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Article

Investigation of the Evolution of Anisotropic Full-Field Strain Characteristics of Coal Samples Under Creep Loading Conditions

1
Shenyang Geological Survey Center, China Geological Survey, Shenyang 110034, China
2
Field Scientific Observation and Research Station for Landslide Disaster in Fushun Open Pit Mine, Ministry of Natural Resources, Fushun 113004, China
3
Department of Mechanical Science and Engineering, School of Resource & Safety Engineering, University of Science & Technology Beijing, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(15), 8355; https://doi.org/10.3390/app15158355
Submission received: 11 April 2025 / Revised: 19 July 2025 / Accepted: 25 July 2025 / Published: 27 July 2025
(This article belongs to the Topic Failure Characteristics of Deep Rocks, Volume II)

Abstract

This work aims to reveal the full-field strain evolution characteristics and failure mechanisms of anisotropic coal samples under creep loading. A series of compression tests combined with digital image correlation (DIC) monitoring were employed to characterize the strain evolution process of coal specimens with bedding angles of 0°, 30°, 60°, and 90°. Testing results show that the peak strength, peak strain, and the creep loading stage of coal are significantly influenced by the bedding angle. The peak strength initially decreases and then increases as the bedding angle increases. In addition, the creep failure of coal manifests as a process of instantaneous deformation, decelerating creep, steady-state creep, accelerating creep, and failure. Under graded creep loading conditions, coal specimens exhibit distinct creep characteristics at high stress levels. Moreover, the bedding angle significantly influences the strain field evolution of the coal samples. Finally, for coal specimens with bedding angles of 0° and 90°, the final macroscopic fracture pattern upon failure is characterized by longitudinal tensile splitting. In contrast, coal samples with bedding angles of 30° and 60° tend to exhibit failure along the bedding interfaces, forming tensile-shear fractures. The results of this study will provide theoretical guidance for the prevention, early warning, and safety management of coal mine disasters.

1. Introduction

Coal, as a naturally discontinuous and heterogeneous geological material, exhibits an inherent anisotropic bedding structure due to prolonged geological sedimentation processes. Influenced by the dip of the coal seam and the surrounding rock stress field, coal is highly susceptible to the formation of random and disordered fractures, which complicate the initiation and propagation of cracks. During the underground mining process, various protective coal pillars are often left in place. However, as mining activities redistribute the stresses around the coal pillars, these pillars are subjected to long-term static loading from the overlying strata, leading to creep instability. Therefore, investigating the anisotropic mechanical behavior of coal rock under the influence of bedding and understanding the failure mechanisms of anisotropic coal rock under creep loading is of significant importance for the prevention, early warning, and safety management of coal mine disasters, ultimately contributing to ensuring safe coal mine operations.
The influence of anisotropic bedding on the macroscopic mechanical properties of coal rock has been extensively studied in recent years. Research findings indicate that the failure characteristics of coal rock are significantly affected by both anisotropy and loading conditions. Through a series of uniaxial compression [1,2,3], triaxial compression [4,5,6,7], and dynamic impact [6,7,8,9] tests, scholars have observed that the bedding angle and peak strength characteristic curves of anisotropic coal rock typically exhibit a “U”-shaped or near “U”-shaped form. Furthermore, it has been noted that the directional distribution of the coal rock’s internal microstructure leads to systematic variations in its mechanical properties [10]. Although the static and dynamic instantaneous strength characteristics of anisotropic coal rock have been extensively validated in previous studies, as a typical soft rock, coal exhibits significant time-dependent rheological properties. Under varying stress levels, coal rock demonstrates distinct creep deformation behaviors, prompting the widespread application of multistage creep loading tests to investigate the creep deformation characteristics of coal rock. Poulsen and Adhikary [11] performed numerical studies to reveal the scale effect of coal samples, and the results indicated macro failure in compression initiated by micro tensile fractures coalescing at mid-height and resulting in a wasting observed underground in over-stressed coal pillars. Yang et al. [12] conducted experimental studies on the deformation and acoustic properties of extremely heterogeneous coal under incremental creep stress, noting that long-term coal creep results from multiple structural deformations, including particle dislocation, pore closure, matrix cracking, and clay mineral compaction. These structural changes in coal led to fluctuations in ultrasonic velocity and dynamic modulus. Zhang et al. [13] performed multistage and graded cyclic creep tests on intact coal rock, finding that the Burgers model could effectively predict the transient and secondary creep behaviors of intact coal rock. Huang et al. [14] conducted triaxial multistage creep tests on coal rock with initial damage, and the results indicated that increased initial damage significantly reduced the creep time and long-term strength of the coal samples. While significant progress has been made in studying the creep deformation characteristics of coal rock, current research primarily focuses on exploring and predicting the axial average deformation evolution process of coal samples. There is limited research on the full-field strain evolution and crack propagation characteristics of anisotropic coal rock under creep loading.
Although plenty of studies have been performed to investigate the anistropic creep behaviors of different type of rock samples [15,16,17,18], the investigations on the full-field deformation and fracture characterization of coal samples subjected to creep loading historites are not well understood. Therefore, the aim of this study is to investigate the full-field strain characteristics and the fracture evolution of anisotropic coal samples under multiple-level creep loading. Using the RFTS 1000 rock mechanics testing system, graded creep loading tests were performed on anisotropic coal rock specimens with varying bedding orientations. Combined with the DIC testing system, this study quantitatively characterizes the full-field strain evolution and crack propagation behaviors of coal rock under creep loading.

