Starting from the concept of Representative Volume Element (RVE) at the mesoscopic scale, a statistical meso-damage mechanical method (SMDMM) is developed to model the trans-scale progressive failure ...process of rock, based on the statistical and continuum damage mechanics theory and the finite element method (FEM). The proposed mesoscopic constitutive law of RVE is established within the framework of elastic–brittle-damage theory in which the double damage functions correspond to a tensile and compressive damage surface. A statistical approach is employed to describe the mesoscopic heterogeneity of rock material. The damage evolution and accumulation of mesoscopic RVEs is used to reflect the macroscopic failure characteristics of rock. The global stress and strain fields are solved by the FEM. An element represents a RVE, the initiation and propagation of meso-macroscopic trans-scale cracks and their interaction are manifested by removing the failed elements. Numerical analyses are carried out on a few groups of laboratory-scale rock specimens and the effects of RVE size, material homogeneity and quasi-static loading step length are investigated. Finally, a full-scale Atomic Energy of Canada Limited (AECL) Mine-by test tunnel is simulated. The proposed SMDMM is calibrated and validated for its trans-scale modeling capability to reproduce the shape and size of excavation damage zone profile around the tunnel. Accordingly, the simulation results are compared with experimental observations and numerical results predicted by other models. It is shown that the SMDMM has good performance for modeling the rock failure process from meso- to engineering/field-scale.
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•We proposed a method to model trans-scale progressive failure process of rock.•Laboratory-scale numerical testing to investigate the influence of different cases.•Failure zone around the full-scale MBE tunnel model is modeled.
In this study, the rockburst definition is comprehensively described and several main rockburst theories (the strength theory, the energy theory, the bursting liability theory, the rigidity theory ...and the instability theory) are analyzed. The two-body interaction theory based on the Newton's law can explain the rockburst mechanism most reasonably. The rockburst development process is a static process and the rockburst occurrence process is within the scope of dynamics. In addition, some precursors exist before rockburst occurrence, reflected by the consistency between acoustic emissions and damage variables in rock mass, which can be summarised as three seismogenic models according to the tempo-spatial distribution. By utilizing the 3S (Stress buildup, Stress shadow and Stress transfer) principle in seismology, three rockburst criteria are proposed in this paper (namely, the stress tempo-spatial evolution, the magnitude, energy and concentration degree of microseismic events, sudden change of apparent volume). Finally, by comparing the results obtained by microseismic monitoring and landsonar positioning, it is shown that the root cause of rockburst occurrence is rock heterogeneity, and the existence of joints and fractures. The fracture intersection points are the locations for rockburst initiation. It is proven that the two-body interaction principle can perfectly explain the rockburst mechanism.
Abstract
The instability of slope has already threatened life and property safety of the people, and improving the monitoring method of slope stability has important theoretical and practical ...significance for disaster prevention and reduction. According to the idea of “Newton force sudden drop and catastrophic occurrence” proposed by M.C. He in the landslide monitoring, a numerical model with constant resistance bolt has been established. Through numerical simulation research, it is found that the maximum principal stress, minimum principal stress and shear stress of the intersection point P of landslide surface and constant resistance bolt are sudden growth and sudden decrease, the vertical displacement and lateral displacement of this point P appear rise and fall before three kinds of stress. When loading to the next step of the step where three stress have reduced to a minimum value the slope is unstable and destroyed. At this time, the constant resistance bolt has undergone larger plastic deformation and damaged. Finally, comparing the stress curves and the acoustic emission (AE) curves, it can be seen that stress decreases from the maximum value and the AE curves begin to show a significant rise, the two curves display opposite law. It can be seen from the AE diagram that the failure mode of the slope is a combined tension and shear failure. The numerical test results provide a new idea for real-time monitoring and forecasting of slope.
