Confining Pressure Unloading Research Articles

Mechanical behaviour and macro-micro failure mechanisms of frozen weakly cemented sandstone under different stress paths

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure.

Effect of stress unloading rate on fine-scale deformation mechanism of rock under high osmotic pressure

To explore the influence of the working face excavation rate on the rock deformation mechanism and seepage characteristics, deformation and seepage tests of sandstone under different loading and unloading stress paths, such as constant axial pressure unloading confining pressure and loading axial pressure unloading confining pressure, were carried out. Particle Flow Code in 3 Dimensions (PFC3D) and Python were used to realize fluid-solid coupling, and numerical simulation calculations were performed along the test path to analyze the influence of the unloading rate on the fine-scale deformation mechanism and permeability characteristics of sandstone, and the relationship between crack type and permeability was obtained. A sandstone fracture mechanics model is established to analyze the stress concentration degree at the end of the branch crack of the test path. The results show that the rate of confining pressure unloading is inversely proportional to the strain. Additionally, permeability correlates with the principal stress difference in an exponential manner. Interestingly, the sensitivity of permeability to stress shows an inverse trend with the unloading rate of confining pressure. Furthermore, there exists a linear relationship between permeability and the number of cracks. During the unloading process, tensile cracks predominate, and the propagation of shear cracks lags behind that of tensile cracks. The proportion of tensile cracks decreases with the increase of the unloading rate when the axial pressure is unchanged but increases when axial pressure is added, resulting in axial compression deformation and expansion deformation along the unloading direction. These research outcomes offer theoretical insights for the prudent selection of mining rates, and they hold significant implications for mitigating water inrush disasters in deep mining operations.

3D DEM investigation on macro-meso mechanical responses of gas hydrate-bearing sediments in process of unloading confining pressure

Well drilling, gas production, and reservoir stimulation can disrupt stress states of gas hydrate-bearing sediments (GHBSs) surrounding wellbores, potentially inducing wellbore instability due to confining pressure unloading. Therefore, it is very important to know about the macro-meso mechanical responses of GHBSs under an unloading confining pressure path (UCPP). Herein, a discrete element method (DEM) was used to perform triaxial tests on three-dimensional numerical GHBSs under the UCPP and a conventional drained path (CDP) to bridge the knowledge gap. Results show that GHBSs under the UCPP are more prone to failure and dilatation than under the CDP, due to the reduced bearing capacity of contact force chains, relatively unstable particle assembly, and rapid cementation breakage development. Additionally, the stress path has little effect on the cohesion and friction angle of GHBSs. Furthermore, under the UCPP, the failure and dilatation risk of GHBSs are positively correlated with unloading confining pressure rate, inversely related to hydrate saturation and initial effective confining pressure. The grey relational analysis illustrates that compared to hydrate saturation and initial effective confining pressure, the unloading confining pressure rate minimally affects the unloading confining pressure effect. These findings can serve for experimental studies and field applications (e.g., optimizing drilling mud density, sand production rate, and fracturing fluid flowback rate) concerning the unloading confining pressure responses of GHBSs.

Study on the energy and damage characteristics of gas-containing coal under confining pressure unloading process

Research on energy and damage evolution patterns of gas-containing coal under constricting pressure unloading conditions is urgently needed in the process of deep underground mining and is crucial for understanding the mechanisms underlying coal and gas composite rockburst occurrences. Prior reaching peak stress, cyclic loading and unloading experiments were carried out on gas-containing coal specimens under varied confining pressures and unloading circumstances. According to the experimental findings, gas pressure significantly degrades the mechanical characteristics of coal specimens, with a higher gas pressure causing worsening of the mechanical properties. The degree of mechanical property deterioration in coal specimens caused by gas pressure steadily reduces as confining pressure rises, indicating that confining pressure has an inhibitory influence on the deterioration of mechanical characteristics brought on by gas. Additionally, the degradation of coal mechanical characteristics is a result of the unloading of confining pressures. The peak stress and elastic modulus of coal decrease as confining pressure unloading increases in magnitude. Prior to the peak stress, the capacity of coal to convert external work into elastic energy is mostly indicated by the compression storage energy coefficient, whereas the peak elastic energy predominantly denotes the upper bound of compressed storage elastic energy for coal. Based on the Weibull statistical damage theory and employing elastic energy as the distribution variable, a statistical damage model is proposed. Comparisons of coal damage evolution curves indicate that both the confining pressures unloading process and gas pressure exert a promoting effect on the damage evolution of coal.

