Bedding Dip Angle Research Articles

Experimental study on the shear failure of layered rock bridges

The structural face of rock plays a decisive role in the stability of geotechnical engineering, and the mechanism of failure destabilization of layered rock masses is still unclear. By preparing rock-like materials, shear failure tests on layered rock masses were carried out under different bedding dip angles, different rock bridge width, different normal forces, and forward and reverse shear effects. With the increase in the rock bridge width, the influence of the joint inclination angle on the shear failure process of the rock sample decreases; the peak shear strength of the specimen is the largest when the joint inclination angle is 60°, followed by 90°, 30° and 0° from large to small; the failure mode in forward shear is mainly tensile failure, and the failure mode in reversed shear is mainly shear failure; the peak number of acoustic emission events is proportional to the joint inclination angle and the rock bridge width of the specimen, and the number of acoustic emission events is proportional to the joint inclination angle and the rock bridge width of the specimen. The number of acoustic emission peak events is proportional to the bedding angle of the sample and the width of the rock bridge. The peak number of acoustic emission events in the reverse shear of the layered rock mass is greater than that in the forward shear. The angle of the lamina and the width of the rock bridge are both important factors affecting the strength of the rock. The results of this study provide a basis for identifying the shear failure mechanism of rock bridge in layered rock masses.

Effects of coal bedding dip angle on hydraulic fracturing crack propagation

As a commonly used and effective technology for increasing the permeability of coal–rock reservoirs, hydraulic fracturing has been widely used in engineering sites to realize the efficient exploitation and utilization of gas resources in coal–rock reservoirs. The core of hydraulic fracturing is the initiation, propagation, and path of hydraulic cracks. In this paper, the combination of true triaxial physical test and numerical simulation is used to study the influence of coal bedding characteristics on the crack propagation of hydraulic fracturing and to discuss the important role of bedding in hydraulic crack formation. Results show that the control effect of the coal bedding dip angle on the hydraulic crack propagation under the same stress conditions is stronger than that of the maximum principal stress, and the control effect of the bedding on the crack propagation is weaker under the bedding dip angles of 0° and 90°. Reasonable fracturing fluid displacement setting is conducive to the formation of complex hydraulic fracture network structure, small displacement is conducive to the opening of primary natural fractures, and large displacement is conducive to hydraulic cracks that pass through the structural surface and the coal–rock interface. Global and local methods of finite element mesh embedding zero-thickness cohesion element and a pore-pressure node merging method to simulate fracturing are established using Python language and ABAQUS numerical analysis platform, respectively. The numerical simulation results suggest that the main fractures are formed along the principal stress direction, and the secondary branch fractures are formed along the bedding direction under the condition wherein the coal bedding dip angle is 30°. Under the conditions of different stress fields and fracturing fluid discharges, the controlling effect of bedding on hydraulic fracture is closely related to the fracturing parameters.

Effect of bedding dip angle and dynamic load on spatial variation of microscopic failure stress of shale

Physico-mechanical properties of shale are important parameters in evaluating the stability of potential wellbore and the design of hydraulic fracturing, which are primarily affected by their non-uniform spatial distribution of the microscopic physical–mechanical properties at particle scale. A series of constant strain rate experiments and stress-cycling experiments on shale specimens with different bedding dip angles were conducted to have a comprehensive understanding of the effect of the non-uniform distribution of microscopic failure stress on macroscopic physico-mechanical properties. According to the experimental results and Weibull distribution, we find that bedding dip angle and the dynamic load applying type affect the spatial distributions of microscopic failure stress. The values of crack damage stress (σcd), σcd/σucs (peak stress), εcd (strain at crack damage stress), Poissons' ratio (ν), elastic strain energy (Ue) and dissipated energy (Uirr) of the specimens with more uniform distribution of microscopic failure stress are overall higher, while εucs (peak strain)/εcd and elastic modulus (E) are lower. The dynamic load enables the spatial distributions of microscopic failure stress trend to be more homogeneous prior to the final failure with the increment of σcd/σucs, ν, Ue and Uirr and the decrement of E.