SUMMARY
A 2‐D numerical model for brittle creep and stress relaxation is proposed for the time‐dependent brittle deformation of heterogeneous brittle rock under uniaxial loading conditions. The model ...accounts for material heterogeneity through a stochastic local failure stress field, and local material degradation using an exponential material softening law. Importantly, the model introduces the concept of a mesoscopic renormalization to capture the co‐operative interaction between microcracks in the transition from distributed to localized damage. The model also describes the temporal and spatial evolution of acoustic emissions, including their size (energy released), in the medium during the progressive damage process. The model is first validated using previously published experimental data and is then used to simulate brittle creep and stress relaxation experiments. The model accurately reproduces the classic trimodal behaviour (primary, secondary and tertiary creep) seen in laboratory brittle creep (constant stress) experiments and the decelerating stress during laboratory stress relaxation (constant strain) experiments. Brittle creep simulations also show evidence of a ‘critical level of damage’ before the onset of tertiary creep and the initial stages of localization can be seen as early as the start of the secondary creep phase, both of which have been previously observed in experiments. Stress relaxation simulations demonstrate that the total amount of stress relaxation increases when the level of constant axial strain increases, also corroborating with previously published experimental data. Our approach differs from previously adopted macroscopic approaches, based on constitutive laws, and microscopic approaches that focus on fracture propagation. The model shows that complex macroscopic time‐dependent behaviour can be explained by the small‐scale interaction of elements and material degradation. The fact that the simulations are able to capture a similar time‐dependent response of heterogeneous brittle rocks to that seen in the laboratory implies that the model is appropriate to investigate the non‐linear complicated time‐dependent behaviour of heterogeneous brittle rocks.
Bisperoxovanadium (pyridine-2-carboxyl) bpV(pic) is a commercially available PTEN inhibitor. Previous studies from us and others have shown that bpV(pic) confers neuroprotection in cerebral ischemia ...injury. We set up to determine whether ERK 1/2 activation plays a role in bpV(pic)-induced neuroprotective effect in cerebral ischemia injury. We found that the phosphorylation levels of Akt (p-AKT) and ERK1/2 (p-ERK 1/2) were down-regulated after cerebral ischemia–reperfusion injury. The injection of bpV(pic) after injury not only increased the level of p-AKT but also the level of p-ERK 1/2. While the inhibition of PTEN mediated the up-regulatation of p-AKT and p-ERK 1/2 by bpV(pic). Interestingly, the ERK 1/2 activation induced by bpV(pic) was also independent of the inhibition of PTEN. Our results indicate that bpV(pic) protects against OGD-induced neuronal death and promotes the functional recovery of stroke animals through PTEN inhibition and ERK 1/2 activation, respectively. This study suggests that the effect of bpV(pic) on ERK 1/2 signaling should be considered while using bpV(pic) as a PTEN inhibitor.
To better understand the interaction of parallel joints and its effect on the mechanical behavior of jointed rock mass models, the results of a physical experiment program undertaken in the ...laboratory were present in this manuscript. The joint spacing and joint overlap are varied to alter the relative positions of parallel joints in geometry. Accordingly, four basic failure modes identified from the testing results are tensile failure across the joint plane, shear failure along the joint plane, tensile failure along the joint plane, and intact material failure. The wing cracks from tensile failure across the joint plane mode represent the interaction between parallel joints which depends on the joint dip angle, joint spacing and joint overlap. With the increment of parallel joint interaction, the corresponding normalized strength and maximum displacement at peak stress of jointed rock mass models reduced generally except at α=0°.
•Jointed rock mass models exhibited four different failure modes.•Wing crack generation and coalescence were found to reflect the interaction between parallel joints.•The parallel joints interaction depended on the joint orientation, joint spacing and joint overlap.•The decrease of joint spacing and joint overlap increased the interaction between adjacent parallel joins.•The increment of parallel joint interaction reduced the strength and deformation behavior of jointed rock mass models except at α=0°.
