scholarly journals Creep Mechanics of the High-Stress Soft Rock under Grade Unloading

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Shunjie Huang ◽  
Xiangrui Meng ◽  
Guangming Zhao ◽  
Yingming Li ◽  
Gang Liu ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Creep Test ◽  
Creep Behavior ◽  
High Stress ◽  
Soft Rock ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Axial Pressure ◽  
Accelerated Creep ◽  
Test Process

In order to study the creep behavior of deep soft rock, gritstone was chosen as the research subject, and a rock triaxial rheometer (Rock 600-50) and acoustic emission (AE) system (SH-II) were used to carry out the grade unloading confining pressure creep test under a high-stress level. The test results showed that the lateral creep behavior of the gritstone was more prominent than the axial creep under the initial high confining pressure. Under the same confining pressure, the creep strain rate (the direction the same as strain) of the gritstone decreases with the increase in axial pressure. As shown by the AE count, AE signals were generated throughout the entire test process, indicating that the creep was a “microdynamic” process. The creep behavior was characterized by a significant confining pressure effect. As the confining pressure was decreased, the degree of creep increases significantly. During the test, the AE energy increased on the whole but decreases during the creep phase. During the entire test process, the overall energy in the constant deviatoric stress grade unloading of the confining pressure was 45% higher than that in the constant axial pressure grade unloading. The degree of failure of the rock was different in these two unloading creep tests, and the constant axial pressure grade unloading of the confining pressure entails greater damage than the constant deviatoric stress grade unloading of the confining pressure. The main reason was that the former had a lower confining pressure level and longer creep process than the latter, and the sample was mainly characterized by creep damage and large cumulative damage, while the latter features mainly unloading damage. Through the inversion of the Burgers constitutive model and nonlinear damage constitutive model for the creep test curve, the nonlinear constitutive equation can better fit the accelerated creep stage, which suggested that this model can describe the accelerated creep characteristics of the high-stress soft rock.

scholarly journals An Improved Nishihara Model for Frozen Loess considering the Influence of Temperature

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Xin Li ◽  
Enlong Liu ◽  
Bingtang Song ◽  
Xingyan Liu
Keyword(s):  
Creep Behavior ◽  
Microscopic Analysis ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Frozen Soil ◽  
Experimental Results ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Tests ◽  
Deviator Stress

A series of triaxial creep tests under the constant confining pressure are performed on frozen loess specimens, and the creep behavior of the frozen loess with respect to variations in both temperature and deviator stress is examined. Experimental results illustrate that the frozen loess specimens present the attenuation creep at the lower deviatoric stress, whereas the nonattenuation creep under the higher deviatoric stress level, and with a drop in the temperature, the deviator stress value which the exhibition of nonattenuation creep needs will increase under the constant confining pressure condition. According to the microscopic analysis on deformation characteristics in the creep process of frozen soil, both temperature and external stress will cause the hardening and weakening effects, affecting the creep properties of frozen loess. By introducing the hardening variable and damage variable to consider the hardening and weakening effects of the frozen loess, an improved Nishihara model is proposed. The correlations between model parameters and the temperature as well as deviator stress are determined. The comparisons between model predictions and experimental results show that the improved creep constitutive model proposed here can not only describe the whole creep process well, but also reveal the influences of the temperature and deviator stress on the creep behavior of frozen loess, which demonstrate its accuracy and usefulness.

scholarly journals Analysis and numerical calculation of a coupled creep and strain-softening model for soft rock tunnels

PLoS ONE ◽  
2021 ◽  
Vol 16 (8) ◽  
pp. e0256243
Author(s):  
Jianjun Zhang ◽  
Baicong Yao ◽  
Yunhe Ao ◽  
Chunzhe Jin ◽  
Chuang Sun
Keyword(s):  
Numerical Calculation ◽  
Stability Analysis ◽  
Plastic Zone ◽  
Creep Behavior ◽  
Strain Softening ◽  
Soft Rock ◽  
Support Design ◽  
Tunnel Support ◽  
Accelerated Creep ◽  
Rock Tunnels

Proper mechanical model selection is critical in tunnel support design and stability analysis, especially to reflect the creep and strain-softening behavior of soft rock. We present a coupled nonlinear Burgers strain-softening (NBSS) model and numerical calculation method to investigate the coupled effects of creep and strain-softening of soft rock tunnels. The nonlinear elastic-viscous model is used to simulate the steady creep behavior of mudstone, and the nonlinear viscoplastic strain-softening model is used to simulate the accelerated creep behavior and post-peak strength attenuation behavior. The experimental results show that the viscoplastic parameters and post-peak softening parameters of mudstone are highly sensitive to confining pressure and exhibit nonlinear characteristics. The accelerated creep curve obtained by the numerical calculation is consistent with the experiments, which verifies the model reliability. We use the NBSS and nonlinear Burgers Mohr-Coulomb (NBMC) models to calculate the plastic zone distribution characteristics and deformation law. The distribution of the plastic zone calculated by the NBSS model is larger with more localized fractures. The NBSS model is useful for studying the evolution of stress and displacement fields of complex surrounding rock mass, which provides important theoretical guidelines for the support design and stability analysis of soft rock tunnel engineering.

