Triaxial Compression Conditions Research Articles

Experiment and discrete element modeling of particle breakage in coral sand under triaxial compression conditions

Particle breakage is a major factor that determines the strength and deformation of coral sand. Consolidated drained triaxial compression tests under different confining pressures have been conducted on coral sands as a basis for 3D discrete element simulations, focusing on the particle breakage characteristics. Considering angular breakage and overall breakage in the numerical model, particle breakage is simulated with a fragment replacement method, and the particle size and the equivalent stress are combined as the criterion to judge the occurrence of particle crushing. The validation of the numerical model is proved by reproducing comparable stress-strain relations, evolutions of grain size distribution and relative breakage rate. The overall behavior of the specimen transit from strain softening to strain hardening with the increase in confining pressure from 100 kPa to 400 kPa. Meanwhile, the number of angular breakages increases at a decreasing rate, while the number of overall breakages increase at an increasing rate. This phenomenon implies that overall breakage overwhelms angular breakage and becomes the dominating particle breakage mechanism gradually with increasing confining pressure. Microscopic analyses reveal that higher confining pressure increases the overall contact force, the portion of strong contact force and the coordination number.

Improving the accuracy of predicting the hazard of the earth’s surface failure formation during underground mining of mineral deposits

Purpose. Development of a new approach to improving the accuracy of predicting situations in which the earth’s surface failures occur as a result of undermining a rock mass during the development of mineral deposits. Methods. The critical situations, including the earth’s surface failures, are predicted on the basis of assessing the value of geoenergy and studying its change as large volumes of rock mass are involved in mining. Analytical solutions based on the fundamental laws of physics and mechanics of continuous media are used. The research is performed using methods of cause-and-effect analysis. Findings. Based on the cause-effect relationship, determined between the change in the value of the mass geoenergy and deformation processes on the daylight surface of the field, an effective method has been developed for ranking it according to the degree of hazard of failure formation with the simultaneous use of two criteria. One of the criteria is determined by the relative change in geoenergy during the system transition from the initial (stable) state to the current one, which becomes unstable under certain conditions. The second criterion is formed on the basis of the change in geoenergy during the transition from the current (possibly unstable) state to the final (stable) state. Originality. For the first time, when zoning the daylight surface of a field according to the degree of hazard of failure formation, two ranking criteria are used simultaneously, based on the assessment of geoenergy accumulated in a heterogeneous mass, when it is undermined in the conditions of triaxial compression. Practical implications. The territory ranking method, developed on the basis of the used criteria for hazard of failure formation, allows improving the quality of situational control, predicting risk situations and their development, as well as optimizing the short-term and long-term plans for the development of mining operations.

Mechanical characteristics of red sandstone under cyclic wetting and drying

The bank slope of the Three Gorges Reservoir is affected by seasonal water level fluctuations, which leads to deterioration of the rock mass, resulting in a series of geological disasters such as landslides and mudslides. Therefore, to thoroughly understand the degradation mechanism of mechanical characteristics under wetting–drying cycles, uniaxial compression tests and triaxial compression tests were used to reveal the relationship between mechanical characteristics and wetting–drying cycles. The results of the uniaxial compression tests show that with the increase in the number of wetting–drying cycles, the mechanical characteristics show a declining trend, and the compaction stage of the sample increases considerably. It was found that the first ten wetting–drying cycles have a greater impact on the mechanical characteristics of red sandstone under the triaxial compression condition, the mechanical parameters such as deviatoric stress, elasticity modulus dropped rapidly under the first 10 cycles and then tend to be stable. Based on the testing data under wetting–drying cycle condition, the mechanical parameters of the statistics damage constitutive model were modified and the results show that the modified damage constitutive model has a high degree of fit with the test data, indicating that the modified mechanical parameters can better reflect the degradation of red sandstone after the wetting–drying cycles. This understanding of the degradation process of the mechanical characteristics under wetting–drying cycles can provide theoretical guidance for the protection of dangerous slopes in the drawdown zone of the Three Gorges Reservoir.

