Stability Of Rock Engineering Research Articles

Mechanical Properties and Acoustic Emission Characteristics of Anchored Structure Plane with Different JRC under Direct Shear Test.

Rock mass, the heterogeneous natural material composed of rock and discontinuities, is an important part of engineering construction. Discontinuities affect the mechanical properties of natural rock mass and further threaten the stability of rock engineering. To study the failure characteristics of anchored structure plane with different JRC, jointed specimens with four different JRC were fabricated by pouring cement mortar. Specimens were tested under four different normal loads to figure out how JRC and anchorage angle affect the mechanical properties of anchored structure plane. Besides, acoustic emission (AE) testing technology was adopted to explore the AE characteristics of anchored structural plane under shearing. The results showed that there exists a positive correlation between the peak shear strength and JRC. The undulation shape of structural plane led to an obvious downward trend in the strain softening stage of the structural plane with JRC of 6–8 and 18–20. When the anchorage angle ranged from 45° to 60°, the potentiation of bolt was the most significant. Based on the AE results, the larger the normal stress, the more likely the cumulative count curves were to enter the fast growth phase before the peak. The characteristics of b-value curves are mainly related to the topography of structural planes and whether the bolt is deformed. In the direct shear test, the cumulative proportion of shear cracks was more than 85%, which is much higher than that of tensile cracks. The variation of cumulative tensile cracks goes through three stages: slow growth, rapid growth, and slow growth. Compared with the unanchored structural plane, the variation range of real-time tensile cracks of the anchored structural plane is large, and sometimes the proportion of real-time tensile cracks may reach 80%.

Experimental study on the fracture and fatigue behaviors of flawed sandstone under coupled freeze–thaw and cyclic loads

This paper investigates the effects of coupled freeze–thaw (FT) cycles and cyclic loads on the mechanical properties, cracking behaviors and fatigue damage mechanism of flawed rocks. The digital image correlation technology is used to monitor the real-time cracking process and to analyze the evolution characteristics of deformation fields for tested samples. The effects of FT cycles and ligament angles on the mechanical evolution properties of flawed rocks subjected to cyclic loads are first analyzed. Secondly, the cracking processes of flawed rocks with different ligament angles subjected to FT cycles are studied in detail. Seven types of cracks including anti-wing crack, wing crack, oblique secondary crack, far-field crack, out-of-plane shear crack, out-of-plane tensile crack and quasi-coplanar secondary crack are observed. Two crack initiation modes including wing crack initiation and anti-wing crack initiation are registered, and seven crack coalescence types in tested samples are discriminated. The apparent displacement fields can be employed to reveal the fracture mechanism of flawed rocks under coupled FT cycles and cyclic loads. Finally, the fatigue damage mechanism of FT cycles coupling with cyclic loading and unloading is discussed in detail. The experimental results are very meaningful to evaluate the safety and stability of rock engineering in cold regions.

Experimental and DEM study on failure behavior and stress distribution of flawed sandstone specimens under uniaxial compression

Rock materials contain various scales of pre-existing flaws that greatly influence the stability of rock engineering. The study of strength and failure behavior of pre-flawed rock enhances the understanding the fracture mechanism of rock. In the present study, uniaxial compression tests were carried out on sandstone specimens containing three pre-existing flaws at various inclination angles. The experiment results indicated that the stress–strain curves, mechanical paprameters, acoustic emission and failure pattern of pre-flawed specimen were affected by the pre-existing flaws. To verify the test results, a PFC modelling was conducted on pre-flawed specimen using a set of calibrated parameters. The stress–strain curve, mechanical paprameters and failure mode of specimen containing three flaws were reproduced in the numerical simulation. Three types of crack, i.e., tensile crack, shear crack and mixed tensile-shear crack, were identified based on the laboratory micro observations and numerical displacement field. As the flaw angle increased from 0° to 90°, the tensile stress concentration gradually deteriorated and transferred from the middle to the tip of pre-existing flaw. The evolution of internal stress surrounding the pre-existing flaw during the crack initiation, propagation and coalescence process was further discussed. This experimental and numerical study aims to investigate the crack characteristic and internal stress evolution in fractured rock.

