Slope Rock Mass Research Articles

Influence of the extra-thick coal seam exploitation on the deformation characteristics of the overlying rock mass in an open-pit mine slope

Coal seam mining causes movement and deformation of the overlying rock mass and ground surface, directly resulting in serious damage to the surface construction facilities. To investigate the deformation mechanism and characteristics of the overlying rock mass, three-dimensional numerical simulation and model test are carried out on an open-pit mine slope. The results show that the sliding instability characteristics of the slope can be identified based on the numerical analysis. Coal mining affects on the deformation characteristics of the overlying rock mass near the inner dump. The closer to the slope boundary, the greater the subsidence of overlying rock mass. The maximum displacement occurs near the inner dump. The slope mining has great influence on the deformation characteristics of inner dump. Moreover, the damage process of overlying rock mass can be further studied via the model test. After coal seams mining out, the overlying rock mass occurs overall settlement failure. There is a large difference between the lower end side of working face and the upper end side at the caving angle of roof. This work can provide a basis for the safe operation of coal mine disaster prevention and mitigation.

Numerical simulation scheme of jointed rock masses using UAV photogrammetry and a disk-based discontinuous deformation analysis model

<abstract><p>The use of unmanned aerial vehicles (UAVs) for photogrammetry allows the rapid acquisition of high-resolution images of geological masses in complex landforms. However, effective analysis of the acquired image information remains a key research issue. At K158 + 837 on the Chongqing-Huaihua Railway, Baima jointed rock masses were reconstructed with high accuracy using UAV close-range photogrammetry technology, and rock discontinuities were extracted from the projected image. The proposed modeling algorithm for jointed rock masses enables the preprocessing of two-dimensional jointed rock mass slopes. Numerical simulations using the disk-based discontinuous deformation analysis method show that the discontinuity network formed by initial cutting significantly affects the subsequent crack development. Meanwhile, simulation results under different scenarios indicate the importance of the pre-reinforcement measures applied to unstable rock masses. The workflow developed based on these results can serve as a reference for the comprehensive acquisition, recognition and numerical modeling analysis of similar jointed rock masses.</p></abstract>

Influence of Fracture Geometric Characteristics on Fractured Rock Slope Stability

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.

Tectonic deformation and landscape evolution inducing mass rock creep driven landslides: the Loumar case-study (Zagros Fold and Thrust Belt, Iran)

Several landscape evolution models have been proposed so far to explain the dynamic feedback between Earth surface processes and tectonics in the Zagros Mountains. Nevertheless, the relationship among time-dependent rock mass deformations, landscape evolution rates, and tectonics in triggering large rock landslides is still poorly studied in this region and worldwide.To fill this gap, here we focus on the previously unknown Loumar landslide affecting the NE flank of the Gavar anticline (Zagros Mountains) through a multi-perspective methodology which includes SAR Interferometry, geomorphometry, linear temporal inversion of river profiles and field survey for independent OSL dating of geomorphic markers of landscape evolution.We estimated that at 93 +21/−16 ka the backlimb of the Gavar fault-propagation fold reached limit equilibrium conditions for the slope failure, caused by an acceleration in the fold growth. The growth of a minor fold also induced the abandonment of a meandering canyon and the river migration to a new narrow gorge. The fluvial downcutting kinetically released the limestone strata that started to deform through Mass Rock Creep (MRC). The MRC process accumulated inelastic strain until 5.52 ± 0.36 ka, when the slope evolved into a failure causing the partial occlusion of the valley and the generation of a pond.The obtained creep timespan of 104–105 years since the initiation of the MRC process is consistent with the typical lifespan of gravity-induced slope deformations in non-glaciated regions. For this reason, such an approach can be used for the reconstruction of slow deforming slope evolution to predict the hazard of slopes prone to massive rock slope failure, linking it to the MRC stages.

