Showing papers in "Canadian Geotechnical Journal in 2023"
TL;DR: In this paper , a caliche stiffened pile (CSP) is proposed to optimize the required pile length in a cost-effective approach without ameliorating soil properties, which can reduce pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at pile head and toe.
Abstract: While design methods of deep foundations are mainly developed for homogenous soil deposits, the presence of highly-cemented layers could lead to underestimation of resistance and overestimation of settlement of pile foundations. This study presents a novel approach using competent caliche layers bonded to the top and bottom of a continuous flight auger (CFA) pile as a new composite foundation system named caliche stiffened pile (CSP). The key objective is to optimize the required pile length in a cost-effective approach without ameliorating soil properties. Settlements of the CSP foundation for a high-rise building were monitored and full-scale tests were conducted to measure piles’ capacity. Finite element back analyses were performed to avoid adverse effect of sample disturbance in settlement calculations. A back calculation of a test fill embankment was performed to determine soil stiffness parameters by simulating an unscheduled imposed load to the structure. Impacts of the CSP on controlling the settlement of pile foundation and optimizing the required pile length are investigated using finite element analysis and a parametric study. The proposed CSP foundation can reduce the pile settlement significantly in the presence of caliche layers with thickness equal or greater than a pile diameter at pile head and toe.
4 citations
TL;DR: In this article , an experimental campaign to capture soil water retention curve (SWRC) and hydraulic conductivity function (HCF) of unsaturated rooted soils was conducted at different temperatures (25, 45 and 60 ℃).
Abstract: Soil temperature of vegetated landfill earthen covers varies with time during their service, due to heat released by the degradation of municipal solid waste. In this study, an experimental campaign to capture soil water retention curve (SWRC) and hydraulic conductivity function (HCF) of unsaturated rooted soils was conducted at different temperatures (25, 45 and 60 ℃). Simplified evaporation tests were conducted by subjecting soil specimens to a prolonged drying period at maintained temperature. Based on the responses of matric suction and water content, SWRC and HCF were determined by the instantaneous profile method. It was found that increasing temperature reduced water-retention capacity, due to root shrinkage, thermal expansion of liquid phase and reduction in forces of capillarity and adsorption. Soil hydraulic conductivity was enhanced by the increase in soil temperature due to reduction of water viscosity and potential preferential flow at root channels induced by root shrinkage. Temperature effects on SWRC and HCF of rooted soils are suction-dependent. A new nonisothermal SWRC model was developed to capture the dual effects of roots and temperature. By using the same set of calibrated parameters, the model demonstrates its ability to predict SWRCs reasonably well within the range of temperature investigated.
3 citations
TL;DR: The degradation in physical and mechanical properties of a 1.5 mm-thick HDPE geomembrane immersed in seven different low pH and three high pH simulated mining solutions is examined at temperatures between 95 and 40oC for 3 years as discussed by the authors .
Abstract: The degradation in physical and mechanical properties of a 1.5 mm-thick HDPE geomembrane immersed in seven different low pH and three high pH simulated mining solutions is examined at temperatures between 95 and 40oC for 3 years. The solutions with pH between 0.5 and 13.5 encompass solutions found in copper, nickel, uranium, gold, and silver heap leach pads. The geomembrane did not exhibit any chemical degradation during the 3 years of incubation in all the low pH solutions. However, in the solutions with pH 9.5, 11.5, and 13.5, the physical and mechanical properties are shown to reach nominal failure at 95 and 85oC. While the examined geomembrane showed superior performance in the examined acidic environments than in basic solutions, its performance in such extremely basic environments was still better than in neutral reduced municipal solid waste leachate. Using Arrhenius modelling the predicted times for the antioxidant depletion stage of the geomembrane examined in composite liner configuration range between 31 years in pH 13.5 to 51 years in pH 0.5 for pad liners at 50oC exceeding a typical leaching period of the ore of around 20 years in different heap leaching operations.
2 citations
TL;DR: In this paper , a hierarchical Bayesian model is proposed to predict the small-strain shear modulus Gmax for a target sand type, which combines the limited target-specific data with the abundant generic data through a hierarchical structure so that the variability of Gmax within one sand type and across different sand types can be captured.
