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1
Jia, Lin, Jingsen Cai, Li Wu, Tiange Qin, and Kun Song. "Influence of Fracture Geometric Characteristics on Fractured Rock Slope Stability." Applied Sciences 13, no. 1 (December 24, 2022): 236. http://dx.doi.org/10.3390/app13010236.
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Analysis of the stability of slopes in fractured rock masses is not trivial and is fraught with uncertainty and risk. A DFN-DEC model (Discrete Fracture Network-Distinct Element Code) based on the MATLAB platform is developed to evaluate the stability of rock slopes with random fractures. Then, the influences of mean values of geometric characteristics (i.e., the trace length T, the dip D, and the spacing S) for both the horizontal (denoted with 1) and inclined (denoted with 2) fractures on the mean slope stability are investigated. The results indicate that the proposed DFN-DEC model based on the MATLAB platform is adequate, robust, and can generate more realistic fracture networks. By means of probabilistic analysis (i.e., Monte Carlo simulation), we can obtain a more accurate stability assessment result of fractured rock slopes. In addition, it is found that the μFs (the mean of Fs) of slopes decreases with the increase in μT1, μT2 (the mean trace length of horizontal and inclined fractures, respectively) and μD1 (the mean dip of horizontal fractures), and increases gradually with the increase in μD2 (the mean dip of inclined fractures), μS1 and μS2 (the mean spacing of horizontal and inclined fractures, respectively). Furthermore, the geometric characteristics related to inclined fractures have a much greater influence on μFS than that related to horizontal fractures. This study can be well applied in engineering practice, e.g., preliminary evaluation of the slope stability according to the statistics of fracture geometric characteristics.
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Zhang, Wen, Jia Wang, Peihua Xu, Junqing Lou, Bo Shan, Fengyan Wang, Chen Cao, Xiaoxue Chen, and Jinsheng Que. "Stability evaluation and potential failure process of rock slopes characterized by non-persistent fractures." Natural Hazards and Earth System Sciences 20, no. 11 (November 5, 2020): 2921–35. http://dx.doi.org/10.5194/nhess-20-2921-2020.
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Abstract. Slope failure, which causes destructive damage and fatalities, is extremely common in mountainous areas. Therefore, the stability and potential failure of slopes must be analysed accurately. For most fractured rock slopes, the complexity and random distribution of structural fractures make the aforementioned analyses considerably challenging for engineers and geologists worldwide. This study aims to solve this problem by proposing a comprehensive approach that combines the discrete fracture network (DFN) modelling technique, the synthetic rock mass (SRM) approach, and statistical analysis. Specifically, a real fractured rock slope in Laohuding Quarry in Jixian County, China, is studied to show this comprehensive approach. DFN simulation is performed to generate non-persistent fractures in the cross section of the slope. Subsequently, the SRM approach is applied to simulate the slope model using 2D particle flow code software (PFC2D). A stability analysis is carried out based on the improved gravity increase method, emphasizing the effect of stress concentration throughout the formation of the critical slip surface. The collapse, rotation, and fragmentation of blocks and the accumulation distances are evaluated in the potential failure process of the rock slope. A total of 100 slope models generated with different DFN models are used to repeat the aforementioned analyses as a result of a high degree of variability in DFN simulation. The critical slip surface, factor of safety, and accumulation distance are selected by statistical analysis for safety assurance in slope analysis and support.
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Gao, Qin, and Gui He Wang. "Numerical Simulation of Fractured Rock Slope with Shear-Slip Behavior." Applied Mechanics and Materials 548-549 (April 2014): 673–77. http://dx.doi.org/10.4028/www.scientific.net/amm.548-549.673.
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The development of shear-slip cracks and motion trend of fracture water were presented for discussing the shear-slip behavior and analyzing the stability of fractured rock slope under hydraulic action. Seepage behavior of epigenetic cracks and the positions of slip or collapse were also investigated by monitoring pore water pressure using DEM. The analysis method of discrete element simulation for fractured rock slope was proposed. The results of numerical simulation indicated that interpenetrating fractures are more likely to be slip planes.
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Guo, Yun Hua, and Wei Shen Zhu. "A New Method to Determining the Strength Parameters of Fractured Rock Mass." Advanced Materials Research 898 (February 2014): 378–82. http://dx.doi.org/10.4028/www.scientific.net/amr.898.378.
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A Hydropower Station is located in the middle reach of the Dadu River in southwest China. The natural slope angles are generally 40°~65° and the relative elevation drop is more than 600m. Complex different fractures such as faults, dykes and dense fracture zones due to unloading are developed. Many abutment slopes were formed during construction of the abutments. The stability of these steep and high slopes during construction and operation period plays an important role for the safe construction and operation of the hydropower station. According to the statistical distribution of joints and fractures at the construction site, the slope is divided into a number of engineering geological zones. For each zone, a stochastic fracture network and a numerical model which is close to the real state of the fractured rock mass are established by the Monte-Carlo method. The mechanical response of fractured rock masses with different sizes of numerical models is studied using FLAC3D. The REV characteristic scale is identified for rock masses in the slopes with stochastic fracture network. Numerical simulation is performed to obtain the stress-strain curve, the mechanical parameters and the strength of the jointed rock mass in the zone. A constitutive relationship reflecting the mechanical response of the jointed rock mass in the zone is established. The Comparison between the traditional method and the method in this paper has been made at the end.
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Liu, Xianshan, and Ming Xu. "The Unsaturated Hydromechanical Coupling Model of Rock Slope Considering Rainfall Infiltration Using DDA." Geofluids 2017 (2017): 1–15. http://dx.doi.org/10.1155/2017/1513421.
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Water flow and hydromechanical coupling process in fractured rocks is more different from that in general porous media because of heterogeneous spatial fractures and possible fracture-dominated flow; a saturated-unsaturated hydromechanical coupling model using a discontinuous deformation analysis (DDA) similar to FEM and DEM was employed to analyze water movement in saturated-unsaturated deformed rocks, in which the Van-Genuchten model differently treated the rock and fractures permeable properties to describe the constitutive relationships. The calibrating results for the dam foundation indicated the validation and feasibility of the proposed model and are also in good agreement with the calculations based on DEM still demonstrating its superiority. And then, the rainfall infiltration in a reservoir rock slope was detailedly investigated to describe the water pressure on the fault surface and inside the rocks, displacement, and stress distribution under hydromechanical coupling conditions and uncoupling conditions. It was observed that greater rainfall intensity and longer rainfall time resulted in lower stability of the rock slope, and larger difference was very obvious between the hydromechanical coupling condition and uncoupling condition, demonstrating that rainfall intensity, rainfall time, and hydromechanical coupling effect had great influence on the saturated-unsaturated water flow behavior and mechanical response of the fractured rock slopes.
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Theune, Ulrich, Dean Rokosh, Mauricio D. Sacchi, and Douglas R. Schmitt. "Mapping fractures with GPR: A case study from Turtle Mountain." GEOPHYSICS 71, no. 5 (September 2006): B139—B150. http://dx.doi.org/10.1190/1.2335515.
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Ground-penetrating radar (GPR) surveys were acquired of rocks on the highly fractured summit of Turtle Mountain in Canada. In 1903 a disastrous rock slide occurred at Turtle Mountain and it still poses a geologic hazard. Dips, shapes, and penetration depths of fractures are important parameters in slope-stability analysis. Determination of fracture orientation at Turtle Mountain has been based mostly on areal geologic mapping and, most recently, on data collected from boreholes. The purpose of GPR surveys was to test, confirm, and extend information about fractures and bedding planes. Data acquisition was complicated by the rough terrain; because slopes are steep and uneven. This also complicated analysis of the data. Measurement of in situ velocity — an important value for migration — was impossible. Instead, data were migrated with different velocities and data results were chosen that were considered to be reasonable. Analysis and interpretation of the data, resulted in confirmation and extension of the a priori information on orientations of fractures and bedding planes at Turtle Mountain. Despite the rough terrain and highly fractured rock mass, GPR surveys provide reliable information about the shapes and density of fractures — information important for slope-stability evaluation. The most reliable migration results obtained for velocities were considerably less than the standard velocities recorded for limestone, the dominant lithofacies at Turtle Mountain. We interpret this observation as an indicator of water within the rock. However, thorough investigation of this conclusion remains a project for future work.
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Ershaghi, I., and R. Aflaki. "Problems in Characterization of Naturally Fractured Reservoirs From Well Test Data." Society of Petroleum Engineers Journal 25, no. 03 (June 1, 1985): 445–50. http://dx.doi.org/10.2118/12014-pa.