Numerical Evaluation of Bearing Capacity of Strip Footing on Rockmass Slope

Numerical Evaluation of Bearing Capacity of Strip Footing on Rockmass Slope

Features and Formation Mechanism of the Jiaopenba Landslide, Southwestern Sichuan Province, China

The Jiaopenba landslide, which represents a typical large basalt high-speed remote landslide, is located in Emeishan City, southwestern Sichuan province, China. Based on the field investigation, the characteristics of the Jiaopenba landslide have been revealed. The Jiaopenba landslide occurred on the steep Mount Emei. Landslide materials with a volume of approximately 6.75×108 m3 slid down from a high position, forming a large-scale high-speed remote debris flow, with the farthest sliding distance of about 7.5 km. The landslide area is located in the west wing of the Emeishan anticline, which is cut by faults to form a monoclinal fault-block mountain. Although the shear outlet of the landslide is near the slope toe and does not have good free conditions, there are faults passing through the slope toe of the bedding slope of the fault hanging wall, the landslide is affected by the fault activity, and the integrity of the layered slope is poor. When the foot of the slope is empty, the fault zone is compressed and plastic extrusion, which leads to bedding slip of the slope rock mass and greatly weakens the interlayer bonding force. When coupled with long structural planes on both sides to form side crack planes, a large-scale inclined plate structure is formed. Under the action of a strong earthquake and other external forces, the rock mass near the fault can be damaged by tension, and a large-scale high-position landslide can be formed by the mode of compression-slip-tension fracture.

Oblique Crack Propagation of Brittle Rock under Uniaxial Compression and Its Influencing Factors

With the development of infrastructure in China, the slope rock mass is affected by external forces such as roads. Tunnel excavation will cause a series of engineering problems, which are essentially caused by the instability caused by the propagation of internal cracks in the rock mass. At the same time, in practical engineering, the rock mass is formed through long-term geological structure, and its internal cracks have a variety of properties. Based on granite samples as the research object, two different angles of sample shapes, cylindrical and circular, are prefabricated. The uniaxial compression test is studied to analyze the law of inclined crack propagation in rock under uniaxial compression. Combined with the theory of fracture mechanics, the influence mechanism of crack inclination and sample shape on crack propagation in rock mass is discussed. The test results show that under uniaxial compression, the stress-strain curves of granite samples can be divided into four stages: compaction, elasticity, plasticity, and residual deformation. For the cylindrical sample, the crack initiation occurs at the tip. The compressive strength of the sample decreases with the increase in the prefabricated crack angle, and the crack initiation angle increases with the increase in the prefabricated crack angle. The fracture of the sample changes from shear slip failure to split shear failure of the penetrating rock mass with the increase in the crack angle. For the disk sample, the crack initiation location gradually increases from the tip to the middle with the increase in the crack angle, and the crack initiation angle increases with the increase in the crack angle. The peak load of the sample decreases first and then increases with the increase in the crack angle and is the minimum at 60°. The fracture mode of the sample is mainly tensile failure. When the crack dip angle is between 30° and 60°, the tensile and shear composite failure of the sample occurs, and the influence mechanism of crack dip angle and sample shape on the crack propagation path is analyzed. The research results have important theoretical significance for engineering design, construction, and stability maintenance.

A Study on the Freeze–Thaw Damage and Deterioration Mechanism of Slope Rock Mass Based on Model Testing and Numerical Simulation

Engineering rock mass in cold regions has obvious freeze–thaw damage as a result of extreme differences in temperature, rainfall, snow, and other factors, which is one of the main causes of frequent geological disasters. Therefore, it is important to investigate the deterioration mechanism and evolution laws of rock mass freeze–thaw damage. Considering a hydropower station’s left bank slope in a cold region, model testing and numerical testing of slope rock mass failure under freeze–thaw conditions are here carried out by developing a generalized model. The results reveal that heat is transmitted from the outside to the inside of the slope and that the rate of temperature change varies with depth; the frost-heave force causes tensile cracks in the rock mass, with crack propagation taking the form of a circular arc; the presence of an original structural plane influences the propagation direction of the frost-heave crack, whereas the freezing rate of the fissure water influences the amplitude and growth rate of the frost-heave force. Additionally, a novel method of measuring frost-heave force is proposed. The largest frost-heave force caused by water–ice phase change is 19.3 kPa, which is equivalent to 3.17 MPa of the actual slope.

