2023
Permanent URI for this collectionhttps://hdl.handle.net/1807/126402
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Item Model for the Prediction of Residual Shear Strength of Unsaturated Soils(Canadian Science Publishing, 2024-05-30) Yang, Xiuhan; Vanapalli, SaiThe residual shear strength (RSS) of unsaturated soils is a crucial parameter for the reliable analysis and design of geo-structures constructed with or within unsaturated soils undergoing large shear deformation. For investigating the RSS of unsaturated soils, two sets of data are specifically generated on the SP-SM and Indian Head till using suction-controlled ring shear tests and three more sets (i.e., SM, SC-SM and CH) are gathered from the literature. A model is proposed extending two approaches for predicting the RSS for both coarse- and fine-grained unsaturated soils. In this model, the suction contribution was calculated considering the loss of degree of saturation due to shearing, which was described as a nonlinear function of degree of saturation. The capability of the proposed model is validated with the five sets of data using two different approaches. The best-fitting approach that is based on three fitting parameters provides good predictions. The approximate approach performs well for four studied soils, except for SM soil; this approach is simple for use in engineering practice because no fitting parameters are required. The proposed model is valid for the suction range where degree of saturation is higher than the residual degree of saturation.Item Large deformation analysis of intermittent pile penetration into dense sand incorporating a state dependent Mohr–Coulomb model(Canadian Science Publishing, 2024-09-08) Ye, Rongrong; Huang, Zhongyuan; Yang, Zhongxuan; Guo, Ning; Jardine, Richard J.; Fu, S.The challenges of predicting the stresses acting around piles driven in sand limits meaningful analysis of their single and group loading responses, aging processes and scale/in-situ stress level dependency. Benchmark local stresses measurements made in the sand mass and pile shaft in Calibration Chamber (CC) models show that sharply different regimes act when the pile is either penetrating or temporarily stationary. This paper presents an Arbitrary Lagrangian–Eulerian (ALE) finite element simulation of installation into dense sand, highlighting the stress changes developed between intermittent penetration stages and exploring the effects of initial stress level. The installation by cyclic jacking of closed-ended model piles studied in a highly-instrumented CC experiments is simulated with a state-dependent Mohr–Coulomb model calibrated to high-quality element tests on the sand employed. The predicted pile head loads and local stresses are compared with the CC experiments, showing generally good agreement over the lower parts of the pile shaft while also matching key field-scale trends from CPT-based practical design approaches. More advanced constitutive modeling appears necessary to eliminate discrepancies noted over the higher shaft levels, which may be linked to currently neglected aspects of the sands’ highly non-linear behavior, including grain crushing and hysteresis under cyclic loading.Item Displacement-based Design of Shield Tunnel Lining Considering Mobilized Strength of Undrained Clay(Canadian Science Publishing, 2023-11-05) Zhang, Dongming; Ye, Zhenwei; Zhang, Jinzhang; Huang, HongweiThis paper presents a displacement-performance design method for the shield tunnel based on the mobilized strength design (MSD) theory. Firstly, the nonlinear relationship between the ground volume loss caused by tunnel excavation and the earth pressure was constructed to obtain the real earth pressure on the tunnel lining. Secondly, the nonlinear relationship between the convergence displacement of the lining and the ground resistance was built to acquire the subgrade reaction working on the tunnel lining. Finally, the proposed method was verified by orthogonal numerical experiments and compared with the finite element method (FEM) results. Compared with the FEM, the average deviation of the bending moment and the axial force are about 9% and 1%. The average variation of the bending moment can be reduced to 1% after calibration. The results calculated by this developed method are better than the traditional beam-spring model. Its accuracy is close to the FEM based on the strata-structure concept. Therefore, the proposed method based on MSD theory in this paper has the characteristics of high efficiency and simplicity, which provides a new auxiliary design approach for the structural design of shield tunnels in clay areas.Item Estimation of confidence in the calculated resistance factor for simple limit states with limited data for load and resistance model bias(Canadian Science Publishing, 2023-12-17) Bathurst, Richard J.; Jamshidi Chenari, RezaEstimation of the resistance factor in load and resistance factor design (LRFD) calibration for simple soil-structure limit states is most often based on model bias data of limited size. Frequently, the bias data are only available or required for the resistance term. In this paper, the confidence in the estimate of the mean of the resistance factor is computed for the case of one resistance factor and one load factor where limited model bias data are available for both load and resistance terms. The bootstrap method is used to compute synthetic load and resistance bias data sets from which confidence intervals on the point (mean) estimate of the resistance factor and load factor are computed. A closed-form solution is used to calculate the resistance factor for a single prescribed load factor and target reliability index, bias data, and nominal load and resistance variables that are lognormally distributed. However, the approach is general using Monte Carlo simulation. The method is demonstrated using the case of the internal stability pullout limit state for steel strip mechanically stabilized earth (MSE) walls. The example demonstrates the quantitative influence on pullout design using upper and lower 95% confidence interval limits for load and resistance factors.Item Research on energy-absorption active control method for large deformation of tunnel surrounding rock through multi-fault fracture zone(Canadian Science Publishing, 2023-12-04) Tao, Zhigang; Mao, Yuting; Sun, Jihao; Zhang, Xiaoyu; Huo, SS.; He, ManchaoIn order to study the problems of large deformation of surrounding rock and water-rich dense fracture zones during tunnel construction through fault fracture zone, the NPR anchor cable control method is studied based on the Tabaiyi tunnel. Firstly, the mechanical deformation mechanism of surrounding rock is analyzed by geological conditions, lithology and strength of surrounding rock, and different surrounding rock zones are obtained. Then, based on the self-developed high-prestressed NPR anchor cable, the tunnel prevention and control measures are designed. The high stress NPR anchor net technology is used to support the common large deformation and fault fracture zone, while in the water-rich dense fracture zones, the combined support of double gradient grouting technology and high stress NPR anchor net technology is adopted. Finally, in order to evaluate the control effect of the support design scheme, the deformation of surrounding rock, the axial force of NPR anchor cable and the pressure of steel arch are monitored in real time. The results show that the high stress NPR anchor net technology can effectively control the large deformation of tunnel surrounding rock caused by fault zone. And in the water-rich zones, the double gradient grouting technology can provide sufficient anchoring force for the NPR anchor cable. The two technologies control the maximum deformation of surrounding rock within 300 mm, and realize the stability of tunnel primary support.Item Behavior of an anchored sheet pile quay in soft clay reinforced by various structural types of cemented soil(Canadian Science Publishing, 2023-12-06) Chen, Shengyuan; Guan, Yunfei; Dai, Jiqun; Han, XunIn this research, the potential benefits of using various structural types of cemented soil, including block-type, column-type, and wall-type, to reinforce the active zone behind a quay wall were investigated by experimental and numerical methods. The response of the quay wall and ground was analysed from aspects of soil movement, quay wall displacement, lateral earth pressure, and bending moment, and a close agreement between the experimental and numerical results was observed. Experimental and numerical results showed that the cemented soil effectively prevented potential deep soil sliding, and then lateral displacement of the quay wall and ground deformation was reduced. Among various structural patterns, the case with the block-type cemented soil exhibited smaller lateral earth pressure on the quay wall, while the case with the wall-type cemented soil more effectively reduced the bending moments and lateral displacements of the quay wall; therefore, wall-type cemented soil seems to be more favourable considering their improved performance under the same load intensities and excavation depth. This research provides a hint and guideline for the preliminary design of cemented soil-stabilised sheet pile quay structures in soft clay based on the lateral load-reduction effect of the varying structural types of the cemented soil.Item Impact of Roots on the Hydrogeological Properties of Silty Soil Covers(Canadian Science Publishing, 2023-09-20) Proteau, Alex; Guittonny, Marie; Bussière, BrunoMine tailings storage poses significant environmental risks such as the formation of acid mine drainage (AMD). Engineered covers offer a solution by controlling water ingress. Their performance is based on specific soil hydrogeological properties (SHPs). They must support vegetation which can impact saturated