| 1. |
- Duan, Hongyu, et al.
(author)
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Sensitivity analysis of hydraulic erosion and calibration of the erosion coefficient
- 2024
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In: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 338
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Journal article (peer-reviewed)abstract
- Hydraulic erosion may pose a threat to the safety and sustainability of geo-related infrastructure, yet quantifying the intricate process of hydraulic erosion still poses a significant scientific and technical challenge. One important step in meeting this challenge is the formulation of a hydraulic erosion model with the erosion coefficient as a central controlling parameter. Calibration of the erosion coefficient (or rate) remains one of the main obstacles to improving predictive modelling, particularly in scenarios lacking long-term laboratory test data. In this study, sensitivity analysis of the key erosion indicators on the parameters controlling hydraulic erosion is conducted. A novel calibration method for the erosion coefficient is presented based on sensitivity analysis. After validating against simulation results and laboratory test findings, the proposed calibration method is applied to a hypothetical long-term hydraulic erosion case. The results show that the maximum hydraulic erosion time is sensitive to all considered parameters (erosion coefficient, initial fraction of fluidized solid particle, initial porosity and maximum porosity), while the erosion curve shape is only sensitive to the initial porosity and the maximum porosity. The validation by existing simulation results shows that the proposed calibration method is robust and internally consistent. The validation by experimental results indicates that the proposed calibration method also has high external validity. Finally, the proposed calibration method is applied to hypothetical long-term erosion in a grouted area. The results show that the hydraulic erosion effect in the grouted area becomes increasingly severe over time. This study contributes toward a more efficient calibration of the erosion coefficient, especially for scenarios in the absence of testing porosity evolution data. The research outcome provides a theoretical foundation for the safety assessment and sustainability analysis of geotechnical structures that are subject to hydraulic erosion.
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| 2. |
- Fang, Zhou, et al.
(author)
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Forecasting the occurrence of injection-induced heterogeneous slip on rock fractures
- 2023
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In: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 325
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Journal article (peer-reviewed)abstract
- Forecasting the slip behavior of a non-uniformly pressurized, heterogeneous creeping rock fracture, either aseismic creep or dynamic slip, is challenging based solely on laboratory and field measurements. Here we reported a simple, robust method to determine whether an aseismic creep is maintained or transitions to a dynamic slip during fluid injection. We reproduced the non-uniformly distributed fluid pressure and the resulting heterogenous aseismic creep on a critically stressed fracture and revealed the ratio of shear stress and frictional resistance corresponding to the fluid pressure front reaching or exceeding unity at the occurrence of dynamic slip. The determination of frictional resistance is based on the Mohr-Coulomb failure criterion with fluid pressure and friction coefficient on discrete segments of the fracture, and the length of fluid pressure front is calculated from hydraulic diffusivity and elapsed time. We used the experimental results of 9 shale fractures and 3 granite fractures to verify this method. We can also observe how the fluid pressure front propagates until the ratio of shear stress and frictional resistance approaches unity or is constrained with the ratio far below unity. This method has the potential for rapidly forecasting the injection-induced slip on a low-permeability rock fracture and simply characterizing the slip behavior of a natural, large-scale fracture during fluid injection.
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| 3. |
- Fransson, Åsa, 1971, et al.
(author)
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Bentonite rock interaction experiment: A hydro-structural-mechanical approach
- 2021
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In: Engineering Geology. - : Elsevier BV. - 0013-7952. ; 281
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Journal article (peer-reviewed)abstract
- Deformation zones and fractures are of major importance to engineering and to the characterisation of the mechanical- and hydraulic behaviour of rock. In this paper we demonstrate how structural mapping can provide key information on fracture sets and their properties, and how it can be used to investigate conformity between different working scales. This is shown by the detailed structural mapping related to the experiment "BRIE" - Bentonite Rock Interaction Experiment. "BRIE" was carried out in a tunnel of the Aspo Hard Rock Laboratory, Sweden, in crystalline rock. The implemented approach relied on a multidisciplinary and trans-stadial investigation to compile and interpret all the hydrogeological, structural and rock mechanical constraints as inputs to modelling. To this end, available data from all BRIE construction- and experimental stages were used to characterise natural and induced rock stresses. Results from detailed structural mapping of the tunnel and drill cores recovered from the tunnel floor were key for sound rock mechanical modelling and were successfully integrated with the available hydrogeological observations. Structural mapping was used to define five systematic fracture sets, key fractures and their properties (size, friction angle and normal stiffness) and to establish a simple deformation history. Furthermore, the structural features exposed in the studied tunnel and in the logged BRIE cores were compared with those of an adjacent Aspo HRL tunnel. Both sites structurally fit the sub regional tectonic framework, thus showing conformity between very different observation scales.
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| 4. |
- Gupta, Abhishek, et al.
