Failure Mechanism Of Rock Research Articles

Experimental Study on the Strength and Failure Mechanism of Hollow Hot Dry Rocks Under Brazilian Splitting Tests

The investigation into the effects of acidizing treatment on the mechanical property of hot dry rocks (HDR) is beneficial for our understanding of the fracturing and stimulation mechanisms in HDR reservoirs. In this article, Brazilian disk tests were first carried out for hollow hot dry rocks with different internal diameters after acidizing treatments. The influences of acidizing treatments on the physical properties, tensile strength, and failure patterns of hot dry rock specimens were presented. Besides, the effects of the diameter of the internal hole on the peak load and failure patterns of the hot dry rock specimens were also investigated. The peak load decreases with the increase in the internal diameter. The results indicated that the acidizing treatments can dissolute the minerals, decrease rock mass, and tensile strength. The investigation of failure patterns demonstrated that the acidizing treatment is beneficial for the fracturing of hot dry rocks. The present study can provide some basic and theoretical data for the development of geothermal reservoir.

A review of experimental and theoretical research on the deformation and failure behavior of rocks subjected to cyclic loading

Rock engineering is highly susceptible to cyclic loads resulting from earthquakes, quarrying or rockbursts. Acquiring the fatigue properties and failure mechanism of rocks is pivotal for long-term stability assessment of rock engineering structures. So far, significant progress has been gained on the mechanical characteristics of rocks subjected to cyclic loading. For providing a global insight of typical results and main features of rocks under cyclic loading conditions, this study comprehensively reviews the state-of-the-art of deformation and failure mechanism and fatigue constitutive relationship of rocks subjected to cyclic loading in the past 60 years. Firstly, cyclic tests on rocks are classified into different types based on loading paths, loading parameters, loading types and environment conditions. Secondly, representative results are summarized and highlighted in terms of the fatigue response of rocks, including the deformation degradation, energy dissipation, damage evolution and failure characteristics; both laboratory testing and numerical results are presented, and various measurement techniques such as X-ray micro-computed tomography (micro-CT) and digital image correlation (DIC) are considered. Thirdly, the influences of cyclic loads on the mechanical characteristics of rocks are discussed, including the cyclic stress, frequency, amplitude and waveform. Subsequently, constitutive relationships for rocks subjected to cyclic loading are outlined, in which typical fatigue constitutive models are compared and analyzed, regarding the elastoplastic model, the internal variable model, the energy-based damage model and the discrete element-based model. Finally, some ambiguous questions and prospective research are interpreted and discussed.

Failure mechanism analysis of rock in particle discrete element method simulation based on moment tensors

Acoustic emission (AE) and moment tensor simulation with discrete element method (DEM) have been proven to be an effective method to analyse the failure mechanism of rock. The ratio (R) of isotropic and deviatoric components of moment tensor is often used to distinguish the failure mechanism of AE events. However, the critical value of R to distinguish different failure mechanism has not been strictly verified, and the method to evaluate the fracture mechanism of macrocrack qualitatively by the failure mechanism of AE events is not clear enough. Therefore, we analyzed the theory of moment tensor with DEM to distinguish failure mechanism and verified this theory by a simulated verification test with four particles and six particles model in 2D and 3D respectively. Furthermore, we simulated three typical laboratory tests of rock. Results show that the critical values of R for distinguishing implosion, shear, and tensile mechanisms are equal to ±40 in 2D and ±35 in 3D. Using the modified critical values of R to identify the failure mechanism of rock is more accurate than counting the microcracks. The fracture mechanism of the macrocrack can be determine quantitatively by the distribution curve of AE events around this macrocrack.

