### Abstract

In this paper, a fracture mechanics model is developed to illustrate the importance of time-dependence for brittle fractured rock. In particular a model is developed for the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value that results in slope instability. A second example is given where variations in some of the material parameters are assumed. A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for relatively short-term rock structures.

Original language | English (US) |
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Pages (from-to) | 27-38 |

Number of pages | 12 |

Journal | Rock Mechanics and Rock Engineering |

Volume | 36 |

Issue number | 1 |

DOIs | |

State | Published - Jan 1 2003 |

### Keywords

- Joint cohesion
- Joint friction angle
- Rock bridge
- Rock fracture
- Rock fracture mechanics
- Rock joint
- Slope stability
- Subcritical crack growth
- Time dependent

### ASJC Scopus subject areas

- Civil and Structural Engineering
- Geotechnical Engineering and Engineering Geology
- Geology