Abstract: This paper develops a hierarchical Bayesian model (HBM) that integrates the physical knowledge and the test data to predict the small-strain shear modulus Gmax for a target sand type. The limited target-specific data is combined with the abundant generic data through a hierarchical structure so that the variability of Gmax within one sand type and across different sand types can be captured. The hyperparameters that characterize the same underlying distribution of physical model parameters across all the sand types are first estimated from the abundant generic data. The model parameters for the new sand type are then updated as the limited site-specific data become available. The approach is illustrated using a generic database and two real examples not covered by the generic database. Multiple possible hierarchical models are compared in terms of model complexity and goodness-of-fit. The results show that the hierarchical modeling of small-strain shear modulus data is reasonable and necessary. The hierarchical model can provide less biased and more accurate predictions of Gmax compared to the commonly used complete pooling model, especially for cases where the site-specific data is quite different from the overall average of the generic database.
2 citations
TL;DR: In this article , a data-driven multi-task Bayesian compressive sensing (MT-BCS) method was proposed to estimate missing data for CPT sounding of interest, and then developed a modified 2D BCS method for fast interpolation for horizontal locations without CPT soundings.
Abstract: Because cone penetration test (CPT) is reasonably rapid, affordable and repeatable, it has been widely used in-situ for subsurface soil stratification and classification in geological and geotechnical engineering practice. When used for soil stratification across a two-dimensional (2D) geological cross section, however, it is often observed that some CPTs probe deeper than others, and that some CPT soundings may contain missing data due to presence of gravel-sized particles or intentional bypassing of gravelly soil layers. Arguments above and frequently encountered problem of a small number of CPT soundings in practice pose a great challenge for 2D soil stratification, especially for non-stationary CPT within multi-layers. While certain methods have been proposed hoping to address these concerns, they are frequently constrained by either stationary assumption of data, autocorrelation function forms, or computational issues. This study introduces a data-driven multi-task Bayesian compressive sensing (MT-BCS) method to estimate missing data for CPT sounding of interest, and then develops a modified 2D BCS method for fast interpolation for horizontal locations without CPT soundings. The proposed method is demonstrated and validated using both numerical and real-world CPT data. Results show that proposed method is both efficient and robust in terms of missing data estimate in each CPT sounding and soil stratification for a 2D geological cross section.
2 citations
TL;DR: In this paper , a study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented, which highlights the importance of specifying the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained.
Abstract: A study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented. At the clay’s in-situ water content, the results of pull-out tests on short length piles revealed no dependency of shaft capacity on overburden stress. Conversely, after achieving a targeted value of swell, a strong dependency on overburden stress was observed. In upper portions of the profile where swell can occur relatively freely, swell-induced softening results in a reduction in pile shaft capacity. However, at greater depths where swell is largely suppressed, so too are the effects of swell-induced softening. For this reason, shaft capacity at depth was found to remain relatively constant before and after swell. The results of an instrumented pile test revealed an overriding dependency of lateral induced swell pressure on the magnitude of heave which has occurred. Irrespective of the level of overburden stress, lateral pressures against the pile were found to increase at early stages of the swelling process, but then reduce as swell continued and softening began to occur. Such a result highlights the importance of specifying the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained.
2 citations
TL;DR: In this article , the effects of both particle size and particle size distribution on the critical state loci were quantified and two soils, a natural soil and a tailings, were selected and CSLs were identified for twelve uniform and well graded particle size distributions.
Abstract: The critical state soil mechanics captures a wide range of stress-strain behaviour in an understandable context. It provides a conceptual framework for predicting soil behaviour and that is why the critical state is a central part of most advanced constitutive models. This study aims at quantifying the effects of both particle size, and particle size distribution on the critical state loci. Two soils, a natural soil and a tailings, were selected and CSLs were identified for twelve uniform and well graded particle size distributions. Mineralogy and particle shapes were rigorously quantified to ensure other factors are not influencing the results. Particle size has a small influence on the CSL in the sand to gravel range, but silts can have a significantly different CSL. In both natural soil and tailings, particle size distribution appears to have a significant influence on the CSL in e-logp’ space and little influence in q-p’ space. Well graded soils have lower CSLs compared to uniform ones, that are generally parallel to the CSLs of their dominant constituent, with the exception of convex distributions where progressively finer particles in larger proportions can form structures noticeably less compressible than any of their constituents.
