A new method to model the non-linear crack closure behavior of rocks under uniaxial compression

Song

et al. 2021

Shock and Vibration

As one of the most catastrophic dynamic hazards in underground coal mines, coal bursts have been a major safety concern around the world for many years. Although the coal bursts can occur in all cases of hard to soft coal if the right stress environment is created, the occurrence of coal bursts is closely related to the intrinsic mechanical properties of coal, such as the bursting proneness. In this study, a total of 27 coal specimens are selected in the open literature studies to obtain a group of fundament data, such as the mechanical parameters, four bursting proneness indices, stress-strain curves, and their geological conditions where the specimens were taken. The relationship between bursting proneness indices and the cohesion of the coal specimens is established by numerically fitting the stress-strain curves and theoretically deduction. By taking into account the coal heterogeneity, eight probability distribution functions are employed to assignment nonuniform cohesion to the numerical model and to study the influence of heterogeneity on bursting proneness. The results reveal that the coal cohesion, which combines the common advantages of the four proneness indices, can be used as bursting proneness index. In the research of heterogeneity, the coal bursting proneness will decrease with the increasing of cohesion scatter degree. The larger the cohesion scatter degree increase is, the lower the bursting proneness will be. The failure of coal specimen is more and more severe with the decrease of cohesion scatter degree. In addition, this paper provides two methods for assigning heterogeneous parameters to the numerical model. The contours of shear strain rate and plastic state between homogeneous and heterogeneous coal specimens are compared to study the failure types of coal specimens and to reveal the mechanism of violent failure in coal bursts.

Section: Numerically Assignment Of Nonuniform Distribution Of Coal Parametermentioning

confidence: 99%

Numerical Investigation of Relationship between Bursting Proneness and Mechanical Parameters of Coal

Song

et al. 2021

Shock and Vibration

International Journal of Damage Mechanics

“…As stress level increases, new cracks appear and propagate until the whole rock specimen is ruptured. Several theoretical models have been proposed that can well describe the deformation behavior of rock mass in the stage of pre-existing joint closure (Ji et al, 2018;Peng et al, 2015). Based on the Weibull distribution function, the relationship between damage and strain has been discussed quantitatively (Caillerie and Dascalu, 2011;Chen et al, 1997;Najar, 1994;Wang et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Time-dependent behavior of rock-like specimen containing multiple discontinuous joints under uniaxial step-loading compression

Yang

Chen

et al. 2021

Rock with multiple discontinuous joints widely exists in rock engineering, and its mechanical properties are complex, which greatly increases the difficulty of engineering design and construction. Time-dependent deformation characteristics and long-term strength evaluation of jointed rock masses remain poorly understood. In this work, the creep experiments of rock-like specimens with multiple discontinuous joints under uniaxial step-loading compression are carried out to explore the influence of joint geometry (rock bridge length, joint length, joint angle, and joint spacing) on creep strain, long-term strength, and failure pattern of specimens with multiple discontinuous joints. The following conclusions are drawn from the test results: 1) The deformation of jointed rock specimens has evident time-dependent effect, and the cumulative creep deformation increases as creep load increases; 2) The strength of jointed rock specimens under loading changes with time, and the ratio of long-term strength and creep peak strength ( σ∞/ σc) of the tested specimens ranges from 41% to 96%; 3) The distribution of initial joints affects the creep fracture modes of rock-like specimens. The rupture of rock-like specimens with different joints distribution is mainly caused by the growth of wing cracks and quasi-coplanar secondary cracks. Three different failure modes are observed from these specimens: i) tensile failure with cracks across the joint plane; ii) shear failure with cracks along the joint plane; and iii) tensile failure with cracks along the joint plane. Based on the principles of damage mechanics and fracture mechanics, a theoretical mechanistic model considering both the closure stage of pre-existing open joints and time-dependent propagation stage of new cracks is established. Considering the influence of joint length, joint angle and joint density, the evolution of creep strain of rock-like specimen with multiple discontinuous joints is analyzed. The theoretical model results agree well with the experimental results, which indicates that the established model can replicate the creep failure process of jointed rock mass. These theoretical and test results help us better understand the effect of multiple joints on the long-term behavior of rock mass.

“…Zhang et al (2020) proposed a numerical manifold displacement method to solve crack propagation, gave the calculation formula of stress intensity factor in the process of crack propagation, and developed a program module to simulate crack propagation. Ji et al (2018) described the distribution of crack direction with the crack tensor analysis method, and discussed the influence of crack strength, crack direction and crack gap on crack closure behavior. Wong and Einstein (2009) conducted uniaxial compression tests on rock specimens with pre-existing cracks and seven different crack types, and the time sequence of different crack types was determined according to crack geometry and crack propagation mechanism (tension/shear).…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation study on the influence of crack characteristics on mechanical properties and impact failure of rock

Chen

Qin

et al. 2021

Arab J Geosci

The rock mass in nature have different degrees of crack development. The different crack characteristics affect the mechanical properties and stability of the rock mass. This paper uses PFC simulation software to perform uniaxial compression tests on rock specimens with different crack characteristics and analyzes the influence of the crack characteristics on the mechanical property, impact energy index, and failure characteristics. The sensitivity analysis is used to analyze the influence degree of crack characteristics. It is concluded that the peak strength is directly proportional to the crack angle and inversely proportional to the crack length, the crack number, and the crack width. The peak strain is directly proportional to the crack angle, the crack number, and the crack width and is inversely proportional to the crack length. The impact energy index of rock specimen increases gradually with the crack angle, crack number, and crack width. The influence degree of crack characteristics is divided into four grades by sensitivity analysis. The crack angle has a more significant influence on the peak stress, peak strain, and impact energy index, and the crack width has a more minor influence on the peak stress and peak strain. The research results can provide the theoretical basis and guidance for preventing the instability and failure of the rock mass with different crack characteristics. KeywordCrack characteristic • Mechanical property • Progressive instability • Impact energy index • Sensitivity analysis * Tan Li