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Abstract This paper presents a critical analysis of some recently published papers on naturally fractured reservoirs. These published papers on naturally fractured reservoirs. These publications have pointed out that for a publications have pointed out that for a matrix-to-fracture-gradient flow regime, the transition portion of pressure test data on the semilog plot develops a portion of pressure test data on the semilog plot develops a slope one half that of the late-time data. We show that systems under pseudosteady state also may develop a 1:2 slope ratio. Examples from published case studies are included to show the significant errors associated with the characterization of a naturally fractured system by using the 1:2 slope concept for semicomplete well tests. Introduction Idealistic models of the dual-porosity type often have been recommended for interpretation of a well test in naturally fractured reservoirs. The evolutionary aspects of these models have been reviewed by several authors. Gradual availability of actual field tests and recent developments in analytical and numerical solution techniques have helped to create a better understanding of application and limitation of various proposed models. Two important observations should be made here. First, just as it is now recognized that classical work published by Warren and Root in 1963 was not the end of the line for interpretation of the behavior of naturally fractured systems, the present state of knowledge later may be considered the beginning of the technology. Second, parallel with the ongoing work by various investigators who progressively include more realistic assumptions in their progressively include more realistic assumptions in their analytical modeling, one needs to ponder the implication of these findings and point out the inappropriate impressions that such publications may precipitate in the mind of practicing engineers. practicing engineers. This paper is intended to scrutinize statements published in recent years about certain aspects of the anticipated transition period developed on the semilog plot of pressure-drawdown or pressure-buildup test data. pressure-drawdown or pressure-buildup test data. The Transition Period In the dual-porosity models published to date, a naturally fractured reservoir is assumed to follow the behavior of low-permeability and high-storage matrix blocks in communication with a network of high-permeability and low-storage fractures. The difference among the models has been the assumed geometry of the matrix blocks or the nature of flow between the matrix and the fracture. However, in all cases, it is agreed that a transition period develops that is strictly a function of the matrix period develops that is strictly a function of the matrix properties and matrix-fracture relationship. Fig. 1 shows properties and matrix-fracture relationship. Fig. 1 shows a typical semilog plot depicting the transition period and the parallel lines. Estimation of Warren and Root's proposed and to characterize a naturally fractured proposed and to characterize a naturally fractured system requires the development of the transition period. The Warren and Root model assumes a set of uniformly distributed matrix blocks. Furthermore, the flow from matrix to fracture is assumed to follow a pseudosteady-state regime. Under such conditions, in theory, this period is an S-shaped curve with a point of inflection. Uldrich and Ershaghi developed a technique to use the coordinates of this point of inflection for estimating and under conditions where either the early- or the late-time straight lines were not available. Kazemi and de Swann presented alternative approaches to represent naturally fractured reservoirs. They assumed a geometrical configuration consisting of layered matrix blocks separated by horizontal fractures. Their observation was that for such a system the transition period develops as a straight line with no inflection point. Bourdet and Gringarten identified a semilog straight line during the transition period for unsteady-state matrix-fracture flow. Recent work by Streltsova and Serra et al emphasized the transient nature of flow from matrix to fracture and pointed out the development of a unique slope ratio. These authors, later joined by Cinco-L. and Samaniego-V., stated that under a transient flow condition, the straight-line shape of the transition period develops a slope that is numerically one-half the slope of the parallel straight lines corresponding to the early- or late-time data. It was further pointed out that the transient flow model is a more realistic method of describing the matrix-fracture flow. As such, they implied that in the absence of wellbore-storage-free early-time data, or late-time data in the case of limited-duration tests, one may use the slope of the transition straight line and proceed with the estimation of the reservoir properties. Statement of the Problem The major questions that need to be addressed at this time are as follows. SPEJ P. 445
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Weber, Samuel, Jan Beutel, Jérome Faillettaz, Andreas Hasler, Michael Krautblatter, and Andreas Vieli. "Quantifying irreversible movement in steep, fractured bedrock permafrost on Matterhorn (CH)." Cryosphere 11, no. 1 (February 16, 2017): 567–83. http://dx.doi.org/10.5194/tc-11-567-2017.
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Abstract. Understanding rock slope kinematics in steep, fractured bedrock permafrost is a challenging task. Recent laboratory studies have provided enhanced understanding of rock fatigue and fracturing in cold environments but were not successfully confirmed by field studies. This study presents a unique time series of fracture kinematics, rock temperatures and environmental conditions at 3500 m a. s. l. on the steep, strongly fractured Hörnligrat of the Matterhorn (Swiss Alps). Thanks to 8 years of continuous data, the longer-term evolution of fracture kinematics in permafrost can be analyzed with an unprecedented level of detail. Evidence for common trends in spatiotemporal pattern of fracture kinematics could be found: a partly reversible seasonal movement can be observed at all locations, with variable amplitudes. In the wider context of rock slope stability assessment, we propose separating reversible (elastic) components of fracture kinematics, caused by thermoelastic strains, from the irreversible (plastic) component due to other processes. A regression analysis between temperature and fracture displacement shows that all instrumented fractures exhibit reversible displacements that dominate fracture kinematics in winter. Furthermore, removing this reversible component from the observed displacement enables us to quantify the irreversible component. From this, a new metric – termed index of irreversibility – is proposed to quantify relative irreversibility of fracture kinematics. This new index can identify periods when fracture displacements are dominated by irreversible processes. For many sensors, irreversible enhanced fracture displacement is observed in summer and its initiation coincides with the onset of positive rock temperatures. This likely indicates thawing-related processes, such as meltwater percolation into fractures, as a forcing mechanism for irreversible displacements. For a few instrumented fractures, irreversible displacements were found at the onset of the freezing period, suggesting that cryogenic processes act as a driving factor through increasing ice pressure. The proposed analysis provides a tool for investigating and better understanding processes related to irreversible kinematics.
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Guo, Yun Hua, Wei Shen Zhu, Da Jun Yu, and Xin Ping Li. "Study of a High Slope Stability Considering the Stochastic Distribution of Rock Joint Set." Applied Mechanics and Materials 90-93 (September 2011): 786–90. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.786.
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A hydropower station is located in the middle reach of the Dadu River in southwest China. The natural slope angles at the project site are generally 40~65 and the relative elevation drop is more than 600m. Complex different fractures such as faults, dykes and dense fracture zones due to unloading are developed. The stability of these steep and high slopes during construction and operation period plays an important role for the safe construction and operation of the project. According to the statistical distribution of joints at the construction site, the slope is divided into a number of engineering geological zones. For each zone, a stochastic fracture network and a numerical model are established by the Monte-Carlo method. The mechanical characters of fractured rock with different sizes are studied using FLAC3D. The REV characteristic scale is identified for rock masses. Numerical simulation is performed to obtain the mechanical parameters and the strength of the jointed rock. With the numerical model and the site monitoring data, a self-developed stochastic mechanical analysis software is applied for back analysis and stability assessment.
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Zhang, Tingting, Ruifeng Zhang, Jianzhang Tian, Lifei Lu, Fengqi Qin, Xianzeng Zhao, and Yuefeng Sun. "Two-parameter prestack seismic inversion of porosity and pore-structure parameter of fractured carbonate reservoirs: Part 2 — Applications." Interpretation 6, no. 4 (November 1, 2018): SM9—SM17. http://dx.doi.org/10.1190/int-2018-0019.1.
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Fractures and fracture-related dissolution pores, as well as cavities, molds, and vugs, provide the major conduit and/or storage space for hydrocarbons in the deeply buried carbonate hill of Hexiwu field, Bohai Bay Basin. The fractured reservoir generally has lower porosity but better permeability than moldic/vuggy reservoir, and it consists of the major part of the buried-hill slope and buried-hill internal reservoirs. The conventional method of characterizing carbonate reservoirs, however, often mixes these two types of reservoirs together because they both have low acoustic impedance and low bulk modulus. The rock-physics analysis of two field wells indicates that a pore-structure parameter defined in a rock-physics model, the so-called Sun model, can help to distinguish the fractured reservoir zones together with porosity. Fractured zones usually have porosity of less than 5% and a pore-structure parameter of greater than six, whereas moldic/vuggy reservoirs of higher porosity have a pore-structure parameter of less than six. Field-scale application demonstrates that simultaneous prestack seismic inversion for the porosity and pore-structure parameter enables 3D mapping of fractured reservoir zones in the buried carbonate hills. It also provides an analog of detecting fractures and/or fracture-related pores in deeply buried carbonates in similar geologic settings.
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Eigenbrod, K. D., and D. Kaluza. "Shallow slope failures in clays as a result of decreased evapotranspiration subsequent to forest clearing." Canadian Geotechnical Journal 36, no. 1 (August 8, 1999): 111–18. http://dx.doi.org/10.1139/t98-077.
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In the Kaministiquia River valley near Thunder Bay, Ontario, shallow ground movements are common on the grassy slopes, whereas the forested slopes generally appear stable. These slope failures may be the result of a rise in the groundwater table due to forest clearing and a subsequent reduction in evapotranspiration. Slope movements on one of the grassy slope in the valley have been monitored and examined since 1989. An explanation as to the cause of these slope failures is presented in this paper.Key words: shallow ground movements, fractured clay, deforestation, evapotranspiration.