Stability analysis of Xiluodu Hydropower Station right bank slope based on discontinuous deformation analysis method

PurposeThe purpose of this study is to investigate the deformation characteristics and failure modes of the right bank slope of Xiluodu Hydropower Station after excavation.Design/methodology/approachMicro-seismic monitoring technology is applied to obtain the microfracture information and study the internal damage evolution law of the slope rock mass. A numerical model for discontinuous deformation analysis (DDA) is established to analyse the deformation characteristics and failure mode of the slope. Micro-seismic monitoring and DDA can verify and supplement each other's results in the investigation of slope failure.FindingsThe results show that the slope has a downhill displacement along the weathered zone under natural conditions; the maximum resultant displacement at the monitoring point is 380 mm. The micro-seismic events are concentrated in an area located 30–100 m horizontally away from the slope surface and at an elevation of 390–470 m. The distribution of these micro-seismic events is consistent with the location of the unloading and weathered zones; it is the same as the DDA simulation result.Originality/valueThe study is anticipated to be used as reference for the stability analysis of rock slopes. By combining the continuous (micro-seismic monitoring technology) and discontinuous (DDA) methods, the entire process starting from the gradual accumulation of internal rock micro-damage to the macroscopic discontinuous deformation and failure of the slope can be investigated.

3D Rock Structure Digital Characterization Using Airborne LiDAR and Unmanned Aerial Vehicle Techniques for Stability Analysis of a Blocky Rock Mass Slope

Airborne light detection and ranging (LiDAR) and unmanned aerial vehicle-structure from motion (UAV-SfM) provide point clouds with unprecedented resolution and accuracy that are well suited for the digital characterization of rock outcrops where direct contact measurements cannot be obtained due to terrain or safety constraints. Today, however, how to better apply these techniques to the practice of geostructural analysis is a topic of research that must be further explored. This study presents a processing procedure for extracting three-dimensional (3D) rock structure parameters directly from point clouds using open-source software and a three-dimensional distinct element code-assisted (3DEC) simulation of slope failure based on carbonate rock cliffs in the Jiuzhaigou Scenic Area. The procedure involves (1) processing point clouds obtained with different remote sensing techniques; (2) using the Hough transform to estimate normals for the hue, saturation, and value (HSV) rendering of unstructured point clouds; (3) automatically clustering and extracting the set-based point clouds; (4) estimating set-based geometric parameters; and (5) performing a subsequent stability analysis based on rock structure parameters. The results show that integrating different remote sensing techniques and rock structure computing can provide a quick way for slope engineers to assess the safety of blocky rock masses.

Aging Stability Analysis of Slope Considering Cumulative Effect of Freeze–Thaw Damage—A Case Study

The change of physical and mechanical properties of slope rock mass in open-pit mines in seasonally frozen area under the action of freeze–thaw cycles is one of the main reasons for slope instability. In this paper, taking the mechanical parameters of coal seam and sandstone layer in the Beitashan Pasture Open-Pit Mine in Xinjiang as the research object, considering the combined effect of the frost-heave tensile stress in the crack perpendicular to the crack surface and the three-dimensional confining pressure in the crack, the criterion for cracking of fractured rock mass under freeze-thaw condition is determined by applying the principle of stress superposition and the theory of strain energy density factor, and the theoretical frost-heave stress required for cracking is deduced. On this basis, the sensitivity analysis of the fixed factors and variable factors to the theoretical frost-heave stress was performed, respectively. Finite element analysis was utilized to analyze the slope stability under the attenuation of five groups of different rock mass mechanical properties and to determine the slope angle required for the slope stability. Seven different slope angles of sidewall mining ranging from 36° to 51° are analyzed. The results of finite element analysis show that considering the timeliness difference of rock mass parameters with time, the safety factor of slope is reduced from the original 1.70 to 1.18, and 91,500 tons of coal resources can be recovered every year, with remarkable economic benefits.