Experimental investigation on the infrared precursors of rockburst in sandstone with different bedding dip angles

Experimental investigation on the infrared precursors of rockburst in sandstone with different bedding dip angles

Anisotropy and microcrack-induced failure precursor of shales under dynamic splitting

The dynamic anisotropy and failure mechanism of shales are greatly affected by bedding surfaces. To reveal the influence of beddings on anisotropic characteristics of shales under dynamic impact, the Brazilian splitting tests were conducted by the split Hopkinson pressure bar system. The fracturing process were monitored by the high-speed camera. Meanwhile, to understand crack initiation and propagation mechanism, the stress buildup, stress shadow and stress transfer were modelled based on the digital image processing and the rock failure process analysis method. The effect of dip angle and bedding spacing on crack initiation, propagation and coalescence was analyzed. Simultaneously, the spatial distribution and energy magnitude of crack-induced acoustic emissions were captured numerically. The results show that the shale discs continue to produce parallel cracks and cambered cracks induced by the high stresses at the tips of initial cracks; the tensile strength under dynamic splitting changes in the U-shaped trend with the bedding dip angle increasing; the cracking percentage of bedding surfaces decreases, and the cracking percentage of rock matrix increases with the bedding dip angle increasing. In addition, the acceleration of crack growth and the rapid growth of AE energy can be regarded as the effective precursors of shale failure.

Numerical studies on micro-cracking behavior of transversely isotropic argillaceous siltstone in Longyou Grottoes under three-point bending

Longyou Grottoes, the underground projects with a rich history of thousands of years, are one of the key cultural relics to be protected in China and are actively preparing to apply for a world cultural heritage site. However, due to the shallow buried argillaceous siltstone with low-strength bedding planes, some cavern roofs experienced apparent breakages or large-scale collapses. Clarifying the roof deformation and failure mechanism is essential for the long-term protection of the historical relic and sustainable development of tourism. Productive previous work proved that three-point bending tests of rock samples could reproduce stress states of cavern roofs. Therefore, three-point bending numerical models with various bedding plane structures for Longyou argillaceous siltstone are created in this study to investigate the rock mechanical behaviors. The simulation results show that as bedding mechanical properties decrease, the bending strength (BS) has a slow to fast decrease, indicating that timely protection in Longyou Grottoes before the BS drops sharply is conducive to preventing roof failures. This declining trend is further accelerated when the bedding dip angle changes from horizontal to vertical. Dip angles, mechanical properties, and spacings of bedding planes control fracture modes of models. Moreover, the fitted Gutenberg–Richter-type relationships between acoustic emission (AE) moment magnitudes and logarithmic AE events present high average activity levels and high proportions of large AE events in both bedding planes and rock matrix for models with strong, dispersedly distributed, and near-horizontal bedding planes. In summary, the simulation results reveal the impacts of transverse isotropy in surrounding rocks on roof bending failures, which may provide a valuable reference for the reinforcement and protection of Longyou Grottoes.

Study on Creep Characteristics of Water Saturated Phyllite

Phyllite is affected by its own bedding, stress environment and water-saturated conditions. There are great differences in its deformation and failure in engineering, and its creep characteristics are an important basis for evaluating the long-term stability of phyllite engineering. Therefore, this study carried out creep tests of water-saturated phyllite under different bedding angles and confining pressures, studied the coupling effect of factors that affect the creep characteristics of phyllite, and investigated and analyzed the deformation characteristics of a phyllite roadway support on site to provide basic support for phyllite roadway mine disaster control and collaborative mining research. The results showed the following: (1) When the bedding dip angle was 30~60°, under the control of the bedding, the sliding deformation along the bedding suddenly increased under the low-stress condition and the specimen did not undergo structural damage. It could continuously bear multi-level stress and generated creep deformation. In this case, a phyllite roadway should adopt the support method of combining flexibility and rigidity. (2) In the process of multi-stage stress loading, the creep instantaneous stress was directly proportional to the initial stress. When the stress was loaded to 50% of the failure strength, the instantaneous stress tended to be stable and maintained a linear, slightly increasing relationship with the stress. When the bedding angle was 30~60°, the creep deformation accounted for more than 50% of the total deformation. The bedding angles of 0° and 90° were dominated by the instantaneous strain during the stress loading process. For the flexible support of the roadway, the deformation caused by disturbance stress should be fully considered. (3) The uniaxial creep specimen mainly displayed compression shear tensile failure, with a small number of parallel cracks along the main fracture surface. The triaxial creep fracture mode changed to single shear failure. The confining pressure showed greater inhibition of the creep of the specimen with a bedding inclination of 0° and 90°. The strength design of the rigid support should refer to the original rock stress value of the roadway. The creep deformation and failure of the specimen with a bedding inclination of 30~60° were mainly controlled by the bedding. The included angle between the bedding dip angle and the maximum principal stress should be kept within 30~60° as far as possible in the roadway layout.