The Effect of Curing under Applied Stress on the Mechanical Performance of Cement Paste Backfill

After placing the Cement Paste Backfill (CPB) slurry in mined cavities underground, during the setting and hardening processes, the weight and hydrostatic pressure of the upper-layer CPB slurry applies an axial load over the bottom-layer CPB materials, which is called the self-consolidation of CPB slurry. Due to this phenomenon, the mechanical properties of in situ CPB could be considerably different from laboratory results. Hence, it is crucial to understand the effect of self-consolidation behaviour on the mechanical properties of backfill material. This paper presents an experimental study on the impact of axial applied stress (As) during curing, which represents the various self-consolidation conditions and curing times on the mechanical properties of CPB material prepared using the tailings of a copper mine in South Australia and a newly released commercially manufactured cement called Minecem (MC). A curing under pressure apparatus (CPA) is designed to cure CPB samples under axial applied stress. The equipment can apply and measure axial load during curing and measure the passive lateral stress due to axial load which represents the horizontal stresses at a certain depth of CPB stope on the retaining structure. The prepared samples with axially applied pressure during curing were tested under uniaxial and triaxial compressive loading conditions. Microstructural tests by scanning electron microscopy (SEM) were also used to study the fabric evolution in response to various applied stresses during curing. Overall, the increase in As during curing leads to higher resultant CPB peak strength and stiffness under uniaxial and triaxial compression tests. For instance, a sample cured under 3.6 MPa axial load for 28 days demonstrates a uniaxial compressive strength (UCS) value of five times more than a sample cured under atmospheric curing conditions. Passive lateral stress was measured during the curing period and was representative of underground barricade stress. Furthermore, during curing, the axial applied stress changed the initial CPB pore structure after placement. With the increase in applied stress, the stress compressed CPB samples at the macroscale, leading to much smaller pores or cracks prior to the hydration process. At an early stage, the increase in UCS due to axial applied stress mainly arises from a dense microstructure caused by the compression of tailings and cement particles. With the increase in curing time, the observation also shows that a CPB matrix with fewer pore spaces may improve the hydration progress; hence, the influence of axial applied stress becomes more pronounced in long-term UCS.

Modeling investigation of coupling between damage and permeability for sandstone

Rock damage due to microcrack propagation leads to changes in seepage characteristics. Therefore, the coupled mechanism of rock damage and permeability plays a significant role in some underground engineering projects, such as mining, excavation, and hydraulic activity. In this study, a rock micro-unit is divided into damaged and undamaged parts. The damaged part only consists of cracks, and the undamaged part includes pores and matrices. A damage evolution function was proposed on the basis of statistical damage theory considering water pore pressure to demonstrate the mechanical behavior under triaxial compression conditions. The damage variable could be obtained with the Weibull distribution function. Then, a novel sandstone permeability model was developed by introducing the damage evolution function. The proposed coupled damage and permeability model covered the matrix and fracture permeabilities. A series of triaxial seepage experimental data of sandstone under different pore water pressures was cited to validate the coupled model. Results showed that the coupled damage and permeability model was remarkably consistent with experimental findings.

Features of clay soil deformation under triaxial block regime cyclic loading, taking into account the formation of micro and macro-cracks

The main purpose of this paper is to study the parameters of strength and deformation of clay soil in conditions of triaxial compression under block regime cyclic loading. To date, there are no data on the results of studies under this loading mode. Theoretical and experimental studies of the strength and deformability of clay soil of triaxial compression 0^02=03 under block regime cyclic loads are carried out. A distinctive feature of the experimental studies is that they were carried out in devices of triaxial compression of a prismatic shape with an aspect ratio of 100x 100x200mm. In the study of vibration creep deformations and changes in the fatigue resistance to the destruction of clay soils under triaxial regime block cyclic loading. It is established that the stress-strain state, deformation, and fatigue strength of soil vary depending on the sequence of alternating blocks with different values of the maximum load of the cycle. The developed and obtained equations describing the deformation of the soil under these conditions with the development of micro-cracks observed in experiments of hardening and softening effect of inhibition at different stages of cyclic triaxial compression allow to accurately estimate vertical deformation (settlement) bases under regime loading and to obtain reliable and economical design solutions.