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Hu, Roger, and Stuart D. C. Walsh. "Effective Continuum Approximations for Permeability in Brown-Coal and Other Large-Scale Fractured Media." Geosciences 11, no. 12 (December 14, 2021): 511. http://dx.doi.org/10.3390/geosciences11120511.
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The stability of open-pit brown-coal mines is affected by the manner in which water is transmitted or retained within their slopes. This in turn is a function of the in-situ fracture network at those mines. Fracture networks in real mines exhibit significant degrees of heterogeneity; encompassing a wide range of apertures, inter-fracture separations, and orientations. While each of these factors plays a role in determining fluid movement, over the scale of a mine it is often impractical to precisely measure, let alone simulate, the behaviour of each fracture. Accordingly, effective continuum models capable of representing the bulk effects of the fracture network are needed to understand the movement of fluid within these slopes. This article presents an analysis of the fracture distribution within the slopes of a brown coal mine and outlines a model to capture the effects on the bulk permeability. A stress-dependent effective-fracture-permeability model is introduced that captures the effects of the fracture apertures, spacing, and orientation. We discuss how this model captures the fracture heterogeneity and the effects of changing stress conditions on fluid flow. The fracture network data and the results from the effective permeability model demonstrate that in many cases slope permeability is dominated by highly permeable but low-probability fractures. These results highlight the need for models capable of capturing the effects of heterogeneity and uncertainty on the slope behaviour.
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Hoteit, Hussein, and Abbas Firoozabadi. "Compositional Modeling of Discrete-Fractured Media Without Transfer Functions by the Discontinuous Galerkin and Mixed Methods." SPE Journal 11, no. 03 (September 1, 2006): 341–52. http://dx.doi.org/10.2118/90277-pa.
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Summary In a recent work, we introduced a numerical approach that combines the mixed-finite-element (MFE) and the discontinuous Galerkin (DG) methods for compositional modeling in homogeneous and heterogeneous porous media. In this work, we extend our numerical approach to 2D fractured media. We use the discrete-fracture model (crossflow equilibrium) to approximate the two-phase flow with mass transfer in fractured media. The discrete-fracture model is numerically superior to the single-porosity model and overcomes limitations of the dual-porosity model including the use of a shape factor. The MFE method is used to solve the pressure equation where the concept of total velocity is invoked. The DG method associated with a slope limiter is used to approximate the species-balance equations. The cell-based finite-volume schemes that are adapted to a discrete-fracture model have deficiency in computing the fracture/fracture fluxes across three and higher intersecting-fracture branches. In our work, the problem is solved definitively because of the MFE formulation. Several numerical examples in fractured media are presented to demonstrate the superiority of our approach to the classical finite-difference method. Introduction Compositional modeling in fractured media has broad applications in CO2, nitrogen, and hydrocarbon-gas injection, and recycling in gas condensate reservoirs. In addition to species transfer, the compressibility effects should be also considered for such applications. Heterogeneities and fractures add complexity to the fluid-flow modeling. Several conceptually different models have been proposed in the literature for the simulation of flow and transport in fractured porous media. The single-porosity approach uses an explicit computational representation for fractures (Ghorayeb and Firoozabadi 2000; Rivière et al. 2000). It allows the geological parameters to vary sharply between the matrix and the fractures. However, the high contrast and different length scales in the matrix and fractures make the approach unpractical because of the ill conditionality of the matrix appearing in the numerical computations (Ghorayeb and Firoozabadi 2000).The small control volumes in the fracture grids also add a severe restriction on the timestep size because of the Courant-Freidricks-Levy (CFL) condition if an explicit temporal scheme is used.
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Binet, Stéphane, Yves Guglielmi, Catherine Bertrandet, and Jacques Mudry. "Unstable rock slope hydrogeology: insights from the large-scale study of western Argentera-Mercantour hillslopes (South-East France)." Bulletin de la Société Géologique de France 178, no. 2 (March 1, 2007): 159–68. http://dx.doi.org/10.2113/gssgfbull.178.2.159.
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Abstract Inventory of unstable hillslopes, hydrogeological mapping and hydrochemical characteristics of natural spring waters were used to determine the long-term relationships between groundwater and gravitational instabilities in the Upper Tinée Valley (South-East French Alps). Water chemistry and flow records allow to propose a conceptual model of water flow within unstable rocky slopes and to back-calculate the volume of infiltrated water and the flow velocity in the aquifers for different deformation states of the slopes. An increase in infiltrated yield, flow velocity and porosity is observed and linked to collapsed and toppled structures in the upper parts of the hillslopes. In these areas, perched aquifers take place in the reworked media. When a large landslide occurs, it modifies the geometry of the slope and bypasses the perched flows down to the foot of the slope. With long-term continuous slope deformation, the associated effect between water flows and slope destabilization changes. In the fractured rock, the coupled effect corresponds to rising water pressures with limited volumes of infiltrated water; in the more fractured and permeable collapsed and toppled areas, the volumes of infiltrated water increase with a lower variation of water pressures.
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Song, Shengyuan, Mingyu Zhao, Chun Zhu, Fengyan Wang, Chen Cao, Haojie Li, and Muye Ma. "Identification of the Potential Critical Slip Surface for Fractured Rock Slope Using the Floyd Algorithm." Remote Sensing 14, no. 5 (March 5, 2022): 1284. http://dx.doi.org/10.3390/rs14051284.
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A rock slope can be characterized by tens of persistent discontinuities. A slope can be massive. The slip surface of the slope is usually easier to expand along with the discontinuities because the shear strength of the discontinuities is substantially lower than that of the rock blocks. Based on this idea, this paper takes a jointed rock slope in Hengqin Island, Zhuhai as an example, and establishes a three-dimensional (3D) model of the studied slope by digital close-range photogrammetry to rapidly interpret 222 fracture parameters. Meanwhile, a new Floyd algorithm for finding the shortest path is developed to realize the critical slip surface identification of the studied slope. Within the 3D fracture network model created using the Monte Carlo method, a sequence of cross-sections is placed. These cross-sections containing fractures are used to search for the shortest paths between the designated shear entrances and exits. For anyone combination of entry point and exit point, the shortest paths corresponding to different cross-sections are different and cluttered. For the sake of safety and convenience, these shortest paths are simplified as a circular arc that is regarded as a potential slip surface. The fracture frequency is used to determine the probability of sliding along a prospective critical slip surface. The potential slip surface through the entrance point (0, 80) and exit point (120, 0) is identified as the final critical slip surface of the slope due to the maximum fracture frequency.
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Gao, Wei, Xu Wang, Shuang Dai, and Dongliang Chen. "Numerical Study on Stability of Rock Slope Based on Energy Method." Advances in Materials Science and Engineering 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/2030238.
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To solve the main shortcoming of numerical method for analysis of the stability of rock slope, such as the selection the convergence condition for the strength reduction method, one method based on the minimum energy dissipation rate is proposed. In the new method, the basic principle of fractured rock slope failure, that is, the process of the propagation and coalescence for cracks in rock slope, is considered. Through analysis of one mining rock slope in western China, this new method is verified and compared with the generally used strength reduction method. The results show that the new method based on the minimum energy dissipation rate can be used to analyze the stability of the fractured rock slope and its result is very good. Moreover, the new method can obtain less safety factor for the rock slope than those by other methods. Therefore, the new method based on the minimum energy dissipation rate is a good method to analyze the stability of the fractured rock slope and should be superior to other generally used methods.
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Mamot, Philipp, Samuel Weber, Saskia Eppinger, and Michael Krautblatter. "A temperature-dependent mechanical model to assess the stability of degrading permafrost rock slopes." Earth Surface Dynamics 9, no. 5 (September 9, 2021): 1125–51. http://dx.doi.org/10.5194/esurf-9-1125-2021.
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Abstract. Over the last 2 decades, permafrost degradation has been observed to be a major driver of enhanced rock slope instability and associated hazards in high mountains. While the thermal regime of permafrost degradation in high mountains has been addressed in several modelling approaches, no mechanical models that thoroughly explain rock slope destabilisation controls in degrading permafrost have been developed. Meanwhile, recent laboratory studies have shown that degrading permafrost affects both, rock and ice mechanical strength parameters as well as the strength of rock–ice interfaces. This study presents a first general approach for a temperature-dependent numerical stability model that simulates the mechanical response of a warming and thawing permafrost rock slope. The proposed procedure is exemplified using a rockslide at the permafrost-affected Zugspitze summit crest. Laboratory tests on frozen and unfrozen rock joint and intact rock properties provide material parameters for discontinuum models developed with the Universal Distinct Element Code (UDEC). Geophysical and geotechnical field surveys reveal information on permafrost distribution and the fracture network. This model can demonstrate how warming decreases rock slope stability to a critical level and why thawing initiates failure. A generalised sensitivity analysis of the model with a simplified geometry and warming trajectory below 0 ∘C shows that progressive warming close to the melting point initiates instability above a critical slope angle of 50–62∘, depending on the orientation of the fracture network. The increase in displacements intensifies for warming steps closer to 0 ∘C. The simplified and generalised model can be applied to permafrost rock slopes (i) which warm above −4 ∘C, (ii) with ice-filled joints, (iii) with fractured limestone or probably most of the rock types relevant for permafrost rock slope failure, and (iv) with a wide range of slope angles (30–70∘) and orientations of the fracture network (consisting of three joint sets). Here, we present a benchmark model capable of assessing the future destabilisation of degrading permafrost rock slopes.