Research on Generalized RQD of Rock Mass Based on 3D Slope Model Established by Digital Close-Range Photogrammetry

The traditional method of obtaining rock quality designation (RQD) cannot fully reflect the anisotropy of the rock mass and thus cannot accurately reflect its quality. In the method of calculating RQD based on three-dimensional network simulation of discontinuities, due to the limited number of samples and low accuracy of discontinuity data obtained by manual contact measurement, a certain deviation in the network is generated based on the data, which has an impact on the calculation result. Taking a typical slope in Dongsheng quarry in Changchun City as an example, in this study, we obtained the discontinuity data of the slope based on digital close-range photogrammetry, which greatly enlarged the sample size of discontinuity data and improved the data quality. Based on the heterogeneity of the rock mass, the optimum threshold of discontinuity spacing was determined when surveying lines were laid parallel to different coordinate axes to calculate the generalized RQD, and the influence of measuring blank areas on the slope caused by vegetation coverage or gravel accumulation was eliminated. The real generalized RQD of the rock mass after eliminating the influence of blank areas was obtained. Experiments showed that, after eliminating the influence of blank areas, the generalized RQD of the slope rock mass more truly represented the complete quality of rock mass and offers a new idea for the quality evaluation of engineering rock mass.

Shear creep mechanical properties and damage model of mudstone in open-pit coal mine

Clarifying the shear creep characteristics of rock and scientifically analyzing its creep deformation law is the key to solving the problem of safe construction and long-term stability analysis of the open-pit coal slope rock mass. Shear creep tests were carried out on mudstone from an open-pit coal mine in Eastern Mongolia to reveal the creep characteristics of mudstone under different normal and shear stresses. Based on the classical Nishihara model, a new composite six-element nonlinear shear creep damage model is established by introducing nonlinear elastomers. Using the least square method, model verification and parameter identification are carried out on the variable test data. At the same time, the influence law of the model parameters on the rock creep deformation is analyzed according to the theoretical curve. The study results showed that the nonlinear shear creeps damage model could better describe the creep characteristics of rock different normal stress and shear stress levels, significantly the non-linear both the strain and time of attenuation creep and accelerated creep. The creep characteristics of the accelerated creep stage described by this model are better than those described by the classical Nishihara model. The model curve is consistent with the changing trend of the experimental data, and the degree of agreement is very high. The correlation coefficients are all above 0.98, which verifies the accuracy and rationality of the model. The influence law of creep parameters is analyzed. The parameters b and c increase nonlinearly with creep. The increase of λ accelerates the process of rock attenuation creep stage; the increase of η10 slows down the progress of rock decay creep stage; with the increase of α, the deformation and creep rate of rock in accelerated creep stage gradually increase. When η2 increases, the deformation in the acceleration stage decreases gradually. The research results can provide important theoretical support for the safe construction and long-term stability analysis of open-pit coal slope rock masses.

STABILITY ANALYSIS OF ROCK SLOPE USING SLOPE STABILITY PROBABILITY CLASSIFICATION (SSPC) METHOD IN PIYUNGAN-PATUK AREA, YOGYAKARTA SPECIAL REGION

Landslide events in an area are manifestations of unstable slope conditions so evaluation of slope stability and mapping of areas prone to landslides is very important as an effort to mitigate landslides. In this study, the Slope Stability Probability Classification (SSPC) method was used to evaluate slope stability in the Piyungan-Patuk area. which is a rock mass classification system for slope stability that classifies 3 (three) different rock masses through a three-step approach namely: Exposure Rock Mass (ERM), Reference Rock Mass (RRM), and Slope Rock Mass (SRM). Slope stability analysis results on 18 selected slopes obtained a probability of slope stability with very low to very high classification with a probability value of stability <0.5 to> 95, where the probability value is strongly influenced by rock mass parameters such as rock strength, discontinuity, and weathering rate.

