The three stages of stress relaxation - Observations for the time-dependent behaviour of brittle rocks based on laboratory testing

Paraskevopoulou, Chrysothemis; Perras, Matthew A.; Diederichs, Mark S.; Amann, Florian; Löw, Simon; Lam, Tom; Jensen, Mark

doi:10.1016/j.enggeo.2016.11.010

Cited by 65 publications

(28 citation statements)

References 45 publications

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“…In accordance with Paraskevopoulou et al, 2017 (35), relaxation behavior consists of three stages as illustrated in Fig. 3.4.…”

Section: Stress Relaxationsupporting

confidence: 83%

“…3.4 shows. Paraskevopoulou et al, 2017 (35) mention that combination of three-dimensional visco-elastic response and crack behavior during stable propagation with a constant axial strain are possibly associated to the different development of the third stage relaxation. Paraskevopoulou et al, 2017 (35) also describe the percentages of the total stress relaxation ( ) that corresponds to each stage.…”

Section: Stress Relaxationmentioning

confidence: 99%

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Numerical Implementation of an Elasto-Viscoplastic Constitutive Model for Prediction of the Mechanical Behavior of Rock Salt

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“…In accordance with Paraskevopoulou et al, 2017 (35), relaxation behavior consists of three stages as illustrated in Fig. 3.4.…”

Section: Stress Relaxationsupporting

confidence: 83%

Section: Stress Relaxationmentioning

confidence: 99%

Numerical Implementation of an Elasto-Viscoplastic Constitutive Model for Prediction of the Mechanical Behavior of Rock Salt

CRUZ¹

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“…axial strain -constant). It has been observed that relaxation behavior is related not only to time-dependent phenomena like creep but also to timedependent damage evolution of new or pre-existing cracks growth and evolution in the specimen that initiates during loading [9,32,33].…”

Section: Relaxation Testsmentioning

confidence: 99%

“…Goodman's [38] approach is usually adopted to derive the Bugers model parameters by curve fitting laboratory creep testing results. Using a similar approach for determining parameters and assuming that the material's behavior can be represented by the linear visco-elastic Burgers body in unconfined compression [33] found that the same parameters (i.e. viscosities and shear moduli) can be also derived from stress relaxation tests, (Figure 7).…”

Section: Time-dependent Modelsmentioning

confidence: 99%

Time-Dependent Behavior of Rock Materials

Paraskevopoulou¹

2021

Engineering Geology

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Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in underground projects such as nuclear waste repositories. The lifespan can exceed one million years or other openings where the project’s lifetime and sustainability are the critical design parameter. In such cases, progressive rock mass deformation that can lead to instabilities, time-dependent overloading of support and delayed failure are considered the product of time-dependent phenomena. Understanding and predicting the overall impact of such phenomena aims to achieve design optimization, avoiding dlivery delays and thus cost overruns. This chapter provides more insight into the time-dependent behavior of rocks. Simultaneously, the emphasis is given to investigating and analyzing creep deformation and time-dependent stress relaxation phenomenon at the laboratory scale, and in-depth analyses are presented. This work further develops the understanding of these phenomena, and practical yet scientific tools for estimating and predicting the long-term strength and the maximum stress relaxation of rock materials is presented. The work presented in this chapter advances the scientific understanding of time-dependent rock, and rock mass behavior increases the awareness of how such phenomena are captured numerically and lays out a framework for dealing with such deformations when predicting tunnel deformations.

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“…Paraskevopoulou et al measured similar stress-time responses at different load levels, indicating the existence of three distinct stages of stress relaxation. In the first stage, 55% to 95% of the total stress relaxation takes place [7].…”

Section: Introductionmentioning

confidence: 99%

Uniaxial Compression Creep Relaxation and Grading of Coal Samples via Tests on the Progressive Failure Characteristics

et al. 2019

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An RMT-150B electrohydraulic servo testing system was used to perform uniaxial compression and uniaxial grading relaxation (creep) tests. The deformation, strength, and failure characteristics of the progressive failure process of coal samples under three loading modes were analyzed. The analysis results show that the prepeak stress-strain curve of the coal samples and the load relationships are not clear and that the whole compression process of coal still showed compression, elastic, yielding, and failure stages. The local stress drop characteristics during our relaxation creep grading tests showed no clear peak value and showed a yield curve with the shape of a conventional single plateau. The values of the mechanical parameters of axial compression were significantly higher than those obtained in the grade relaxation (creep) tests, which showed the mechanical parameters of coal samples with aging characteristics. In the relaxation (creep) tests, when the stress ratio was less than 70%, the relaxation (creep) characteristics of the sample were not clear. When the ratio of stress relaxation (creep) was more than 70% in the relaxation (creep) tests during displacement (stress) with a constant relaxation (creep) over the duration of the test, the evolution, development, and convergence of microcracks in the coal samples were observed. Relaxation (creep) stress was higher, failure duration was shorter, and the duration of failure was longer. For fully mechanized coal faces, increasing the support resistance and timely moving the support after coal cutting may prevent rib spalling accidents by reducing coal stress and exposure time in the front of the working face. Additionally, routine uniaxial compressive failures showed a simple form, having a clear tension-shear dual rupture surface. The staged relaxation creep failure testing of coal is more complex. The entire coal samples were divided into many thin-sheet debris via gradual collapse and shedding, and the number of cracks increased significantly, showing evident lateral expansion characteristics that are similar to the rib spalling characteristics in high coal mining working faces.

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The three stages of stress relaxation - Observations for the time-dependent behaviour of brittle rocks based on laboratory testing

Cited by 65 publications

References 45 publications

Numerical Implementation of an Elasto-Viscoplastic Constitutive Model for Prediction of the Mechanical Behavior of Rock Salt

Numerical Implementation of an Elasto-Viscoplastic Constitutive Model for Prediction of the Mechanical Behavior of Rock Salt

Time-Dependent Behavior of Rock Materials

Uniaxial Compression Creep Relaxation and Grading of Coal Samples via Tests on the Progressive Failure Characteristics

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