2 citations
TL;DR: In this article , the effect of the urease enrichment degree of high-purity commercial ureases and plant-derived crude Ureases from sword bean (SWCU), soybean (SCU), and pigeon pea (PCU) on bio-cementation efficacy via enzyme-induced carbonate precipitation was investigated.
Abstract: This study aims to investigate the effect of the urease enrichment degree of high-purity commercial urease and plant-derived crude ureases from sword bean (SWCU), soybean (SCU), and pigeon pea (PCU) on bio-cementation efficacy via enzyme-induced carbonate precipitation. The urease enrichment degree is defined as the urease activity per gram of organic matter in the urease solution. Bio-cementation efficacy was evaluated by the distribution and morphology of the precipitates and unconfined compressive strength. The results show that the urease enrichment degrees of the high-purity commercial urease, SWCU, PCU, and SCU are 1.08, 1.05, 0.57, and 0.31 mmol/min/g, respectively. The urease enrichment degree is the dominant factor influencing the pattern of CaCO3 distribution by affecting the organic matter distribution. The high-purity commercial urease-treated sand has the smallest calcite crystals (13-23 μm) and the lowest strength (172 kPa). For the plant-derived crude urease, with the decrease of the urease enrichment degree, the generated crystals become smaller, the CaCO3 distribution becomes less uniform, and the soil strength decreases. The SWCU-treated sand exhibits the best bio-cementation efficacy and is recommended to enhance soil strength.
2 citations
TL;DR: In this paper , the authors investigated the multiscale structural properties of granite residual soil using stereo microscopy, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and computed tomography.
Abstract: While the anisotropy of sedimentary soil—particularly the underlying role of soil structure—is well understood, similar knowledge about granite residual soil formed by weathering is scarce. In particular, the evolution of soil structure during the hollow cylinder torsional shear tests (among the most appropriate for studying soil strength anisotropy) remains largely unknown. This study systematically investigates the multiscale structural properties of granite residual soil using stereo microscopy, scanning electron microscopy, energy-dispersive spectrometry, and computed tomography. Furthermore, the structural evolution during hollow cylinder torsional shear tests is traced. Results indicate the strength anisotropy of residual soil is associated with horizontal fissures which cause low shear strength when the soil is sheared with a principal stress direction of 45°. The cementation via Fe is characterized by a uniform distribution. Different evolutionary patterns are observed for soils within the shear band, inside the necking area, and in other regions. It is not always the case that particles are rearranged with their long axis perpendicular to the major principal stress. This study improves the understanding of natural residual soil structure and provides some insights into its anisotropic behavior.
2 citations
TL;DR: In this article , the authors developed a new model called Hybrid Trench Model (HTM) by combining the linear soil stiffness and non-linear hysteretic seabed interaction model to resolve these problems.
Abstract: The gradual trench formation of steel catenary risers (SCRs) in the touchdown zone (TDZ) is known to have a significant effect on the SCR’s fatigue life. However, there is still no coherent agreement amongst the researchers on the beneficial or detrimental effects of the trench on fatigue. Recent studies have shown that a potential source of contradictory fatigue results would be the methodology to incorporate the trench in the numerical simulations. The predefined mathematical trench profiles would create non-realistic contact pressure hot spots in the seabed, and the non-linear hysteretic seabed interaction models may cause premature trench stabilization, both of which distort the damage distribution. The current study has developed a new model called Hybrid Trench Model (HTM) by combining the linear soil stiffness and non-linear hysteretic seabed interaction model to resolve these problems. The hybrid model provides a non-linear elastic seabed stiffness distribution in the touchdown zone to simulate the trench profile obtained from a non-linear riser-seabed interaction model. The capability of the HTM in developing deep trenches, e.g., 5D, was examined along with perfect compatibility with the natural catenary shape of the riser, showing the reliability of the developed model to incorporate the trench into the fatigue analysis.
