Development and verification of a micromechanics-based continuum theory for long-term deterioration of hard rock

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 16560408
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural engineering/Earthquake engineering/Maintenance management engineering
• Research Institution: Saitama University
• Principal Investigator: OKUI Yoshiaki Saitama University, Dept.of Civil & Environmental Eng., Associate Professor, 工学部, 助教授 (40214051)
• Co-Investigator(Kenkyū-buntansha): ODA Masanobu Saitama University, Dept.of Civil & Environmental Eng., Professor, 工学部, 教授 (90008855)
• Project Period (FY): 2004 – 2005
• Keywords: hard rock / creep / stress corrosion cracking / micromechanics / fabric tensor / elastic wave velocity / long-tem deterioration

Research Abstract

The purpose of this study is to establish a micromechanics-based continuum damage model to analyze short- and long-term behavior of brittle rocks under compression. The model developed in this study provides information on not only the macroscopic mechanical responses of rock such as strength, but also microscopic information such as crack lengths and crack density during inelastic deformation. A small number of parameters are involved in this model and can be identified from the results of triaxial compression tests, creep tests and microscopic observation of microcracks. The model is derived from the mechanics of tensile microcracks. It is assumed that local tensile stress thereby sliding up on asperities causes microcracks growth. By generalizing the analysis of one single microcrack and also, including the effects of interaction among neighboring microcracks directly on cracks growth, the proposed model for brittle rocks under compression is derived.
In order to illustrate the predi ctive capability of the proposed model, the model is applied to simulation of short-term mechanical tests of Inada granite. Numerical results are compared with experimental data from triaxial compression tests results and microscopic observations of microcracks. The peak stress obtained numerically is in good accordance with the one observed in triaxial compression tests under a confining pressure higher than 10 MPa.
Furthermore, the present model is capable of reproducing the three characteristic stages of long-term behavior commonly observed in laboratory creep tests. The sub-critical microcrack growth parameters can be determined for Inada granite by fitting the numerical results of elapse time to failure versus the creep stress ratio curve with the experimental data under both dry and wet conditions. Use of the extended model makes it possible to analyze not only the extension of microcrack length, but also the development of the excavation damage zone around tunnels as a function of time.

Research Products

• [Journal Article] A micromechanical model for brittle failure of rock and its relation to crack growth observed in triaxial compression tests of granite (2006)
  • Author(s): Golshani, A., Okui, Y., Oda, M., Takemura, T.
  • Journal Title: Mechanics of Materials 38 Pages: 287-303
  • Description: 「研究成果報告書概要(和文)」より
• [Journal Article] Hydraulic behaviour of Inada granite in the excavation disturbed zone around underground openings (2005)
  • Author(s): Golshani, A., Okui, Y., Oda, M., Takemura, T.
  • Journal Title: The Seventh International Summer Symposium, JSCE, 30 July 2005 Tokyo, Japan Pages: 153-156
  • Description: 「研究成果報告書概要(欧文)」より
• [Journal Article] Simulation of damage around a circular opening in rock (2005)
  • Author(s): Golshani, A., Okui, Y., Oda, M., Suzuki, K.
  • Journal Title: The 11th International Conference of IACMAG, 19-24 June, 2005, Turin, Italy Pages: 33-40
  • Description: 「研究成果報告書概要(欧文)」より
• [Journal Article] Time-dependent continuous damage model for brittle failure of rocks (2004)
  • Author(s): Golshani, A., Okui, Y., Takemura, T., Oda, M.
  • Journal Title: 53rd Geomechanics Colloquy and EUROCK 2004, 7-9 October, 2004, Salzburg, Austria Pages: 701-706
  • Description: 「研究成果報告書概要(欧文)」より