AXIAL COMPONENT OF PLASTIC MODULUS OF SAND UNDER SLOW PERIODIC LOAD

Soil deformation under slow periodic load is of particular importance to predict the functionality of soil structure in a variety of engineering practices. However, lacking quantification on plastic deformation hinders the deformation analysis of soil subjected to slow periodic load. The axial component of plastic modulus is pivotal and is determined to calculate axial plastic strain and overall soil deformation. In this study, a static triaxial compression system was designed to perform a series of static cyclic triaxial tests and cyclic confined compression tests on a silica sand. The results showed that plastic strain increments decreased gradually, as the loading cycle proceeded, and finally only the elastic strain increment existed. The empirical equation of axial component of plastic modulus was formulated considering the effects of stress states, void ratios, and loading cycles. In combination with the description of elastic modulus, the axial strain increment in each loading cycle was formulated. In addition, in the unloading process of loading cycle, the volume contraction phenomenon was explained by unloading plastic strain and microscopic particle motion based on the present results.

Development of a constitutive model for fibre reinforced cemented Toyoura sand

In this study, the modified Severn-Trent constitutive model is used to simulate the mechanical behaviour of unreinforced, cemented, fibre, and fibre reinforced cemented Toyoura sand consolidated under drained and undrained triaxial compression and extension loading conditions. The model parameters are derived based on the experimental results in the current study, parametric study, trial and error, and by comparison with previous research studies. The comparisons covered ranges of material from 0–3% fibre, 0–3% cement, and 20–60% relative densities. The experimental results and model simulations were compared in terms of deviatoric stress versus axial strain, volumetric strain versus axial strain, and stress path behaviour. Two additional parameters () obtained from the laboratory tests are added to the standard Severn-Trent model to simulate the stress–strain behaviour of cement and fibre reinforced Toyoura sand. Calibration exercises based on studies in the literature and comparisons with the experimental studies herein are conducted with the modified version of the Severn-Trent model. A close agreement of model simulations with the experimental results is observed for many of the tests performed on pure Toyoura sand, cemented, fibre, and fibre reinforced cemented Toyoura sand. The modified model successfully captured the main features of the behaviour (e.g., increase in strength and stiffness with cement additive, increase in volumetric dilatancy due to fibre and cement additives, and general stress path behaviour for drained and undrained conditions) for different types of composite materials with reasonable accuracy. Hence, the current study might serve and should be considered as a step towards modelling of the behaviour of composite materials.

Time effect and prediction of broken rock bulking coefficient on the base of particle discrete element method

Bulking characteristics of gangue are of great significance for the stability of goafs in mining overburden in the caving zones. In this paper, a particle discrete element method with clusters to represent gangue was adopted to explore the bulking coefficient time effect of the broken rock in the caving zone under three-dimensional triaxial compression condition. The phenomena of stress corrosion, deformation, and failure of rock blocks were simulated in the numerical model. Meanwhile, a new criterion of rock fragments damage was put forward. It was found that the broken rock has obvious viscoelastic properties. A new equation based on the Burgers creep model was proposed to predict the bulking coefficient of broken rock. A deformation characteristic parameter of the prediction equation was analyzed, which can be set as a fixed value in the mid- and long-term prediction of the bulking coefficient. There are quadratic function relationships between the deformation characteristic parameter value and Talbot gradation index, axial pressure and confining pressure.

Effects of stress path on brittle failure of sandstone: Difference in crack growth between tri-axial compression and extension conditions

The tri-axial testing of rocks under compression is a widely popular measure for the assessment of strength of geological materials in the laboratory. In this regard, mechanical complexities of true tri-axial testing machines impel researchers to opt for simpler conventional tri-axial testing machines. To account for influential factors that affect quality of experimental data, observations derived from laboratory experiments that enable overcoming some drawbacks are presented herein. In the present study, a series of tri-axial tests on Kimachi sandstone under Conventional Tri-axial Compression (CTC), Conventional Tri-axial Extension (CTE), Reduced Tri-axial Compression (RTC), and Reduced Tri-axial Extension (RTE) conditions were carried out. The results suggested higher compressive strengths for the rock under tri-axial extension tests than the compression tests. This observation proves that the effect of intermediate confining pressure on material behavior is important and if feasible, should not be sacrificed for more economical alternatives. Generally, the loading and unloading experiments for a specific test type rendered the same results and the conventional and reduced paths in both the compression and extension tests did not affect the failure strength of the specimens. The effect of pre-existing cracks orientation with respect to the principal loading directions on crack growth was focused upon and related conclusions were subsequently drawn.