Study on the Structural Plane Characteristics and Disaster-Induced Mechanism of the Yellow River Jingtai Stone Forest, Northwestern Loess Plateau, China

The Yellow River Jingtai Stone Forest (YJSF) is situated in the northwestern margin of the Chinese Loess Plateau, and it is not only one of the most precious and rare types of natural landforms in the Loess Plateau but also a protected area of valuable geological relics and landscapes in northwest China. Massive rock structural planes are present in the stone forest. However, few studies have been conducted on the rock mass structural planes for the slope’s stability. Based on the detailed field investigation, structural planes and their combination types are classified based on the rock mass. On this basis, combined with physical, mechanical, and hydraulic tests, the disaster-induced mechanism of the rock mass structural planes is classified and discussed. Results show that the structural planes of the YJSF can be divided into three types, namely, the primary structural plane, tectonic structural plane, and secondary plane. They not only combine with each other to cut the rock mass into different shape blocks but also jointly control the stability of the rock mass slope. The physical and mechanical tests and water sensitivity characteristics show that the conglomerates and muddy sandstones which are the main components of the YJSF have strong tensile and shear strengths under natural situations, while their strengths are reduced under immersion infiltration; in particular, the muddy sandstones are more sensitive to water and have a lower strength than that of the conglomerates. Finally, the disaster-induced mechanism of the YJSF is mainly related to the combination of various structural planes, which can be divided into four failure patterns, namely, creeping slide-tension failure, gradual failure, slipping failure, and dumping failure; coupling action of endogenic and exogenic geodynamic processes was responsible for their formation. The studied results will provide critical, theoretical, and technical support for the slope stability analysis, scenic geological heritage protection, and disaster warning in this area.

Experimental Study on the Evolution Mechanism of Landslide with Retaining Wall Locked Segment

The failure of locked segment-type slopes is often affected by rainfall, earthquake, and other external loads. Rainfall scours the slope and weakens the mechanical properties of rock-soil mass. At the same time, rainfall infiltrates into cracks of slope rock mass. Under the action of in situ stress, hydraulic fracturing leads to the development and expansion of rock cracks, which increases the risk of slope instability. Under seismic force, the slope will be subjected to large horizontal inertial force, resulting in slope instability. In this paper, a self-developed loading device was used to simulate the external loads such as rainfall and earthquake, and the model tests are carried out to study the evolution mechanism of landslide with retaining wall locked segment. Three-dimensional laser scanner, microearth pressure sensors, and high-definition camera are applied for the high-precision monitoring of slope shape, deformation, and stress. Test results show that the retaining wall locked segment has an important control effect on landslide stability. The characteristics of deformation evolution and stress response of landslide with retaining wall locked segment are analyzed and studied by changing the slope shape, earth pressure, and the displacement cloud map. The evolutionary process of landslide with retaining wall locked segment is summarized. Experimental results reveal that as the landslide with retaining wall locked segment is at failure, the upper part of the landslide thrusts and slides and the retaining wall produces a locking effect; the middle part extrudes and uplifts, which is accompanied with shallow sliding; and compression-shear fracture of the locked segment leads to the landslide failure.

A universal elliptical disc (UED) model to represent natural rock fractures

Since natural fractures are often non-equidimensional, the circular disc model still has great limitations. By contrast, the elliptical disc model is more applicable to representing natural fractures, especially for slender ones. This paper developed a universal elliptical disc (UED) model by incorporating the center point, size, and azimuth of fractures as variables. Specifically, with respect to the azimuth of elliptical fractures in three-dimensional (3D) space, we proposed a paradigm to construct its probability density function (PDF) by coupling the orientation and rotation angle of long axis based on three coordinate transformations. To illustrate the construction process of the PDF of the fracture azimuth, we took the orientation following the Fisher distribution and the rotation angle following Von Mises distribution as an example. A rock slope is used to show the use of the developed UED model, and the 3D DFNs for the slope rock mass are generated by Monte Carlo simulation. In addition, the DFNs for the rock mass are also generated based on the existing circular disc model and non-universal elliptical disc model. The comparison results from the three models clearly illustrate the superiority of the UED model over the existing circular and non-universal elliptical disc models.