hydraulic conductivity (ksat) and water retention curve (WRC). This study assesses the impact of four-year-old willow root colonization on silty soil covers using flexible wall permeameters and water retention tests. The obtained SHPs were compared with root traits. Results suggested that the hydrogeological properties of the studied in situ samples were not significantly affected by roots. The variation of measured and predicted ksat values spanned an order of magnitude, regardless of the root colonization intensity, up to a root length density (RLD) of 2.98 cm/cmItem Experimental Approach for Assessing Dissipated Excess Pore Pressure Induced Settlement(Canadian Science Publishing, 2023-09-22) Bayoumi, Aya; Chekired, Mohamed; Karray, MouradUpon dynamic loading, saturated soil loses its strength and behaves differently with respect to the excess pore pressure variation resulting in volumetric-induced settlements. Traditionally, these settlements have been evaluated using standard charts based on one soil type and its relative density (RD). To assess these settlements, this study established a unique experimental methodology based on two laboratory tests: triaxial simple shear and piezoelectric ring actuator technique. Fifty-seven tests were performed on Ottawa F65 sand under strain-controlled cyclic and post-cyclic conditions. A chart was generated, revealing a relationship between the dissipated energy from cyclic loading and volumetric strain (v), based on the shear wave velocity as a controlling factor. This study was compared with previous studies to verify the compatibility of the proposed approach. Another novelty was revealed by studying v variation with the dissipated pressure. This variation is presented in a post-seismic chart, in which deformations are tracked based on the initial soil state and maximum excess pore pressure generation ratio (Rumax). For each RD, the soil is divided between liquefied and non-liquefied states according to a specific Rumax (Rumax-trigger point). The calculation of the volume compressibility coefficient is proven to serve as a liquefaction-triggering criterion identifying the liquefied state.Item Deformational response of a marine silty-clay with varying organic content in the triaxial compression space.(Canadian Science Publishing, 2023-11-16) Ponzoni, Elisa; Muraro, Stefano; Nocilla, Alessandra; Jommi, CristinaThis study characterises the effects of naturally varying organic content on the compression and shear behaviour of a marine silty-clay from the Netherlands. Index properties and mechanical properties are determined through laboratory tests, including oedometer and multistage loading-unloading triaxial stress paths. The results indicate a significant impact of the organic content on the compression response, with both the loading and reloading indexes increasing as the loss on ignition increases from 3% to 7%. Additionally, the study suggests a directional response of the compression behaviour, with the loading index increasing with the stress ratio. The influence of the organic content on shear strength appears to be less significant. No brittle response is observed during shearing and a similar ultimate stress ratio is attained by all samples. However, a unique critical state line can only be identified for samples with similar organic content, as its intercept and slope are found to increase with increasing organic content. The experimental results from stress paths at constant stress ratio reveal an anisotropic pre-failure plastic deformation mode, which depends on the previous stress history and loading direction. This suggests that the stress-dilatancy relationship cannot be formulated as a unique function of the stress ratio. The high-quality experimental data presented in the paper enlarge the database on soft organic soils in view of the development of advanced constitutive models.Item Development and outcomes of a tailings slope stability comparative design exercise(Canadian Science Publishing, 2023-09-20) Reid, David; Fourie, AndyTailings storage facilities (TSFs) have undergone an unacceptably high failure rate for decades, leading to an increased focus on improving the safety of these structures. One aspect that has not received sufficient attention is examining how reliably and consistently engineers analyse the stability of TSFs. An understanding of the current state of practice is needed as there are a range of analytical methods available to engineers, while the high failure rate of these structures strongly points to some deficiencies in practice. To examine some of these issues, a tailings-focussed slope stability comparative design exercise was organised to compare the methods and results used by tailings engineers to analyse the same slope within which the phreatic surface was to rise under a specified pattern. Twenty-eight practitioners participated in the exercise to predict at what phreatic surface level the slope