Influence of Unloading Conditions of Confining Pressure on the Compressive Strength and Permeability of Deep Mudstone

To investigate the compressive strength and permeability of deep mudstone under stress disturbance, a triaxial rheometer is used to conduct seepage experiments on mudstone specimens with different buried depths under triaxial compression and unloading conditions. The experimental results show that the compressive strength of mudstone specimen with a depth of 1000 m is much lower than that of specimen with a depth of 200 m, and the compressive strength of mudstone increases with the increase in confining pressure. Under constant axial pressure and unloading of the confining pressure, the mudstone with a depth of 200 m exhibits brittle failure, and the strain fluctuates in a pointwise manner with the increase in axial stress. In this case, the mudstone with a depth of 1000 m exhibits a transition from brittle failure to ductile failure, and the strain fluctuates linearly with the axial stress. Further, when the volumetric strain change reaches 0.01, it shows an oblique “Z” fluctuation. During the initial stage of unloading of confining pressure, the permeabilities of both the mudstone specimens (with depths of 200 and 1000 m) decrease gradually. As the confining pressure is unloaded, the permeability of mudstone with a depth of 1000 m increases. Until the specimen is completely destroyed, the permeability of mudstone increases rapidly. Overall, this study can serve as a useful reference for analyzing the engineering disasters associated with deep rock mass, tunnel ventilation, and gas storage.

Study on Mechanical Properties of Gravelly Sand under Different Stress Paths

To investigate the strength and deformation characteristics of gravelly sand on the Qinghai-Tibet Plateau under different stress paths, a series of triaxial shear tests was conducted under confining pressures of 50–400 kPa in four types of stress path conditions of conventional triaxial compression (CTC) (drained and undrained), triaxial compression (TC), and reduced triaxial compression (RTC). We can see from the test results that gravelly sand samples show strain hardening and shear contraction under the CTC (drained), TC, and RTC during the shearing process but exhibit strain softening under the CTC (undrained). To explore the microscopic deformation mechanism of gravelly sand, a characteristic angle θ was defined to reflect the relative movement of soil particles. The relationship between principal stress ratio σ1/σ3 and characteristic angle θ and that between void ratio e and characteristic angle θ were derived. Subsequently, the relationship expression of stress ratio η (q/p) and void ratio e was established, and the trend of void ratio e with the stress path was studied. To describe the strain hardening and strain softening characteristics of gravelly sand in different stress paths, a new dilatancy equation was obtained by introducing the characteristic state stress ratio Mc into the dilatancy equation of the modified Cam-Clay model based on the state-dependent dilatancy theory. Finally, an elastoplastic constitutive model of gravelly sand was established by applying a nonassociate flow rule. All model parameters can be determined by triaxial shear tests under different stress paths, and the comparison results show that the proposed model can well reflect the mechanical behaviors of gravelly sand under different stress paths.

Unconfined and Triaxial Compression Tests on Hollowed Cylindrical Sandstones to Explore the Infilling Effects on the Deformation and Mechanical Behaviors

In practical engineering, the mechanical properties of the surrounding rock often reflect the bearing capacity of the support. To investigate the relations between the surrounding rock and the support, solid specimens, hollowed cylinders, and hollowed cylinders filled with two kinds of cement mortars are tested under unconfined and conventional triaxial compressions. The effects of the infilling on the stress‐strain curves, deformation features, mechanical properties, and failure patterns are schematically investigated. The results show that under the triaxial compression condition, each infilled specimen exhibits obvious residual carrying capacity though a slight stress drop occurs after the peak stress. The cement mortar exerts a positive effect on the carrying capacity of the rock, and the infilling having a higher strength and stiffness contributes to a more pronounced enhancement of the overall strength of the specimens. Under the triaxial compression condition, merely a dominated shear fracture can be seen on the surfaces, and with relatively high confining pressure (σ3 = 20 and 30 MPa), both the rock and cement mortar were cut into two parts by the dominated shear fracture. The laboratory tests in this study provide a simple and feasible way of investigating the interaction of the support system with the surrounding rock.