2. Sample Preparation and Experimental Methods

2.1. Principles of Digital Image Correlation (DIC) Technology

Digital image correlation (DIC) technology utilizes the black-and-white speckle pattern sprayed onto the surface of the coal sample or the natural surface texture of the specimen. Based on a grayscale recognition digital matching algorithm, it calculates the displacement vectors of corresponding pixels across sequential deformation images of the loaded sample. This enables the determination of the full-field displacement and strain information of the coal rock surface [19,20,21,22,23]. The fundamental principles of digital image correlation are illustrated in Figure 1.
Figure 1 illustrates the process of displacement of a single subset and its internal coordinate points before and after deformation. Let the center of the subset before deformation be denoted as point P, and its position after deformation shifts to point P’. For any arbitrary coordinate point Q within the subset, its position after deformation moves to point Q′. Since the deformation of the coordinate points within the subset includes translational, shear, and other deformation types, the displacement components along the x and y axes, u and v, are complex functions of x and y. From this, the following relationships can be derived:
x = x r e f c + u ( x , y ) y = y r e f c + v ( x , y )
x = x + u ( x , y ) y = y + v ( x , y )
x ~ c u r i = x + x y ~ c u r j = y + y
u ( x , y ) = u ( x , y ) x x + u ( x , y ) y y v ( x , y ) = v ( x , y ) x x + v ( x , y ) y y
By simultaneously solving Equations (1)–(4), the coordinates of any point within the subset after deformation can be determined as follows:
x ~ c u r i = x r e f c + u x , y + 1 + u x , y x x + u ( x , y ) y y y ~ c u r j = y r e f c + v x , y + v ( x , y ) x x + [ 1 + u x , y y ] y
From Equation (5), it can be seen that once the deformation information of the subset’s center point is obtained, the deformation information of any arbitrary point within the subset can be derived accordingly from the deformation of the center point.

2.2. Sample Preparation and Speckle Spraying

In order to investigate the influence of bedding angle on the anisotropic characteristics of coal samples, rectangular specimens with bedding angles of 0°, 30°, 60°, and 90° were first drilled using a core drilling machine, with the drilling angle β controlled, where β is the angle between the drilling direction and the horizontal plane, as shown in Figure 2a. Here, 0° represents horizontal bedding, and 90° represents vertical bedding. The drilled cores were then cut into rectangular samples with dimensions of 60 mm × 30 mm × 120 mm using an automatic cutting machine. Following this, the ends of the coal specimens were ground flat using a double-end grinding machine. During the grinding process, the parallelism error between the two end faces of the specimen was controlled to within 0.005 mm, the flatness error of the top and bottom faces was limited to 0.02 mm, and the diameter error of the specimen’s end faces was kept within 0.3 mm. Furthermore, the top and bottom faces were ensured to be perpendicular to the central axis of the specimen, with the maximum angular error not exceeding 0.25°. The prepared samples are shown in Figure 2b.
The spraying of the speckle pattern on the surface of the specimen is crucial for the accuracy of the DIC measurement process. Therefore, prior to the experiment, a spray nozzle was used to apply a speckle pattern to the prepared specimens. Before spraying, it is essential to ensure that the specimen surface is smooth, clean, and flat, so that the speckles can adhere firmly to the surface and the speckle images exhibit good contrast. The spraying procedure involves first applying a matte white base coat to the specimen’s surface, followed by the application of black speckle paint to create a high-contrast random pattern. Typically, each speckle should occupy 4 to 6 image pixels. The speckle pattern on the coal rock specimens is shown in Figure 3.