would fail. A wide range of predictions were made, ranging from assuming the slope would liquefy and fail instantly (i.e. before any rise in phreatic surface), to a range of techniques based on (i) yield strength ratios, (ii) stress path methods, and (iii) numerical analyses, each predicting various failure levels, and finally some predictors who applied drained strengths, resulting in predictions that the slope would not fail.Item Performance of an Asymmetric Pit-in-Pit Excavation Supported by Diaphragm Wall and Multi Uplift Piles System in Coastal Areas(Canadian Science Publishing, 2023-11-05) Wang, Ruisong; Dong, Hongyuan; Shen, Daoxu; Li, Jianfeng; Ni, Pengpeng; Zhao, ChenyangThe performance of asymmetric pit-in-pit excavation supported by diaphragm wall and multi uplift piles in coastal areas has been rarely reported. In this work, case study is conducted to investigate the mechanical characteristics of such excavation. A numerical model is established using the ABAQUS finite element platform, and its effectiveness is evaluated by comparing with the field monitoring data. After evaluation, the effects of uplift piles on excavation-induced deformations are investigated. Results show that the maximum wall deflections (δhm) are 0.02%~0.22% of the excavation depth (He), with the ground surface settlements of less than 0.6%·He and the settlement influence zone extending beyond 4He. As the soil is excavated, the top wall shows outward deformations to the active zone, and the transverse support is under tension. The use of combined diaphragm wall and multi uplift piles reduces the embedment ratio of diaphragm wall to a minimum value of 0.14, and decreases the δhm and rebound of base soil (δvrm) by 42% and 63%, respectively. A design suggestion is proposed for pile diameter (D), pile length (L) and pile spacing (S) to fall within the range of 0.4~0.8 m, 10~20 m and 6D~8D, respectively.Item Suction and anisotropy effects on the stiffness characteristics of a compacted lateritic clay from small to large strains(Canadian Science Publishing, 2023-12-20) Bentil, O. T.; Zhou, ChaoLateritic clay has distinct properties from other clays due to its high sesquioxide content. Its stiffness characteristics have not been well understood, especially when the soil is unsaturated and anisotropic. This study investigated the stiffness characteristics of compacted lateritic clay through suction-controlled triaxial compression tests equipped with local strain measurements. Both vertically and horizontally cut specimens were tested to determine the evolution of stiffness anisotropy during shearing. Three suctions (0, 10 and 150 kPa) and two confining pressures (50 and 200 kPa) were considered. When strains are relatively small (e.g., less than 0.2%), the secant Young’s modulus Esec of vertical specimens is consistently higher than that of horizontal specimens at all suctions and stresses due to the inherent anisotropic structure. The degree of anisotropy increases with increasing suction since suction enhances the stiffness significantly more in vertical specimens than in horizontal specimens. This behaviour may be due to an enhanced force chain in the vertical direction during shearing. As strains increase, the degradation of Esec normalized by the maximum Young’s modulus E0 is almost independent of suction and anisotropy. Lateritic clay has a higher degradation rate than other clays with a similar plasticity index because of its aggregated microstructure.Item An empirical equation predicting the saturated hydraulic conductivity of tailings(Canadian Science Publishing, 2023-11-05) Fan, Jiying; Rowe, R. Kerry324 data points on the saturated hydraulic conductivity (k) of various hard rock mine tailings are collected from previous publications. The applicability of existing empirical equations for hard rock mine tailings are assessed based on this database collected. Results show that with a greater exponent of d10, the correlation between the measured and predicted k is greatly improved. An empirically modified version of the Kozeny-Carman equation is then proposed for predicting the saturated k of tailings and compared with the database. The proposed equation gives the best fit with a varying exponent greater than 2 for d10. Finally, the impact of particle shape on k is discussed.Item Generalized hydro-mechanically coupled hypoplastic constitutive model for unsaturated collapsible soils(Canadian Science Publishing, 2023-10-26) Tafili, Merita; Machacek, JanIn this paper, a generalized hypoplastic constitutive model for unsaturated soils based on the work of Fuentes and Triantafyllidis [2013] is presented. The constitutive model is formulated in terms of effective stresses, degree of saturation and suction. The main feature of the model is a Limiting Surface (LS) which describes the maximum achievable void ratio as a function of mean effective stress and degree of saturation. The LS allows to capture the wetting-induced