Laboratory investigation of the anisotropic confinement-dependent brittle-ductile transition of a Utah coal

This paper was developed as part of an effort by the National Institute for Occupational Safety and Health (NIOSH) to identify risk factors associated with bumps in the prevention of fatalities and accidents in highly stressed, bump-prone ground conditions. Changes of failure mechanism with increasing confinement, from extensional-to shear-dominated failure, are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses. In the previous analysis conducted in 2018, both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of some specimens of a Utah coal, including the spalling limits, the ratio of apparent unconfined compressive strength (AUCS) to unconfined compressive strength (UCS), the damage characteristics, and the post-yield dilatancy. These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction. However, the transition from extensional to shear failure at the given confinements was not clearly identified. In this study, a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive conditions. The different confining stresses are used as analogs for different width-to-height (W/H) ratios of pillar strength. Although the W/H ratios of the specimens were not directly considered during testing, the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an existing empirical solution. According to this relationship, the W/H at which in-situ pillar behavior would be expected to transition from brittle to ductile is identified.

Analysis and Modeling of the Micro-Cutting Process of Ti-6Al-4V Titanium Alloy with Single Abrasive Grain

Modeling of material displacements in the microcutting zone is complex due to the number and interdependence of factors affecting the results of the process. An important problem in the modeling process is the selection of the constitutive model and its parameters, which will correctly describe the properties of the material under the conditions of triaxial compression, which is characteristic for the areas of the contact zone of the blade and the processed material in abrasive machining processes. The aim of the work was to develop computer models (with the use of the finite element method) of the microcutting process with a single abrasive grain, which were verified with the results of experimental tests. The paper presents the methodology of modeling the processes of microcutting with abrasive grains, whose geometrical models were created based on optical scanning methods. Observations of the microcutting process were carried out with the use of a high-speed camera and an optical profilometer. This enabled a detailed observation of the chip formation process, as well as the analysis of the surface topography of microcutting traces. The results presented in the paper indicate the convergence of the results of the numerical and experimental simulations with regard to the geometric parameters describing the scratches formed in the microcutting process and the compliance of the chip-forming process. Thus, the correctness of the selection of the constitutive model (Johnson Cook equation) and its parameters was demonstrated, as well as the correctness of the applied methodology for creating a geometric model that allowed for a reflection of the geometrical parameters of the abrasive grains that coincided with the real objects, thanks to which it was possible to reflect in detail the phenomena occurring in the vicinity of the abrasive grain tip.

Model for predicting the variation of shear stress in unsaturated soils during strain-softening

Several of the geotechnical structures constructed with unsaturated soils undergo a large deformation prior to reaching failure conditions (e.g., progressive failure of a soil slope). During this process, the shear stress in soils typically increases initially and then reduces with an increase in the shear strain. The prediction of the stress–strain relationship is critical for reasonable interpretation of the mechanical behavior of those geo-structures that undergo large deformation. This paper introduces a model based on the disturbed state concept (DSC) to predict the variation of shear stress in unsaturated soils during the strain-softening process under consolidated drained triaxial compression condition. In this model, the apparent stress–strain relationship is formulated as a weighted average of a hyperbolic hardening response extending the pre-peak state stress–strain curve and a linear response extending the critical state stress–strain curve with an assumed disturbance function as the weight. The prediction procedure is described in detail and the proposed model is validated using several sets of published data on unsaturated soils varying from coarse- to fine-grained soils. Finally, a comprehensive error analysis is undertaken based on an index of agreement approach.

Quantitative analysis of fracture dynamic evolution in coal subjected to uniaxial and triaxial compression loads based on industrial CT and fractal theory

The dynamic evolution characteristics of fractures in coal under different compressive loads are of great significance to the recovery of coalbed methane (CBM). In this paper, the X-ray computer tomography (CT) detections of coal samples under uniaxial and triaxial compressive loading conditions were performed by using a developed triaxial in situ rig and an industrial CT scanner. The image processing technique, three-dimensional reconstruction method and statistical principles were employed to describe two-dimensional and three-dimensional fracture evolution in coal under uniaxial and triaxial compressive loads. The results showed that the developed triaxial in situ rig has an enough scanning resolution and is suitable to carry out CT scanning inspections under uniaxial and triaxial compressive loads for porous materials of coal and rock. The two-dimensional cross-sectional CT images effectively reflect the dynamic evolution of two-dimensional fractures during the deformation of coal. Confining pressure and minerals have a significant effect on fracture propagation in coal. The evolution characteristics of three-dimensional fractures can be clearly revealed by the reconstructed three-dimensional digital fracture models of coal. Euler number effectively reflects the fracture connectivity in coal at different deformation stages. During the deformation of coal, the fracture volume, fracture rate, fracture density and fracture connectivity mainly undergo a slow decrease stage, a slow increase stage and a sharp increase stage, display a good linear correlation with fractal dimension, and quantitatively characterize the evolution process of the three-dimensional fractures in coal. The fractal dimension calculated by the box-counting method effectively mirrors fracture propagation and fracture geometric complexity and can be employed to uncover the fracture dynamic evolution in coal under different compressive loading conditions.