Study on Mechanical Properties and Crack Propagation of Raw Coal with Different Bedding Angles based on CT Scanning.

The deformation and damage characteristics of coal are the important foundation that affects the fracturing potential of coal reservoirs and the development plan of coalbed methane (CBM). To reveal the influence regulation of primary fractures and the bedding angle of coal on its failure and provide theoretical basis for CBM development, raw coal samples of no 16 coal seam in Wenjiaba Coal Mine, Zhijin County, Bijie City with different bedding angles were selected as the research object, and uniaxial compression tests were carried out on them, and CT scanning and crack reconstruction before and after sample failure were carried out. The results show that (1) the compressive strength, elastic modulus, and Poisson’s ratio of coal show a strong bedding angle effect, and the changing trend of each index is basically the same. The coal samples with bedding angles of 0 and 90° are the highest, while the coal samples with bedding angles of 30° are the lowest, and the overall distribution is an approximate “U” with the increase in bedding angle. With the increase in bedding angle of 0–90°, the failure modes of coal samples are tension-shear combined failure, shear-slip failure, and splitting tension failure in turn. (2) The observation of raw coal and CT scanning show that the primary cracks in coal samples are well developed, especially in the lower part of 0° samples, the cracks in 30° samples, 60° samples, and 90° samples are evenly distributed and develop at a certain angle with the weak bedding surface, and microcracks parallel to and nearly perpendicular to the weak bedding surface are developed in 45° samples. At the same time, banded minerals in coal and rock samples are also well developed. (3) The characteristics of crack propagation and evolution in coal samples with different bedding dip angles are significantly different. The bedding dip angles and primary cracks of coal seam have a great influence on crack propagation. With different bedding angles, the propagation modes are different. The crack propagation mainly includes two ways: forming a certain angle with bedding and extending along the bedding plane. (4) The fracture characteristic parameters of coal in the primary state and after failure have the same law with the bedding dip angle, showing a trend of high at both ends and low in the middle, which is an irregular “U”-shaped distribution and has a similar law with mechanical characteristic parameters.

Dynamic mechanical properties and constitutive model of shale with different bedding under triaxial impact test

With the gradual depletion of traditional energy sources such as oil and natural gas. As an unconventional energy that can replace traditional resources, shale gas has attracted the attention of the world energy department. The storage environment of shale gas (oil) is usually accompanied by in-situ stress, and the exploitation of shale gas is actually a dynamic process. Therefore, it is of great significance to study the dynamic mechanical characteristics of shale under in-situ stress. In this paper, the dynamic mechanical parameter and constitutive relationship of shales with different bedding (0°, 30°, 45°, 60°, 90°) was studied by the triaxial SHPB tests with the confining pressure from 0 to 15 MPa. The effects of confining pressure on the mechanical properties of shale with different bedding were discussed from the aspects of the dynamic compressive strength, elastic modulus, failure strain, energy characteristics as well as the dynamic failure mode. The experimental results showed that, the dynamic mechanical properties of shale mainly depended on the interaction of the bedding dip angle and various confining pressures. The failure modes of shale under confining pressure mainly present compression shear failure or only damage crack. In additional, a modified dynamic constitutive model of shales was based on the ZWT viscoelastic constitutive relationship, which simplified the low frequency term and took into account shale material damage characteristics. The modified constitutive model is simple in structure and can predict the strength characteristics of shale under confining pressure in a certain range when the basic mechanical parameters and empirical parameters are known.

Influence of microwave irradiation on the permeability of coal with different bedding dip angles

Microwave irradiation (MI) is a prospective method for increasing CBM production. Due to the permeability anisotropy caused by bedding structural plane, the spatial relationship between underground microwave irradiation drillings (MID) and the coal bedding plane has become an important factor affecting the effect of MI on enhancing production. The self-developed MI device numberer WY3S02 was used to carry out the MI experiment on samples with different bedding angles (BDA). The permeability of coal before and after MI was tested by the steady-state seepage method. The surface temperature and ultrasonic data of samples during the test were collected, and the influence of MI on the permeability of coal with different BDA was studied. The experiments indicate that the permeability of samples with different BDA increases by 30.2–100.1 times after MI under external axial load, and the increase of permeability is positively correlated with the BDA. The permeability after MI shows the variation law of K (90°) > K (60°) ≥ K (45°) > K (30°) > K (0°), showing an obvious bedding effect. The standard deviation of the lateral surface temperature of the specimen increases with the increase of the BDA, which makes the thermal fracture degree of the sample with large BDA higher, resulting in more dominant seepage channels, which is manifested as greater permeability growth. These results provide a scientific basis for the design of MID in the method of enhanced coalbed methane by microwave irradiation (MI-ECBM).