collapse of initially unsaturated soils. The performance of the proposed model is demonstrated by backcalculation of a well-documented experimental study on over 30 samples of compacted Pearl clay by Sun et al. [2004] under isotropic as well as triaxial loading conditions. For this purpose, the proposed model is coupled with a hypoplastic model for the soil-water retention curve, which interrelates the effective degree of saturation with the suction and the void ratio.Item Fusion of Sparse Non-co-located Measurements from Multiple Sources for Geotechnical Site Investigation(Canadian Science Publishing, 2023-10-13) Guan, Zheng; Wang, Yu; Phoon, Kok-KwangA profile of geotechnical properties is often needed for geotechnical design and analysis. However, site-specific data might be characterized as MUSIC-X (i.e., Multivariate, Uncertain and Unique, Sparse, Incomplete, and potentially Corrupted with “X” denoting the spatial/temporal variability), posing a significant challenge in accurately interpreting geotechnical property profiles. Different sources, or types, of data are commonly available from a specific site investigation program, and they are usually cross-correlated, and thus can provide complementary information. This leads to an important question in geotechnical site investigation: how to integrate multiple sources of sparse data for enhancing the profiling of different geotechnical properties. To address this issue, this study proposes a novel method, called fusion Bayesian compressive sampling (Fusion-BCS), for integrating sparse and non-co-located geotechnical data. In the proposed method, the auto- and cross-correlation structures of different sources of data are exploited in a data-driven manner through a joint sparse representation. Then, profiles of different geotechnical properties are jointly reconstructed from all measurements under a framework of compressive sampling/sensing. The proposed method is illustrated using simulated and real geotechnical data. The results indicate that accuracy of the interpreted geotechnical property profiles may be significantly improved by integrating multiple sources of site investigation data.Item Detection of outliers with respect to a MUSIC geotechnical database(Canadian Science Publishing, 2023-09-02) Ching, Jianye; Phoon, Kok-Kwang; Huang, PengshengThis paper proposes a novel method that addresses a non-traditional class of outlier detection problems. The purpose of most outlier detection methods in the literature is to detect outliers within a dataset. A record can be considered as an outlier if it is distinct from the regular records in the dataset. However, the purpose of the novel outlier detection method proposed by this paper is to detect outlier data groups (a data group may denote a site or a project) with respect to a soil/rock property database. A data group is an outlier group if its characteristics (mean, variance, correlation, or higher order dependency) are distinct from the regular data groups in the database. This paper frames the outlier detection problem into a formal hypothesis testing problem with the null hypothesis “the target data group is identically distributed as the regular groups in the database”. With the hierarchical Bayesian model (HBM) previously developed by the first two authors, the p-value for this hypothesis testing problem can be estimated rigorously. Numerical and real examples show that the p-value can effectively detect outlier data groups as well as outlier records with respect to a database.Item A SHANSEP approach to quantifying the behaviour of clayey soils on a constant shear drained stress path(Canadian Science Publishing, 2023-09-18) Reid, David; Fanni, Riccardo; Fourie, AndyAssessing the risk of slope failures of earth structures comprising loose, saturated soils has seen increased focus recently owing to a series of prominent tailings and water dam failures. The potential for the triggering of slope instability by a rising phreatic surface – commonly referred to as the constant shear drained (CSD) stress path – has been well documented over the past few decades for sands and sandy soils under a wide range of loading modes. Alternatively, there has been limited CSD element testing of more clayey soils, with the available data rather showing a dilative tendency through the CSD stress path and mobilised strengths greater than the critical friction ratio, even for specimens commencing CSD shearing from an initially loose state. The current paper expands on the CSD data of clayey soils by testing an iron ore tailings (IOT) and kaolin clay in both triaxial and direct simple shear (DSS) devices, with an emphasis on the DSS. Owing to the tendency for the CSD stress path to result in an overconsolidated condition (i.e. unloading) the tests in the current study were interpreted in the SHANSEP framework given its frequent use to analyse clay behaviour. The results indicated that the SHANSEP framework