2.3. Experimental Equipment and Test Scheme

The coal sample creep tests were conducted using the RTFS 2000 rock mechanics testing system, as shown in Figure 4a, with loading applied, and the DIC digital image correlation testing system, shown in Figure 4b, was used to precisely measure the deformation and displacement of the speckle-marked coal rock specimens in the Figure 3. The digital image correlation system is an optical observation system for full-field, non-contact deformation measurement, primarily consisting of a camera module, LED light source, trigger acquisition unit, and numerical image processing software.
The graded creep test loading scheme is depicted in Figure 5. The load was first stabilized at 4 kN with a loading rate of 0.06 mm/min until the first creep stage was reached, followed by a creep loading phase lasting 1 h. Upon completion of the initial creep phase, the loading was continued in increments of 4 kN for each creep stage, until the specimen failed.

3. Experimental Results and Analysis

3.1. Stress and Strain Responses

Figure 6a shows the stress–strain curves of coal rock at different bedding angles. The peak strengths of coal rock with bedding angles of 0°, 30°, 60°, and 90° were 30.59 MPa, 19.61 Mpa, 11.69 Mpa, and 28.93 Mpa, respectively. The peak strength of coal rock initially decreases and then increases as the bedding angle increases, indicating that the peak strength of coal rock under creep loading is significantly influenced by the bedding angle. For coal samples with bedding angles of 0° and 90°, the peak strengths are the highest, and the strength values for these two bedding angles are nearly identical. For coal samples with a bedding angle of 30°, the peak strength is reduced by 35.9% compared to the 0° bedding angle specimens. For samples with a bedding angle of 60°, the weakening of peak strength is even more pronounced, with a 61.8% decrease compared to the 0° bedding angle samples. Therefore, in the process of strip mining in coal mines, attention should be paid to the influence of the bedding angle on the overall strength of coal pillars. It is recommended to retain coal samples with bedding angles close to 0° or 90° for use as supporting pillars.
The post-peak behavior of the stress=-strain curve of coal samples is closely related to the failure mode of the coal body. Based on the post-peak characteristics of the specimens, the post-peak stage can be divided into two types: (I) linear type and (II) buffering type. The linear type post-peak failure mode is characterized by the specimen’s stress rapidly decreasing along a straight line with a certain slope after reaching the peak stress, typically with a steep slope, as seen in coal samples with bedding angles of 0°, 30°, and 90°. This failure mode involves significant damage, with the specimen losing stability rapidly within a short period and no plastic buffering time. In field engineering, this mode is the most destructive, making it difficult to maintain the coal body after the peak stress using engineering techniques. The buffering type post-peak failure mode refers to a stress drop after the peak stress that reaches the residual strength and then maintains this load-carrying capacity for a period of time, as shown in the stress–strain curve of the coal sample with a bedding angle of 60°. In this mode, the coal body does not immediately and completely lose stability, offering the potential for reinforcement and stabilization through engineering measures in the later stages.
The time-strain curves of coal with different bedding angles, as shown in Figure 6b, clearly demonstrate that the peak strain characteristics and creep loading stages of coal rock are also controlled by the bedding angle. For coal rock with bedding angles of 0°, 30°, 60°, and 90°, the peak strains are 1.95%, 1.59%, 1.24%, and 1.79%, respectively, with 7, 5, 3, and 7 creep loading stages applied. Under the same creep stages, the coal samples are subjected to the same stress levels. Coal samples with bedding angles of 0° and 90° exhibit greater resistance to deformation, while the sample with a bedding angle of 60° demonstrates the weakest resistance to deformation, making it more prone to creep slip failure along the bedding planes.