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Civan, Faruk. "Effective Correlation of Stress and Thermal Effects on Porosity and Permeability of Naturally Fractured Formations by a Modified Power Law." SPE Journal 24, no. 05 (September 9, 2019): 2378–97. http://dx.doi.org/10.2118/198893-pa.
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Summary Effective theory and methodology are proposed and validated for accurate correlation of stress–dependent petrophysical properties of naturally fractured or induced–fractured reservoir formations by means of a matrix/fracture dual–compressibility treatment. Inspection of various experimental data indicates a sudden change in trends at a certain critical net effective stress in the stress dependence of petrophysical properties of porous rocks as a result of a stress shock caused by the opening or closing of fractures. The variation of petrophysical properties in fractured–rock formations subjected to stress loading/unloading and thermally induced stress occurs mainly by deformation of the fractures below the critical effective stress and the deformation of the matrix above the critical effective stress. The alteration of petrophysical properties and a slope discontinuity might also be experienced when the stress exceeds the onset of other rock–alteration/damaging processes, such as pore collapsing and grain crushing. Proper formulations of the relevant processes and special correlation methods are presented in a manner to capture this nature of the petrophysical experimental data obtained by testing of cores extracted from naturally fractured or induced–fractured reservoir–rock formations. The dependency of porosity and permeability of fractured–rock samples under stress because of thermal, hydraulic, and mechanical effects is represented accurately by a modified–power–law equation derived from a kinetics model as confirmed by effective correlations of various experimental data. It is shown that this new model represents the thermal effect better than the frequently used Arrhenius (1889) equation and Vogel–Tammann–Fulcher (VTF) equation (Vogel 1921; Fulcher 1925; Tammann and Hesse 1926).
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Lu, Lei, Chunxue Liu, Gang Chen, and Liang Guo. "Numerical estimation of fracture network permeability based on GEOFRAC model for groundwater modeling in a tin mine." Journal of Water and Climate Change 10, no. 2 (August 30, 2018): 243–48. http://dx.doi.org/10.2166/wcc.2018.283.
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Abstract Numerous geological research studies and mining operations have proved that fracture is one of the important factors controlling groundwater flow, mineralization, and ore distribution in metallic deposits. Most current approaches to groundwater flow simulation of naturally fractured media rely on the calculation of equivalent permeability tensors from a discrete fracture network (DFN). This study is aimed at developing a rational two-dimensional DFN by GEOFRAC, a geostatistical method of fracture direction and locations of sample data from a tin mine in the Gaosong area, Gejiu city, southwest China, and utilizing 3,724 outcrop fractures sampled on the ground of mountain Gaosong. Principal inputs of the DFN are density, direction, and continuity of disks that constitute a fracture plane. Fractures simulated by GEOFRAC were validated in that their directions corresponded well with those of the sample fractures. The permeability tensor of each modeling grid was then calculated based on the fracture network constructed. The results showed that GEOFRAC is valuable for two-dimensional DFN modeling in mines and other fracture-controlled geological phenomena, such as groundwater flow and slope failure.
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Zhou, Xin, Jianping Chen, Yunkai Ruan, Wen Zhang, Shengyuan Song, and Jiewei Zhan. "Demarcation of Structural Domains in Fractured Rock Masses Using a Three-Parameter Simultaneous Analysis Method." Advances in Civil Engineering 2018 (December 6, 2018): 1–13. http://dx.doi.org/10.1155/2018/9358098.
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A structural domain represents a volume of a rock mass with similar mechanical and hydrological properties. To demarcate structural domains (or statistically homogeneous regions) in fractured rock masses, this study proposes a three-parameter simultaneous analysis method (3PSAM) that simultaneously considers rock fracture orientation, trace length, and aperture to evaluate statistical homogeneity between two regions. First, a 102-patch three-dimensional Schmidt net, which represents a new comprehensive classification system, is established to characterize rock fractures based on their orientation and aperture. Two populations of rock fractures can then be projected to the corresponding patches. Second, the Wald–Wolfowitz runs test is used to measure the similarity between the two populations by considering the fracture trace lengths. The results obtained by applying the 3PSAM to seven simulated fracture populations show that the homogeneity is influenced by both the distributions of the fracture parameters and the sequences of the fracture parameters. The influence of a specific combination sequence makes it impractical to analyze the rock fracture parameters individually. Combined with previous methods, the 3PSAM provides reasonable and accurate results when it is applied to a fractured rock slope engineering case study in Dalian, China. The results show that each fracture population should be identified as an independent structural domain when using the 3PSAM. Only the 3PSAM identifies the west exploratory trench 2 and the east exploratory trench as being nonhomogeneous because the difference in the aperture of the two fracture populations is considered. The benefit of the 3PSAM is that it simultaneously considers three parameters in the demarcation of structural domains.
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Abousleiman, Y., A. H. D. Cheng, and H. Gu. "Formation Permeability Determination by Micro or Mini-Hydraulic Fracturing." Journal of Energy Resources Technology 116, no. 2 (June 1, 1994): 104–14. http://dx.doi.org/10.1115/1.2906014.
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This paper presents a theory and its application for post-fracture pressure-transient analyses. The proposed procedure, known as “impulse fracture test,” is an injection/falloff test designed for the determination of formation permeability and reservoir pressure. The hydraulically induced fracture can pass the near wellbore damaged zone and expose a larger formation area to flow. The permeability and reservoir pressure determined are therefore more representative of the reservoir. The theory is based on the distribution of sources with variable intensity along the fracture trajectory. For field applications, asymptotic solutions are derived to give the “type-curve” capability for the estimation of formation permeability and reservoir pressure. Assorted slope behaviors, such as −1, −2, +1/2 and +1 slopes, are predicted from various pressure and pressure derivative plots. Analyses of data from two wells which were inadvertently fractured support these behaviors.
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Tongkul, F., H. Benedick, and F. K. Chang. "Geology of slopes in the Crocker Range, Sabah, Malaysia." Journal of Nepal Geological Society 34 (October 9, 2006): 73–80. http://dx.doi.org/10.3126/jngs.v34i0.31881.
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Slope failures are frequent occurrences along roads in Malaysia. Not until recently, geological inputs were rarely sought when designing and constructing roads on mountainous areas. This paper highlights the result of a geological study on selected slopes along a major road across Sabah's main mountain range, the Crocker Range, which is comprised mostly of folded Eocene sedimentary rocks. A total of 48 slopes facing potential failure problems were studied. The following four main potential sources of failures were recognised: 1) related to intensely sheared mudstones within a localised fault zone; 2) related to unfavourable orientation of discontinuity planes whereby bedding and joint planes of sandstone beds occur parallel or sub-parallel to the slope face; 3) related to the presence of intensely fractured and sheared sandstone and mudstone beds within a regional fold hinge; and 4) related to the presence of old landslide deposits. The recommendations to stabilise problematic slopes include covering the unstable slope face with concrete or vegetation and cutting back the slopes further.
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Marino, Pasquale, Luca Comegna, Emilia Damiano, Lucio Olivares, and Roberto Greco. "Monitoring the Hydrological Balance of a Landslide-Prone Slope Covered by Pyroclastic Deposits over Limestone Fractured Bedrock." Water 12, no. 12 (November 25, 2020): 3309. http://dx.doi.org/10.3390/w12123309.
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Many mountainous areas in Campania, Southern Italy, are characterized by steep slopes covered by loose unsaturated pyroclastic deposits laying upon fractured limestone bedrock. The soil covers are mainly constituted by layers of ashes and pumices. Large and intense rainfall events trigger shallow landslides, often turning into debris flows that cause huge damage and casualties. The slope of Cervinara, around 40 km Northeast of Naples, was involved in a catastrophic flowslide on 16 December 1999, triggered by a rainstorm of 325 mm in 48 h. To capture the main effects of precipitation on the slope stability, hydro-meteorological monitoring activities have been carried out at the slope to assess the water balance for three years (2017–2020). The field monitoring data allowed the identification of the complex hydrological processes involving the unsaturated pyroclastic soil and the shallow groundwater system developing in the limestone bedrock, which control the conditions that potentially predispose the slope to landslide triggering. Specifically, late autumn has been identified as the potentially most critical period, when slope drainage processes are not yet effective, and soil covers already receive large amounts of precipitation.
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Serrano, Alcibíades, Claudio Olalla, and Jesús Manzanas. "Stability of highly fractured infinite rock slopes with nonlinear failure criteria and nonassociated flow laws." Canadian Geotechnical Journal 42, no. 2 (April 1, 2005): 393–411. http://dx.doi.org/10.1139/t04-087.