Effect of Confining Pressure Unloading Rate on Mechanical and Energy Characteristics of Coal-Rock Combinations

Effect of Confining Pressure Unloading Rate on Mechanical and Energy Characteristics of Coal-Rock Combinations

A novel relationship between elastic modulus and void ratio associated with principal stress for coral calcareous sand

Elastic moduli, e.g. shear modulus G and bulk modulus K, are important parameters of geotechnical materials, which are not only the indices for the evaluation of the deformation ability of soils but also the important basic parameters for the development of the constitutive models of geotechnical materials. In this study, a series of triaxial loading-unloading-reloading shear tests and isotropic loading-unloading-reloading tests are conducted to study several typical mechanical properties of coral calcareous sand (CCS), and the void ratio evolution during loading, unloading and reloading. The test results show that the stress-strain curves during multiple unloading processes are almost parallel, and their slopes are much greater than the deformation modulus at the initial stage of loading. The relationship between the confining pressure and the volumetric strain can be defined approximately by a hyperbolic equation under the condition of monotonic loading of confining pressure. Under the condition of confining pressure unloading, the evolution of void ratio is linear in the e-lnp′ plane, and these lines are a series of almost parallel lines if there are multiple processes of unloading. Based on the experimental results, it is found that the modified Hardin formulae for the elastic modulus estimation have a significant deviation from the tested values for CCS. Based on the experimental results, it is proposed that the elastic modulus of soils should be determined by the intersection line of two spatial surfaces in the G/K-e-p'/pa space (pa: atmosphere pressure). “Ye formulation” is further proposed for the estimation of the elastic modulus of CCS. This new estimation formulation for soil elastic modulus would provide a new method to accurately describe the mechanical behavior of granular soils.

Experimental and DEM Simulation Study on the Mechanical Characteristic and Strain Energy Evolution of Longmaxi Shale under a Confining Pressure Unloading Path

Drilling vertical and horizontal wellbores in the shale reservoir may trigger the in-situ stress release around the wellbore walls and change the original stress equilibrium state, leading the wellbores to instability. This stress change in the wellbore corresponds to the stress paths of confining pressure unloading and axial stress loading under laboratory conditions. In this paper, according to the conventional triaxial compression test results, laboratory experiments and DEM simulations by PFC2D were conducted to deeply study the strength, failure, strain energy evolution, and micro-crack damage mechanism of shale specimens under confining pressure unloading conditions. The shale specimens at different bedding inclinations were tested under different initial axial stress levels and confining pressure unloading rates, with fixed initial unloading confining pressure. This research revealed that confining pressure unloading induces greater plastic deformation, more micro-crack damage and strain energy dissipation, and a more complex failure pattern. The strain energy dissipation and dilatation under confining pressure unloading conditions are mainly induced by the generation and accumulation of tensile cracks. Moreover, the unloading rate has a significant effect on the mechanical properties, and the high unloading rate enhances the failure strength and induces more strain energy dissipation and micro tensile cracks. For the wellbore drilling in shale formations, when the buried depth and vertical stress are fixed, the lower the lateral stress is, the easier it is to form tensile failure around the wellbore wall in the drilling process, and the more induced fractures will be generated in the formation around the wellbore.

