Damage Characteristics Of Rock Research Articles

Constitutive Characteristics of Rock Damage under Freeze–Thaw Cycles

Freeze–thaw effect is one of the most important environmental conditions that rocks may be subjected to. Through laboratory model tests, the damage characteristics of rocks under the FTC were studied. Based on assuming that the strength of rocks subject to the FTC follows the Weibull distribution, the cumulative damage variable of the number of FTCs was introduced. A cumulative damage constitutive model of shear strength attenuation of rock that meets the Mohr–Coulomb criterion is established. The rationality and applicability of the proposed damage constitutive model are verified by comparing the results of rock shear strength parameters under cyclic freeze–thaw loads.

Damage characteristics of rock induced by unloading in hole under true triaxial boundary stresses: Experimental study

In order to study the effect of unloading of underground rock excavation on the stability of surrounding rock, the true triaxial compression (TTC) and coupled true triaxial compression and in-hole loading-unloading tests (TTC-HU) were conducted on hollow cubic rock (100mm × 100mm × 100mm). The experimental results indicate that the compressive strengths of the specimens increase as confining pressure increases in the equal biaxial stressand increase with increasing intermediate principal stresses in the unequal biaxial stress. At low confining pressure (σ < 30 MPa), the internal stress at unloading damage in the hole of hollow cubic specimen increases with the increase of the three-directional boundary stresses. At high confining pressure (σ ⩾ 30 MPa), the specimen will not be damaged during the entire unloading process in the hole. The damage mode of the specimen is dominated by tensile damage. The shape of the holes in the specimens did not significant change, and hole wall of specimen have layered destruction along the circumference in low confining pressure. In high confining pressure, the hole area of the specimen undergoes significant deformation damage, forming a V-groove along the direction of the minimum principal stress, and the wall of the hole is completely peeled off. This study can reasonably predict the actual engineering damage patterns and guide the optimization of surrounding rock support.

Damage analysis and safety control of surrounding rock around peripheral hole of diversion tunnel

The control of overbreak in blasting excavation is a significant technical challenge and a subject of extensive research in the field of engineering. This study examines the damage characteristics of the surrounding rock in a tunnel section through blasting test and numerical simulation conducted as part of the San Gavan diversion tunnel project in Peru. The orthogonal test of peripheral holes under the influence of explosive spacing, blasthole spacing and smooth blasting layer thickness was designed to analyze the characteristics of rock damage under different parameter combinations and the influence of various factors on rock damage. Based on the USBM formula, this paper deduces a mathematical model considering blasthole spacing and explosive spacing to predict the rock damage range. The main conclusions are as follows: on the tunnel section, the average damage range of vault and arch springer is slightly larger than that of spandrel and haunch. For a single blasthole, the rock damage range in different sections is: explosive > air > stem, and the degree of rock damage at the bottom of blasthole is the highest. Smooth blasting layer thickness has a significant effect on rock damage rate on the side of non-reflect boundary. When smooth blasting layer thickness is 45 cm and 55 cm, the boundary conditions of numerical model have a significant effect on the rock damage. The reflection of blasting stress wave on the free surface leads to the further increase of rock damage range. The blasthole spacing and explosive spacing have a significant effect on rock damage range on the side of non-reflect boundary, and both show a negative correlation. Based on the prediction model of rock damage, the combination of peripheral hole parameters satisfying the standard is obtained, which provides guidance for blasting design.

Discontinuous fracture behaviors and constitutive model of sandstone specimens containing non-parallel prefabricated fissures under uniaxial compression