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The effect of the dilatancy phenomenon on rock masses is not usually considered when calculating slope stability. A theoretical analysis has been conducted on the stability of infinite rock slopes, with varied hypotheses of simplified seepage flow nets. The calculations were made in the most general way possible, for any type of failure criterion and for linear-type flow laws. When the calculations were completed they were applied to the original and modified HoekBrown failure criteria and also to the associated flow and constant-dilatancy conditions. The study reveals the great importance of the dilatancy value and the "non-conservative" nature of an associated flow law hypothesis, which is the hypothesis that is generally used. The important effect of groundwater flow in the slope has also been enhanced. A quantitative estimation of the stability is provided for homogeneous and isotropic rock media under different angles of dilatancy and water flow nets. Lastly, the equilibrium is dependent on the following parameters: slope inclination angle (α), specific weight of the rock mass (γR*), type of rock (m0), unconfined compression strength (σc*), and geological strength index (GSI).Key words: infinite rock slope, Hoek Brown, dilatancy.
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Al-Jawadi, Azealdeen. "Theoretical Models of Slope Stability Analysis in The Maqlub Mountain Rock Cut Routes, North Iraq." Iraqi Geological Journal 54, no. 1A (January 31, 2020): 55–68. http://dx.doi.org/10.46717/igj.54.1a.6ms-2021-01-27.
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In many sections, the road leading up to the top of Maqlub Mountain is dangerous due to the fall of several rocks. There were six locations recognized for this dynamic geological process, rockfalls of varying sizes, with very large measurements up to 230 x 120 x 110 cm are falling on the road. The study suggested three theoretical models explain the causes of rockfall, through a comprehensive study in the area. The first model showed that the cause of rockfall was the presence of rocky slopes with a reverse slope. The second model has shown that the rockfall is caused by weak engineering properties of marl beds and it can be squeezed under thick and fractured beds of hard and fractured limestone rocks. The third model determined the small area of the rock base at the rocky slope surface and its large height that reduced their stability. A field survey was performed to study an area that included measuring the height and inclination of the slope surface and measuring the attitude of all discontinuities and their engineering characteristics to classify the slope stability, as well as the technical parameters of the road that determine the risk and consequence factors. Two computer programs were designed to evaluate slope stability, one used to classify risk and consequence (Rockfall Hazard Rating System Program) and the other to classify slope stability based on its geotechnical properties (Slope Mass Rating System Program) in addition to the areas where a rock climb previously occurred, the study concluded that dangerous sites have been recognized along the road to Maqloub Mountain. The size of the falling rock cuttings was classified between small and medium size. The study indicated that this road requires support in hazardous locations to prevent accidents causing losses of property and humans.
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Li, Hong, Hongyuan Tian, and Ke Ma. "Seepage Characteristics and Its Control Mechanism of Rock Mass in High-Steep Slopes." Processes 7, no. 2 (February 1, 2019): 71. http://dx.doi.org/10.3390/pr7020071.
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In Southwest China large-scale hydropower projects, the hydraulic conductivity and fracture aperture within the rock mass of a reservoir bank slope has dramatically undergone a time series of evolution during dam abutment excavation, reservoir impounding and fluctuation operation, and discharge atomization. Accordingly, seepage control measures by hydro-structures such as drainage or water insulation curtains should be guided by scientific foundation with a dynamic process covering life-cycle performance. In this paper, the up-to-date status of studying the evolution mechanism of seepage characteristics relating to fractured rock hydraulics from experimental samples to the engineering scale of the rock mass is reviewed for the first time. Then, the experimental findings and improved practice method on nonlinear seepage flow under intensive pressure drives are introduced. Finally, the scientific progress made in fractured rock seepage control theory and optimization of the design technology of high-steep slope engineering is outlined. The undertaken studies summarized herewith are expected to contribute to laying a foundation to guide the further development of effective geophysical means and integrated monitoring systems in hydropower station construction fields.
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Yang, Xi, Wei Yu, Kan Wu, and Ruud Weijermars. "Assessment of Production Interference Level Due to Fracture Hits Using Diagnostic Charts." SPE Journal 25, no. 06 (March 5, 2020): 2837–52. http://dx.doi.org/10.2118/200485-pa.
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Summary The objective of this study is to develop a new method that leads to diagnostic charts that quantify the pressure response between two interfering wells. Analytical linear flow models for single hydraulic fracture are used to develop a fracture hit model, which is next verified with a numerical model for validity. An analytical two-fracture model is then developed to simulate flowing bottomhole pressure (BHP) of a shut-in well, which interferes with the other well through a fracture hit, during well-testing for a short-term period. From the insight of two-fracture analytical model, a dimensionless pressure scalar, which is proportional to square root of time, is proposed to summarize the interference level between two wells. Utilizing such proportionality between the defined dimensionless pressure scalar and square root of time, a diagnostic chart for quick assessment of the production interference level between wells is developed. Such diagnostic chart is also applied to interference caused by multifracture hits that a multistage fractured horizontal well with history match performed from the Eagle Ford formation is considered as a parent well for production interference quantification. A new identical horizontal well, which is just fractured but is not in production, is assumed parallel to the pre-existing well. The result shows that when the percentage of fracture connection increases, the slope of dimensionless pressure scalar vs. square root of time increases proportionally to the percentage of fracture connection. Because the slope of dimensionless pressure scalar vs. square root of time is between 0 and 1, it can be used to quantify the well production interference level under different situations.
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Liu, Shujun. "Experimental Study on Physical Model of Prestressed Anchorage Mechanism of Fractured Rock Slope." E3S Web of Conferences 352 (2022): 01087. http://dx.doi.org/10.1051/e3sconf/202235201087.
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In view of some problems in the application of prestressed anchoring technology in broken rock slope, this study, combined with the prestressed anchoring project of K+276 broken rock slope of Chengdu-Chongqing Expressway (CCE), based on the field geological survey and key data monitoring, adopts physical model test to study the diffusion mode of prestressed anchor cable. The concrete influence of rock mass quality, anchor cable tensioning tonnage and other factors on the stress and deformation of broken rock slope is analyzed, and the application mechanism of prestressed anchorage technology in the reinforcement of broken rock slope is discussed.
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Li, Hai Feng, Guo Xing Zhang, Tao Huang, and Qiu Jing Zhou. "Stability Analysis of Dangerous Rocks on the Slope of a Hydropower Station." Applied Mechanics and Materials 405-408 (September 2013): 621–29. http://dx.doi.org/10.4028/www.scientific.net/amm.405-408.621.
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Dangerous rocks are among the most significant factors in analyzing the stability of high slopes, and are the main geological hazards on such slopes. These rocks are typical spatial blocks. The unstable failure of dangerous rocks poses evident spatial features. Consequently, their stability should be calculated by considering it as a three-dimensional (3-D) problem. In this research, the general block method of fractured rock mass and 3-D discontinuous deformation analysis (DDA) are used to study the stability of dangerous rocks on the slope of a hydropower station. The general block method of fractured rock mass is used to generate dangerous rocks and to assess the geometric mobility of blocks. The progressive unstable failure of dangerous rocks is also analyzed. Moreover, 3-D DDA is implemented to examine the stability of dangerous rocks, including the regularity of their unstable failure. The failure sequence of each batch of blocks estimated by general block theory is the same as that in the results of 3-D DDA. The decrease in the shear parameters of the structural plane shortens the time interval of failures, but increases the number and capacity of blocks.
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Hasler, A., S. Gruber, and W. Haeberli. "Temperature variability and offset in steep alpine rock and ice faces." Cryosphere 5, no. 4 (November 10, 2011): 977–88. http://dx.doi.org/10.5194/tc-5-977-2011.
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Abstract. The thermal condition of high-alpine mountain flanks can be an important determinant of climate change impact on slope stability and correspondingly down-slope hazard regimes. In this study we analyze time-series from 17 shallow temperature-depth profiles at two field sites in steep bedrock and ice. Extending earlier studies that revealed the topographic variations in temperatures, we demonstrate considerable differences of annual mean temperatures for variable surface characteristics and depths within the measured profiles. This implies that measurements and model related to compact and near-vertical bedrock temperatures may deviate considerably from conditions in the majority of bedrock slopes in mountain ranges that are usually non-vertical and fractured. For radiation-exposed faces mean annual temperatures at depth are up to 3 °C lower and permafrost is likely to exist at lower elevations than reflected by estimates based on near-vertical homogeneous cases. Retention of a thin snow cover and ventilation effects in open clefts are most likely responsible for this cooling. The measurements presented or similar data could be used in the future to support the development and testing of models related to the thermal effect of snow-cover and fractures in steep bedrock.
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Li, Yanlin, Aijun Yao, and Yifei Gong. "Deformation and Failure Mechanism of a Massive Ancient Anti-Dip River-Damming Landslide in the Upper Jinsha River." Sustainability 14, no. 20 (October 12, 2022): 13048. http://dx.doi.org/10.3390/su142013048.