CREEP ANALYSIS FOR A WIDE STRESS RANGE BASED ON STRESS RELAXATION EXPERIMENTS

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5413-5418 ◽  
Author(s):  
HOLM ALTENBACH ◽  
KONSTANTIN NAUMENKO ◽  
YEVGEN GORASH
Keyword(s):  
Experimental Data ◽  
Creep Rate ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Power Law ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
High Stress ◽  
Stress Range ◽  
Power Law Creep

Many materials exhibit a stress range dependent creep behavior. The power-law creep observed for a certain stress range changes to the viscous type creep if the stress value decreases. Recently published experimental data for advanced heat resistant steels indicates that the high creep exponent (in the range 5-12 for the power-law behavior) may decrease to the low value of approximately 1 within the stress range relevant for engineering structures. The aim of this paper is to confirm the stress range dependence of creep behavior based on the experimental data of stress relaxation. An extended constitutive model for the minimum creep rate is introduced to consider both the linear and the power law creep ranges. To take into account the primary creep behavior a strain hardening function is introduced. The material constants are identified for published experimental data of creep and relaxation tests for a 12% Cr steel bolting material at 500°C. The data for the minimum creep rate are well-defined only for moderate and high stress levels. To reconstruct creep rates for the low stress range the data of the stress relaxation test are applied. The results show a gradual decrease of the creep exponent with the decreasing stress level. Furthermore, they illustrate that the proposed constitutive model well describes the creep rates for a wide stress range.

Study on nonlinear damage creep constitutive model for high-stress soft rock

2016 ◽  
Vol 75 (10) ◽  
Author(s):  
Ping Cao ◽  
Wen Youdao ◽  
Wang Yixian ◽  
Yuan Haiping ◽  
Yuan Bingxiang
Keyword(s):  
Constitutive Model ◽  
High Stress ◽  
Soft Rock ◽  
Creep Constitutive Model

A Creep-Damage Constitutive Model for Sandstone

2012 ◽  
Vol 170-173 ◽  
pp. 289-294 ◽  
Author(s):  
Wei Wang ◽  
Jun Lv ◽  
Hai Cheng Wang
Keyword(s):  
Constitutive Model ◽  
Creep Test ◽  
Creep Damage ◽  
Creep Model ◽  
Whole Process ◽  
Proposed Model ◽  
Accelerated Creep ◽  
Damage Constitutive Model ◽  
Triaxial Creep ◽  
Triaxial Creep Test

Based on the results obtained by the triaxial creep test, a creep-damage constitutive model for sandstone is presented by using the damage theory and by introducing the concept of “the whole process of damage” into Burgers creep model. The parameters of the model are determined by fitting the creep test data. The result shows that the proposed model can not only describe efficiently the variation of decay and steady creep under relatively low stress condition, but also give a satisfied representation of damage behavior in accelerated creep stage.

scholarly journals A Nonlinear Constitutive Model for Disintegrated Carbonaceous Mudstone Based on Logarithmic Functions

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiang Qiu ◽  
Jinhong Li ◽  
Huangbin Jiang ◽  
Hongyuan Fu ◽  
Shun Yang
Keyword(s):  
Constitutive Model ◽  
Axial Strain ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Triaxial Tests ◽  
Lateral Strain ◽  
Logarithmic Function ◽  
Stress Strain ◽  
Nonlinear Constitutive Model ◽  
Nonlinear Stress

To study the mechanical characteristics of the disintegrated carbonaceous mudstone (DCM), consolidated drained triaxial tests were conducted on the DCM with three degrees of compaction (i.e., 90%, 93%, and 96%). Then, the nonlinear constitutive model suitable for the DCM was established based on test results using a logarithmic function. The stress-strain characteristics of the DCM were analyzed. The results revealed that the axial strain of the DCM was positively correlated with the deviatoric stress and lateral strain. The slopes of deviatoric stress-axial strain curves decreased with the increase of axial strain and so did the slopes of the axial strain-volumetric strain curves. The strength of the DCM increased with the increase of the confining pressure and the degree of compaction. In addition, the axial strain induced by dilatancy was also positively correlated with the degree of compaction and the confining pressure. Furthermore, under triaxial loading conditions, the relationship between the stress and strain of the DCM can be expressed by a logarithmic function; based on this, a nonlinear constitutive model with ten material parameters was derived. In addition, the results of numerical tests using the model showed similar stress-strain characteristics of the DCM comparing with the triaxial tests. Hence, it indicated that the nonlinear constitutive model based on the logarithmic function can reflect the nonlinear stress-strain characteristics of the DCM.