Experimental study on seepage evolution and microscopic characteristics of initially damaged concrete under variable confining pressure

This study aims to examine the impact of service loading and dry-wet-freeze–thaw environments on the initial damage caused to concrete, and conducts initial damage concrete permeability testing and microscopic characterization under varying confining pressure. The evolution pattern and mechanism of specimen permeability are analyzed using the confining pressure sensitivity coefficient, permeability recovery rate, and causeless radial strain. The results indicate that permeability exhibits nonlinear characteristics during the process of confining pressure loading and unloading. The initial permeability increases with increasing load level and the number of dry-wet-freeze–thaw cycles. The loading process can be divided into a sensitive area, a transition area, an insensitive area, and a steady area, according to the confining pressure sensitivity coefficient. The permeability in the sensitive area decreases the most with the increase of confining pressure, while the permeability in the steady area hardly changes. A smaller permeability recovery rate after confining pressure unloading leads to a larger dimensionless radial strain and lower permeability value. Utilizing nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), it was observed that the initial damage caused the expansion of microcracks and micropores in the specimen, leading to a subsequent amplification of the seepage channels, ultimately resulting in a substantial increase in the specimen's permeability. When confining pressure is loaded, the internal pore structure of the specimen undergoes elastic–plastic deformation. Upon confining pressure unloading, the proportion of macropores in the specimen decreases by 78.79%, resulting in incomplete restoration of the permeability value.

Reloading Mechanical Properties and Particle Flow Simulation of Pre-Peak Confining Pressure Unloading Sandstone

The excavation-unloading damage effects of western high-geostress slopes on rock were explored by testing the pre-peak confining pressure unloading sandstone reloading mechanical properties. The deformation and failure mechanisms were studied from a mesoscopic perspective using the particle discrete-element method. (1) Approaching the unloading failure, confining pressure increased the specimen bearing capacity attenuation. (2) The confining pressure unloading promoted microdefect propagation and development; the specimens increased rapidly to the damage stress value after reaching the initiation stress value. The penetration fracture zone was more evident and expansive in the model, and the distribution of the dense crack areas was more concentrated in the fracture zone and area. (3) The average interval of the tangential contact force was the largest in the direction of crack expansion and propagation. The strong force chains were shown to primarily bear external loads, whereas the weak force chains played a key auxiliary role in maintaining stability. (4) The number of cracks developing in the confining pressure unloading damage process indicated that the loading process did not cause damage to the specimens. The fracture zones further propagated and formed on the dominant fractures based on the damage caused by the confining pressure unloading disturbance.

The effect of cyclic stress amplitude on macro‐meso failure of rock under triaxial confining pressure unloading

AbstractThis work aims to explore the impact of cyclic stress amplitude (CSA) on the macro‐meso failure characteristics of deeply buried rock under confining pressure unloading process. The experimental results show that the deterioration of rock structure is influenced by the disturbed stress amplitude. It is found that the lateral expansion induced by confining pressure unloading has a great impact on rock volumetric deformation, damage propagation, and failure characteristics. Additionally, a damage evolution model is proposed and expressed using the irreversible lateral strain. The model is available to express the progressive damage evolution pattern. Finally, CT images investigate the complexity of the crack network, and it decreases with increasing CSA. It is suggested that the final volumetric deformation does not simply depend on the stimulated crack pattern but also on the failure modes. A specimen with the pure shear failure mode has the largest volumetric deformation.

Energy Chaos Characteristic Evolution Analysis of Sandstones during Multilevel Unloading Subject to Different Confining Pressures

Abstract In this study, multilevel and conventional unloading triaxial compression tests under different confining pressures are separately carried out to systematically reveal the deformation, energy evolution, and fracture characteristics of sandstone samples. Results show that under the multilevel unloading condition, the increase of the initial confining pressure has a more obvious inhibitory effect on the radial strain of sandstone, and the samples can fully exhibit elastic deformation and partial plastic deformation, showing obvious plastic characteristics. The radial energy growth factor is more sensitive than the axial energy growth factor during the process of confining pressure unloading, and the larger the initial confining pressure, the earlier the period-doubling bifurcation region and chaotic region are reached. To better understand the deformation and failure process of rock during engineering excavation, it is necessary to establish a constitutive relation describing the mechanical properties of rock. The three-step failure mode also proves that there are tensile and shear fractures in sandstone samples, in which the effects of tensile stress and shear stress are more or less interdependent in the failure process. It can be seen that multilevel unloading makes the energy conversion more adequate and reduces the sudden release of energy when the rock fails, reducing the possibility of rockburst and making the excavation unloading process safer. This will deepen the understanding of rock failure behavior and contribute to the better application of energy characteristics to relevant engineering practices.