1 citations
TL;DR: In this article , the impact of resins on the behavior of cable bolts under varying load and stress regimes over their long service life was investigated. But the results showed that the resin product had a relatively low load capacity regardless of the cable type and that loading type had a minimal impact on the results.
Abstract: The ease of use and the design flexibility of cable bolts have made them a popular choice for rock support. Cable bolts can be encapsulated with cementitious grout or resin. There is a need to better understand the impact of resins on the behaviour of cable bolts under varying load and stress regimes over their long service life. This study reports on 18 large scale resin pull-out tests using a 1000 kN pull-out apparatus. The testing apparatus minimised the rotational movement of the cable at the exit point by using a fully grouted anchor tube. Six cable bolts, ranging from 50 to 100 tonnes in capacity, anchored using a fast-curing urea silica resin, were tested under monotonic and cyclic loading. Each cable type was tested twice in monotonic loading and then the average initial peak load was used to generate a cyclic loading pattern. The study found that the resin product had a relatively low load capacity regardless of the cable type, and that loading type had a minimal impact on the results. The cable diameter had a minor influence on the pull-out results. The resin provided a stiff behaviour and an excellent response to repeated loading.
TL;DR: In this paper , a multi-component model employing a tandem combination of different sub molecular oedometers for different minerals and the total swelling strain of soil was calculated by integrating the swelling strain for each mineral.
Abstract: The accurate prediction of swelling deformation and/or swelling pressure if confined for expansive soil is essential to a better design and construction of geotechnical structure that is built on or in expansive soils. In this paper, we proposed a new method to quantify the swelling strain and/or swelling pressure of expansive soil with considering the mineralogical components and their different swelling properties. The proposed multi-component model employs a tandem combination of different sub molecular oedometers for different minerals and the total swelling strain of soil was calculated by integrating the swelling strain of each mineral. A linear relationship between potential energy and swelling strain is identified based on molecular dynamics simulation, which is then incorporated into diffuse double layer theory to calculate the relationship between confining pressure and swelling strain for each mineral. The numerical model was then validated by experimental results from the literature, which shows a good agreement with the experimental data in the literature. This model provides a cost-effective way to estimate the swelling behavior of expansive soil.
TL;DR: The TAMU-MineSlope database as discussed by the authors contains 134 cases of open pit slope failures that occurred at 76 mines worldwide, and the average width to height ratio of the failing slope mass is 2.7 and that, for this ratio, the 3D factor of safety can reach a value 15% higher than the 2D FS.
Abstract: In mining, open pits have slopes cut as steep as possible to ensure efficient mining yet not too steep to jeopardize safety. Building on existing contributions, the Texas A&M University Mine Slope database (TAMU-MineSlope) was created to provide global-scale insights into the runout mechanics of open pit slope failures and offer the database to engineers for further study. The database includes 134 cases of open pit slope failures that occurred at 76 mines worldwide. Based on energy principles and an analysis of the TAMU-MineSlope data, an equation to predict the travel distance of the slope failure mass is presented in this paper. Furthermore, based on the case histories analysis, an equation to predict the setback distance is proposed. Finally, the TAMU-MineSlope database shows that the average width to height ratio of the failing slope mass is 2.7 and that, for this ratio, the 3D factor of safety (FS) can reach a value 15% higher than the 2D FS. The database has been released in the public domain.
TL;DR: In this paper , four bridge scour depth prediction models were assessed in terms of two statistical parameters, termed the mean absolute percentage error (MAPE) and conservatism, the percentage of cases the predicted scour depths exceeded the measured scours.
