岩石力学---从物理试验到数值试验

1 引言

在大型岩石工程项目中, 进行试样的岩石力学试验是必不可少的, 最基本的测试参数是单轴抗压强度, 根据岩石性质以及工程性质的不同, 可能还需要作剪切试验和三轴试验. 本文首先回顾了一些常规的岩石力学试验, 然后基于过去笔记的相关内容, 简要总结了岩石力学的数值试验 。

2 岩石力学试验类型

这个部分回顾常规的岩石力学试验, 这些试验在大多数岩石力学教材中都有介绍,在此不作赘述. 

(1) 静水压力试验 (Hydrostatic Compression)

静水压力试验各个方向施加的载荷相同, 类似静水压力.

(2) 单轴压缩试验 (Uniaxial Compression)

单轴抗压强度试验只在纵向受压, 没有围压. 

(3) 三轴压缩 (Triaxial Compression)

三轴抗压强度试验纵向压力大于围压,围压相等.

(4) 三轴拉伸 (Triaxial Extension)

三轴拉伸试验围压相同并且大于纵向压力.

(5) 真三轴 (True Triaxial)

真三轴试验每个方向的压力不同.

(6) 直剪 (Direct Shear)

直剪试验用来测定节理的力学行为.

(7) 点载荷试验 (Point Load Test)

点载荷试验在点载荷机上进行.

(8) 硬度试验(Rebound Hardness Test)

硬度试验类似于土力学中的笔式贯入仪.

(9) 巴西抗拉强度试验 (Brazilian Tensile Strength Test)

间接的抗拉强度测试方法.

3 岩石力学数值试验

随着数值模拟技术的发展, 现在可以使用数值模拟技术来做岩石力学试验, 特别是近年逐渐流行的合成岩体(Synthetic Rock Mass)技术能够帮助工程师更真实地了解岩石的力学特性. SRM是Bonded Particle Model 与 Smooth-Joints的结合, 使用线性平行粘结模型(linear parallel bond model: contact cmat default model linearpbond ) 创建粘结颗粒模型，使用平滑节理模型(smooth joint model: fracture contact-model model 'smoothjoint' install) 模拟节理和裂隙。这种把DFN内嵌到原岩模型的方法，极大地扩展了PFC的使用能力，从而可以更真实地模拟岩体内节理的力学行为.

smoothjoint 节理模型能够更好地预测这种破坏机理。建模方法是把断裂几何形状和特性叠加到BPM模型上。BPM对完整岩石建模，通过修改断裂接触点处的接触模型引入断裂的力学行为。由于PFC模型本质上是离散的，因此破坏可能在完整的BPM区域和沿断裂面发生。

建立SRM的思路可以扩展到3DEC中, 使用Voronoi块体表示原岩，与DFN相结合能够模拟岩体真实的破坏行为. 不过这种计算代价太大，需要性能非常高的计算机才能在短时间内得出结果。

4 References

1. Potyondy, D. and Cundall, P.A. (2004) A bonded particle model for rock. Int. J. Rock Mech. Min. Sci., 41: 1329-1364. 

2. Pierce, M.E., and C. Fairhurst. “Synthetic Rock Mass Applications in Mass Mining,” in Harmonising Rock Engineering and the Environment (Proc. 12th ISRM Int. Congress, Beijing, China, October 2011), pp. 109-14, Q. Qian and Y. Zhou, eds., ISBN 978-0-415-80444-8, London: Taylor & Francis Group (2012).

3. Potyondy, D. O. “The Bonded-Particle Model as a Tool for Rock Mechanics Research and Application: Current Trends and Future Directions,” Geosystem Engineering, 18(1), 1–28 (2015), DOI:10.1080/12269328.2014.998346.

4. Manouchehrian, A., et al. (2014). "A bonded particle model for analysis of the flaw orientation effect on crack propagation mechanism in brittle materials under compression." Archives of Civil and Mechanical Engineering 14: 40-52. 

5. Cundall, P. A. “Numerical Experiments on Rough Joints in Shear Using a Bonded Particle Model,” in Aspects of Tectonic Faulting, pp. 1-9. F. K. Lehner and J. L. Urai, Eds. Berlin: Springer-Verlag (2000).

6. Yoon, J., H. Lee and S. Jeon. “New Way of Determining Microparameters for 2D Bonded Particle Model Generation in Uniaxial Compression Simulations,” in DEM 07, CD Proceedings of the Discrete Element Modelling Conference (Brisbane, Australia, August 27-29, 2007). Minerals Engineering International (2007).

7. Reyes-Montes, J. M., W. S. Pettitt and R. P. Young. “Validation of a Synthetic Rock Mass Model Using Excavation Induced Microseismicity,” in Rock Mechanics: Meeting Society’s Challenges and Demands (1st Canada-US Rock Mechanics Symposium, Vancouver, Canada, May 2007), Vol. 1: Fundamentals, New Technologies & New Ideas, pp. 365-369. E. Eberhardt, D. Stead and T. Morrison, eds. London: Taylor & Francis Group (2007).