Studies on Gas Seepage Characteristics in Different Stress Zones of Bottom Coal in Steeply Inclined and Extra-Thick Coal Seams under Mining Action.

The gas released from the bottom coal of the horizontal slicing mining face in steeply inclined and extra-thick coal seams seriously threatens the safety of the upper slicing mining face. To explore the seepage characteristics of bottom coal gas, the coal deformation and gas permeability evolution law of four coal samples in different stress zones of bottom coal in the working face were analyzed through true triaxial fluid–solid coupling seepage experiments. At the same time, the seepage capacity of bottom coal gas was partitioned according to the field test. The results show the following: (1) The gas permeability of the bottom coal stress concentration zone first decreased and then increased with axial pressure loading and confining pressure unloading. The gas permeability of the bottom coal stress relief zone increased rapidly with decreasing axial pressure and confining pressure. The gas permeability of the bottom coal stress recovery zone gradually decreased with the cyclic loading and unloading of axial pressure and tended to be stabilized. (2) The evolution law of gas permeability in the bottom coal was closely related to the damage and deformation of coal. (3) From the original stress zone to the stress recovery zone, the gas seepage capacity of bottom coal can be divided into four zones, namely, the original seepage zone, the seepage reduction zone, the seepage sharp increase zone, and the seepage reduction zone. The gas seepage capacity in the stress concentration zone was more substantial than that of the stress recovery zone. The results of this study are of great significance for strengthening the dynamic disaster prevention and control of bottom coal gas in the horizontal slicing mining face of steeply inclined and extra-thick coal seams.

Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

Investigating the Macro-Micromechanical Properties and Failure Law of Granite under Loading and Unloading Conditions

The excavation of rock significantly changes the initial stress state of rock slopes, which makes rock in complex loading and unloading conditions. However, the failure mechanisms and macro-micromechanical properties of rock under loading and unloading conditions are not very clear. This study investigates the macro-micromechanical properties and failure law of granite under loading and unloading conditions through traditional laboratory tests and particle flow simulations. Granite specimens are taken from Shuichang iron mine, and stress unloading experiments are designed based on the engineering practices. The stress-strain curves and failure modes under different confining pressures and unloading paths are obtained to analyze the granite properties from the viewpoint of the macroscopic mechanism. Moreover, numerical models are established in PFC software. The microcracks developments, failure characteristics, and energy evolutions under loading and unloading conditions are obtained and discussed. Results show that compared with the loading tests, the brittle failure characteristics of specimens under unloading tests are more obvious. When the confining pressure reduces to about 66% of the initial confining pressure, the specimen loses its load-bearing capacity and destroyed due to the lateral expansion. For loading tests, an inclined plane can be produced as the main failure surface. While for confining pressure unloading tests, there are many damage zones parallel to or intersecting with the main failure surface.

Study on the Deformation and Permeability of Raw Coal With Variable Confining Pressure Unloading Rate

Study on the Deformation and Permeability of Raw Coal With Variable Confining Pressure Unloading Rate

An Insight into the Excavation-Induced Stress Paths on Mechanical Response of Weak Interlayer Zone in Underground Cavern Under High Geostress