The deformation and damage laws of non-homogeneous irregular structural planes in rocks are the basis for studying the stability of rock engineering. To investigate the damage characteristics of rock containing non-parallel fissures, uniaxial compression tests and numerical simulations were conducted on sandstone specimens containing three non-parallel fissures inclined at 0°, 45° and 90° in this study. The characteristics of crack initiation and crack evolution of fissures with different inclinations were analyzed. A constitutive model for the discontinuous fractures of fissured sandstone was proposed. The results show that the fracture behaviors of fissured sandstone specimens are discontinuous. The stress–strain curves are non-smooth and can be divided into nonlinear crack closure stage, linear elastic stage, plastic stage and brittle failure stage, of which the plastic stage contains discontinuous stress drops. During the uniaxial compression test, the middle or ends of 0° fissures were the first to crack compared to 45° and 90° fissures. The end with small distance between 0° and 45° fissures cracked first, and the end with large distance cracked later. After the final failure, 0° fissures in all specimens were fractured, while 45° and 90° fissures were not necessarily fractured. Numerical simulation results show that the concentration of compressive stress at the tips of 0°, 45° and 90° fissures, as well as the concentration of tensile stress on both sides, decreased with the increase of the inclination angle. A constitutive model for the discontinuous fractures of fissured sandstone specimens was derived by combining the logistic model and damage mechanic theory. This model can well describe the discontinuous drops of stress and agrees well with the whole processes of the stress–strain curves of the fissured sandstone specimens.

Energy transfer efficiency and rock damage characteristics of a hydraulic impact hammer with different tool shapes

The energy transfer efficiency and damage characteristics are the theoretical basis for the selection and optimization of hydraulic impact hammer tools. In this paper, quarter three-dimensional models of the piston-tool-rock system are established based on the continuum and discontinuum element method. The incident and reflected stress waves and rock damage characteristics obtained from the simulation model are in good agreement with experimental and theoretical results. The effects of piston impact velocity, tool shape, rock strength, confining pressure and repeated impacts on rock damage zone and energy transfer efficiency between tool and rock are analyzed. The force-penetration curves and penetration coefficients under different impact velocities, rock strength, and confining pressure conditions are obtained. The results illustrate that the energy transfer efficiency and penetration coefficient increase with the increase of rock strength, confining pressure and tip area of tool, but decrease with the increase of impact velocity. Based on the simulation results, a prediction formula for penetration force with consideration of the shape of the tool tip is proposed and the calculation accuracy is verified. Finally, the proportion of energy actually used for rock fracturing is analyzed.

Experimental study of the damage characteristics of rocks containing non-penetrating cracks under cyclic loading

The damage evolution process of non-penetrating cracks often causes some unexpected engineering disasters. Gypsum specimens containing non-penetrating crack(s) are used to study the damage evolution and characteristics under cyclic loading. The results show that under cyclic loading, the relationship between the number of non-penetrating crack(s) and the characteristic parameters (cyclic number, peak stress, peak strain, failure stress, and failure strain) of the pre-cracked specimens can be represented by a decreasing linear function. The damage evolution equation is fitted by calibrating the accumulative plastic strain for each cycle, and the damage constitutive equation is proposed by the concept of effective stress. Additionally, non-penetrating cracks are more likely to cause uneven stress distribution, damage accumulation, and local failure of specimen. The local failure can change the stress distribution and relieve the inhibition of non-penetrating crack extension and eventually cause a dramatic destruction of the specimen. Therefore, the evolution process caused by non-penetrating cracks can be regarded as one of the important reasons for inducing rockburst. These results are expected to improve the understanding of the process of spalling formation and rockburst and can be used to analyze the stability of rocks or rock structures.

Investigation on damage creep constitutive model of rock under the coupled effect of freeze–thaw cycles and loading

AbstractThe investigation on damage creep properties of rock under freeze–thaw conditions are essential for assessing the long‐term stability of rock mass engineering in cold regions. This research analyzed the damage characteristics of rock under the coupled effect of freeze–thaw cycles and loading; the damage variable under the coupled effect of freeze–thaw cycles and loading was proposed. A damage creep constitutive model was developed, and the determination method for the model parameters was proposed. The rationality of the model was calibrated using test data, and the calculation results of the proposed model were compared with classical Nishihara model. Additionally, the research analyzed the variation of model parameters with the number of freeze–thaw cycles and discussed the damage creep mechanisms of rock under the coupled effect of freeze–thaw cycles and loading.