Abstract: To design the foundation system of waterway bridges, Load and Resistance Factor Design guidelines suggest use of deterministic scour depth prediction models. Understanding the inherent bias of deterministic scour depth prediction models will advance the development of reliability index-based foundation design regime. Four bridge scour depth prediction models were assessed in terms of two statistical parameters, termed herein mean absolute percentage error (MAPE), and conservatism, percentage of cases the predicted scour depth exceeded the measured scour depth. Live-bed laboratory and field scour depth databases were used in analyses to quantify model scatter by comparatively assessing the computed scour depth versus measured data. For live-bed laboratory data, values of MAPE ranged from 23.5% to 59.8%, whereas conservatism ranged from 28.4% to 97.8%. For live-bed field data, conservatism varied from 93.3% to 95.1%, while MAPE ranged from 205.6% to 319%. Statistical models were applied to ascertain the biasness of the four deterministic models. Accuracy and conservatism of a given model were consequently adjusted through proposed modification factors. The proposed approach allows for the selection of a suitable modification factor to satisfy a target probability of deceedance or a target conservatism.
TL;DR: In this paper , the deformation, pore pressure and water content measurements were used to investigate and separate the mechanisms governing the run-out of fly ash deposits following a loss of lateral confinement.
Abstract: Numerous industries are concerned by the humanitarian, environmental, and economic consequences of debris flows, landslides and material run-outs. However, the run-out behavior following a loss of confinement e.g., dam failure, is not well understood. The material’s complex constitutive behavior means multiple mechanisms contribute to the deformation e.g., slope instability, seepage forces, erosion or static liquefaction. In this study, centrifuge models of fly ash deposits, with varying initial deposit density and water table height, were subjected to a rapid loss of lateral confinement. Deformation, pore pressure and water content measurements were used to investigate and separate the mechanisms governing the run-out. Static liquefaction was observed in deposits initially looser than the critical state and led to a rapid material outflow. Slope instability was the initial failure mechanism for denser deposits or those with reduced water tables, with transient stability due to dilation-induced negative excess pore pressures followed by progressive failures caused by seepage pressures from drainage and pore pressure dissipation. Cone penetration tests, performed before the loss of confinement at different penetration rates, were used to characterize the material run-out and volume change tendencies and demonstrate a practical tool for assessing the run-out risk of deposits in the field.
TL;DR: In this paper , a database called CYCU/RockTip/51 consisting of 51 rock-socketed drilled shafts installed at different sites worldwide covering a wide variety of rock properties and shaft geometries was compiled.
Abstract: This study compiled a database called CYCU/RockTip/51 consisting of 51 rock socketed drilled shafts installed at different sites worldwide covering a wide variety of rock properties and shaft geometries. The tip resistances from seven representative prediction models are compared to the measured values. These measured values are obtained from the load-displacement curves of field load tests using three interpretation criteria. It was found that the prediction models of Teng, Coates, Rowe and Armitage, and ARGEMA over–predicted the measured capacity, while Zhang and Einstein, Vipulanandan et al., and Zhang are less biased. These tip prediction models also could be classified according to displacement requirements. The proposed tip prediction models of this study are presented based on different interpretation methods and the displacement ranges that they are mobilized. Finally, the normalized load displacement curve is fitted to hyperbolic curve with two model parameters (a and b). The a and b parameters define the reciprocal of the initial slope and the asymptotic resistance, respectively. The statistics of (b, a) for rock-socketed drilled shafts in CYCU/RockTip/51 are mean = (0.76, 1.09), COV = (0.13, 0.59), and a correlation coefficient = −0.79. These statistics are useful for reliability-based design.
TL;DR: In this article , the axial forces and wall strains of MDPE gas distribution pipes were investigated using full-scale laboratory tests, and it was shown that axial force on the branch and wall strain on the main pipe depend on the burial depth, backfill soil density, and pipe diameter due to the effects on the shearing resistance of the soil.
Abstract: Buried medium-density polyethylene (MDPE) pipes are widely used for gas distribution systems in Canada and worldwide. When exposed to geotechnical hazards such as ground movements, these pipes can experience excessive distresses, leading to leaking or failure. This research investigates the effects of ground movement near a tee connection of MDPE gas distribution pipes. If the ground movement is parallel to a branch, the branch pipe experiences an axial force, and the main pipe experiences bending deformation/strains. The axial forces and the wall strains were investigated in this study using full-scale laboratory tests. Test results showed that the axial force on the branch and strains on the main pipe depend on the burial depth, backfill soil density, and the pipe diameter due to the effects on the shearing resistance of the soil. The soil shearing resistance was less for shallow buried pipes, resulting in a lower axial force in the branch but higher bending strain in the main pipe. The axial pullout resistance of the main pipe also contributed to the wall strains of this laterally loaded pipe at large displacements. The conventional beam-on-elastic foundation solution reasonably estimated the pipe wall strains within the linear range of deformations. Nonlinear analyses, including lateral and axial soil springs, are recommended to capture the nonlinear responses at large displacements.