Experimental Study on the Failure Mechanism of Tunnel Surrounding Rock under Different Groundwater Seepage Paths

The influence of groundwater on tunnel engineering is very complicated. Due to the complexity of water flow water pressure transfer and uncertain defects in the stratum, all of which are key factors with regard to the design of tunnel engineering. Therefore, the variation of surrounding rock during excavation and the deformation and failure of soft surrounding rock under different seepage paths of underground water after excavation systematically. Experimental results showed that the stress change of surrounding rock caused by tunnel excavation can be divided into 3 stages: stress redistribution, stress adjustment, and stress rebalancing. In the process of water pressure loading, water flow rate is closely related to the experimental phenomenon. The between stable loading water pressure pore water pressure of the tunnel surrounding rock and the distance from the measuring point to the edge of the tunnel obey the exponential function of the decreasing growth gradient. With the increase of loading pressure, the pore water pressure and stress at the top of the tunnel increase, and the coupling of stress field and seepage field on both sides of surrounding rock more and more intense. The failure process of the tunnel can be divided into 6 stages according to the damage degree. The final failure pattern of the surrounding rock of the tunnel is mainly determined by the disturbed area of excavation. The arched failure area and the collapse-through failure area are composed of three regions. The surrounding rock is characterized by a dynamic pressure arch in the process of seepage failure, but it is more prone to collapse failure at low water pressure. The results of this study are the progressive failure mechanism of tunnel under different groundwater seepage paths and would be of great significance to the prevention of long-range disasters.

Research on Creep Deformation and Control Mechanism of Weak Surrounding Rock in Super Large Section Tunnel

In order to solve the difficulties of creep deformation of surrounding rock in super large section tunnel, taking Letuan tunnel of Binlai expressway, a typical super large cross-section tunnel as research background, the creep mechanical characteristics of surrounding rock are taken into consideration, and the influence of different supporting forms such as bolt reinforcement, rock grouting, high-strength arch and concrete lining on surrounding rock deformation and failure mechanism is comprehensively studied. The creep failure mechanism and high strength control mechanism of surrounding rock are obtained. Research results show that the surrounding rock shows obvious creep mechanical characteristics, the continuous growth of surrounding rock deformation has brought severe challenges to the tunnel support; the surrounding rock of super large cross-section tunnel shows unstable creep deformation failure mechanism with obvious acceleration of creep stage under the condition of no support; the influence mechanism of different support forms on the control effect of surrounding rock creep deformation is systematically studied, and the evaluation indexes of deformation control rate and creep control rate of surrounding rock prove that confined concrete, as a high-strength support type, has significant advantages for surrounding rock creep control. Based on the large-scale mechanical test system of tunnel, the mechanical test of confined concrete arch is carried out, and the bearing mechanism and mechanical characteristics of confined concrete arch are clarified. The field application results show that the confined concrete arch can effectively control the creep deformation. The research results can provide theoretical basis for relevant projects.

Calculation of stability reliability of soft base controlled unstable rock and parameter sensitivity analysis

There are a large number of unstable rocks whose stability are controlled by soft base layer in the mountainous areas of southwest China, and they have caused serious harm to people’s lives and local economic development. Therefore, it is of great practical significance to study the stability and failure mechanism of such unstable rock. Taking the in Wulong District, Chongqing as an example, this paper analyzes the failure probability and reliability index of the unstable rock under different conditions by use of Monte Carlo method and on this basis, the sensitivity of the stability of dangerous rock mass to the main influencing factors is analyzed. The results show that the stability coefficient, failure probability and reliability index of are equal to 1.151, 26.245% and 0.642 under natural condition. However, the stability coefficient of decreases rapidly and the reliability index and failure probability increase obviously when combined with other factors such as rainfall or earthquake. The sensitivities of the influencing factors of the unstable rock are from top to bottom internal friction angle of soft layer, the horizontal seismic force, the cohesion of soft layer, the water content in the crack and the weight of soft layer. The research results can provide some reference for the stability analysis and engineering prevention of such unstable rocks.

Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model.