A weak interlayer zone (WIZ) is a poor zonal geotechnical system with loose structure, weak mechanical properties, variable thickness, random distribution, and strong extension, that occurs between different rock strata (e.g., tuff and basalt), due to the intense tectonic movement, representing a potential threat to the overall stability of rock masses with WIZs in large underground cavern excavations. Focusing on the excavation-induced hazards in the weak interlayer zone (WIZ) occurring in underground cavern under high geostress, the mechanical response of WIZ under different loading and unloading stress paths has been well investigated and unearthed, by a series of automatic stress path controlled triaxial tests, as well as through scanning electron microscope (SEM) analysis. Results show that the mechanical characteristics of WIZ are closely related to the initial confining pressure and stress paths. Sudden increases in the circumferential strain and strong dilations of WIZ occur from the start of unloading, among which the unloading total strains are most strongly promoted by stress path II (i.e., axial pressure loading and confining pressure unloading), whereas the unloading stress path IV (i.e., axial pressure and confining pressure unloading) has the greatest promotion on enhancing the plastic volumetric dilatation. The deformation modulus and the Poisson’s ratio follow a deterioration law under the unloading process of confining pressure, and it is the unloading stress path II that most influences the damage of elastic parameters. The ultimate bearing strength, the internal friction angle, and the cohesion of WIZ appear extremely obvious degradation in course of unloading, among which the damage effect of stress path IV is the most remarkable. The macroscopic and mesoscopic analyses reveal that the failure mechanism of WIZ under complicated unloading stress paths lays in the accumulation and propagation of axial and circumferential cracks and fractures, as well as pervasive particle breakage, with the intergranular fractures, transcrystalline fractures, and the shear scratches on a meso level. The research could provide an effective basis and good lessons for the mechanical response and failure mechanism of WIZ under unloading stress paths in underground cavern under high geostress.

Influence of Confining Pressure Unloading Rate on the Strength Characteristics and Fracture Process of Granite Using Lab Tests

In order to study the mechanical behaviors and fracture process properties of granite under confining pressure unloading with constant axial pressure, RMT‐150B rock mechanics test system and acoustic emission detector were used to study the mechanical properties and fracture process characteristics of deeply buried granite specimens under different combinations of initial confining pressures and unloading rates. The results show that when the unloading rate is small, the deviatoric stress‐strain curve of granite specimens will yield an unloading platform, and the specimens show significant characteristics of ductility; when the unloading rate is large, the specimens show characteristics of brittleness. Besides, the axial strain rate increases with the increase of initial confining pressure and unloading rate, and the axial strain rate fluctuates. The ratio of axial strain increment to confining pressure increment of granite specimens decreases with the increase of the unloading rate, and a faster unloading rate and a higher initial confining pressure will restrain the axial deformation of granite sample. The normalized confining pressure decreased parameter of granite specimen increases with the increase of initial confining pressure. When the unloading rate is relatively high, it plays a dominant role in the compressive strength of granite specimens. The Mohr–Coulomb strength criterion can better reflect the strength characteristics of specimens under confining pressure unloading. The cohesion of granite specimens decreases with the increase of unloading rate, and the internal friction angle increases with the increase of unloading rate. Notably, the unloading rate presents a weakening effect on the cohesion of the specimen and a strengthening effect on the internal friction angle of the specimen, and the former effect is stronger than the latter one. When the unloading rate is small, the acoustic emission ringing count increases more evenly, and the deformation and damage of the specimen develop slowly; when the unloading rate is high, the acoustic emission ringing count increases to the maximum instantaneously at the initial stage of confining pressure unloading, and the specimen is damaged rapidly, showing the characteristic of sudden fracture. The fracture mode of granite specimens is affected by the unloading rate and initial confining pressure. At the same unloading rate, the specimens with high initial confining pressure show typical tensile fracture characteristics, while the specimens with low initial confining pressure mainly suffer from shear fracture or shear‐tension composite fracture. With the increase of unloading rate, the fracture characteristics of specimens show a transition from shear or shear‐tension composite fracture to tensile fracture.