(author)
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Identification of key thermal couplings affecting the bentonite behaviour in a deep geological nuclear waste repository
- 2023
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In: Engineering Geology. - 0013-7952. ; 324
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Journal article (peer-reviewed)abstract
- Deep geological nuclear waste repositories use the multi-layer Engineered Barrier System (EBS) to isolate nuclear waste from the environment. The key component of the barrier is densely compacted bentonite, closely resembling claystone. Therefore, to ensure safety, we need a numerical model for the bentonite and the barrier that predicts EBS behaviour during transient thermal, hydraulic, mechanical and chemical conditions. The paper identifies key mechanisms and processes affecting the bentonite in the barrier due to temperature changes (thermal couplings) based on advanced fully-coupled Finite Element Method simulations. The paper investigates 1) non-isothermal infiltration experiment on FEBEX bentonite (Villar and Gomez-Espina, 2009) and, 2) Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (Ciemat) test (Martin et al., 2006), presenting 10 simulation configurations that are set up by inactivating one thermal coupling/variable at a time. The difference between these simulations and the baseline model results, examined in terms of the net mean stress (swelling pressure), suction and fluid flow, give insights into the significance of investigated coupling. Results suggest that thermal couplings related to vapour density, viscosity, water retention curve, and molecular diffusivity are among the most influential. The study additionally highlights the importance of water transport as liquid and gas, and water evaporation and condensation.
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| 5. |
- Hu, Yingtao, et al.
(author)
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Evaluating the long-term barrier performance of fractured granite for nuclear waste disposal: Impact of fast water-conducting path
- 2024
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In: Engineering Geology. - : Elsevier B.V.. - 0013-7952 .- 1872-6917. ; 337
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Journal article (peer-reviewed)abstract
- Granite has relatively low-permeability and it has been considered as one of favorable geological formation for final disposal of high-level radioactive waste (HLW). However, the granite is often fractured and characterized as complex discrete fracture-matrix systems with considerable degree of uncertainties in its physical and geometrical properties. Prediction of nuclide migration in fractured granite at large spatial and long temporal scales is important for safety assessment of HLW disposal. In the present study, parametric studies are performed to evaluate the long-term barrier performance of fractured granite using the Beishan granite barrier as an illustration example. As the distance between the fast water-conducting path (FWCP) and the disposal pit decreased from 80 m to 0, the nuclides' arrival time (Tt) in the biosphere decreased from 9000 to approximately 2000 years when the effects of the fault and the FWCP are considered. The maximum nuclide concentration (Cmax) increases from 0.0019 (350,000 years) to 0.0121 mSv/y (150,000 years), exceeding the limit of 0.01 mSv/y. In addition, as the permeability (equivalent hydraulic aperture) of the FWCP increased from 5.0 × 10−5 m to 1.0 × 10−4 m, the Tt of Cs-135 further decreases to about 15,000 years, and the Cmax increases to 0.0256 mSv/y (100,000 years), suggesting a significant reduction in the long-term performance of the geological barrier. These findings are helpful for site assessment of HLW repositories built in fractured granite.
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| 6. |
- Jiang, Xiangang, et al.
(author)
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Internal erosion of debris-flow deposits triggered by seepage
- 2023
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In: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 314, s. 107015-
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Journal article (peer-reviewed)abstract
- Debris flows can be triggered by runoffs at considerably steep natural channels and streams. Specifically, runoffgenerated debris-flow deposits are loose mixtures, comprising coarse and fine particles. Owing to seeping water, these fine particles are eroded and transported through the skeleton formed by the coarse particles. Such erosion can modify the porosity of deposits and influence their mechanical characteristics, which can be non-negligible for geotechnical and geological engineering. In this study, seven groups of seepage tests on gravel-sand-clay mixtures with different coarse particle content proportions (48%, 52%, 60%, 70%, 80%, 90%, and 100%) were conducted to investigate the erosion characteristics of debris-flow deposits triggered by seepage flows. In particular, concentrated leak erosion, internal instability erosion, and piping were noted in the soil with a coarse particle content of 48%-80%. Further, when the coarse particle content exceeds 80%, the soil does not disintegrate. A model coupling seepage and internal erosion was also developed to characterise internal erosion. For this model, mass conservation equations were reformulated for different types of internal erosion, based on the assumptions for the pore channel erosion of suspended materials and general erosion. Moreover, an equation based on the internal erosion rate, considering the pore size distribution and hydraulic gradient, was firstly introduced for concentrated leak and internal instability erosion. This equation could efficiently evaluate the mass of particles eroded from the soil. Lastly, the model was calibrated based on experimental data; the corresponding results are discussed herein.
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| 7. |
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| 8. |
- Löfroth, Hjördis, et al.