Variable Weight Matter–Element Extension Model for the Stability Classification of Slope Rock Mass

The slope stability in an open-pit mine is closely related to the production safety and economic benefit of the mine. As a result of the increase in the number and scale of mine slopes, slope instability is frequently encountered in mines. Therefore, it is of scientific and social significance to strengthen the study of the stability of the slope rock mass. To accurately classify the stability of the slope rock mass in an open-pit mine, a new stability evaluation model of the slope rock mass was established based on variable weight and matter–element extension theory. First, based on the main evaluation indexes of geology, the environment, and engineering, the stability evaluation index system of the slope rock mass was constructed using the corresponding classification criteria of the evaluation index. Second, the constant weight of the evaluation index value was calculated using extremum entropy theory, and variable weight theory was used to optimize the constant weight to obtain the variable weight of the evaluation index value. Based on matter–element extension theory, the comprehensive correlation between the upper and lower limit indexes in the classification criteria and each classification was calculated, in addition to the comprehensive correlation between the rock mass indexes and the stability grade of each slope. Finally, the grade variable method was used to calculate the grade variable interval corresponding to the classification criteria of the evaluation index and the grade variable value of each slope rock mass, so as to determine the stability grade of the slope rock. The comparison results showed that the classification results of the proposed model are in line with engineering practice, and more accurate than those of the hierarchical-extension model and the multi-level unascertained measure-set pair analysis model.

Evaluation of Slope Stability Analysis using Kinematic and Chart Method: A Case Study

Abstract The variability and unpredictability of climatic conditions are adding to the complexity in the prediction of the natural hazards. The Himalayan region is having a very complex geological and tectonic setting. Besides, climatic conditions and geological setting of the area, human encroachment is adding to the vulnerability of mountain slopes. The landslide, particularly rockfall, became a big problem for commuters and inhabitants in the hilly region. The landslides are mostly occurring either in the summer season or in the rainy season due to the percolation of water along the jointed weathered rock mass slopes. The researchers/scientists have investigated various reasons for the slope failure using conventional methods like kinematic and limit equilibrium method or using numerical methods like finite difference method (FDM), finite element method (FEM), discrete element method (DEM). The numerical methods FEM, FDM, and DEM has wide application but these are very costly and requires high end computation system. On the other hand, the conventional methods, which were used in the present study, is economical and requires geological experiences only. In the present study, slope stability analysis was performed for roadcut slopes of National Highway -109 (NH-109) from Bhowali to Almora (53 km) in the district of Nainital and Almora, Uttarakhand, India. A total of fourteen vulnerable locations were identified and their instability was evaluated. The types of failure were determined using the kinematic method, stability and classification of the slope were examined using slope mass rating (SMR). In addition, the chart method was used to calculate the factor of safety (FoS) for only wedge type of failure. A new graph has been proposed to find out vulnerability of slope considering only field-based approach.

Freeze-Thaw Effects on Stability of Open Pit Slope in High-Altitude and Cold Regions

The cycle of the freeze-thaw action must be taken into account in the stability analysis of an open pit slope in the high-altitude and cold regions, because the natural process of freeze-thaw poses a significant effect on mechanical properties of the rock mass. To achieve this purpose, a linear relationship between the geological strength index (GSI) and the Tianshan slope rock mass rating (TSMR) system is established considering the effect of the freeze-thaw action by introducing a freeze-thaw correction coefficient δ. The GSI value is modified for rock mass in high-altitude and cold regions. The improved Hoek-Brown criterion considers the influences of the freeze-thaw action and steep and gentle slopes. The research outcome is applied in the No. 4 minefield open pit coal mine in the Muli mining area. Numerical calculations are performed by inputting rock mass mechanical parameters obtained in traditional and modified criterions, to discuss the influences of the freeze-thaw action on the stabilities of both the present mining slope and the final slope at the end of the designed mining. The results show that the safety factors of the original slope are 2.33 and 1.67, respectively, while after the modification, they are 2.14 and 1.61, respectively. In terms of the No. 4 minefield open pit coal mine, the slope stability meets the design requirement, although taking the freeze-thaw cycle into account.