Crack Propagation Process and Seismogenic Mechanisms of Rock Due to the Influence of Freezing and Thawing

A common problem in cold regions is the influence of freeze–thaw damage on the stability of rock engineering. Therefore, a series of uniaxial compression tests of sandstone after freeze–thaw treatment was carried out in this study. The purpose was to express the initial damage of rock after freezing and thawing treatment more quantitatively and to study the influence of freeze–thaw damage on the rock crack growth process to provide some reference for the stability evaluation of rock engineering in cold regions. The results showed that the number of freeze–thaw cycles and the lowest freeze–thaw temperature had a significant effect on the rock damage and characteristic stress value, and the number of cycles had a more obvious effect: with an increase in the number of freeze–thaw cycles and a decrease in the freeze–thaw temperature, the initial damage DNT had an increasing trend. In addition, the intrinsic mechanism of the freeze–thaw effect on the rock characteristic stress was explained from the perspective of a meso-mechanical mechanism. From the inversion results of the acoustic emission (AE) moment tensor, it was found that the proportion of tensile cracks gradually increased with the increase in the initial damage of the rock in the stable and unsteady stages of the rock crack propagation.

Coupled seepage-damage effect in fractured rock masses: model development and a case study

The stability of rock engineering is generally dominated by existing seepage , particularly the seepage evolution due to the rock masses damage. However, the current research generally overlooks the seepage-damage coupling when studying the hydraulic-mechanical coupling effect in rock masses. This study aims to propose a dual-medium model, including equivalent continuous and discrete fracture media to study the coupled seepage-damage effect in fractured rock masses . The dual-medium seepage model considers the substantial water storage of the fracture network and the high conductivity of major large-scale fractures. Also, the seepage evolution is constructed to be a function of stress, seepage pressure and length of crack propagation in the rock mass. To illustrate the new model's application, a case of high-pressure water injection in a coal seam has been investigated to reveal the damage evolution in the coal seam. The results indicate that during the initial stage of the water injection, the seepage pressure in the discrete fracture medium increases faster than that in the equivalent continuous medium. Moreover, the seepage pressure difference between the two media gradually decreases with the increase of the seepage time, eventually forming a stable seepage field in the coal seam. Notably, the high-pressure water injection in the coal seam significantly affects the distribution of the coal seam's stress field, resulting in the effective minimum principle stress changing from compression to tension states. Also, during coal seam water injection, the damage zone and major fracture apertures in the coal seam gradually increase with increasing injection time .

Experimental investigation on rock mechanical properties and infrared radiation characteristics with freeze-thaw cycle treatment

The effect of freeze-thaw weathering cycles caused by diurnal and seasonal temperature changes is a significant disadvantage in the stability of rock engineering in cold regions. To investigate the evolution rule of rock strength and infrared radiation characteristics of igneous, metamorphic, and sedimentary rock subjected to freeze-thaw weathering cycles, freeze-thaw weathering cycle treatment was conducted on coarse-grained granite, fine-grained marble and soft red sandstone from cold regions in Western China. The nondestructive detection technique of nuclear magnetic resonance (NMR) was used for rock damage detection. Infrared thermography was used to monitor the rock debris movement, crack propagation and average infrared radiation temperature (AIRT) during unconfined compressive strength (UCS) testing. The mechanisms of rock damage and change in AIRT induced by freeze-thaw weathering cycles were carefully analyzed. According to the UCS evolution rule, the ranking order (from high to low) of the results of rock resistance to freeze-thaw weathering processes is as follows: marble, granite and sandstone. An indicator called the infrared radiation rate was proposed to measure the rate of increase in infrared radiation temperature with increasing stress during the UCS tests. The rank order (from high to low) of the infrared radiation rate results is as follows: sandstone, marble and granite. Based on the infrared images and photographs of the failed rock specimens, the failure patterns and processes of the different rock types are investigated.

Related Rule Study of Subcritical Crack Growth and Threshold Values in Transversely Isotropic Slates

Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor K I versus the subcritical crack growth velocity V , the fracture toughness K I C , the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (β) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the β angle. In addition, its fracture toughness is minimal when the β angle of the slates is 45°, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lg K I - lg V relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K 0 / K I C for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.