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

Deformation and Failure Mechanism of Surrounding Rock in Mining-Influenced Roadway and the Control Technology

Aiming at the problem of surrounding rock deformation and failure of mining roadway and its control, a mechanical model of the circular roadway under the mining environment is established, and the implicit equation of the plastic zone boundary is derived. By analyzing the morphologic evolution law of the surrounding rock plastic zone in the mining roadway, the key factors affecting the morphologic change of the plastic zone are obtained, that is, the magnitude and direction of principal stress. The influence law of the magnitude and direction of principal stress on the plastic zone of the mining roadway is analyzed by using numerical simulation software, and the deformation and failure mechanism of surrounding rock of the mining roadway is revealed. The results showed that the size and morphology of the plastic zone were closely related to the confining pressure ratio (η). Taking the boundary of η valuing 1, the larger or smaller η value was, the more serious the deformation and failure of surrounding rock would be; the morphology of the plastic zone changed with the deflection of the principal stress, with the location of the maximum plastic zone influenced by the principal stress direction. For the surrounding rock control in the mining-influenced roadway, it is advised to take the following methods: firstly, it is necessary to consider how to reduce or remove the influence of mining on surrounding rock, improve the stress environment of surrounding rock, and reduce the failure depth of the plastic zone, so as to better maintain the roadway. Secondly, in view of the deformation and failure characteristics of the mining roadway, the fractional support method of “yielding first and then resisting” should be adopted, which applies the cable supplement support after mining instead of the one-off high-strength support during roadway excavation, so as to control the malignant expansion of the surrounding rock plastic zone and prevent roof falling accidents.

Failure Mechanism and Effect of Nozzle Parameters on Abrasive Water Jet Rock Breaking

Abrasive Water Jet (AWJ) technology has vast application prospects in the assisted drill-blasting of tunnel excavation, with the advantages of fast-breaking speed, low tool wear, less dust, and good mobility. Nevertheless, AWJ technology has some limitations and shortcomings, such as the small effective fracturing range and parameter mismatch, which influence the fracturing effect of AWJ. To solve the abovementioned issues, it is necessary to study the failure mechanism of rock impacted by AWJ and nozzle parameter effects on rock fragmentation. Based on the coupling algorithm of Smooth Particle Hydrodynamics and Finite Element Method (SPH-FEM), in this research, the numerical model of AWJ impacting rock was established, and the result was verified with Computed Tomography (CT) scanning after the AWJ impacting rock experiment and image processing technology. Through the analysis of the stress characteristics of typical particles in the rock model at different stages and positions, the formation and expansion mechanisms of the crater and the cracks were revealed. Additionally, in this research, the comprehensive damage factor of rock (X) representing the fragmentation degree was defined. By comparatively analyzing X-values with certain technical parameters of AWJ, the importance ranking of the nozzle parameters, the effect of each nozzle parameter on the rock fragmentation, and the optimal parameter combination were also investigated.

Investigating the Effects of Rock Failure Mechanism on its Bearing Capacity Using the Three Dimensional Particle Flow Code (PFC3D)

One of the most important issues in geotechnical studies is bearing capacity. It is also defined as the resistance when the maximum pressure is exerted from the footing to the foundation without creating shear failure therein. Since earing capacity is highly correlated with the stability of surface and subsurface structures, researchers have become interested in this subject. The area and geometry impacts on the footing are considered as the two important issues in this regard. In this research, a numerical model based on particle flow code was used in PFC3D software. To do experiments in numerical models, two triple-facet footings were utilized in square, rectangular and circular geometric shapes. Furthermore, these footings held a total area of 64 cm2 and other series included a full area of 49 cm2. In the modeling, the mechanical properties of granite were put into practice and the results of the numerical tests were scrutinized, as well. As a result, it was ascertained that the bearing capacity depends on both the footing geometry and the footing area.

Failure mechanism of fractured rock and associated acoustic behaviors under different loading rates

Mechanical and associated temporal-spatial microcracking behaviors of fractured sandstones, a hard and stiff rock, were tested and observed under different uniaxial loading rates with the aid of acoustic emission (AE) monitoring. Based on the principle of microcracking nucleation and multiple locked-patches failure theory borrowed from seismology, some experimental phenomena during crack propagation process, AE generated mechanisms as well as the static loading rate effects of loaded fractured rock were illustrated semiquantitatively. Results show that there are significant static loading rate effects on the mechanical, acoustic and microcracking process of fractured hard rock. With the loading rates increase, the dominant failure modes of fractured sandstones change from mode-II shear to mode-I tensile fracture. Acoustic signals gradually increase with the applied axial stress. Especially, in the meta-instable stage, AE counts show repeated “suddenly increasing then quiet” features which can be used for the early-warning of rock catastrophic failure. The failure of rock mass can be considered as the continuous brittle fracture of locked-patches inside. And each locked-patch rupture corresponds to a drop of stress and an extremum value of AE counts.