Experimental study on law of limit storage energy of rock under different confining pressures

To investigate the effects of different unloading rates on rockbursts, the conventional triaxial compression tests and confining pressure unloading tests have been conducted on rock samples. The variation law of stress and stress thresholds for structural failure of rock sample under different confining pressures was analyzed, and the influence of different unloading confining pressure rates on limit storage energy during rock sample failure process was revealed. Experimental results showed that under uniaxial compression, the stress for structural failure of the rock sample is the same as stress thresholds for structural failure. In the conventional triaxial test, the stresses for structural failure and stress thresholds for structural failure of the rock sample will increase with the increase of confining pressure. Compared with the stresses for structural failure, the stress threshold for structural failure of rock samples increases by 32.88%, 53.63%, and 78.51%, respectively when the confining pressures are 10 MPa, 20 MPa, and 30 MPa. Under different confining pressure unloading rates, the limit storage energy of samples is also different. The higher the confining pressure unloading rate is, the smaller the limit storage energy is. When confining pressure increases, the limit storage energy of rock samples increases. Under the same initial confining pressure and confining pressure unloading rate, the change of axial pressure has little effect on the limited storage energy of rock, i.e., the energy required for rock failure is a definite value under certain conditions and is not affected by the stress loading path. This research can be helpful to understand and assess the rockburst during the deep rock mass excavation by different tunneling methods.

Mining‐Induced Pressure‐Relief Mechanism of Coal‐Rock Mass for Different Protective Layer Mining Modes

The protective layer mining method of the traditional deep coal seam in has been confronted with great challenges, and it is difficult for coal and gas to be extracted together. Taking the occurrence conditions of III1 mining area of Luling Coal Mine located at Huaibei, China, as engineering background, the influence law of the lithology on stress environment in front of the stope was analyzed by theoretical analysis and numerical simulations. The mining‐induced mechanical effect of coal‐rock mass was studied under different protective layer mining modes. The results showed that the peak value of the advanced abutment pressure decreased with the decrease of lithologic strength under the same mining conditions. For simulated geological conditions, the stress concentration coefficient of soft rock and coal seam protective layer mining modes was 1.9 and 1.7, respectively. Under the mining stress path of different protective layers, the ratio of axial stress increase and confining pressure unloading in secondary unloading phase were 2 : 1 and 1.5 : 1, respectively. The axial stress‐strain curves of different protective layer mining modes had similar trends, and they had a volume expansion at the end of unloading (failure stage). In addition, it revealed the pressure‐relief antireflection mechanism of the protective layer mining. Under the same confining pressure condition, the peak stress and peak strain increased with the increase of loading and unloading velocity ratio. The reduced value of the confining pressure increased, while the volume expansion decreased at failure. The results were applied to III1 mining area in soft rock protective layer mining, which created the mining way of traditional coal seam protective layer. Furthermore, the gas control technology of soft rock protective layer working face was put forward for deep coal seam with low permeability and high gas, enriching the pressure‐relief mining theory of protective layer.

Fracture Evolution and Energy Characteristics During Marble Failure Under Triaxial Fatigue Cyclic and Confining Pressure Unloading (FC-CPU) Conditions

This work aims at investigating the fracture evolution and energy characteristics of marble subjected to fatigue cyclic loading and confining pressure unloading (FC-CPU) conditions. Although rocks under separated fatigue cyclic loading and triaxial unloading conditions have been well studied, little is known about the dependence of the fatigue damage accumulation on the subsequent confining pressure unloading condition that influences the rock fracture behaviors. In this work, the servo-controlled GCTS 2000 rock mechanical system combined with the post-test X-ray computed tomography (CT) scanning technique were used to reveal the fracture behaviors of the marble samples. The samples were tested at three stages: the static loading stage, the fatigue cyclic loading stage, and the confining pressure unloading stage. Results show that the damage index-cycle number curve shows a different pattern—the damage increasing rate is different for the samples experiencing different fatigue damage. The damage accumulation at the fatigue cyclic stage influences the final failure mode and energy conversion. In addition, post-test CT scanning further reveals the effects of fatigue cycles on the crack pattern, as well as the stimulated crack scale and density after FC-CPU testing depending on the fatigue cycle. Furthermore, the stored elastic energy decreases and the dissipated energy increases with increasing fatigue cycle at the fatigue loading stage, and the energy conversion is consistent with the crack pattern analysis. By investigating the failure mechanism of marble under FC-CPU conditions, a theoretical basis for rock dynamic disaster prediction can be created.