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Landslides are a typical geological hazard that can cause large numbers of casualties and huge economic losses, and the overflow of a weir from a blocked river landslide can have even more disastrous consequences. Of the different types of landslides, about 33% of landslides happen in anti-dip slopes. This paper reports a massive ancient anti-dip river-damming landslide on the Jinsha River: the Zongrongcun landslide. Field investigation and theoretical analysis were used to reveal the potential mechanism of this ancient landslide, and the block discrete element software 3DEC was used to replicate its landslide process. The findings from the present study are as follows: (1) blocks in this landslide were classified into significant slide, significant toppling, and significant slide categories based on Df. (2) The whole landslide was divided into significant sliding and toppling zones by Df = 0.5. (3) The results show that the river-damming landslide was likely to be triggered by river erosion, heavy rainfall, gravity. Under strong valley trenching, the rocks on the slope fractured under gravity and tectonic stress. These factors caused rock blocks tensile fracture failure. Then a penetrating sliding surface formed on the slope, which subsequently caused this river-damming landslide.
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Hamel, James V. "Re-evaluation of the 1941 Rock Slide at Brilliant Cut, Pittsburgh, Pennsylvania." Environmental and Engineering Geoscience 27, no. 3 (June 4, 2021): 269–85. http://dx.doi.org/10.2113/eeg-d-20-00076.
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ABSTRACT On March 20, 1941, more than 110,000 yd3 (84,000 m3) of rock slumped from Brilliant Cut in Pittsburgh, Pennsylvania. Failure was triggered by water pressure buildup due to ice blockage of drainage outlets on the slope face. I investigated this slide as part of my Ph.D. research at the University of Pittsburgh in 1968–1969 and have continued to study it. Historical photographs discovered in 1997 provided new insights on the construction and failure of Brilliant Cut and led to this re-evaluation. In this paper, my 1968–1969 work is summarized and then additional geological and historical information is presented along with key observations from the historical photographs. These photographs reveal that slope excavation at Brilliant Cut in 1930–1931 removed lateral support, in turn initiating stress release and progressive failure that loosened or broke bedrock adjacent to the cut. This fractured rock mass remained marginally stable for a decade but then collapsed in March 1941. The 1941 failure was triggered by water held back in rock fractures by a frozen crust over talus and fractured rock on the slope face. A progressive failure mechanism by Brooker and Peck explains the behavior of Brilliant Cut from 1931 to 1941. Sliding Block stability analyses demonstrate the mechanism of progressive failure and suggest that friction angles were reduced gradually to near-residual values along the failure surface, with low water levels in the slope. With drainage blocked in 1941, a water level developed about 30 ft (9 m) above the basal failure surface to initiate the catastrophic failure. This water level is below that previously inferred to have existed at the time of failure.
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Binet, Stéphane, Jacques Mudry, Claudio Scavia, Stefano Campus, Catherine Bertrand, and Yves Guglielmi. "In situ characterization of flows in a fractured unstable slope." Geomorphology 86, no. 1-2 (April 2007): 193–203. http://dx.doi.org/10.1016/j.geomorph.2006.08.013.
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Prager, C., C. Zangerl, G. Patzelt, and R. Brandner. "Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas." Natural Hazards and Earth System Sciences 8, no. 2 (April 24, 2008): 377–407. http://dx.doi.org/10.5194/nhess-8-377-2008.
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Abstract. Some of the largest mass movements in the Alps cluster spatially in the Tyrol (Austria). Fault-related valley deepening and coalescence of brittle discontinuities structurally controlled the progressive failure and the kinematics of several slopes. To evaluate the spatial and temporal landslide distribution, a first comprehensive compilation of dated mass movements in the Eastern Alps has been made. At present, more than 480 different landslides in the Tyrol and its surrounding areas, including some 120 fossil events, are recorded in a GIS-linked geodatabase. These compiled data show a rather continuous temporal distribution of landslide activities, with (i) some peaks of activity in the early Holocene at about 10 500–9400 cal BP and (ii) in the Tyrol a significant increase of deep-seated rockslides in the Subboreal at about 4200–3000 cal BP. The majority of Holocene mass movements were not directly triggered by deglaciation processes, but clearly took a preparation of some 1000 years, after ice withdrawal, until slopes collapsed. In view of this, several processes that may promote rock strength degradation are discussed. After the Late-Glacial, slope stabilities were affected by stress redistribution and by subcritical crack growth. Fracture propagating processes may have been favoured by glacial loading and unloading, by earthquakes and by pore pressure fluctuations. Repeated dynamic loading, even if at subcritical energy levels, initiates brittle fracture propagation and thus substantially promotes slope instabilities. Compiled age dating shows that several landslides in the Tyrol coincide temporally with the progradation of some larger debris flows in the nearby main valleys and, partially, with glacier advances in the Austrian Central Alps, indicating climatic phases of increased water supply. This gives evidence of elevated pore pressures within the intensely fractured rock masses. As a result, deep-seated gravitational slope deformations are induced by complex and polyphase interactions of lithological and structural parameters, morphological changes, subcritical fracture propagation, variable seismic activity and climatically controlled groundwater flows.
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Han, Guofeng, Yuewu Liu, Wenchao Liu, and Dapeng Gao. "Investigation on Interference Test for Wells Connected by a Large Fracture." Applied Sciences 9, no. 1 (January 8, 2019): 206. http://dx.doi.org/10.3390/app9010206.
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Pressure communication between adjacent wells is frequently encountered in multi-stage hydraulic fractured shale gas reservoirs. An interference test is one of the most popular methods for testing the connectivity of a reservoir. Currently, there is no practical analysis model of an interference test for wells connected by large fractures. A one-dimensional equation of flow in porous media is established, and an analytical solution under the constant production rate is obtained using a similarity transformation. Based on this solution, the extremum equation of the interference test for wells connected by a large fracture is derived. The type-curve of pressure and the pressure derivative of an interference test of wells connected by a large fracture are plotted, and verified against interference test data. The extremum equation of wells connected by a large fracture differs from that for homogeneous reservoirs by a factor 2. Considering the difference of the flowing distance, it can be concluded that the pressure conductivity coefficient computed by the extremum equation of homogeneous reservoirs is accurate in the order of magnitude. On the double logarithmic type-curve, as time increases, the curves of pressure and the pressure derivative tend to be parallel straight lines with a slope of 0.5. When the crossflow of the reservoir matrix to the large fracture cannot be ignored, the slope of the parallel straight lines is 0.25. They are different from the type-curves of homogeneous and double porosity reservoirs. Therefore, the pressure derivative curve is proposed to diagnose the connection form of wells.
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Ghazali, Mohamad Anuri, Abd Ghani Rafek, Kadderi Md Desa, and Suhaimi Jamaluddin. "Effectiveness of Geoelectrical Resistivity Surveys for the Detection of a Debris Flow Causative Water Conducting Zone at KM 9, Gap-Fraser’s Hill Road (FT 148), Fraser’s Hill, Pahang, Malaysia." Journal of Geological Research 2013 (March 10, 2013): 1–11. http://dx.doi.org/10.1155/2013/721260.
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This study reports the findings of resistivity surveys which were conducted at the initiation area of debris flow at KM 9, Fraser’s Hill Gap road (FT148). The study involves three slope parallel survey lines and two lines perpendicular to the slope face. The parallel lines are FH01, FH02, and FH03, while the lines FH04 and FH05 are perpendicular. A granite body was detected at the central part of the east line and is nearest to the ground surface along FH02. The existence of low resistivity zones within the granite body is interpreted as highly fractured, water conducting zones. These zones are continuous as they have been detected in both the east-west as well as the north-south lines. The residual soil layer is relatively thin at zones where weathered granite dominates the slope face of the failure mass. The weak layer is relatively thick with an estimated thickness of 80 m and water flow occurs at the base of it. The high water flow recorded from the horizontal drains further supports the possible existence of these highly fractured, water conducting zones located within the granite. The shallow fractured granite is virtually “floating” above the water saturated zone and therefore is considered unstable.
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Al-Rbeawi, Salam. "Bivariate Log-Normal Distribution of Stimulated Matrix Permeability and Block Size in Fractured Reservoirs: Proposing New Multilinear-Flow Regime for Transient-State Production." SPE Journal 23, no. 04 (June 7, 2018): 1316–42. http://dx.doi.org/10.2118/189993-pa.