can reasonably characterise some aspects of CSD behaviour of clays in DSS loading, with some caveats.Item The influence of viscous behavior and static shear stress on the cyclic strengths of plastic soils: a numerical study(Canadian Science Publishing, 2023-12-01) Oathes, Tyler J; Carey, TrevorAn accurate understanding of the cyclic behavior of clays and plastic silts is important for system performance predictions during earthquake loading. This paper presents the results of a numerical investigation into the individual and combined influences of static shear stress and viscous strength gain on the cyclic resistance of clays and plastic silts. Using the viscoplastic constitutive model PM4SiltR implemented in the finite difference program FLAC 8.1, the cyclic behaviors of the plastic soils were simulated using single-element cyclic direct simple shear simulations. A parametric analysis was performed with different combinations of viscous strength gains and static shear stresses. The effects of static shear stress and viscous strength gain varied under monotonic and cyclic loading conditions. Empirical correlations developed using scant laboratory data may not accurately predict the reduction of cyclic strengths with increasing static shear stress. Furthermore, sizeable magnitudes of monotonic viscous strength gains only produced a marginal increase in cyclic strengths. The findings from this study highlight the need for future experimental laboratory testing to validate the numerical findings, in order to improve the accuracy of performance predictions of geosystems constructed with clays and plastic silts during and following earthquake loading.Item Use of recycled tyre segments to enhance the stability of ballasted track by increased confinement(Canadian Science Publishing, 2023-04-24) Mishra, Soumyaranjan; Indraratna, Buddhima; Rujikiatkamjorn, Cholachat; Ngo, TrungThe most common railway ballast is produced by quarrying, and its mechanical characteristics are crucial for both stability and drainage for safer and faster rail operations. Ballasted tracks have certain drawbacks, primarily because ballast starts to degrade over time. In this regard, reducing the rate of ballast degradation is vital to enhance track longevity and minimise maintenance costs. This paper demonstrates how segments of waste rubber tyres (e.g. 3m in diameter) from the mining industry can improve stability of tracks, while contributing to reduced ballast deformation and degradation. By placing arched segments along the track shoulders beyond the edge of sleepers, the in-situ lateral confining pressure can be increased from 20-25 kPa (standard track) to 40-50 kPa. This novel idea of Confined-Caterpillar Track (CCT) was tested at a prototype physical model (1:1 scale) at the National Facility for the Heavy-haul Railroad Testing (NFHRT), and the experimental outcomes compared to the performance of a conventional track. Apart from constributing to at least 25% saving of quarried aggregates, the test results prove that the CCT concept can curtail the lateral displacement and settlement of the ballast layer, while reducing particle breakage and effecting significant stress reduction in the underlying substructure layers.Item Sequentially Coupled Thermal-Hydraulic-Mechanical Simulation for Geomechanical Assessments of Caprock Integrity in SAGD(Canadian Science Publishing, 2023-09-08) Zhang, Bo; Chalaturnyk, Rick; Boisvert, JeffOil sand reservoirs and caprock undergo deformations triggered by pore pressure increases and thermal induced stresses during the steam-assisted-gravity-drainage (SAGD) processes. Geomechanical assessments are mandated by energy regulators to evaluate the caprock integrity and ensure the safe SAGD operations. Commercial reservoir simulation packages started to incorporate geomechanical effects when predicting flow response; however, these geomechanical modules are not able to correctly model the plastic deformations caused by thermal-hydraulic-mechanical (THM) interactions, which has a first order effect on predicting steam chamber propagation and evaluating caprock integrity. An integrated coupled THM modeling methodology is proposed here to improve the modeling of reservoir deformations and caprock integrity in a heterogeneous oil sand reservoir with interbedded shale barriers. The pressure and temperature front are found to propagate at different speed and that dominate the elastic and plastic deformations caused by changes of shear and mean effective stress. Therefore, four stages are divided in the SAGD process that can be interpretations of changes in stress paths including buildup of pore pressure, generation and dissipation of thermal induced stresses. The response surfaces of minimum factor of safety (FOS) are introduced and computed to provide a conservative estimate for caprock integrity during SAGD of a heterogeneous reservoir with multiple layers of caprocks in Athabasca oil sands.