An elastoplastic model of frost deformation for the porous rock under freeze-thaw

Freeze-thaw action has caused many engineering geology disasters in cold regions, such as frost cracking of tunnel and pavement, rockfall of rock slope, falling off of building materials. The freeze-thaw damage of porous rock is mainly induced by the frost heaving pressure due to pore water freezing. Although some elastic crystallization theories have been proposed to model the freezing process of pore water, the long-term frost heave characteristics under cyclic freeze-thaw are rarely studied. The ice crystallization and frost heave theory under freeze-thaw have been developed in the elastoplastic regime in this study. A novel elastoplastic model has been proposed to estimate the long-term frost heave and frost damage under freeze-thaw. This model has considered the influence of the pore size, yield stress of matrix and degree of water saturation on the development of the frost heaving pressure in pores. During freezing, a plastic region will produce inside the matrix around the pore. This plastic region gradually expands outwards with the increase of this pressure. During thawing, the elastic deformation will be recovered but a considerable residual plastic strain is accumulated. However, the growth rate of the residual plastic strain will decrease under freeze-thaw due to the production of new empty voids. Therefore, the freezing of pore water in porous rock is an elastoplastic problem. Besides, the water saturation and mechanical properties of the porous rock are very important to quantify the frost heave. This study provides a better understanding of the frost damage of the porous rock and a reference for the stability of rock engineering under freeze-thaw in cold regions.

Cracking behavior of rock containing non-persistent joints with various joints inclinations

Non-persistent joints are commonly observed in the rock mass, and play a significant role in the stability of rock engineering. A detailed understanding of the cracking process is critical for the evaluation and control of the stability of surrounding rock. Using a three-dimensional Particle Flow Code (PFC), the influence of the joints inclination on the mechanical behavior and the associated cracking process and displacement field of specimens containing non-persistent joints were investigated in this study. First, the micro parameters used in the PFC3D model were calibrated based on the mechanical properties of the experimental material. Next, cubical specimens containing 9 non-persistent joints were created using the particle deletion method. The results of the simulated compressive experiment show that different joints inclinations result in variations in the mechanical properties and failure modes of specimens containing non-persistent joints. The internal fracture patterns in PFC3D were compared with that of the reconstructed model from X-ray CT scanning. Finally, further detailed research on the cracking process and displacement field mode were conducted to reveal the failure mechanism of specimens containing non-persistent joints with various joints inclinations.

Experimental study on fracture behaviour of three‐flawed sandstone specimens after high‐temperature treatments

AbstractThe crack coalescence of rocks significantly affects the stability of rock engineering, and extensive studies have been performed on preflawed rock specimens without thermal treatment. However, the fracturing behaviour of preflawed specimens after thermal treatment has not been investigated comprehensively. In this study, three‐flawed sandstone specimens with different flaw inclinations after high‐temperature treatments were tested under uniaxial compression. Photographic, acoustic emission and digital image correlation techniques were used to investigate the crack initiation, propagation and coalescence behaviour. Experimental results show that the peak strength, elastic modulus and peak strain of the three‐flawed specimens were lower than those of intact specimens and that they gradually recovered with increasing flaw angle. The peak strength and elastic modulus first increased and then decreased, whereas the peak strain increased with temperature. Noncoalescence, indirect coalescence and direct coalescence were three patterns observed between the two adjacent pre‐existing flaws. Finally, the mechanism of high temperature in alteration of the mechanical properties of sandstone was revealed through microobservations.

Development of a DEM-Based Method for Modeling the Water-Induced Failure Process of Rock from Laboratory- to Engineering-Scale

Abstract The time-dependent hydromechanical behavior of rocks is crucial to assessing the long-term stability of rock engineering, such as reservoir rock slopes and underground waste storage facili...

Shear Failure of Bolted Joints considering Mesoscopic Deformation Characteristics of Rock

In rock engineering of the cold region, there are a lot of rock joints. The shear characteristics of joints play a decisive role in the stability of rock engineering in the cold area. In this paper, based on the numerical simulation method of particle flow, reasonable microscopic parameters are selected for the numerical simulation of the direct shear test of bolted joints. The results show that the shear stiffness and contact modulus are linearly and positively correlated. The greater the contact modulus, the greater the residual stress, the better the synergetic effect between rock and bolt, and the more developed the microcrack. The smaller the contact stiffness ratio, the greater the residual stress. The shear stiffness decreases with the increase in the contact stiffness ratio, and the larger the contact stiffness ratio, the slower the shear stiffness decreases, while the shear strength does not change with the contact stiffness ratio. The contact stiffness ratio has a weak effect on the number of cracks in the model. The shear stiffness increases with the increase in the parallel bond modulus, and the shear strength decreases with the increase in the parallel bond modulus. The binding stiffness is independent of the shear stiffness, and the peak shear stress decreases with the increase in the binding stiffness ratio. The greater the bond stiffness ratio, the greater the number of cracks.

