Abstract It was found that the crack damage stress threshold, σ cd , is a phase transition point during the deformation process of rock and is equivalent to the unstable fixed point of renormalization group theory. Thus, a relationship exists between the renormalization group theory and the rock deformation process, through which we can investigate the critical behavior of rock deformation. Therefore, an improved renormalization group model, which takes into account the different stress transfer mechanisms that are closer to the actual mechanical processes, is introduced to reveal the critical behavior of the rock deformation process. Finally, a quantitative relationship between the crack damage stress threshold and peak strength, σ critical / σ peak , is theoretically established. To test the theoretical relationship we additionally present experimental results of an investigation of the ratio of the crack damage stress threshold to uniaxial compressive strength, σ cd / σ ucs , based on different rock types. The results show that the overall average and standard deviation of σ cd / σ ucs is 0.80 ( ± 0.10 ) for low-porosity igneous, metamorphic and sedimentary rocks, a figure that is closer to the theoretical solution of σ critical / σ peak from the improved renormalization group model with a stress transfer mechanism of S T M − 1 / r 3 . Our study implies that the σ critical / σ peak ratio may be intrinsic to low-porosity rocks, and therefore can be considered as a reliable predictor of the peak strength of rock samples in the laboratory.
When rock samples are loaded until macroscopic fractures develop, the failure process can be divided into several stages based on axial and lateral strain responses or the acoustic emission sequence during uniaxial compression tests. Several stress thresholds may be identified: the crack closure stress σ cc, crack initiation stress σ ci, crack damage stress σ cd, and uniaxial compressive strength σ ucs; these may be used as a warning indicator for rock rupture. We investigated the crack damage s...
#2Erling Nordlund(Luleå University of Technology)H-Index: 16
The aim of this paper was to compare the stress and strain quantities that are related to the failure–deformation process of hard rock. The data used here was obtained from laboratory uniaxial compression tests performed on different types of Fennoscandian hard rocks. The failure–deformation process quantities were compared at each deformation stage and for each single specimen. Moreover, geological information such as the rock origin process and the rock characteristics of the specimens were st...
Abstract Material characterization is usually based on the stress–strain constitutive laws directly derived from the load–displacement relations of uniaxial compression tests. This approach, which implies a uniform distribution of deformation along the specimen axis and an energy dissipation within a volume, does not permit to correctly describe the mechanical behavior and the damage evolution by varying the structural size and slenderness. In this paper, three different approaches are used to e...
Abstract The damage of an oolitic limestone during quasi-instantaneous compressive tests and multi-step creep tests was studied using an experimental device which enabled the simultaneous and continuous measurement of strains and elastic wave velocities under mechanical loading and controlled hydrous conditions. The simultaneous measurements of five elastic wave velocities (3 P -waves and 2 S -waves) in different directions of propagation and polarisation allowed us to assess the acoustic tensor...
Abstract The micromechanical damage mechanisms induced by coupled thermal and mechanical loadings and their impacts on the evolution of the effective thermal conductivity of brittle rocks are formulated in this study with a homogenization scheme based on the Eshelby solution. The recovery of degraded stiffness due to normal closure of closed microcracks is modeled with an empirical hyperbolic relation between normal deformation and local normal stress. The sliding behavior of the microcracks is ...
Loading rate has an important influence on rock mechanical properties.The influence degree is closely related to the microstructure of rock,loading and unloading paths and states,etc..Based on the uniaxial compression tests of coarse crystal grain marble with nine strain rate levels in range of static loading rate,the influences of loading strain rate on stress-strain curve,failure pattern,strength,elastic modulus,deformation modulus and strain energy dissipation and release of the marble are in...
Some literatures state that long-term rock strength can roughly be determined according to the maximum value of rock sample's bulk strain under uniaxial compression.In order to study the relationship between rock's bulk strain and long-term strength,the uniaxial compression tests on four sandstone samples have been carried out with the measurement of sample deformation in radial direction using a micrometer.The result shows that the curve of bulk strain-stress in axial direction is extremely irr...
Last. Manfred Blümel(Graz University of Technology)H-Index: 4
view all 5 authors...
The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal, underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France) in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovere...
Abstract Acoustic emission (AE) methods are now widely used for damage evaluation. For a better understanding of the damage mechanics of materials such as rocks, AE has been used to monitor stresses which induce crack closure, crack initiation and crack damage. In the present study, an AE system was used to study the damage behaviour of some Australian black coal samples subjected to uniaxial compression. Several samples were left in a container filled with 100% carbon dioxide (CO 2 ) at a certa...