Fracture Characteristics and Anisotropic Strength Criterion of Bedded Sandstone

Bedded sandstone is classified as sedimentary rock, which is a typical bedded rock with obvious layered structure characteristics. Bedded rocks formed different bedding orientations in the long and complicated geological tectonic evolution and thus have anisotropic mechanical characteristics. Therefore, the strength anisotropy of bedded sandstone depends on the bedding dip angles. In this study, the fracture characteristics and strength criterion of bedded sandstone were studied by triaxial compression tests on rock specimens with different bedding dip angles under different confining pressure. The test results show that the failure mode and strength of the bedded sandstone are related to the bedding dip angles, showing obvious anisotropy. The experimental data are broadly in line with the Jaeger’s surface of weakness (JPW) model. However, considering the difference in the strength of sandstone specimens with horizontal bedding dip (β = 0°) and vertical bedding dip (β = 90°), an improved JPW model is proposed to distinguish the strength criteria for the aforementioned differences. On the basis of considering the nonlinear relationship between confining pressure and rock strength, the JPW model is improved accordingly to make it suitable for predicting the strength behavior of bedded rocks.

Investigation on the Deformation and Failure Characteristics of Shale Samples Containing Circular Hole considering the Bedding Angle Effect under Uniaxial Compression

The drilling and blasting method (DBM) is widely used in the excavation of tunnel engineering, and it is essential to first drill circular holes. This paper experimentally explored the influence of bedding angles on crack propagation of shale containing a circular hole. Specifically, the uniaxial compression tests were carried out on shale samples with a single prefabricated hole combined with digital image correlation technology (DIC) to obtain the real-time deformation process near the macro damage. The results show that the peak strength, global shear strain field, failure mode around the circular hole and macro crack failure mode of shale with prefabricated circular hole are closely related to the bedding dip angle. The strength generally increases with the decrease of the bedding angle. Two transitions of failure mode were observed at the point of 45° and 75°: tensile shear mixed failure around the circular hole (less than 45°) first transits into no damage around the circular hole (60° and 70°), and then, tensile failure occurs around the circular hole (90°). In addition, for the cases of 60° and 75°, tensile failure away from the circular hole occurs along the weak surface of bedding, while for the other cases, the tensile failure through the circular hole mainly occurs. These findings have implied that the bedding angle is one essential parameter that needs to be considered for the stability of tunnel surrounding rock.

Tectonostratigraphy and major structures of the Georgian Greater Caucasus: Implications for structural architecture, along-strike continuity, and orogen evolution

AbstractAlthough the Greater Caucasus Mountains have played a central role in absorbing late Cenozoic convergence between the Arabian and Eurasian plates, the orogenic architecture and the ways in which it accommodates modern shortening remain debated. Here, we addressed this problem using geologic mapping along two transects across the southern half of the western Greater Caucasus to reveal a suite of regionally coherent stratigraphic packages that are juxtaposed across a series of thrust faults, which we call the North Georgia fault system. From south to north within this system, stratigraphically repeated ~5–10-km-thick thrust sheets show systematically increasing bedding dip angles (<30° in the south to subvertical in the core of the range). Likewise, exhumation depth increases toward the core of the range, based on low-temperature thermochronologic data and metamorphic grade of exposed rocks. In contrast, active shortening in the modern system is accommodated, at least in part, by thrust faults along the southern margin of the orogen. Facilitated by the North Georgia fault system, the western Greater Caucasus Mountains broadly behave as an in-sequence, southward-propagating imbricate thrust fan, with older faults within the range progressively abandoned and new structures forming to accommodate shortening as the thrust propagates southward. We suggest that the single-fault-centric “Main Caucasus thrust” paradigm is no longer appropriate, as it is a system of faults, the North Georgia fault system, that dominates the architecture of the western Greater Caucasus Mountains.