Rock fracture mechanism of air-deck charge blasting considering the action effect of blasting gas

This paper primarily focuses on examining the impact of blasting gas, studying the rock fracture mechanism of air-deck charge blasting, and analyzing the evolutionary characteristics of blasting stress, the law of damage distribution, and the fracture characteristics in rock specimens. Firstly, indoor blasting model experiments are conducted and analyzed by combining the computed tomography (CT) scanning method, three-dimensional (3D) reconstruction technology, and fractal damage theory. The experimental results indicate that the distribution characteristics of rock damage in air-deck charge blasting are mainly determined by factors such as charge segment position, air-deck length, and position. Next, a numerical simulation method based on the coupling analysis of Lagrangian finite element and Euler finite volume is proposed to enable the numerical simulation of rock blasting fracture while considering the action effect of blasting gas. The analysis of the numerical simulation results reveals that the rock failure near the blasthole, under the influence of blasting gas, is primarily due to tensile failure, whereas the rock failure in the distant area is predominantly caused by shear failure. Furthermore, during the process of rock fragmentation by blasting gas, the initial interaction between the blasting gas and rock is the main controlling factor for rock damage and failure, whereas the subsequent reflection and transmission of blasting gas have a relatively minor impact on rock damage and failure.

Analysis of spatial damage characteristics of rock under multiple high-voltage pulse discharges: I. Cross-section characteristics

Rock breaking by high-voltage pulse discharge (rock breaking by high-voltage pulse discharge, RHPD) is an efficient technology for rock breaking. A single discharge will lead to the initiation or expansion of cracks inside the rock, and the expansion of cracks after multiple discharges will lead to the destabilization of the rock and finally produce a fractured zone. Because of the difficulty in quantifying the spatial damage characteristics of the fractured zone, in this paper, based on the discrete element method and theoretical analysis, the spatial damage model (spatial damage model, SDM) of rock is established. For a typical liquid-solid combination, from the microscopic point of view, the damage characteristics of the fractured zone on the radial cross-section of the plasma are quantified. The changing characteristics of the damage characteristics were analyzed for multiple discharges. In addition, an experimental platform has been built, and the accuracy of the SDM has been verified by the experimental results. The results show that the increase in the discharge distance will improve the deposition energy and crushing effect, and will also improve the accuracy of the model. The findings of this paper provide a technical reserve for the application of RHPD.

Chemical Corrosion-Water-Confining Pressure Coupling Damage Constitutive Model of Rock Based on the SMP Strength Criterion.

Aiming at the problem of chemical-mechanics-hydro (C-M-H) action encountered by rocks in underground engineering, chemical damage variables, water damage variables, and force damage variables are introduced to define the degree of degradation of rock materials. Stone is selected as the sample for acid corrosion treatment at pH 3, 4, and 7, and a chemical damage factor is defined that coupled the pH value and duration of exposure. Then based on the spatial mobilized plane (SMP) criterion and the Lemaitre strain equivalence hypothesis, this research develops a constitutive model considering rock chemical corrosion-water-confining pressure damage. The proposed damage constitutive model employs the extremum method to ascertain the two Weibull distribution parameters (m and F0) by theoretical derivation and exhibits satisfactory conformity between the theoretical and experimental curves. The damage constitutive model can be consistent in the stress-strain characteristics of the rock triaxial compression process, which verifies the rationality and reliability of the model parameters. The model effectively represents the mechanical properties and damage characteristics of rocks when subjected to the combined influence of water chemistry and confinement. The presented model contributes to a better understanding of tangible rock-engineered structures subjected to chemical corrosion in underwater environments.

Study of rock damage characteristics in decoupled slit charge blasting based on computer tomography scanning

