media using random sampling at a given grain-size distribution to account for inherent uncertainty of the size of clay clusters being transported. Results demonstrated that the model proposed in this work can evaluate upper and lower boundaries of retention profiles of clay particles in a sand medium at given mean and standard deviation of grain-size distributions. In addition, the deterministic approach (using median sizes of sand and clay particles in the simulation) underestimated the mass of retained particles at small size ratios of clay particle size/sand particle size when compared with the stochastic prediction, which would result in nonconservative design.Item Open Access Tensile monotonic capacity of helical anchors in sand: interaction between helices(Canadian Science Publishing, 2018-11-01) Hao, Dongxue; Wang, Dong; O'Loughlin, Conleth D; Gaudin, ChristopheThis note examines the interaction between the helices of a multi-helix anchor in terms of the mobilized drained capacity response in tension. Assessments are made on the basis of centrifuge tests in dense silica sand, supplemented with data from existing studies. The centrifuge tests were designed to isolate potential anchor installation effects from those due to the interactions between helices. The data show that additional helices will only contribute to anchor capacity if they are located outside the region of soil mobilized in the failure mechanism of the lower helices. In the dense sand considered in these centrifuge tests, this required helices to be separated by greater than nine diameters, and hence for the lowermost helix to be located at a depth greater than nine diameters. This separation distance is much higher than suggested in previous studies, which tended to attribute the low or nil contribution of additional helices to the soil disturbance generated during anchor installation.Item Open Access Evaluation of equivalent hydraulic aperture (EHA) for rough rock fractures(Canadian Science Publishing, 2018-11-05) Xiao, Fei; Zhao, ZhiyeMost existing models for fluid transportation within a single rock fracture tend to use a channel with two smooth parallel plates, whereas real fracture surfaces are usually rough and tortuous, which can produce a flow field significantly different from the smooth plate model. For fluid flow in a rough fracture, there are surface concave areas (SCA), where the fluid velocity is extremely low, contributing little to the fluid transportation. It is of great significance to quantitatively evaluate the impact of rough surfaces on fluid flow. Therefore, a numerical model for simulating Newtonian fluid through rough fractures is proposed, where synthetic surfaces are generated according to statistical analysis of natural rock fractures and can be quantified by several characteristic parameters. Equivalent hydraulic aperture (EHA) is proposed as one quantitative indicator for evaluating the impact of fracture roughness. Systematic studies were conducted for evaluating EHAs of rough fractures, which, combined with characteristic parameters of fractures, are used to build surrogate models for EHA prediction. It is found that the EHA is directly correlated with the fracture roughness, the mean mechanical aperture, and the standard deviation of aperture distribution. The developed surrogate models were verified to have a high accuracy for EHA prediction.