TL;DR: In this article , the authors revisited the 2010 Saint-Jude spreading landslide by using the Coupled Eulerian-Lagrangian (CEL) approach within ABAQUS to reveal the failure mechanism of spreading landslides.
Abstract: Spreading landslides are geohazards that often occur in sensitive clay areas. A unique characteristic of the spreads is that an initial small local slope failure may cause a catastrophic landslide above the horizontal failure surface, forming horsts and grabens. Although, many hypotheses were proposed to explain the failure mechanism of spreads, however, some topography of the landslides observed from field investigations cannot be well explained by the existing hypotheses. This study revisits the 2010 Saint-Jude spreading landslide by using the Coupled Eulerian-Lagrangian (CEL) approach within ABAQUS to reveal the failure mechanism of spreading landslides. Two types of cross-sections (static and dynamic cross-sections) are selected to monitor the total horizontal force of the sliding mass during the process of migration. It is found that there are two spreading failure mechanisms to form horsts and grabens. The first one is the static spread failure mechanism that global failure occurs accompanied by spreading failure. The other one is the dynamic spreading failure mechanism that after the global failure, the sliding masses break into horsts and grabens during the forward movement under the pushing of the sliding mass at the back and the blocking action of the soil mass in the front. These two failure mechanisms of spreads can well explain various geomorphologic shapes found in the Saint-Jude landslide.
TL;DR: In this article , a series of pullout tests were conducted on anchor cables with five different anchor lengths and three grouting methods and the in-situ pullout test results showed that both ultimate pullout resistance and ultimate displacement increase with anchor length.
Abstract: This study focuses on the in-situ pullout behavior of grouted anchor cables using Brillouin Optical Time-Domain Analysis (BOFDA) technique. A series of pullout tests were conducted on anchor cables with five different anchor lengths and three grouting methods. Distributed fiber optic sensors were used to measure the strain distribution of cable bolts from tip to top. The in-situ pullout test results show that both ultimate pullout resistance and ultimate displacement at the ultimate pullout resistance increase with anchor length. The bond strength suffers a slight variation with an increase in anchor length. Both ultimate pullout resistance and the ultimate displacement for Type-B grouting (grouting with reaming) and Type-C grouting (secondary grouting) are larger than those for Type-A grouting (one-time grouting). The shear bond strength of Type-C grouting is greater than that of Type-A grouting. Results from Gaussian functions analysis show that it is feasible to use the function to characterize the axial stress of anchor cables. Furthermore, the overall mobilized percentage η was evaluated. The anchor cables with smaller anchor lengths will result in greater η. The η for the anchor cables of 6 m reaches 92% at the last load, whereas the anchor cables of 18 m were mobilized by only 29% at the last load. The grouting method has a negligible effect on the η.
TL;DR: In this paper , a decision-making approach based on the fuzzy VIKOR method is proposed to identify the optimal risk-control scheme, where a triangular fuzzy set is adopted to express the experts' judgements.
Abstract: Risk events can be frequently encountered in karst geological environments during excavation construction; thus, a suitable risk-control scheme is essential to reduce the negative impact of accidents. A decision-making approach based on the fuzzy VIKOR method is proposed to identify the optimal risk-control scheme, where a triangular fuzzy set is adopted to express the experts’ judgements. A decision hierarchy is constructed based on four criteria and twelve sub-criteria, which are determined based on engineering experience and the construction environment. The developed approach was utilized to determine the optimal risk-control scheme to address risk events for excavation construction in karst regions. A countermeasure scheme, i.e., pressure grouting with a two-phase liquid system, was implemented. The basic principles and steps of the implementation of the proposed scheme are presented. The applicability of the identified scheme was verified by the core recovery and modified number of blows using a standard penetration test. A flowchart of optimal scheme identification for geotechnical engineering practice is provided.