Failure Process of Rock Strata Due to Multi-seam Coal Mining: Insights from Physical Modelling

With an increasing number of multi-seam mining projects, the problem of strata movement caused by multi-seam mining has attracted increasing attention. Previous studies have shown that the rock failure mechanism for multi-seam mining is obviously different from single-seam mining. When a lower coal seam is being mined, two issues are apparent: the activation that the upper goaf will suffer and the difference in the break mechanism of the stratum between single-seam and multi-seam mining. The research regarding these two issues is still inadequate. In this paper, a physical model experiment was used to simulate the full longwall mining process of multiple seams. Then, the failure mechanics of the stratum and the influence of mining the lower coal seam on the activation of the upper goaf are discussed under the condition that the upper coal seam has been fully mined. The results show that a part of the fracture zone that formed by mining the upper coal seam will be converted into a caving zone when the lower coal seam is mined. In multi-seam mining, the cracks in the overlying fractured rock mass will widen and propagate upward. During the process of mining the lower coal seam, the interburden rock mass presents a typical plate bending failure, and the break location is greatly affected by the distribution of the periodic weighting in the upper coal seam mining. Multi-seam mining will cause the surface subsidence trough produced by upper coal mining to move towards the end of the mining panel. The mechanism of rock stratum movement revealed by the test has a certain practical guidance for the control of roof pressure in multi-seam mining and the subsidence of surface.

Strength Characteristics and Failure Mechanism of a Columnar Jointed Rock Mass Under Uniaxial, Triaxial, and True Triaxial Confinement

Columnar jointed basalt is a composite rock mass consisting of many prismatic rock blocks with irregular polygons in the transverse section. Similar material was used to simulate a columnar jointed rock mass with different dip angles (β = 0°–90°), and uniaxial compression, triaxial compression and true triaxial unloading tests were conducted to determine the anisotropic properties, and unloading failure mechanism of jointed basalt rock. The results show that the dip angle has significant effects on the strength anisotropy of the columnar jointed rock mass. The stress–strain curves under uniaxial and true triaxial unloading indicate strain softening, and the stress–strain curves under triaxial compression reflect strain hardening. The specimen with β = 60°–75° has the lowest strength and is most sensitive to the confining pressure. The analysis of the failure mode and failure mechanism of the columnar jointed rock mass under different load conditions indicate that the failure mode can be divided into three types: stress-controlled failure, structure-controlled failure, and stress-structure-controlled failure. The peak stress growth coefficient is higher under triaxial compression than under true triaxial unloading. Finally, the applicability of different strength criteria to the columnar jointed rock mass is analyzed by evaluating the fitting accuracy and comparing the test results with measured data. Regression analysis demonstrates that the Mogi-Coulomb strength criterion is better suited to the study data than the Drucker-Prager strength criterion. The research results have reference significance for the stability analysis of excavated tunnels in columnar jointed rock masses.

Experimental study on the mechanical and permeability behaviors of limestone under hydro-mechanical-coupled conditions