Controlling blast load damage and destruction of the remaining rock mass in rock blasting has been the focus of scientific research. By studying various decoupling ratios of the slit charges, blasting experiments and numerical calculations of the small charge were carried out on the glauconite specimen. The internal fracture and damage characteristics of the damaged specimens (post blast) were quantified by computed tomography (CT) scanning and three-dimensional (3D) model reconstruction. The results showed that the damage to the glauconite specimens was mainly radial, with the main crack surface in the slit direction and the “X-type” and “Y-type” non-slit directions. With the increase in the decoupling ratio of the slit charge, the fractal dimension of the explosion crack face tends to increase, and the degree of damage gradually increased; When the decoupling ratio was 1.67, the fractal dimension of the explosive crack surface decreased, the smallest degree of damage. LS-DYNA simulation software was used to study the dynamic fracture process and the effective stress peak of the blasthole wall in the slit and non-slit directions for different decoupling ratios of the slit charge. The numerical calculation results showed that with the increase in the decoupling ratio, the peak effective stress of the blasthole wall characteristic unit in the slit direction was larger than that in the non-slit direction; The effective stress peak showed an increasing trend, and the maximum peak effective stress was 567.7 MPa when the decoupling ratio was 1.67. Therefore, this method can be a suitable means to reconstructing the spatial distribution of internal cracks and numerical calculation to evaluate the damage mechanism of slit charge blasting; Furthermore, within the range of the optimal slit charge decoupling ratio, this method can guide the site to prevent the damage and destruction of the remaining rock mass, allowing for more, allocation and utilization of the explosion energy.

Damage Characteristics and Energy Evolution of Bituminous Sandstones under Different Cyclic Amplitudes

In many underground engineering projects, rocks are often subjected to cyclic loading and unloading, such as repeated excavation of roadway surrounding rock, which will lead to damage to underground rocks, and the energy of rocks also changes. Therefore, to study the energy evolution and damage characteristics of rocks under cyclic loading and unloading, different cyclic loading and unloading tests of bituminous sandstones under constant amplitude were conducted. Under cyclic loading and unloading, the lower limit stress was 40% of the rock peak intensity, the cyclic amplitude was 20–40% of the peak intensity, and the number of loading–unloading cycles was 10–30. The quantitative characterization of the damage degrees of bituminous sandstone was realized by the ultrasonic wave velocity and elasticity modulus methods. The energy evolution and damage characteristics of bituminous sandstone under different amplitudes and number of loading–unloading cycles were investigated through the energy dissipation method. Results showed that under cyclic loading and unloading, the ultrasonic wave velocity and elasticity modulus of bituminous sandstone decreased gradually; The damage variable shows a trend of rapid and then stable growth and has a power function relationship with the number of cycles; The input energy density and dissipation energy density curves were in L-shaped distribution, whereas the elastic energy density remained stable. The results of this study can provide some theoretical references to underground engineering construction.

Damage properties of basaltic rocks under multilevel stress loading and microwave irradiation

The deterioration of mechanical strength and damage characteristics of rock under microwave is the primary focus in evaluating the applicability of microwave-efficient rock-breaking technology. This study analyzed the mechanical strength deterioration and damage characteristics of basalt under microwave irradiation and performed an X-ray digital radiography (DR) image analysis of the damage process of basalt under a multilevel stress loading (MSL) path. The research results show that basalt with a large porosity had a better thermal effect on microwave irradiation and significantly enhanced the resistance to deterioration. The microwave thermal effect of polar minerals is critical to plastic failure behavior. This study also proposes a rock damage characteristic evaluation model based on X-ray DR image quantitative analysis and X-ray absorption dose threshold segmentation. The image analysis model can accurately describe the evolution process of rock damage characteristics. A modified model for basalt damage characteristic analysis is provided. The elastic–plastic damage model based on the Cast3M finite element software was compared with the proposed damage model based on X-ray DR images. The calculated results show that the change in the damage zone was consistent with the damage crack propagation process of basalt. Therefore, the proposed damage evaluation model can provide guidance for the scientific evaluation of the adaptability of microwave-assisted tunnel boring machine (TBM) efficient rock-breaking technology.