Experimental Study on the Anisotropy of Layered Rock Mass under Triaxial Conditions

Weak and hard inhomogeneous rock formations are typically encountered during tunnel excavations. The physical and mechanical properties and geological conditions of these rock formations vary significantly; thus, it is crucial to investigate the mechanical characteristics of deep bedded composite rock formations. Three-dimensional (3D) scanning and 3D printing were used to prepare composite rock specimens to simulate natural rock laminae. Triaxial compression tests were conducted to determine the influence of the bedding angle, rock composition, and confining pressure on the mechanical properties of the composite rock specimens. The anisotropic strength characteristics and the damage patterns of the composite rock specimens were analyzed under different confining pressures, and the failure mechanism during triaxial loading was revealed. The results show that the damage of the composite rock specimens with a bedding structure depends on the bedding dip angle and the rock formation. The stress-strain curves and peak strengths of the composite rock specimens have anisotropic characteristics corresponding to their failure modes. As the bedding dip angle increases, the peak strength of the three groups of specimens first decreases and then increases under different confining pressure levels. The compressive strength has a nonlinear relationship with the confining pressure, and the difference between the compressive strengths of specimens with different inclination angles decreases as the confining pressure increases. The Hoek–Brown strength criterion is a good predictor of the nonlinear increase in peak strength of the composite rock specimens under different confining pressures. The specimen with a β = 60°dip angle shows the most significant increase in the strength difference with increasing confining pressure. The results can be used as a reference for testing and analyzing the anisotropic mechanical properties of bedded rock masses.

Analysis of the effect of bedding attitude on relaxation deformation characteristics of the surrounding rock of an underground powerhouse in a layered rock mass

To study the stability of an underground powerhouse in layered rock mass, a series of numerical simulations was conducted using three-dimensional distinct element code to investigate the effect of bedding attitude on the relaxation deformation characteristics of the surrounding rock of an underground powerhouse. The results showed that when the bedding dip angle was less than 30°, the maximum deformation of the surrounding rock occurred at the arch crown and bottom plate. However, when the dip angle was greater than 60°, the maximum deformation occurred at the side wall. Under the same conditions, with the increase in dip angle, the maximum deformation of the surrounding rock and the depth of the relaxation deformation zone (RDZ) increased first and then decreased, and their peak values were observed when the dip angle reached 60°–70°. With the increase in the angle between the bedding strike and longitudinal axis of the cavern, the maximum deformation and depth of the RDZ decreased gradually and stabilized when the angle was greater than the threshold. For the steeply inclined layered rock mass, when designing the underground powerhouse, the angle between the bedding strike and longitudinal axis of the cavern should not be less than 60°.

Study on Anisotropic Mechanical Properties and Failure Modes of Layered Rock Using Uniaxial Compression Test

Abstract To reveal the failure mechanisms and strength anisotropy of layered rock, uniaxial compression tests were conducted on dolomite samples with seven different bedding dip angles, and the compressive strength and the Young’s modulus with dip angle β were analyzed. Meanwhile, five failure modes (rock tensile cracking, rock shearing failure, bedding cracking, bedding sliding failure, and rock bending) were observed from laboratory phenomena, and the corresponding anisotropy constitutive model was further developed based on the transversely isotropic model and the plastic mechanics flow rules. Finally, the self-defined anisotropic constitutive model was coded in FLAC3D to carry out a numerical simulation of uniaxial compression. Results showed that the numerical simulation agreed well with experimental tests results, which proved that the assumption of a transversely isotropic model was reasonable. Furthermore, the proposed model could be applied to evaluate the stability of rock slopes with different bedding dip angles, and the bedding dip angle played an important role on failure modes and the stability of slope.

Research on the anisotropic fracture behavior and the corresponding fracture surface roughness of shale

Understanding the anisotropic fracture mechanism of shale is of significance to assess the development of a stimulated reservoir volume. In this study, three-point bending tests were carried out using notched deep beam specimens of shale with 7 different bedding dip angles to investigate the anisotropic fracture behavior. The anisotropic characteristics of the fracture toughness, energy release rate, inelastic zone and crack propagation path were comprehensively analyzed and highlighted. The results showed that the fracture toughness decreases with increasing bedding dip angle. When the bedding dip angle is 0° and 90°, the fracture toughness reaches the maximum and minimum values, respectively, with a ratio of 1.60. The variation tendency of the energy release rate with the bedding inclination angle is consistent with that of the fracture toughness, but the ratio of the maximum value to the minimum value of the energy release rate is about 3.24. The size of the inelastic zone first decreases and then increases at different bedding inclination angles from 0° to 90° and reaches the maximum size of 1.51 mm when the bedding plane inclination angle is 45°. The crack propagates along the bedding plane rather than straight along the initial crack direction when the bedding dip angle is higher than 45°. As the bedding plane dip angle increases from 0° to 45°, the crack surface roughness of the tested shale first increases, then decreases and finally reaches the maximum. The discussion indicated that the presence of the Mode II fracture has a considerable influence on the crack surface roughness and crack propagation path, although it has little effect on the failure load. Compared with the maximum energy release rate (MERR) criterion, the maximum tangential stress (MTS) criterion seems more accurate in predicting the anisotropic Mode I fracture toughness. The applicability of these two classical crack initiation criteria of fracture mechanics has been analyzed based on our experimental results, which demonstrates the validity of the MTS criterion to assess the anisotropic fracture toughness of shales.