In situ stress and underground water are known to significantly influence the deformation and stability of deep underground caverns. These factors should be considered in the design of excavation and supporting schemes. However, the rock failure mechanism and permeability characteristics under the coupling condition remain largely unexplained. Based on the Xianglushan diversion tunnel in Central-Yunnan Water Diversion Project, we conducted triaxial compression experiments on both intact rock specimens and cracked rock specimens with three confining pressures (11 MPa, 18 MPa, and 25 MPa) and three osmotic pressures (2 MPa, 6 MPa, and 10 MPa). The experimental results show that rock strength can be expressed as a function of confining pressure and osmotic pressure. Osmotic pressure can reduce rock strength, while the effect of confining pressure is opposite. With the increase of osmotic pressure, the initial permeability and the peak permeability increase. Compared with the stress-strain curve, the variation of permeability-strain curve is “hysteretic.” For cracked specimens, the stress-strain curve after failure presents a “step down” trend, and the permeability-strain curve appears a “bimodal shape.” The failure pattern changes from shear failure to tensile failure as the osmotic pressure increases. With the increase of osmotic pressure, the crack increases gradually and becomes tortuous and rough. The generation and propagation of cracks gradually develop towards vertical load.

Micro-failure process and failure mechanism of brittle rock under uniaxial compression using continuous real-time wave velocity measurement

In this study, the micro-failure process and failure mechanism of a typical brittle rock under uniaxial compression are investigated via continuous real-time measurement of wave velocities. The experimental results indicate that the evolutions of wave velocities became progressively anisotropic under uniaxial loading due to the direction-dependent development of micro-damage. A wave velocity model considering the inner anisotropic crack evolution is proposed to accurately describe the variations of wave velocities during uniaxial compression testing. Based on which, the effective elastic parameters are inferred by a transverse isotropic constitutive model, and the evolutions of the crack density are inversed using a self-consistent damage model. It is found that the propagation of axial cracks dominates the failure process of brittle rock under uniaxial loading and oblique shear cracks develop with the appearance of macrocrack.

Rock failure criteria and mechanisms of failure for excavation stability design: a chronological evolution

Failure of rock, when it does occur, follows definite mechanical laws and that its probability, can, at least in some instances, be predicted sufficiently in advance of actual occurrence so as to prevent any great danger to the miner. The article chronologically describes rock failure criteria of some practical and most frequently featured strength criteria for predicting failure mechanism of rocks from rock sample or models (lab scale) to total structure or rock mass breakdown (field scale). A cross section range of criteria, from the typical and indispensable to state of the art ones, categorised under isotropic or anisotropic, stress, strain and energy related failure criteria that are predominantly derived on the basis of Coulomb, von Mises and Griffith theories of failure are reviewed. More attention and discussion has been given to most practical criteria like the Mohr-Coulomb and Hoek-Brown. Evolution of mechanisms of rock failure over time by various authors. The paper demonstrates progression of rock failure criteria, and that current theories hinge on classical ones.

Microscopic Failure Mechanism Analysis of Rock Under Dynamic Brazilian Test Based on Acoustic Emission and Moment Tensor Simulation

The dynamic tensile failure of rock is a main failure mode in deep underground engineering projects. The microscopic failure mechanism analysis of this failure mode plays a key role in dynamic disaster warning. Moment tensor inversion is a very well-known method used to analyze failure mechanisms. However, an acoustic emission (AE) event cannot be accurately distinguished in rock dynamic experiments at the laboratory scale, because there are hundreds of AE events generated within a few hundred microseconds in one dynamic test. Therefore, moment tensor analysis is rarely applied in rock dynamic tests with laboratory scale. In this paper, AE and moment tensor simulations with the discrete element method (DEM) are introduced to analyze the microscopic failure mechanism of rock under a dynamic Brazilian test. Comparing the simulation results of AE and moment tensor analysis with the simulation results of micro-crack with DEM, the moment tensor discriminant method can obtain the mechanical mechanism and energy level of micro-cracks. Furthermore, R, which is the ratio of isotropic and deviatoric components of the moment tensor, is used to analyze the AE source mechanism. The implosion, shear, and tensile of the AE source mechanism can better explain the evolution process of main axial crack and the shear failure zones of the Brazilian disc specimen under dynamic tensile simulation. These findings contribute to a better understanding of the microscopic failure mechanism of rock under a dynamic tensile test than the statistical types of micro-cracks based on break bonds with DEM.