Deformation behavior and hydraulic properties of rock are the two main factors that influence safety of excavation and use of rock engineering due to in situ stress release. The primary objective of ...this study is to explore deformation characteristics and permeability properties and provide some parameters to character the rock under unloading conditions. A series of triaxial tests with permeability and acoustic emission signal measurement were conducted under the path of confining pressure unloading prior to the peak stress. Deformation behavior and permeability evolution in the whole stress—strain process based on these experimental results were analyzed in detail. Results demonstrate that, under the confining pressure unloading conditions, a good correspondence relationship among the stress—axial strain curve, permeability—axial strain curve and acoustic emission activity pattern was obtained. After the confining pressure was unloaded, the radial strain grew much faster than the axial strain, which induced the volumetric strain growing rapidly. All failures under confining pressure unloading conditions featured brittle shear failure with a single macro shear rupture surface. With the decrease in deformation modulus during the confining pressure unloading process, the damage variable gradually increases, indicating that confining pressure unloading was a process of damage accumulation and strength degradation. From the entire loading and unloading process, there was a certain positive correlation between the permeability and volumetric strain.
To reveal the size effect and lateral pressure effect of columnar jointed basalts (CJBs), the meso-damage mechanics, statistical strength theory, continuum mechanics and digital image correlation are ...combined, and a series of heterogeneous numerical models of CJBs orthogonal and parallel to column axis are established. The elastic modulus, Poisson's ratio, uniaxial compressive strength, friction angle, residual strength coefficient, heterogeneity index of basalts 60 GPa, 0.2, 120 MPa, 56.15°, 0.1 and 5, respectively. The gradual fracture processes and acoustic emission characteristics of CJBs suffering various lateral pressures are numerically simulated under the axial loading rate of 0.05 mm/min, and the influence of model size on the anisotropy and lateral pressure effect of CJBs is analyzed. The results show that: for the direction I/Ⅱ orthogonal to column axis, when the lateral pressure is 2 MPa and 6 MPa, the critical value of size effect is 4 m and 6 m, respectively; for the direction parallel to column axis, the compressive strength of specimen can be obviously improved by increasing lateral pressure for the certain sizes; when the lateral pressure is 6 MPa and the distance ratio of the secondary joint set is 0% or 50%, the compression strengths of the 3 m and 6 m specimens change in a U-shape and a V-shape with the column dip angle increasing, respectively. The results can contribute to understanding the non-linear deformation and failure behaviors of CJBs.
•The digital image correlation, meso-damage mechanics, statistical strength theory and continuum mechanics are combined.•The fracture mechanism and AE energy evolution characteristics of columnar jointed basalts are revealed.•The size effect for CJBs under different lateral pressures is discussed.•The influence of column dip angle, residual strength, irregularity, model boundaries, etc., is analyzed.
Landslides and slope failures are very common phenomena in hilly regions, Southwestern China. These are hazardous because of the accompanying progressive movement of the slope-forming material. To ...minimize the landslide effects, slope failure analysis and stabilization require in-depth understanding of the process that governs the behavior of the slope. The present paper first briefly describes a three-dimensional numerical brittle creep model for rock. The model accounts for material heterogeneity, through a stochastic local failure stress field, and local material degradation using an exponential material softening law. Then a case study of the Jiweishan rockslide that occurred in China is numerically investigated considering the effect of the mining activity. Numerical simulations visualize the entire process of the Jiweishan rockslide from the fracture initiation, propagation and coalescence. The distribution and evolution of associated stress and deformation field during the slide are also presented. Numerical simulations show that the underground mining excavations have remarkably negative effect on the stability of the rock slope, which is one of the important triggering factors of the rockslide. Moreover, it is possible to take some precautions for the unstable failure of rock mass by monitoring acoustic emission (AE) events or microseismicities since the occurrence of clusters of AE events prior to the final unstable rockslide. The results are of general interest, because they can be applied to the investigation of time-dependent instability in rock masses, to the mitigation of associated rock hazards in rock engineering, and even to a better understanding of the seismic activities in geological and geophysical phenomena occurring in the earth’s crust.
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