(author)
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Challenges in slope stability assessment of contaminated fibrous sediments along the northern Baltic coast of Sweden
- 2021
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In: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 289
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Journal article (peer-reviewed)abstract
- In several locations along Sweden's northern Baltic coast there are deposits of contaminated fibrous sediments that are known as fiberbanks. Historically, these anthropogenic fiberbanks and associated contaminants were formed outside pulp and paper factories because of unregulated waste discharges. Some of the fiberbanks are located on seafloor slopes that are unstable and may fail, which could result in large amounts of fiber and contaminant dispersion. Hydroacoustic surveys have revealed that some parts of the fiberbanks have been dispersed to a wider area by submarine landslides. However, the unusual nature of these cellulose-rich sediments makes it difficult to apply conventional techniques for assessing submarine slope stability. Therefore, a combination of investigation techniques and interpretation methods was tested to assess the stability and triggering mechanisms for submarine slope failure identified in fiberbanks from the Ångermanälven river estuary on the Baltic sea coast. The integration of bathymetric data, sediment lithology and geotechnical characteristics from in-situ and laboratory measurements, enabled the characterisation of underlying natural sediments and the fiberbanks at two sites. Despite low densities, which indicate that the fiberbank material is near the buoyancy level, the fiberbank deposits seem to be relatively stable. Our results indicate the underlying natural sediments are also stable and would require an external triggering mechanism to generate the observed slope failures. We suggest that pore water pressure, potentially related to groundwater table fluctuations, may be an important trigger for submarine landslides in the study area.Management of fiberbanks and associated fiber-rich sediments, which are numerous along Sweden's north east coast, requires that sites are risk assessed and prioritized for remediation. To do so, under water slope stability should be considered as a possible dispersion pathway and therefore needs to be investigated. The study illustrates the value of using a combination of geophysical and geotechnical field and laboratory methods, together with empirical relationships, to assess relevant input parameters for slope stability calculations for this type of sediment.
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| 9. |
- Manzoor, Sohail, et al.
(author)
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Establishing relationships between structural data from close-range terrestrial digital photogrammetry and measurement while drilling data
- 2020
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In: Engineering Geology. - : Elsevier. - 0013-7952 .- 1872-6917. ; 267
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Journal article (peer-reviewed)abstract
- Geologists, mine planners, geotechnical, and mining engineers always strive for maximum information to get a better insight of the rock mass before interacting with it. Over the recent decades, close-range terrestrial digital photogrammetry (CRTDP) has been increasingly used for data acquisition and to support the conventional methods for rock mass characterization. It provides a safe, time-saving and contact-free way to gather enough data to minimize user dependent biases. However, it requires an expensive camera, fieldwork and some software to extract the information from images. In addition, it can over-estimate the rock fracturing sometimes due to weathering of the rock face or poor blasting practices. Measurement while drilling (MWD) data include the responses of different drilling parameters to the variations in the rock mass. MWD data are produced in large quantity, as they come from every hole drilled. These data correspond to the inside variations of rock rather than the surface ones counted in photogrammetry.In this paper, structural data are obtained from different bench faces of an open pit mine using a commercial software package, ShapeMetriX3D (by 3GSM). These data are compared to the MWD data of the boreholes that were blasted to produce these bench faces to establish certain relationships between drilling parameters and rock mass structures. Half casts of the boreholes with MWD data were visible on the bench faces of the pre-split wall that allowed a better correlation. The results show abrupt changes in MWD parameters for open joints or cavities with some infilling material and overall increases or decreases in parameters for closely spaced bedding planes, fractures or foliations. The results are promising and suggest the method can be used to characterize the rock mass, modify the charging of explosives in blasting operations and facilitate the geological modeling of the rock mass.
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| 10. |
- Molron, Justine, et al.
(author)
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GPR-inferred fracture aperture widening in response to a high-pressure tracer injection test at the Äspö Hard Rock Laboratory, Sweden
- 2021
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In: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 292
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Journal article (peer-reviewed)abstract
- We assess the performance of the Ground Penetrating Radar (GPR) method in fractured rock formations of very low transmissivity (e.g. T ≈ 10−9–10−10 m2/s for sub-mm apertures) and, more specifically, to image fracture widening induced by high-pressure injections. A field-scale experiment was conducted at the Äspö Hard Rock Laboratory (Sweden) in a tunnel situated at 410 m depth. The tracer test was performed within the most transmissive sections of two boreholes separated by 4.2 m. The electrically resistive tracer solution composed of deionized water and Uranine was expected to lead to decreasing GPR reflections with respect to the saline in situ formation water. The injection pressure was 5000 kPa leading to an injection rate of 8.6 mL/min (at steady state) that was maintained during 25 h, which resulted in a total injected volume of 13 L. To evaluate the fracture pathways between the boreholes, we conducted 3-D surface-based GPR surveys before and at the end of the tracer tests, using 160 MHz and 450 MHz antennas. Difference GPR data between the two acquisitions highlight an increasing fracture reflectivity in-between the boreholes at depths corresponding to the injection interval. GPR-based modeling suggests that the observed increasing reflectivity is not due to the tracer solution, but rather to a 50% widening of the fracture. Considering prevailing uncertainties in material properties, a hydromechanical analysis suggests that such a degree of widening is feasible. This research demonstrates that field-scale in situ GPR experiments may provide constraints on fracture widening by high-pressure injection and could help to constrain field-scale elastic parameters in fractured rock.
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