3.2. Graded Creep Deformation Characteristics

Coal rock exhibits different creep deformation characteristics under varying stress levels. Therefore, Figure 7 presents the strain evolution patterns of coal rock at different creep stages. From the figures, it can be observed that the deformation of the coal sample is primarily concentrated during the static loading phase. During the creep stage, the deformation is relatively small and tends to stabilize. However, when the specimen reaches failure, the deformation rapidly increases, and the specimen enters the accelerated deformation phase. Different creep stages correspond to different stress levels, with higher stress levels leading to greater creep deformation. Creep deformation gradually accumulates over time. For each creep stage, the deformation process is divided into two phases: the transition from the accelerated deformation phase to the stabilized deformation phase, and, when the specimen enters the failure stage, it again undergoes accelerated deformation.

3.3. Full-Field Strain Evolution Analysis

The generation, propagation, and stress concentration of microcracks are not easily visible to the naked eye but can be captured by DIC technology. By solving the full-field displacement and strain data obtained from DIC, the Lagrangian full-field strain information, as shown in Figure 8, can be derived. This provides a clear representation of the entire process of crack initiation, propagation, and through-going failure during the creep failure process of anisotropic coal rock. The figure clearly demonstrates the influence of bedding angle on the strain field evolution of the coal samples. The regions of concentrated displacement changes are typically located at the intersections between bedding planes, where cracks generally initiate and propagate along the bedding interfaces. Throughout the compressive strain process of the coal rock, the specimen remains in a compressed and densified state for a relatively long duration in the early stages. However, in the final few seconds before failure, as the stress approaches the peak value, and the strain exhibits a sharp change, leading to the formation of a crack strain band that eventually results in overall macro-scale failure.
For the coal sample with a bedding angle of 0°, as shown in Figure 8a, it can be observed that during the loading process, the coal sample remains in a long-term compressed and densified state. Stress concentration exists at the horizontal bedding interface, but no obvious crack initiation or propagation occurs. Just before failure, cracks suddenly initiate and propagate, leading to localized spalling of the coal sample, which results in brittle failure. For the coal sample with a bedding angle of 30°, crack initiation typically concentrates at the junction points of the X-shaped shear strain damage zone. At these junctions, the stress concentration is most pronounced. After reaching the yield limit, local tensile stress is released, causing crack initiation perpendicular to the direction of maximum tensile stress. Often, after cracks initiate, spalling of the material occurs due to the reduced constraint between blocks at the edges of the coal rock sample. The energy release during crack propagation causes the blocks to “bounce” and spall off. The continued propagation of these cracks and their connection with the locally spalled regions contribute significantly to the overall macroscopic failure of the specimen. For the coal sample with a bedding angle of 60°, the strength of the specimen is the lowest, and a shear failure surface, consistent with the bedding angle of 60°, is clearly visible. This indicates that the coal sample with a 60° bedding angle fails along the structural weakness of the interface, where the coal rock is more likely to form tensile or tensile-shear type fractures at the bedding junction, eventually leading to single-shear plane failure or X-shaped conjugate shear failure. For the coal sample with a bedding angle of 90°, the final macroscopic failure mode of the coal sample is longitudinal tensile splitting failure. During loading, longitudinal tensile cracks first initiate at the edges of the specimen and extend inward. After local penetration, the sample experiences localized spalling. As the longitudinal cracks gradually develop, the coal rock sample undergoes overall failure.

3.4. Evolution Characteristics of Spatial Shifting Along Measurement Lines

In order to more clearly depict the displacement and sliding behavior of the bedding planes during the failure process and to reveal the displacement-strain evolution of anisotropic bedding during failure, characteristic monitoring lines were arranged on coal rock samples with different bedding angles, as shown in Figure 9, to record the displacement changes. The monitoring results of the characteristic displacements for coal rock samples with different bedding angles are shown in Figure 10 and Figure 11. These figures present the vertical spatial displacement along Monitoring Line 1 and the horizontal spatial displacement along Monitoring Line 2 for different bedding angles, along with the variations corresponding to different loading stages.
As shown in Figure 10 and Figure 11,the vertical and horizontal spatial displacement distances for coal samples with different bedding angles are not uniformly distributed along the monitoring lines. The vertical spatial displacement along horizontal Monitoring Line 1 is notably influenced by the bedding angle. For coal samples with bedding angles of 30° and 60°, the vertical displacement shows a characteristic shift along the bedding planes, whereas for coal samples with bedding angles of 0° and 90°, the vertical displacement is parallel to the horizontal Monitoring Line 1. However, for the coal sample with a bedding angle of 90°, significant lateral displacement during failure causes a large variation in the vertical displacement along the horizontal direction.
The distribution of the horizontal spatial displacement along Monitoring Line 2 is significantly influenced by the end effects of the sample during loading. The horizontal displacement at the bottom of the sample is larger, while the top is constrained by the platen, resulting in smaller horizontal displacement at the upper end. As the load increases, both the vertical spatial displacement at the monitoring points along Monitoring Line 1 and the horizontal spatial displacement at the points along Monitoring Line 2 gradually increase. However, for coal samples exhibiting X-shaped conjugate shear failure, there is a sharp reverse increase in the horizontal spatial displacement near failure, just moments before the sample undergoes catastrophic failure.