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Summary This paper investigates the impacts of varied stimulated matrix permeability and matrix-block size on pressure behaviors and flow regimes of hydraulically fractured reservoirs using bivariate log-normal distribution. The main objective is assembling the variance in these two parameters to the analytical models of pressure and pressure derivative considering different porous-media petrophysical properties, reservoir configurations, and hydraulic-fracture (HF) characteristics. The motivation is eliminating the long-run discretization treatment in the porous media required by applying analytical models to describe the variance in the previously discussed parameters with the distance between HFs. Several analytical models for pressure response were generated in this study for hydraulically fractured reservoirs with rectangular-shaped drainage areas. These models take into account the change in stimulated matrix permeability from the maximum value close to the HF face to the minimum value at the so-called no-flow boundary between fractures. They also consider the change in the matrix-block size, corresponding to the change in the induced-fracture density (number of fractures per foot of length), from the minimum value close to the fracture face to the maximum value at the no-flow boundary. Bivariate log-normal distribution was used to describe the change in the stimulated matrix permeability and matrix-block size. The formations of interest are composed of stimulated reservoir volume (SRV), where the matrix is stimulated by the fracturing process, and unstimulated reservoir volume (USRV), where the stimulation process does not affect the matrix. The outcomes of this study can be summarized as Generating new analytical models for pressure and pressure derivative in hydraulically fractured reservoirs that consider the change in stimulated matrix-block size and permeability using bivariate log-normal distribution Understanding the effect of using the probability-density function (PDF) of matrix-block size and permeability in the pressure distribution of different reservoirs Observing the new multilinear-flow regime that develops at intermediate production time and represents several simultaneous linear-flow regimes inside HFs, SRV, and USRV Developing analytical models for the new multilinear-flow regime Studying the effects of petrophysical properties of HFs, induced fractures, and matrix as well as reservoir size and configuration on pressure behavior The most interesting points in this study are The applicability of bivariate log-normal distribution for describing the variance and nonuniform distribution of matrix-block size and permeability. The large variance in the matrix-block size and permeability causes significant decrease in wellbore-pressure drop. Small value of standard deviation of matrix-block size and permeability indicates the possibilities for significant decrease in wellbore pressure drop. The means of matrix-block size and permeability may not have significant effects on reservoir-pressure distribution. The new multilinear-flow regime is characterized by a one-eighth slope on the pressure-derivative curve and is seen always after HF linear flow and before boundary-dominated flow regime. Multilinear-flow regime develops to bilinear-flow regime with a one-quarter slope for uniform distribution of equal matrix-block size and permeability.
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Mei, Xuefeng, Nengfeng Wang, Guotao Ma, Jie Wang, Yan Wang, Jianli Wu, Mei Han, and Bin Cai. "Deformation Process and Mechanism Analyses of a Rock Slope Based on Long-Term Monitoring at the Pubugou Hydropower Station, China." Geofluids 2021 (February 12, 2021): 1–17. http://dx.doi.org/10.1155/2021/6615424.
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This paper presents a typical 450 m high rock slope in a highly jointed and fractured rock mass at Pubugou (PBG) hydropower station on the Dadu River. We established a set of multiphase field geological survey combined with GPS, inclinometers, and piezometer monitoring system to analyze the deformation and failure mechanism of rock slope. The results show that small-scale excavation in road construction disrupted the balance of the Pubugou rock slope (PBGRS), and several local retrogressive failures occurred at the toe. Monitoring data regarding surface and subsurface movements show that the PBGRS is stable as a whole. The deformation concentrated mainly in the loosened fractured zone, which was a feature with sliding-compression cracking. Highly loosened rock mass was the predominant factor affecting the stability of the PBGRS, while the role of reservoir water level fluctuation, though positive, was not significant. Overall, the PBGRS still has a high potential for further development, especially in the slope’s upper zone. To reinforce the slope, measurements mainly consist of the concrete frame combined with anchor cables constructed on the slope. In this study, the analysis was carried out of pre- and postreinforcement measure slope stability with numerical simulation, and safety factor increased from 1.09 to 1.21. This study’s findings have important implications to the analytical method and reinforcement design with geological settings like that of the PBGRS.
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Pan, Yongjian, Huajun Wang, Yanlin Zhao, Qiang Liu, and Shilin Luo. "Numerical Analysis of the Mud Inflow Model of Fractured Rock Mass Based on Particle Flow." Geofluids 2021 (April 9, 2021): 1–16. http://dx.doi.org/10.1155/2021/5599748.
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Water inrush and mud outburst are one of the crucial engineering disasters commonly encountered during the construction of many railways and tunnels in karst areas. In this paper, based on fluid dynamics theory and discrete element method, we established a fractured rock mass mud inflow model using particle flow PFC3D numerical software, simulated the whole process of fractured rock mass mud inflow, and discussed the effect of particle size and flow velocity on the change of pressure gradient. The numerical simulation results show that the movement of particles at the corner of the wall when the water pressure is first applied occurs similar to the vortex phenomenon, with the running time increases, the flow direction of particles changes, the vortex phenomenon disappears, and the flow direction of particles at the corner points to the fracture; in the initial stage, the slope of the particle flows rate curves increases in time, and the quadratic function is used for fitting. After the percolation velocity of particles reaches stability, the slope of the curve remains constant, and the primary function is used for fitting; the particle flow rate and pressure gradient are influenced by a variety of factors, and they approximately satisfy the exponential function of an “S” curve.
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Sanati, Ali, and Mohammad Yousefi Khoshdaregi. "Experimental investigation of dispersion phenomenon in a fractured porous medium." International Journal of Engineering & Technology 4, no. 1 (February 10, 2015): 209. http://dx.doi.org/10.14419/ijet.v4i1.4136.
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Dispersion of fluids flowing through porous media is an important phenomenon in miscible displacement. Dispersion causes instability of miscible displacement flooding; therefore, to obtain and maintain the miscibility zone, the porous medium dispersivity should be considered in displacing fluid volume calculation. Many works have been carried out to investigate the dispersion phenomenon in porous media in terms of theory, laboratory experiments and modeling. What is still necessary is to study the effects of presence of fracture in a porous medium on dispersion coefficient or dispersivity. In this work dispersion phenomenon in a fractured porous medium has been investigated through a series of miscible displacement tests on homogeneous sandstone core samples. Tests were repeated on the same core samples with induced fracture in the flow direction. The effects of fracture on miscible displacement flooding have been studied by comparison of the results of dispersion tests in the absence and presence of fracture. In the presence of fracture, breakthrough time reduced and the tail of effluent S-shaped curve smeared. Moreover, the slope of S-shaped curve at 1 pore volume of injected fluid was lower than homogeneous case which means dispersion coefficient increased. The results presented in this work provide an insight to the understanding of dispersion phenomenon for modeling of miscible displacement process through naturally fractured reservoirs.
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Chang, Zhiguo, Qingxiang Cai, Wei Zhou, Izhar Mithal Jiskani, and Rui Wang. "Effects of the Loading and Unloading Conditions on Crack Propagation in High Composite Slope of Deep Open-Pit Mine." Advances in Civil Engineering 2019 (May 28, 2019): 1–11. http://dx.doi.org/10.1155/2019/3168481.
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In the process of open-pit excavation and stacking of dump along the side wall, the rock mass inside the composite slope undergoes complicated loading and unloading effect, which are manifested as triaxial stress → horizontal unloading → axial loading. In this study, a corresponding mechanical model of crack propagation in composite slope under loading and unloading effects was established. The stress-strain curves and deformation characteristics of rock under different stress paths were studied. A series of different tests under unloading pressure condition were carried out to study the behavior of the rock fracture under different confining pressure paths. The results showed that under the same initial stress conditions, the deviator stress required for rock unloading failure was less than that of the conventional triaxial compression. The axial deformation of rock samples was gradually increased with the increase of unloading, and the unloading easily led to rock failure. By analyzing the crack propagation mechanism under loading and unloading stress field, the analytic relation of the limit height of the composite slope with the crack morphology as the variation was determined when crack propagation occurred near the slope surface. This study provides a technical note on local damage and cracks propagation of a fractured rock mass under the loading-unloading effects in high composite slope.
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Hasler, A., S. Gruber, and W. Haeberli. "Temperature variability and thermal offset in steep alpine rock and ice faces." Cryosphere Discussions 5, no. 2 (March 1, 2011): 721–53. http://dx.doi.org/10.5194/tcd-5-721-2011.
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Abstract. The thermal condition of high-alpine mountain flanks can be an important determinant of climate change impact on slope stability and correspondingly down-slope hazard regimes. In this study we analyze new time-series from 17 shallow temperature-depth profiles at two field sites in steep bedrock and ice. Extending earlier studies that revealed the topographic variations in temperatures, we demonstrate considerable differences of annual mean temperatures for variable surface characteristics and depths within the measured profiles. This implies that measurements and models related to compact and near-vertical bedrock temperatures may deviate considerably from conditions in the majority of bedrock slopes in mountain ranges that are usually non-vertical and fractured. For radiation-exposed faces, for instance, mean annual temperatures at depth are up to 3 °C lower and permafrost is likely to exist at lower elevations than reflected by current estimates based on the near-vertical case. Retention of thin snow cover and ventilation effects in open clefts are most likely responsible for this cooling. The presented or similar data could be used in the future to support the development and testing of models related to the thermal influence of snow-cover and fractures in steep bedrock. This would allow generalizing the here-presented findings.
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Zhang, Wen, Qihua Zhao, Jianping Chen, Runqiu Huang, and Xiaoqing Yuan. "Determining the critical slip surface of a fractured rock slope considering preexisting fractures and statistical methodology." Landslides 14, no. 3 (February 8, 2017): 1253–63. http://dx.doi.org/10.1007/s10346-017-0800-4.