8. Sainsbury, B., M. E. Pierce and D. Mas Ivars. “Analysis of Caving Behaviour Using a Synthetic Rock Mass – Ubiquitous Joint Rock Mass Modelling Technique,” in SHIRMS 2008 (Proceedings of the 1st Southern Hemisphere International Rock Mechanics Symposium, Perth, Western Australia, September 2008), Vol. 1, pp. 343-352. Y. Potvin et al., eds. Nedlands, Western Australia: Australian Centre for Geomechanics (2008).

9. Pierce, M., Cundall, P., Potyondy, D. and Mas Ivars, D. (2007)  “A Synthetic Rock Mass Model for Jointed Rock,” in Rock Mechanics: Meeting Society’s Challenges and Demands (1st Canada-US Rock Mechanics Symposium, Vancouver, Canada, May 2007), Vol. 1: Fundamentals, New Technologies & New Ideas, pp. 341-349. E. Eberhardt, D. Stead and T. Morrison, eds. London: Taylor & Francis Group (2007).

10. Pierce, M., D. Mas Ivars and B. Sainsbury. “Use of Synthetic Rock Masses (SRM) to Investigate Jointed Rock Mass Strength and Deformation Behavior,” in CD Proceedings of the International Conference on Rock Joints and Jointed Rock Masses (Tucson, Arizona, January 2009), paper 1091. P. H. S. W. Kulatilake, ed. Tuscon: Kulatilake & Associates (2009).

11. Mas Ivars, D., Deisman, N., Pierce, M. & Fairhurst, C. (2007) “The Synthetic Rock Mass Approach – A Step Forward in the Characterization of Jointed Rock Masses,” in The Second Half Century of Rock Mechanics (11th Congress of the International Society for Rock Mechanics, Lisbon, Portugal, July 2007), Vol. 1, pp. 485-490. L. Ribeiro e Sousa, C. Olalla and N. Grossman, eds. London: Taylor & Francis Group (2007).

12. Ivars, D., Pierce, M., Darcel, C., Reyes-Montes, J., Potyondy, D., Young, R., and Cundall, P. (2011). The synthetic rock mass approach for jointed rock mass modelling. International Journal of Rock Mechanics and Mining Sciences, 48(2), 219-244.

13. Elmo D., K. Moffitt and J. Carvalho. 2016. Synthetic rock mass modelling: experience gained and lessons learned. 50th U.S. Rock Mechanics Symposium. Houston, Texas, June 2016. Paper 777.

14. Vazaios, I., Farahmand, K., Vlachopoulos, N., Diederichs, M.S. (2017) The Effects of Confinement on the Rockmass Modulus: A Synthetic Rockmass Modelling (SRM) Study. Journal of Rock Mechanics and Geotechnical Engineering. Submitted on 18 June 2017

16. Martin, C. D., et al. (2012). "Scale effects in a synthetic rock mass." Harmonising Rock Engineering and the Environment: 473-478.

17. Poulsen, B. A., et al. (2015). "Convergence of synthetic rock mass modelling and the Hoek-Brown strength criterion." International Journal of Rock Mechanics and Mining Sciences 80: 171-180.

18. Esmaieli, K., J. Hadjigeorgiou and M. Grenon. “Estimating Geometrical and Mechanical REV based on Synthetic Rock Mass Models at Brunswick Mine,” Int. J. Rock Mech. Min., 47(6), 915-926 (2010).

19. Farahmand, K., and Diederichs, M. (2015). A Calibrated Synthetic Rock Mass (SRM) Model for Simulating Crack Growth in Granitic Rock Considering Grain Scale Heterogeneity of Polycrystalline Rock. San Francisco, USA: Proceedings of the 49th US Rock Mechanics Symposium. 14 pages.

20. Farahmand, K., Vazaios, I, Diederichs, M.S., and Vlachopoulos, N. (2015). Generation of a Synthetic Rock Mass (SRM) Model for Simulation of Strength of Crystalline Rock using a Hybrid DFN-DEM Approach. In Proceedings of the EUROCK 2015, Salzburg, Austria. 7 pages.

21. Farahmand, K., Vazaios, I., Diederichs, M.S., Vlachopoulos, N. (2017) Investigating the Scale Dependency of the Mechanical Properties of a Moderately Jointed Rockmass using a Synthetic Rock Mass (SRM) Approach. Journal of Computers and Geotechnics. Submitted on 7 July 2017 

22. Mas Ivars, D., Pierce, M., DeGagné, D. and Darcel, C. (2008a) Anisotropy and scale dependency in jointed rock-mass strength—A synthetic rock mass study. Continuum and Distinct Element Numerical Modeling in GeoEngineering, Proceeding First International FLAC/DEM Symposium on Numerical Modeling, R. Hart, C. Detournay and P. Cundall (editors) 24–26 August, Minneapolis, Itasca