4. Discussions

The present study systematically investigates the anisotropic creep behavior and failure mechanisms of coal under sustained loading, employing DIC-based full-field strain monitoring. The results demonstrate that bedding orientation plays a crucial role in governing the mechanical response, creep deformation, and ultimate failure mode of coal specimens. The bedding orientation has obvious influence on the creep properties of coal. The observed non-monotonic variation in peak strength—initially decreasing and then increasing with bedding angle—aligns with previous studies on anisotropic rocks (e.g., shale and layered coal). The minimum strength at intermediate angles (30–60°) suggests that bedding planes act as weak interfaces, facilitating shear slip under load. In contrast, at 0° and 90°, the load is primarily resisted by the intact coal matrix, leading to higher strength. The creep behavior, characterized by distinct stages (instantaneous deformation, decelerating, steady-state, and accelerating creep), is consistent with classic rock creep theory. However, the pronounced creep deformation at high stress levels highlights the time-dependent weakening effect, which is critical for long-term stability assessment in coal mine roadways. The DIC analysis reveals that strain localization evolves differently depending on bedding orientation. For 0° and 90° specimens, strain concentrates along axial planes, culminating in tensile splitting fractures—a typical brittle failure mode under uniaxial compression. In contrast, 30° and 60° specimens exhibit strain accumulation along bedding planes, leading to combined tensile-shear failure. This transition from matrix-dominated to bedding-controlled failure underscores the importance of structural anisotropy in coal’s mechanical behavior. Similar observations have been reported in layered rock mechanics, but the present study provides quantitative strain-field evidence, enhancing understanding of progressive damage evolution.
The findings have direct implications for coal mine disaster prevention. The strong dependence of creep behavior on bedding angle suggests that roadway support strategies should account for local bedding orientation. For instance, in areas with intermediate bedding angles (30–60°), where shear failure dominates, enhanced reinforcement (e.g., bolting and grouting) along weak planes may be necessary. Additionally, the accelerating creep stage prior to failure could serve as a precursor for early warning systems, allowing for timely intervention. While this study provides valuable insights, certain limitations should be addressed in future research. The experiments were conducted under uniaxial conditions, whereas in situ coal is typically under triaxial stress. Future tests should incorporate confining pressure to better simulate underground conditions. A constitutive model incorporating bedding angle effects should be developed to predict coal’s time-dependent deformation under various stress paths.

5. Conclusions

This study investigates the full-field strain characteristics of anisotropic coal samples under creep loading using the DIC testing system to investigate the anisotropic deformation characteristics. The full-field strain evolution and crack propagation characteristics under creep loading were obtained, revealing the influence of anisotropic bedding angles on the strength and deformation characteristics of coal samples. The main results are summarized as follows:
(1)
The peak strength of coal under creep loading is significantly affected by the bedding angle. As the bedding angle increases, the peak strength first decreases and then increases. Under the same stress level, coal samples with bedding angles of 0° and 90° exhibit stronger resistance to deformation, while coal samples with a bedding angle of 60° show the weakest deformation resistance, making them more prone to creep sliding failure along the bedding planes.
(2)
For coal samples with different bedding orientation, creep failure is characterized by a process of instantaneous deformation, decelerating creep, steady-state creep, accelerating creep, and eventual failure. Under multi-stage loading conditions, coal samples show significant creep behavior under higher loading levels in the final stage.
(3)
The bedding angle significantly affects the strain field evolution of coal samples. Regions of concentrated displacement changes typically occur at the intersections between bedding planes, and cracks tend to initiate and propagate at bedding interfaces. During the early stages, coal samples remain in a compressed and densified state. Just before failure, within seconds of reaching the peak stress, the strain range shows dramatic changes, followed by the formation of crack bands and overall macro failure.
(4)
The post-peak stress–strain curve behavior is closely related to the failure modes of the coal structure. For coal samples with bedding angles of 0° and 90°, the final macroscopic failure mode is characterized by longitudinal tensile splitting failure; for coal samples with bedding angles of 30° and 60°, failure tends to occur along the bedding interfaces, forming tensile or tensile-shear failure, leading to single-shear plane failure or X-shaped conjugate shear failure.