To better investigate the effect of high temperatures on the b-values of acoustic emissions (AEs), the fracturing of sandstone when subjected to uniaxial compression testing after different heat treatments is monitored by examining the AEs. The results show that the b-values are rapidly reduced around the yield stress and reduce to the lowest value at the peak stress during the loading process. After 550°C, the b-value of the yield stress of sandstone begins to decrease with temperature increase...
#1He Zhang(Xi'an University of Science and Technology)H-Index: 2
#2Qiang Sun(Xi'an University of Science and Technology)H-Index: 1
Last. Zhenlong Ge(Xi'an University of Science and Technology)H-Index: 1
view all 3 authors...
It is difficult to observe changes in the internal structure of natural rocks when under certain pressure ranges. However, such rocks have specific magnetic properties that are established during their formation process. Through studying changes in their magnetic properties while under pressure, which are readily observed and analyzed, as combined and contrasted with their associated structural changes, the relationship between the stress–strain and the magnetic field intensity can be establishe...
Abstract For a full understanding of the cracking processes in granite, uniaxial compression tests are conducted on prismatic specimens with pre-existing flaws, and digital imaging and AE techniques are applied to monitor real-time rupture behaviors. The digital image correlation (DIC) method is used to detect the process zone nucleation characteristics in granite. A novel approach for representing AE data in terms of the inter-event time (IET) function F(τ) is employed to analyze fracture-relat...
#1Yuan Li(CAS: Chinese Academy of Sciences)H-Index: 2
#2Ke Zhang(CAS: Chinese Academy of Sciences)H-Index: 1
Last. Xiaowa Wu(Beijing University of Technology)H-Index: 1
view all 3 authors...
Changes in the velocity, amplitude and attenuation of ultrasonic waves are accompanied by physical changes during rock failure. A large number of triaxial compression tests were performed to study the progressive failure of shale rock according to these physical properties. The tested shale samples had different bedding planes and were subjected to different confining pressures. During the experiments, ultrasonic wave testing was used to monitor the progressive failure process and to evaluate di...
The mechanical properties and fracture propagation of Longmaxi shale loading under uniaxial compression were measured using eight cylindrical shale specimens (4 mm in diameter and 8 mm in height), with the bedding plane oriented at 0° and 90° to the axial loading direction, respectively, by micro computed tomography (micro-CT). Based on the reconstructed three-dimensional (3-D) CT images of cracks, different stages of the crack growth process in the 0° and 90° orientation specimen were revealed....
Cracks have a significant effect on the uniaxial compression of rocks. Thus, a theoretically analytical approach was proposed to assess the effects of randomly distributed cracks on the effective Young's modulus during the uniaxial compression of rocks. Each stage of the rock failure during uniaxial compression was analyzed and classified. The analytical approach for the effective Young's modulus of a rock with only a single crack was derived while considering the three crack states under stress...
#1Miaomiao Wang(CAS: Chinese Academy of Sciences)H-Index: 2
#2Pei Li(CAS: Chinese Academy of Sciences)H-Index: 2
Last. Dan Xu(CAS: Chinese Academy of Sciences)H-Index: 1
view all 4 authors...
The effect of structural discontinuities on the progressive failure process of anisotropic rocks should be paid particular attention. The crack damage stress σcd, also considered as the yield strength, and the relationship between σcd and the uniaxial peak strength σucs of anisotropic rocks for different orientations θ of the isotropy planes with respect to the loading directions were investigated theoretically and experimentally. A theoretical relation of σcd/σucs with the function of the shape...
#1Li Guoliang(CAS: Chinese Academy of Sciences)H-Index: 2
#2Siqing. Qin(CAS: Chinese Academy of Sciences)H-Index: 1
Last. Xiaowa. Wu(CAS: Chinese Academy of Sciences)H-Index: 1
view all 5 authors...
The rock mass failure process can be divided into several distinct deformation stages: the compaction stage, elastic stage, stable failure stage, accelerated failure stage, and post-peak stage. Although each stage has been well studied, the relationship among the stages has not been established. Here, we establish two models which are the Strain model Q and Energy density model S by using the renormalization group theory and investigate the mechanical relationship between the volume dilatant poi...
Previous experimental studies showed that the variation of Radon (Rn) emission is closely related to the development of rock deformation: Rn emission has a rapid increase with the growth of cracks and their surface areas (i.e. onset of fracture coalescence point), and reaches the maximum at rock failure. In this study, the stress level at the onset of fracture coalescence λ c is predicted with the renormalization group theory. It is assumed that rock is a strain-softening medium whose strength c...