TL;DR: In this article , new empirical predictive relationships for earthquake-induced crest settlement of earth-core rockfill dams (ECRDs) were developed, which correlate the intensity measure (IM) of the earthquake records with the observed settlements, and thus, employing IMs that appropriately describe the severity of ground motion is of vital importance.
Abstract: In this study, new empirical predictive relationships for earthquake-induced crest settlement of earth-core rockfill dams (ECRDs) were developed. A case history database of 19 dams that had been subjected to earthquakes was utilized. The presented relationships correlate the intensity measure (IM) of the earthquake records with the observed settlements, and thus, employing IMs that appropriately describe the severity of ground motion is of vital importance. It is well known that the dynamic properties of an ECRD can change significantly depending on the severity of an earthquake, and that this phenomenon can substantially impact the dynamic responses of dams. Accordingly, two IMs were suggested, taking into account the essential characteristics of ground motions affecting the nonlinear behaviour of ECRDs. The results indicate that the proposed relationships effectively address the limitations of the existing ones, and that they are practical tools that efficiently predict the seismic settlements of ECRDs.
TL;DR: In this paper , numerical analyses of the impoundments loaded with a variety of ground motions with different frequencies, scaled at two different levels of intensity representative of two mining regions of Eastern Canada.
Abstract: Tailings impoundments can fail during or after a seismic event, mainly because of the liquefaction of loose, cohesionless tailings. To improve the seismic stability of impoundments, the density of the tailings can be increased or waste rock inclusions (WRI) can be added in the impoundment. This paper presents the results of numerical analyses of the impoundments loaded with a variety of ground motions with different frequencies, scaled at two different levels of intensity representative of two mining regions of Eastern Canada. The results show that the conventional impoundments are subjected to medium to high displacements at the end of shaking; these show a high probability of rupture during the earthquake or in the post-seismic phase. Tailings densification can decrease the volume of liquefied tailings and displacements during the seismic phase but does not significantly reduce the probability of post-seismic failure. WRI can slightly reduce the volume of liquefied tailings, depending on the intensity of the motions, but the reinforcement reduces significantly the lateral displacements; impoundments with WRI show even better performances during the post-seismic phase. The use of WRI is deemed a good approach to ensure the seismic stability of tailings impoundments and reduce the risk of seismically induced failure.
TL;DR: In this paper , the results of a series of cyclic nonsymmetrical thermally loaded model-scale tests conducted on floating pile groups, with and without a rigid cap in saturated clay, were presented.
Abstract: This paper presents the results of a series of cyclic nonsymmetrical thermally loaded model-scale tests conducted on floating pile groups, with and without a rigid cap in saturated clay. The energy pile in each group was subjected to ten two-way (heating-cooling) thermal cycles with an amplitude of 15 °C to investigate the potential effects of a rigid cap on the thermo-mechanical behavior of energy pile groups. It was found that the rigid cap restrained the expansion/contraction of the energy pile in response to temperature change and reduced its irreversible settlement, resulting in a lower differential settlement between the energy pile and non-energy piles. Consequently, a lower tilting was observed at the pile group with a rigid cap. In addition, the thermally induced axial load was significantly increased (especially in cooling mode) due to the restriction of a rigid cap. The thermo-mechanical load transfer profile of the energy pile was also affected by it, resulting in the downward transmission of shaft resistance.
TL;DR: In this paper , a unified indicator, i.e., the time-dependent fracture potential index (ξTFPI), is proposed to conveniently describe the effect of applied stress on the creep process.