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Li, Xinxin, Jianshe Liu, Wenping Gong, Yi Xu, and Victor Mwango Bowa. "A discrete fracture network based modeling scheme for analyzing the stability of highly fractured rock slope." Computers and Geotechnics 141 (January 2022): 104558. http://dx.doi.org/10.1016/j.compgeo.2021.104558.
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Ezung, Meripeni, Temsulemba Walling, and C. Chelladura C. Chelladura. "Application of Vertical Electrical Sounding for Subsurface Characterization to Determineslope Instability at Perizie, Nagaland." Current World Environment 17, no. 3 (December 30, 2022): 657–71. http://dx.doi.org/10.12944/cwe.17.3.14.
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Vertical Electrical Sounding (VES) technique which employs the Schlumberger depth sounding method was used to investigate the subsurface conditions at the landslide in Perizie colony, Kohima. The interpretation of the VES curves shows differing lithology consisting of weathered shales with associated clay, which is considered an important factor for slope instability. The shear strength of the slope materials, including the country rocks and the soil cover, is also significantly reduced and easily detached due to the effects of weathering and erosion, causing the landslides. Three to six possible geo-electric layers are delineated from the variations in the resistivity values, with the lithologies consisting of topsoil followed by alternate layers of weathered and fractured rocks of varying thickness. The analysis also points to the presence of a weak zone at a depth of about 10 m, which is not apparent from the surface. The formation of groundwater aquifers in the fractured zones indicates high risk for slope failure as this accelerates the weak country rocks to weather. The results obtained by this study correspond well with the available borehole data of the area.
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Nobakht, Morteza, and C. R. R. Clarkson. "A New Analytical Method for Analyzing Linear Flow in Tight/Shale Gas Reservoirs: Constant-Flowing-Pressure Boundary Condition." SPE Reservoir Evaluation & Engineering 15, no. 03 (May 31, 2012): 370–84. http://dx.doi.org/10.2118/143989-pa.
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Summary Many tight/shale gas wells exhibit linear flow, which can last for several years. Linear flow can be analyzed using a square-root-of-time plot, a plot of rate-normalized pressure vs. the square root of time. Linear flow appears as a straight line on this plot, and the slope of this line can be used to calculate the product of fracture half-length and the square root of permeability. In this paper, linear flow from a fractured well in a tight/shale gas reservoir under a constant-flowing-pressure constraint is studied. It is shown that the slope of the square-root-of-time plot results in an overestimation of fracture half-length, if permeability is known. The degree of this overestimation is influenced by initial pressure, flowing pressure, and formation compressibility. An analytical method is presented to correct the slope of the square-root-of-time plot to improve the overestimation of fracture halflength. The method is validated using a number of numerically simulated cases. As expected, the square-root-of-time plots for these simulated cases appear as a straight line during linear flow for constant flowing pressure. It is found that the newly developed analytical method results in a more reliable estimate of fracture half-length, if permeability is known. Our approach, which is fully analytical, results in an improvement in linear-flow analysis over previously presented methods. Finally, the application of this method to multifractured horizontal wells is discussed and the method is applied to three field examples.
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Binet, S., L. Spadini, C. Bertrand, Y. Guglielmi, J. Mudry, and C. Scavia. "Variability of the groundwater sulfate concentration in fractured rock slopes: a tool to identify active unstable areas." Hydrology and Earth System Sciences 13, no. 12 (December 8, 2009): 2315–27. http://dx.doi.org/10.5194/hess-13-2315-2009.
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Abstract. Water chemical analysis of 100 springs from the Orco and the Tinée valleys (Western Italy and Southern France) and a 7 year groundwater chemistry monitoring of the 5 main springs were performed. All these springs drain from crystalline rock slopes. Some of these drain from currently active gravitational slope deformations. All groundwaters flowing through presently unstable slopes show anomalies in the sulfate concentrations compared to stable aquifers. Particularly, an increase of sulfate concentrations was observed repeatedly after each of five consecutive landslides on the La Clapière slope, thus attesting to the mechanical deformations are at the origin of this concentration change. Significant changes in the water chemistry are produced even from slow (mm/year) and low magnitude deformations of the geological settings. Pyrite nuclei in open fractures were found to be coated by iron oxides. This suggests that the increase of dissolved sulfate relates to oxidative dissolution of Pyrite. Speciation calculations of Pyrite versus Gypsum confirmed that observed changes in the sulfate concentrations is predominantly provided from Pyrite. Calculated amounts of dissolved minerals in the springs water was obtained through inverse modelling of the major ion water analysis data. It is shown that the concentration ratio of calculated dissolved Pyrite versus calculated dissolved gneiss rock allows us to unambiguously distinguish water from stable and unstable areas. This result opens an interesting perspective for the follow-up of sliding or friction dynamic in landslides or in (a) seismic faults.
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Belghali, Mounir, and Zied Saada. "Seismic stability analysis of rock slopes by yield design theory using the generalized Hoek-Brown criterion." MATEC Web of Conferences 149 (2018): 02026. http://dx.doi.org/10.1051/matecconf/201814902026.
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The stability of rock slope is studied using the kinematic approach of yield design theory, under the condition of plane strain and by considering the last version of the Hoek-Brown failure criterion. This criterion, which is suitable to intact rock or rock mass highly fractured regarded as isotropic and homogeneous, is widely accepted by the rock mechanics community and has been applied in numerous projects around the world. The failure mechanism used to implement the kinematic approach is a log-spiral rotational mechanism. The stability analysis is carried out under the effects of gravity forces and a surcharge applied along the upper plateau of the slope. To take account of the effects of forces developed in the rock mass during the passage of a seismic wave, the conventional pseudo-static method is adopted. This method is often used in slope stability study for its simplicity and efficiency to simulate the seismic forces. The results found are compared with published numerical solutions obtained from other approaches. The comparison showed that the results are almost equal. The maximum error found is less than 1%, indicating that this approach is effective for analyzing the stability of rock slopes. The relevance of the approach demonstrated, investigations are undertaken to study the influence of some parameters on the stability of the slope. These parameters relate to the mechanical strength of the rock, slope geometry and loading.
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Zhao, Jian Bin, Hai Dong Song, Di Li, and Zheng Zhang. "Research on Water Temperature Change of Hot Dry Rock Fracture Storage Layer in Shenyang." Applied Mechanics and Materials 580-583 (July 2014): 349–54. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.349.
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Hot dry rock(HDR) provides heat through fracture storage layer. The purpose of research on water temperature change of hot dry rock fracture is to study that whether heat energy can satisfy five months winter heating or not. Research method is establishing model of hot dry rock fractured storage layer by means of numerical simulation software FLUENT according to the rock physical properties in Shenyang region. The depth of drilling is 4000m and the water flow rate is 1cm/s. Research principle is high temperature underground rock transfer heat to medium water in the fracture by coupling. Conclude water temperature change equation every two weeks. The results of the study is that fracture water temperature distribution can be approximated taken as linear distribution. According to the slope K, we can conclude water temperature change formula(3.10), and we can use it to infer fracture water temperature.
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Greco, R., L. Comegna, E. Damiano, A. Guida, L. Olivares, and L. Picarelli. "Hydrological modelling of a slope covered with shallow pyroclastic deposits from field monitoring data." Hydrology and Earth System Sciences 17, no. 10 (October 16, 2013): 4001–13. http://dx.doi.org/10.5194/hess-17-4001-2013.
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Abstract. A one-dimensional hydrological model of a slope covered with pyroclastic materials is proposed. The soil cover is constituted by layers of loose volcanic ashes and pumices, with a total thickness between 1.8 m and 2.5 m, lying upon a fractured limestone bedrock. The mean inclination of the slope is around 40°, slightly larger than the friction angle of the ashes. Thus, the equilibrium of the slope, significantly affected by the cohesive contribution exerted by soil suction in unsaturated conditions, may be altered by rainfall infiltration. The model assumes a single homogeneous soil layer occupying the entire depth of the cover, and takes into account seasonally variable canopy interception of precipitation and root water uptake by vegetation, mainly constituted by deciduous chestnut woods with a dense underbrush growing during late spring and summer. The bottom boundary condition links water potential at the soil–bedrock interface with the fluctuations of the water table of the aquifer located in the fractured limestone, which is conceptually modelled as a linear reservoir. Most of the model parameters have been assigned according to literature indications or from experimental data. Soil suction and water content data measured between 1 January 2011 and 20 July 2011 at a monitoring station installed along the slope allowed the remaining parameters to be identified. The calibrated model, which reproduced very closely the data of the calibration set, has been applied to the simulation of the hydrological response of the slope to the hourly precipitation record of 1999, when a large flow-like landslide was triggered close to the monitored location. The simulation results show that the lowest soil suction ever attained occurred just at the time the landslide was triggered, indicating that the model is capable of predicting slope failure conditions.