Numerical Investigations on Shear Behavior and Failure Mechanism of Non-persistent Jointed Rocks

The shear behavior of the discontinuities has a significant influence on the stability of rock engineering. In this paper, the numerical and experimental direct shear tests were performed to investigate the shear behavior of non-persistent jointed rocks. Through a comprehensive calibration of shear stress-displacement curves and failure mode, good agreement was successfully achieved. Further numerical analysis was conducted to study the macro–micro failure mechanism. The results indicate that the shear failure of fractured rock mass begins at the end of crack in the rock mass where the crack initiation appears and as the crack expands inward of rock a macroscopic shear fracture zone is formed along the fracture plane finally. The rotation radian of particles appears obvious zoned phenomenon. The particles with larger rotation radian are mainly distributed at the location where the cracks occurred. The process of specimen failure is the process of unceasing redistribution of the rotation radians of particles inside the specimen. The distribution of contact force is obviously regional and directional and the distribution area of crack is always consistent with that of compressive stress concentration. The failure process of rock is the process of energy dissipation within the specimen, and the failure of the specimen is a kind of instability phenomenon driven by energy.

The creep behaviour and permeability evolution of breccia lava in triaxial creep tests

Breccia lava is a comparatively weaken rock material that has been widely distributed in the Southwest China. Its creep behaviour and permeability evolution are significantly important to the long-term safety and stability of rock engineering. This paper presents the experimental results of breccia lava under triaxial creep tests. The microstructure of the breccia lava before and after the creep tests was studied by scanning electron microscopy and optical microscopy. The results suggested that the erosion of calcite induced by pore-water pressure contributes greatly in increasing the permeability in creep stage.

Experimental Investigation on the Shear Properties of Heterogeneous Discontinuities

The shear behaviour of rock discontinuities is a key factor affecting the stability of rock engineering. To study the effect of heterogeneity on the shear behavior of rock joints, laboratory tests were performed on heterogeneous rock joints with different joint roughness coefficient (JRC). As a comparison, two groups of tests were also conducted on the corresponding homogeneous rock joints. Test results showed that, the shear stress–displacement curves of low strength rock joints, heterogeneous rock joints and high strength rock joints with low roughness are all in line with the trend of the typical single peak value curve, while the curves of high strength rock joints with JRC greater than 12–14 accord with the trend of strain hardening curve. The shear displacement corresponding to the peak shear strength of heterogeneous rock joints is smaller than that of the homogeneous rock joints. The shear strengths of the three types rock joints all grow exponentially with the increase of roughness. The shear strength and its growth rate of heterogeneous rock joints were between those of two corresponding homogeneous rock joints. The surface damage of rock joints increases with the increase of JRC and the damage degree of high strength rock joints is more serious than that of low strength rock joints with the same JRC. The surface damage of heterogeneous rock joints presents obvious heterogeneous characteristics.

Development of a damage rheological model and its application in the analysis of mechanical properties of jointed rock masses

AbstractFossil fuel resources (eg, coal, oil, and natural gas) exist in underground reservoirs, where discontinuities are widespread and influence the stability of rock structures. The mechanical behavior of jointed rock masses significantly affects the long‐term stability of rock engineering. A major challenge in this area is to link the time‐dependent deformation with damage influence induced by distribution of joints in rock masses. In this paper, a damage mechanical theory is adopted which deals with several groups of joints distributed in rock masses. Based on the geometrical distribution of joints, a damage model considering the influence of normal vector and area density of joints is used to describe the discontinuities. A damage rheological model for jointed rock masses is developed and programmed in the finite difference software FLAC3D, and an example of jointed rock masses is used to verify the validity of the model. The damage rheological model could predict the visco‐elastic strain which corresponds to primary creep property, visco‐plastic strain which corresponds to steady state creep property, and damage strain which reflects the damage effect of joints to rock masses. Finally, we use this model to predict the displacements and damage zones in the rock masses surrounding an underground opening.