Abstract: To understand the time-dependent fracture behaviour of hard rock in the excavation damage zone (EDZ), a series of stress paths are designed to obtain the same initial damage extent induced by excavation. The influence of initial damage under different stress states on the creep process of Beishan granite is investigated experimentally. A unified indicator, i.e. the time-dependent fracture potential index (ξTFPI), is proposed to conveniently describe the effect of applied stress on the creep process. The results show that the time-dependent strain increases with increasing initial damage extent and is significantly affected by the applied stress at a given initial damage extent. Under the same initial damage extent, with the increase in ξTFPI, the larger the primary creep strain rate and secondary creep strain rate are, and this phenomenon is more obvious in the lateral creep results. The secondary creep strain rate increases with increasing ξTFPI, and the increasing trend of the axial secondary creep strain rate with ξTFPI is greater with a higher initial damage. Finally, a quantitative relationship of the secondary creep strain rate with the initial damage and ξTFPI is established and validated against the experimental results.
TL;DR: In this article, the authors describe recent instrumented driving, monotonic testing to failure and re-strike tests conducted on large open steel piles driven in primarily low-to medium-density chalk at a site in North-western France.
Abstract: The design of large open steel piles driven at chalk sites suffers from considerable uncertainty, leading to major difficulties in many significant onshore and offshore projects. This paper describes recent instrumented driving, monotonic testing to failure and re-strike tests conducted on large open steel piles driven in primarily low- to medium-density chalk at a site in North-western France. The experiments are described and interpreted with reference to a high-quality site characterisation, dynamic and static methods of test analysis and alternative predictive design approaches. Important new conclusions flow regarding driving behaviour, the set-up that took place over up to 65 days after installation and the resistances available under compression and tension loading. Surprisingly large differences are shown between tension and compression shaft capacity which are postulated to be due to Poisson straining in the steel pile shaft and its interaction with the surrounding chalk mass. The field tests contribute to building a high-quality dataset that allows proposed axial capacity design methods to be tested and potentially refined to provide reliable and representative design tools.
TL;DR: In this paper , the mechanics of filtered compacted normally consolidated (NC) and overconsolidated (OC) iron ore tailings were studied by performing triaxial testing at high pressures of up to 120 MPa.
Abstract: The mechanics of filtered compacted normally consolidated (NC) and overconsolidated (OC) iron ore tailings (IOT) was studied by performing triaxial testing at high pressures of up to 120 MPa. The OC specimens were obtained by isotropically compressing compacted IOT to 120 MPa, unloading it to distinct confining pressures, and shearing at constant radial stress. Particle size distribution analyses were used to examine the effect of compression and shear stresses on particle breakage. Additionally, the triaxial test results illustrate the stress history influence on the deviatoric stress – axial strain – volumetric strain curves, as well as on the IOT peak strength. Furthermore, these results also show that the amount of breakage during the shearing stage plays an essential role in the geomaterial’s response, marking the existence of curved Critical State Locus (CSL) in both v - ln p' and q – p' planes, which is unique in the studied confined stress range (4 to 120 MPa) for the compacted NC and OC (considering OC ratio up to 30) iron ore tailings.
TL;DR: In this paper , a closed-form solution for evaluating the layered slope stability with tension cracks without any priori assumptions is presented. And the results show that the dominant failure mode of layered slopes could change from toe failure (without cracks) to face/base failure (with tension crack), which has not been previously reported.
Abstract: Evaluating the stability of layered slopes, a common type of terrain in nature and engineering practice, poses a fundamental challenge in the field of geotechnique. The emergence and extension of tension cracks play a crucial role in the failure process of layered slopes, but accurately predicting the location of layered slope cracking and assessing its impact on layered slopes remains a challenge using conventional analytical methods. Herein, we present a closed-form solution for evaluating the layered slope stability with tension cracks without any priori assumptions. The presented closed-form solution enables the location and depth of tension crack, the critical failure surface in different soil layers, and the corresponding normal stress distribution to be determined for all single/layered slopes. Effects of tension cracks on layered slopes are investigated, considering slope inclination, soil properties, layer thickness and dominant failure mechanism. Note that, the results show that the dominant failure mode of layered slopes could change from toe failure (without cracks) to face/base failure (with tension crack), which has not been previously reported. Multiple cracks are possible to develop in layered slopes. The proposed closed-form solution can be applied to improve the stability assessment and engineering design of layered slopes considering tension crack.