Mechanism of anisotropic characteristics of layered limestone and a constitutive model for different bedding angles based on a Brazilian tensile test

Layered limestone contains a large number of bedding planes, which leads to the anisotropy of mechanical properties. In this research, a Brazilian tensile test was conducted on limestone samples with seven different bedding dip angles to study the effect of different bedding angles on the tensile mechanical properties. The relationship curves for the horizontal tensile stress and strain were plotted. These curves underwent three stages of compaction, elasticity, and destruction. Furthermore, the variation law of the tensile strength and the tensile modulus with the bedding dip angles were studied, and a directivity index was proposed to quantitatively evaluate both the spatial directionality and the magnitude variability of the tensile strength of laminated rock samples. Additionally, the fracture patterns could be divided into three types, including “perpendicular splitting” in a roughly straight shape (the bedding angle ranged from 0 to 30°), “shearing and splitting” in an arc shape (30 to 75°), and “parallel splitting” in a smoothly straight shape (75 to 90°). The curves of the acoustic emission (AE) ringing counts with the bedding angles of the rock samples exhibited obvious three-stage patterns, and the rock samples had a large variation in the cumulative amplitude of the AE ringing counts because of the anisotropic characteristics. Based on the elastic theory, the anisotropic constitutive model was established to calculate the expression for the axial stress and strain during the test. The theoretically calculated curves could be well matched with the test values. These research results indicated that the tensile strengths, tensile moduli, and fracture patterns of the laminated limestone samples all displayed distinct anisotropy and directionality, which implied the necessity of considering anisotropy in the study of failure mechanisms, the theoretical calculation, and the engineering application of laminated limestone rocks.

A complex slide-buckling-toppling failure of under-dip soft rock slopes

This study investigates a complex slope failure that occurred in Chongqing Xi railway station. The studied slope belongs to a under-dip shale slope. Onsite surveys and UDEC numerical modelling were conducted to describe the deformation characteristics and potential failure mechanism of this slope. The simulated results suggest that sliding, buckling and toppling can occur in the deformation process, which is verified by the actual deformation characteristic of the slope and monitoring results. Moreover, the effects of bedding dip angle, slope angle, bed thickness on the deformation characteristics of the slope were also investigated with UDEC models. Finally, the possible slope structure for occurrence of slide-buckling-toppling failure and several numerically validated remedial measures were proposed.

Experimental investigation of anisotropic fatigue characteristics of shale under uniaxial cyclic loading

The influence of combining the inherent anisotropy and fatigue loading on shale’s mechanical behaviors is rarely investigated. To study the anisotropic fatigue behaviors of shale, uniaxial fatigue tests under different cyclic stress limits and loading frequencies are conducted using shale specimens with 7 different bedding orientations. The anisotropic characteristics of the fatigue failure mechanism, stress-strain behavior, cycle numbers, irreversible strain and energy evolution of each hysteresis loop are analyzed. The combined effects of bedding and fatigue loading can cause crack branching and coalescence, which generates a crack network. Maximum and minimum fatigue cycle numbers are obtained when the bedding orientations are 90° and 75°, respectively; correspondingly, the maximum and minimum energies of each hysteresis loop are obtained. The irreversible strain and energy of each hysteresis loop decrease, become approximately constant and then increase before failure when the bedding orientations are 0°, 15°, 30°, 45° and 90°; this rate is approximately constant for the bedding dip angles of 60° and 75°. Increasing either the loading frequency or cyclic stress limit increases the energy and irreversible strain of each hysteresis loop as well as decreases the cycle number. Fatigue damage indicators defined by the secant modulus, irreversible strain, dissipated energy and accumulated hysteresis loop area cannot reflect the effects of shale’s inherent anisotropy. Multiscalar or tensorial damage factors, which can describe the anisotropic fatigue damage features of shale, need be further studied.