Author Contributions

Experiments and writing, X.L.; funding acquisition, Y.W.; methodology, X.Y.; software, X.B. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Geological Survey Project of the China Geological Survey (DD20230437).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The basic principle of the digital image correlation method.
Figure 1. The basic principle of the digital image correlation method.
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Figure 2. Coal sample preparation of different bedding angles. (a) Core sampling of coal with different bedding angles; (be) Square coal samples with different bedding angles.
Figure 2. Coal sample preparation of different bedding angles. (a) Core sampling of coal with different bedding angles; (be) Square coal samples with different bedding angles.
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Figure 3. Speckle pattern creation on coal samples with different bedding angles.
Figure 3. Speckle pattern creation on coal samples with different bedding angles.
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Figure 4. Experimental equipment used for creep digital image correlation testing of coal samples.
Figure 4. Experimental equipment used for creep digital image correlation testing of coal samples.
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Figure 5. Graded creep loading test scheme.
Figure 5. Graded creep loading test scheme.
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Figure 6. Stress–strain response of coal specimens with different bedding angles. (a) Typical stress strain curves; (b) The strain–time curves.
Figure 6. Stress–strain response of coal specimens with different bedding angles. (a) Typical stress strain curves; (b) The strain–time curves.
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Figure 7. Strain evolution patterns of coal rock at different creep stages: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
Figure 7. Strain evolution patterns of coal rock at different creep stages: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
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Figure 8. Lagrangian strain field evolution contour maps of coal rock with different bedding angles: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
Figure 8. Lagrangian strain field evolution contour maps of coal rock with different bedding angles: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
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Figure 9. Feature line selection diagram.
Figure 9. Feature line selection diagram.
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Figure 10. Vertical spatial migration evolution characteristics of Monitoring Line 1: (ad) The bedding angles are 0°, 30°, 60° and 90°, respectively.
Figure 10. Vertical spatial migration evolution characteristics of Monitoring Line 1: (ad) The bedding angles are 0°, 30°, 60° and 90°, respectively.
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Figure 11. Evolution characteristics of horizontal spatial displacement along characteristic Measurement Line 2: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
Figure 11. Evolution characteristics of horizontal spatial displacement along characteristic Measurement Line 2: (ad) Bedding angles of 0°, 30°, 60°, and 90°, respectively.
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Li, X.; Wang, Y.; Yi, X.; Bai, X. Investigation of the Evolution of Anisotropic Full-Field Strain Characteristics of Coal Samples Under Creep Loading Conditions. Appl. Sci. 2025, 15, 8355. https://doi.org/10.3390/app15158355

AMA Style

Li X, Wang Y, Yi X, Bai X. Investigation of the Evolution of Anisotropic Full-Field Strain Characteristics of Coal Samples Under Creep Loading Conditions. Applied Sciences. 2025; 15(15):8355. https://doi.org/10.3390/app15158355

Chicago/Turabian Style

Li, Xuguang, Yu Wang, Xuefeng Yi, and Xinyu Bai. 2025. "Investigation of the Evolution of Anisotropic Full-Field Strain Characteristics of Coal Samples Under Creep Loading Conditions" Applied Sciences 15, no. 15: 8355. https://doi.org/10.3390/app15158355

APA Style

Li, X., Wang, Y., Yi, X., & Bai, X. (2025). Investigation of the Evolution of Anisotropic Full-Field Strain Characteristics of Coal Samples Under Creep Loading Conditions. Applied Sciences, 15(15), 8355. https://doi.org/10.3390/app15158355

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