scholarly journals Mechanical properties and constitutive analyses of basalt fiber crumb rubber mortars in soft rock roadways

2021 ◽  
Vol 303 ◽  
pp. 01023
Author(s):  
Qiao Wei-Guo ◽  
Vladimir Pershin ◽  
Qin Jun-Ling ◽  
Zhang Shuai
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Compressive Stress ◽  
Triaxial Compression ◽  
Basalt Fiber ◽  
Soft Rock ◽  
Confining Pressure ◽  
Crumb Rubber ◽  
Roadway Support ◽  
Uniaxial Compressive Stress

Uniaxial compressive stress-strain curves of several groups of basalt fiber crumb rubber mortars (BF-CRM) with different contents are tested. By comparing with the GZH model, the improved values of the parameters of the BF-CRM constitutive model based on the GZH model are obtained. Then, taking the supporting scheme of main substation of the mine as the background, using FLAC3D to simulate the roadway support, using BF-CRM to replace the ordinary mortars in the original support, and combining with the triaxial compression test of different confining pressure, the application effect of BF-CRM in roadways support is studied and analyzed.

scholarly journals Microstructural change in ice: II. Creep behavior under triaxial stress conditions

1999 ◽  
Vol 45 (151) ◽  
pp. 438-448 ◽  
Author(s):  
I. L. Meglis ◽  
P. M. Melanson ◽  
I.J. Jordaan
Keyword(s):  
Creep Behavior ◽  
Axial Strain ◽  
Confining Pressure ◽  
Fine Grained ◽  
Dominant Deformation Mechanism ◽  
Accumulated Strain ◽  
Accelerated Creep ◽  
Confining Pressures ◽  
Time Required ◽  
Deviatoric Stresses

AbstractThis work investigates the deformation of ice under deviatoric stresses and confining pressures expected during ice–structure interaction. Granular ice was tested under a range of confining pressures (5–60 MPa) and deviatoric stresses (up to 25 MPa), with sample temperatures between –8° and –10°C. Samples were deformed to increasing end-levels of axial strain, and were thin-sectioned and photographed immediately following testing.At all confinement levels, the original texture of the sample is completely transformed within the first 10–15% strain, to a fine-grained matrix with a few larger, isolated grains. At low confinements, grain-size reduction is associated with extensive microcracking. At high confinements, few cracks are observed. Observations suggest that microcracking, melting and recrystallization are active at all levels of confinement, though the relative importance of each depends on the confinement, stress and accumulated strain.Deviatoric stress is a strong factor in controlling the creep, reflected in both the time required for the sample to reach accelerated creep and the tertiary creep rate itself. Two exceptions to this pattern were noted. First, some samples experienced strain localization and eventual rupture. These specimens tended to have higher creep ratesevenin the initial stages of strain. Second, prior damage resulted in rapid softening compared with the behavior of undamaged specimens. However, when strain rates are compared among all samples at a given level of cumulative axial strain, the creep behavior obeys a power law over the whole range of strain levels tested. Effective viscosity decreased from 107.8to l06.4MPa−ns within the first 10% strain, during which the most substantial microstructural changes occurred, and then stayed relatively stable. The stress exponent,n, remained within the range 4.0–4.6.The dominant deformation mechanism appears to depend strongly on confining pressure (cracking at low pressure and dynamic recrystallization at high pressure). Creep rates at high confinement appear to increase relative to those at intermediate confinement, but the influence of temperature must be addressed further.

scholarly journals Failure Behavior and Constitutive Model of Weakly Consolidated Soft Rock

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Wei-ming Wang ◽  
Zeng-hui Zhao ◽  
Yong-ji Wang ◽  
Xin Gao
Keyword(s):  
Constitutive Model ◽  
Failure Mechanism ◽  
Triaxial Compression ◽  
Soft Rock ◽  
Confining Pressure ◽  
Western China ◽  
Failure Behavior ◽  
Correction Coefficient ◽  
Compression Tests ◽  
Mining Areas

Mining areas in western China are mainly located in soft rock strata with poor bearing capacity. In order to make the deformation failure mechanism and strength behavior of weakly consolidated soft mudstone and coal rock hosted in Ili No. 4 mine of Xinjiang area clear, some uniaxial and triaxial compression tests were carried out according to the samples of rocks gathered in the studied area, respectively. Meanwhile, a damage constitutive model which considered the initial damage was established by introducing a damage variable and a correction coefficient. A linearization process method was introduced according to the characteristics of the fitting curve and experimental data. The results showed that samples under different moisture contents and confining pressures presented completely different failure mechanism. The given model could accurately describe the elastic and plastic yield characteristics as well as the strain softening behavior of collected samples at postpeak stage. Moreover, the model could precisely reflect the relationship between the elastic modulus and confining pressure at prepeak stage.

Sign in / Sign up

Export Citation Format

Share Document