Determination of Rheological Properties of Frozen Soils by Relaxation Method

This article discusses the possibility of using the stress relaxation method to determine rheological characteristics of frozen soils based on a multistage test scheme under triaxial compression conditions (using a stabilometer). The analysis of the test results shows that the proposed method has good application potential.

A modified Hoek-Brown failure criterion for unsaturated intact shale considering the effects of anisotropy and hydration

The mechanical strength of shale is highly influenced by anisotropy and hydration, which cannot be ignored for the stability evaluation of the geotechnical structures related to shale after water invasion. In the present work, a modified Hoek-Brown failure criterion for unsaturated intact shale considering the effects of anisotropy and hydration has been developed in order to obtain an accurate strength evaluation for unsaturated intact shale. In this proposed failure criterion (abbreviated as the proposed criterion), the effect of anisotropy on shale strength is determined by a piecewise functions for uniaxial compression and the parameter kβ added in Hoek-Brown (HB) failure criterion for triaxial compression condition, and the effect of incomplete hydration on shale strength is regarded as an effective stress decrease by incorporating a discount function related to moisture content. The proposed criterion is defined by 8 parameters, including a material parameter of HB failure criterion (m), 4 material parameters (ξ, η, R and r) describing the hydration effect and 3 model parameters (g, h and kβ) describing the anisotropy effect. The physical meanings and determination procedures of these parameters are described. The predicted values of the proposed criterion agree well with the experimental data, showing that R2 = 0.966 and AAREP (average absolute relative error percentage) = 4.393% for all the predicted results. The proposed criterion is then compared with other two failure criteria which consider the effects of water invasion and anisotropy on rock strength, showing that the proposed criterion has higher accuracy and better stability. The error of the predicted values for the proposed criterion compared with the tested results increases for the shale specimen for which β (bedding plane orientation relative to the axial loading in degrees, °) is closer to 30°, is bigger for the shale specimen with a higher moisture content, and is bigger for the shale specimen under a higher confining pressure. The sensitivity analysis of the 4 hydration parameters on the predicted results shows that the predicted values are more sensitive to R and r than ξ and η. This proposed criterion can improve the reliability for the stability evaluation of the geotechnical structures related to shale after water invasion.

Influence of stress amplitude on the dynamic characteristics of phyllite samples under triaxial multi-stage cyclic loading

The generation of a rockslide in an earthquake event is strongly dependent on the dynamic characteristics of the rock materials constituting the rock slope. In this study, phyllite samples were extracted from the Donghekou landslide area of Qingchuan County. The landslide occurred during the 2008 Wenchuan earthquake and the samples were made to undergo multi-stage cyclic loading and unloading tests under triaxial compression conditions. The confining pressure during the tests was 10 MPa, the loading frequency was 2 Hz, the loading waveform was sine wave, and 60 loading cycles were carried out at each level of stress. From the dynamic axial stress–strain curves, the effect of stress amplitude on the hysteresis loop area, the dynamic elastic modulus, the dynamic damping ratio, and the damping coefficient of the phyllite samples was analyzed. The results are as follows. (1) The strain–stress hysteresis loop area experienced a rapid increase as the stress amplitude exceeded a certain value, indicating that the rock samples have entered an accelerating crack propagation stage under high levels of cyclic loading. (2) As the stress amplitude increases, the dynamic elastic modulus, the dynamic damping ratio, and the damping coefficient of the rock sample followed a similar two-phase evolution law. There was a rapid reduction in the three parameters relative to the initial value in Phase I. Moreover, there was a minor change in Phase II. (3) The effect of the number of loading cycles number on dynamic elastic modulus and damping parameters was much more obvious under the lower levels of cyclic loading than under the higher levels.