Effect of strong dielectric substances on the damage characteristics of rocks exposed to microwave radiation: Insight from experiments and mechanisms

It has been demonstrated that microwave pretreatment can weaken rocks, reduce tool wear, and improve mechanical rock breaking efficiency. The dielectric properties of rock minerals are a major factor affecting the ability of rocks to absorb microwaves, so it is important to conduct experimental research on rock modification to improve the microwave absorption capacity of rocks. The concept of “microwave-assisted absorbing reagents” has been proposed to increase the microwave absorption capacity of rocks. Sandstone specimens are first pretreated with strong dielectric substances before being exposed to microwave radiation to increase their microwave absorption capacity, then they are exposed to microwave fields and finally conducted to uniaxial compression tests. Enhancement in microwave absorption capacity of sandstone specimens is showed by P-wave velocity, nuclear magnetic resonance, and mechanical tests before and after microwave treatment. The results showed that barium titanate suspension and water are both effective microwave-assisted absorbing agents. The specimens treated with barium titanate suspension exhibited better microwave absorption capacity; in 5 kW microwave power irradiation, its p-wave velocity falls by 14.04%, porosity rises by 25.43%, and uniaxial compressive strength falls by 24.98%. Additionally, the failure form of sandstone specimens changes from brittle to plastic once it has fully absorbed microwave energy.

Research on the Characteristics of Acoustic Emission Activities of Granite and Marble under Different Loading Methods

Abstract At present, there is no corresponding standard for the engineering application of rock acoustic emission technology. To better apply acoustic emission technology to engineering practice, in this paper, the acoustic emission characteristics of different rock samples of marble and granite under uniaxial compression were analyzed by indoor acoustic emission test, the factors affecting the acoustic emission characteristics of rocks are studied, and the failure mechanism and damage characteristics of rock are discussed. The research contents include analyzing the curve fitting relationship between the acoustic emission event rate, the number of events, the stress time, and study of the similarities and differences of acoustic emission characteristics of marble and granite; analysis of damage characteristics of marble and granite based on acoustic emission parameters; by analyzing the relationship between the Felicity ratio of different rocks and the stress level during cyclic loading, the applicability of studying the Kaiser and Felicity effects of rocks; variation of acoustic emission event rate and rock peak intensity under different loading methods and loading rates. The results show that the acoustic emission of marble and granite has experienced the initial compaction zone, the rising zone, the peak zone, and the falling zone, and the two kinds of rocks have different acoustic emission phenomena in different stages, and the duration of each stage is also different; before the instability of the two kinds of rocks, there is a quiet period of acoustic emission, and the higher the rock strength, the longer the duration of this quiet period, which means that the calm period can be used as a precursor feature of rock mass instability for disaster prediction; during the cyclic loading process of rock, the damage development law is divided into three stages: initial stage, stable stage, and instability stage. When the Kaiser effect did not appear for the two rock stresses before 20%, between 20% and 70% of the peak strength, the Kaiser effect is obvious. When the stress exceeds 80% of the peak value, the Kaiser effect fails, and the Felicity effect appears; the variation of the loading rate affects the variation of the acoustic emission event rate, and the increase of the loading rate leads to aggravated rock damage. The theoretical stress-strain curve can reasonably reflect the actual stress-strain characteristics of rock by combining the number of acoustic emission events with the rock damage model. The results are consistent with the acoustic emission test, which verifies the inevitable relationship between acoustic emission and damage to the rock.

Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2

Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2

Predicting the failure of different rocks subjected to freeze-thaw weathering using critical slowing down theory on acoustic emission characteristics

Freeze-thaw weathering effectively deteriorates the physical and mechanical properties of rocks and seriously threatens the stability of engineering projects in cold regions. This study investigates the influence of freeze-thaw action on mechanical behaviors and failure prediction of different rocks i.e., sandstone, marble, and granite. The rock samples were subjected to a quasistatic compressive test, and a real-time acoustic emission (AE) monitoring technique was used to reveal the damage characteristics of rocks treated with 0, and 25 freeze-thaw cycles. The autocorrelation coefficient (AC) and variance of the AE count were then calculated by applying the Critical Slowing Down (CSD) theory, and the precursory features of rocks failure under the action of freeze-thaw were examined. The results unveiled that after the freeze-thaw action, the uniaxial compressive strength (UCS) of sandstone, marble, and granite was reduced by 16.5%, 8.36%, and 7.75% respectively. The AE count and the accumulative count correspond effectively to the failure of different rocks under compressive loading. Even though the samples have shown the same variation for AE count and accumulative count but those subjected to freeze-thaw weathering have shown an earlier rise in both AE counts and accumulative counts. It was noted that the AE signals had a CSD phenomenon. The sudden and significant increase in AC and variance curves of AE count, RA, and AF parameters can be used to predict rock failure. Furthermore, the precursory characteristics of different rocks treated with freeze-thaw weathering were compared. The ratios of the early warning to the main fracture and complete failure in terms of time are the highest for sandstone followed by granite, and marble. Moreover, the precursory points of treated samples were earlier than those of untreated samples. It was concluded from the results that AE counts' early warning precursory characteristics are more noticeable than other AE parameters, especially in the variance curves. Hence, the results of this study will provide significant importance to predicting rock failure in cold regions.