Failure Mechanism and Acoustic Emission Characteristics of Rock Specimen with Edge Crack Under Uniaxial Compression

There are many cracks in rock mass which have a significant influence on the stability of rock engineering. Most of current researches on the failure mechanism of cracked rock are mainly focused on the internal cracks. However, edge cracks around underground openings are common in many engineering fields. Understanding the failure mechanism of rock with edge cracks is essential to assess the stability of underground structures. Rock failure is closely related to the cracking processes and acoustic emission characteristics is deemed as an effective means of monitoring the cracking processes of rock. In this study, a series of numerical simulations utilizing particle flow software PFC2D were performed to investigate the influence of the length and position of edge crack on the failure mechanism and acoustic emission characteristics of rock specimens with edge cracks under uniaxial compression. The results show that: the strength of specimens is sensitive to the change of crack length and position; the directions of crack propagation in each specimen is in good agreement, the different crack tip position and the specimen boundary lead to different failure modes; the influence of crack length on acoustic emission is greater than that of crack position.

Mesoscopic Weakening Feature of Marble During Water Rock Interaction

Research on the water–rock interaction has become an important subject in rock mechanics field, the link between the mineral particles is weakened and the microstructure of rock mass is changed because of chemical corrosion effect after water–rock interaction. In this paper, double torsion testing of marble specimens has been adopt to determine subcritical crack propagation parameters during rock interaction, the morphological characteristics in this process were also quantified while the surface was scanned by a three-dimensional high-accuracy non-contact laser morphology instrument Talysurf CLI 2000. It shows the discreteness and deviation degree of datum plane on the surface of the rock specimens are increased after water–rock interaction, the highness difference decreased and become more coordinated. Meanwhile, the corresponding relationship between stress intensity factor KI and subcritical crack growth velocity v shows that rock interaction speeds up the subcritical crack growth. Those testing results provide a basis for the micro damage mechanism studying for rock engineering stability which are related to hydrochemistry.

Study on Macro–Meso Failure Mechanism of Pre-fractured Rock Specimens Under Uniaxial Compression

There are many fractures in natural rock mass which have a significant influence on the stability of rock engineering. Rock is a kind of aggregate made up of various particles, the research on the meso level can fundamentally reveal the failure mechanism. In order to comprehensively research the effect mechanism of fractures on the failure characteristics of fractured rock, uniaxial compression numerical experiments were conducted based on discrete element method. The macroscopic and mesoscopic mechanical response of pre-fractured rock specimens with varying fracture length and dip angle were studied. The evolution process of macroscopic and mesoscopic physical quantities was obtained. The results show that the macroscopic failure process of fractured rock was an evolution process of rock from the microscopic level to macroscopic level that resulted from the interaction of internal particles under compression loading. In this process, the energy dissipation was also evolving. There was an obvious relativity between the particle rotation radian region-related feature and the distribution location and number features of cracks. The distribution pattern of prefabricated fractures had a great influence on the failure mode and plays an important role in the macroscopic characteristics and the evolution of internal components of pre-fractured rock specimens. Research result is full of important theory significance and engineering value to evaluate the stability of rock engineering.

Study of Influence of Environmental Factors on Deep Shale Creep Properties

In order to study the influence of environmental factors on creep properties of deep shale, a series of creep tests of deep black shales are performed under different environmental conditions, including stress deviation, temperature, and chemical pH value. The influence of these conditions on creep properties of deep shale is studied. The results show that the creep and creep rate of shale will grow with the increase of temperature, stress difference, and acidity‐alkalinity. We get nonlinear creep model of deep shale when pH = 4 and T = 30°C. The critical stress difference of deep shale is no larger than 31.04 MPa when the chemical pH value is 4 and the temperature is 30°C. By scanning shale after corrosion, we know that the effects of chemical pH value on the creep characteristics are mainly determined by the feldspar dissolution and corrosion caused by chemical action. Our work has important theoretical significance and practical value for evaluating rock engineering stability.