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Pure and Applied Geophysics

, Volume 176, Issue 11, pp 4797–4808 | Cite as

Shear Creep Tests on Fissured Mudstone and an Improved Time-Dependent Model

  • L. Z. Wu
  • S. H. Li
  • P. SunEmail author
  • R. Q. Huang
  • B. Li
Article

Abstract

All rocks undergo creep when under a long-term load, and shear sliding is a major failure mode of natural slopes. However, the mechanical properties of fractured mudstone differ from those of intact rock. To investigate these properties and the influence of normal stress and pre-cut crack length on mudstone shear creep characteristics, we performed shear creep tests on fractured mudstone. The experimental results show that axial load magnitude and crack length have a marked influence on the rock’s shear creep behavior. The larger the axial compressive stress, the smaller the shear creep deformation. The longer the crack, the more significant the shear creep deformation. When stress is low, existing creep models can reflect the creep properties of mudstone well. However, most published creep models cannot accurately portray the nonlinear creep behavior of mudstone in a tertiary creep stage. We propose an improved time-dependent creep model that overcomes the shortcomings of the traditional models in describing nonlinear creep. The new model has fewer parameters and can be applied to practical engineering problems involving soft rock. During the shear creep tests on soft argillaceous samples under different loads, shear failure zones in fractured mudstone exhibited both gradual and sudden failure. The shear time-dependent model for mudstone developed in this study can effectively explain mudstone instability.

Keywords

Fractured mudstone shear creep improved Nishihara creep accelerated creep landslides 

List of Symbols

\(\tau_{1}\)

First level of shear loading

\(\tau_{2}\)

Second level of shear loading

\(\tau_{4}\)

Fourth level of shear loading

\(\tau_{5}\)

Fifth level of shear loading

\(\tau_{\text{s}}\)

Long-term shear strength of the samples

\(\varepsilon\)

Strain

\(\varepsilon_{\text{c}}\)

Limit strain (the initial zone) of the improved viscoplastic body (N/St.V)

\(\eta_{\text{c}}\)

Viscous coefficient of the new creep body for \(\varepsilon < \varepsilon_{\text{c}}\)

n

Rheological index (> 1)

\(\eta_{\text{c}}^{'} = \eta_{\text{c}} \left( {{{\varepsilon_{\text{c}} } \mathord{\left/ {\vphantom {{\varepsilon_{\text{c}} } \varepsilon }} \right. \kern-0pt} \varepsilon }} \right)^{n}\)

Viscous coefficient, which is nonlinear for \(\varepsilon \ge \varepsilon_{\text{c}}\)

\(t_{\text{c}}\)

Time for the model to enter the tertiary creep stage

tp

Failure time, \(t_{\text{p}} = {{n\eta_{\text{c}} \varepsilon_{\text{c}} } \mathord{\left/ {\vphantom {{n\eta_{\text{c}} \varepsilon_{\text{c}} } {\left( {n - 1} \right)\sigma_{0} }}} \right. \kern-0pt} {\left( {n - 1} \right)\sigma_{0} }}\)

\(\varepsilon_{\text{H}}\)

Strain of the Hooke body (H)

\(\varepsilon_{\text{K}}\)

Strain of the viscoelastic body (N/H)

\(E_{\text{H}}\)

Elasticity modulus of the Hooke body

\(E_{\text{K}}\)

Elasticity modulus body

\(\eta_{\text{k}}\)

Viscous coefficients of the Kelvin body for \(\varepsilon_{\text{c}}\)

\(\eta_{\text{c}}\)

Viscous coefficient of the new creep body

\(\tau_{\text{s}}\)

Long-term strength

τ0

Shear stress

Notes

Acknowledgements

The authors thank the National Key R&D Program of China (2018YFC1504702), the National Natural Science Foundation of China (nos. 41672282 and 41472296), and the China Geological Survey (DD20190717). The authors thank Mr. S. H. Li for some suggestions, and the Innovation Team of the Chengdu University of Technology.

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.State Key Laboratory of Geohazard Prevention and Geoenvironment ProtectionChengdu University of TechnologyChengduPeople’s Republic of China
  2. 2.Institute of GeomechanicsChinese Academy of Geological SciencesBeijingPeople’s Republic of China
  3. 3.Key Laboratory of Active Tectonics and Crustal Stability AssessmentBeijingChina

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