A Study of Constitutive Model of Rock Damage under the Joint Effect of Load and Moisture

To study the mechanical damage characteristics of rock under the effect of subversion, a series of mechanical experiments, including both uniaxial and triaxial mechanical compression experiments under various levels of water content were performed. In this study, researchers investigate the impact of water content on the mechanical characteristics of rock, based on the compliance of the rock damage variants to the Weibull statistic distribution, and Drucker–Prager strength rule, aiming to construct a constitutive model under the joint effect of load and moisture. In addition, the established constitutive model is tested in the experiment. According to the test results, during the initial phase of the submersion, the water content in the rock increases following the exponential function until reaching the threshold. The water content remains stable after the threshold. Under the uniaxial and triaxial loads, the damage detected in the rock and the elasticity modulus decreases linearly as the water content increases. The rock’s mechanical parameters and the damage evolution rate are significantly impacted by the surrounding pressure. As the surrounding pressure increases, the weakening effect of the water in the rock decreases. The theoretic curves developed to describe the rock damage under the joint effect of the water and load are consistent with the curves drafted based on the test, indicating that the constitutive model can accurately describe the stress and strain behaviors of rock under various water contents and loading conditions.

Dynamic damage characteristics of rock under multiple loads during high-voltage pulse fragmentation

To analyze the damage characteristics of rocks during high-voltage pulse fragmentation (HVPF), two kinds of loads, shockwave and cavity, are determined by optical observation, and the pressure–time characteristics of these two and their mechanism of damage to rocks in mesoscopic view are analyzed. A model of dynamic damage characteristics of brittle rock under multiple loads is established, which includes numerical calculation and discrete element simulation. In the discrete element simulation, the rock is simplified as a circular region without reflection boundary with a certain size of the circular hole inside, and the grains in the region are discretized as rigid spheres with a definite bonding relationship. The shockwave is considered the time-varying pressure loaded to the grains of the circular hole, and the cavity is considered the quasi-static pressure loaded to the grains on both sides of the fracture. The results of the model show that shear cracks and tensile cracks are produced during the shockwave action, but tensile cracks are predominant. The shockwave acts as a preload for the expansion of cracks, and the damage radius is small. Most of the cracks in HVPF are caused by the cavity. A comparison of the numerical calculation results with the discrete element simulation results shows that the model can describe the distribution characteristics of cracks under multiple loads, which lays a foundation for further analysis of the internal mechanism of HVPF.

Experimental and Numerical Investigation of the Damage Characteristics of Rocks under Ballistic Penetration

Rock penetration is an inevitable problem in the study of drilling and projectile penetration. The penetration resistance of red sandstone and limestone was investigated at projectile speeds ranging from 600–1200 m/s. The damage characteristics of these rocks were studied via experimental tests and numerical simulations. The damage condition of the target surface, internal damage state and crack distribution were obtained. It was concluded that the maximum error of the numerical simulation and experimental results was not more than 10%. The penetration resistance of limestone was approximately 23.8% stronger than that of red sandstone. However, the energy absorption effect of limestone was weaker than that of red sandstone, and large cracks can be more easily formed. The compaction area of red sandstone was softer, with obvious crack compaction in the crater area, and particle detachment can more easily occur. Red sandstone was more sensitive to the impact angle of the projectile. With oblique penetration, the projectile was more likely to deflect inside the red sandstone target.