Influence of radial stress on strainbursts under true triaxial conditions: Insights from a distinct element modelling

The radial (minimum) stress of the near-boundary rockmass in deep excavations plays a key role in inducing rock failures such as spalling and strainbursts. In this study, a strainburst is treated as a structural failure of the near-boundary rockmass. The influence of the radial stress acting asymmetrically on one boundary surface of the burst volume on strainbursts is numerically investigated using a 3D bonded block distinct element method (DEM). The 3D DEM model for simulating the overall process of strainbursts is introduced and its effectiveness is verified by comparing with the analogous true triaxial experiments. Then based on the simulation results, the influence of radial stress on strainbursts is studied from the perspectives of deformation and strength characteristics, fracturing process, crack development, failure mode and energy balance. In addition, discussions of the mechanisms of the influence of radial stress on strainbursts are presented from the perspectives of fracture mechanics and a graphical explanation. Results show that, as the radial stress increases, the strength of the strainburst sample exhibits a quadratic law that increases first and then decreases, the number of shear cracks increases remarkably, the degree of accumulated rock damage precedes burst is getting higher and higher, the failure mode of strainbursts transforms gradually from a tensile-type to a shear-type, and the kinetic energy is getting higher and higher. The fundamental influence of radial stress on strainbursts is concluded as its suppression effect on the tensile failure mechanism of brittle rocks.

Effects of dynamic strain rate on the energy dissipation and fragment characteristics of cross-fissured rocks

Internal initiation and propagation of micro cracks in rock materials might result in macroscopic fragmentation and energy dissipation under dynamic strain rate. Understanding the internal mechanism of rock failure and energy consumption is significant in assessing the stability of engineering rock mass under dynamic disturbance. This study experimentally investigated the energy dissipation and fragment distribution of rock specimens containing symmetrical and asymmetrical cross fissures under static and dynamic loadings. Our results reveal that the dynamic strength of rock specimens evidently increases with increasing strain rate, while the dynamic elastic modulus does not depend on the loading rate. For a given dynamic strain rate, the rock specimens containing asymmetrical cross fissures (one of the fissures had a relatively large dip angle) had higher dynamic strengths than those containing symmetrical cross fissures. During loading process, tensile cracks and shear cracks significantly affect the failure patterns of cross-fissured rock specimens under static and dynamic loadings, respectively. All the cross-fissured specimens show similar “X” shaped shear failure mode regardless of fissure configuration subjected to dynamic strain rate. The cross-fissured rock specimens with higher strain rates feature smaller location parameter and scale parameter of the fragment size distribution by GEV fitting. The fractal dimension of cross-fissured specimens show an evident loading rate dependence, and the size distribution of the fragments in asymmetrically cross-fissured specimens under dynamic loading is most homogeneous. The dissipated energy density of all the rock specimens obviously increase as the dynamic strain rate increases, while the energy utilization efficiency is less affected by the strain rate.

Instability Modes and Stability Analysis of Perilous Rock Groups with Control Fissures Under the Conditions of Excavation and Rainfall

Influenced by external factors, perilous rock is prone to evolve into geo-hazard. Prevention and control design of geo-hazard is closely related to the correct quantitative analysis of the stability as well as in-depth study of the instability mode. As the main rock, limestone is widely exposed in the study area, which has resulted in perilous rock groups with control fissures at trailing edges. Monitoring data and investigation reveal that rainfall and roadway excavation are the main external inducing factors of perilous rock groups. Representative geo-mechanical models of the perilous rock groups were constructed based on the engineering geological investigation. Their mechanical behaviour affected by different inducing factors was analyzed, and the instability mode under the most dangerous condition was examined by the numerical simulation based on the discrete element theory. It is found that influenced by rainstorm and excavation, the overall instability mode of perilous rocks with specific geological structure can be divided into sliding and toppling tensile-shear failure. Furthermore, the overall stability of perilous rocks corresponding to these two modes was quantitatively analyzed using the limit equilibrium and fracture mechanics theories. The calculation results are considered to be reasonable and reliable due to the good agreement of the calculation theories with the failure mechanism of perilous rocks.