بررسی عددی رفتار هیدرومکانیکی درزه‎های سنگی منفرد تحت بارگذاری برش مستقیم

نوع مقاله: پژوهشی

نویسندگان

گروه مهندسی مکانیک سنگ، دانشگاه تربیت مدرس

10.29252/anm.7.13.35

چکیده

نفوذپذیری توده سنگ یکی از مهمترین پارامترهای کنترل کننده پروژه‎‎های مختلف مهندسی سنگ اعم از مخازن دفن زبالههای اتمی، پی سدها، فضاهای زیرزمینی همانند تونل‍‌ها و مغارها، پروژه های ژئوترمال و تولید نفت و گاز است. به طور کلی نفوذپذیری توده سنگ متشکل از نفوذپذیری سنگ بکر و ناپیوستگی های موجود در آن است اما در حوضههای با سنگ میزبان سخت و کریستالی نفوذپذیری سنگ بکر تقریباً ناچیز و قابل اغماض است و کنترل کننده اصلی جریان عبوری از توده سنگ، درزهها و ناپیوستگی ها هستند. در چنین شرایطی، علاوه بر پارامترهای هندسی درزه لازم است تاثیر عواملی همانند جابجایی برشی و تنش نرمال نیز بررسی گردد. در این مقاله با روش عددی المان مجزاء یک کد عددی توسط نرم افزار UDEC برای بررسی کوپل هیدرومکانیکی درزه های منفرد تحت برش با مدل درزه داری بارتن- باندیس توسعه داده شده است. در کد عددی توسعه داده شده تاثیر پارامترهایی همانند جابجایی برشی، تنش نرمال و سختی درزه بررسی شده است. برای راستی آزمایی مدل عددی نتایج آن با نتایج تجربی بدست آمده توسط السون- بارتن (2001) مقایسه شده است. بررسی های انجام شده، نشان میدهد که نتایج مدلسازی عددی هماهنگی خوبی با نتایج آزمایشگاهی السون ـ بارتن (2001) دارد. همچنین تحلیل های عددی انجام شده حاکی از آنست که متناسب با افزایش جابجایی برشی، مقدار بازشدگی هیدرولیکی و نرخ جریان افزایش مییابد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical Modeling of Hydro-Mechanical Behavior of Rock Joints under Direct Shear Loading

نویسندگان [English]

  • Behnam Ghobadi
  • Hamidreza Nejati
  • Kamran Goshtasbi
Dept. of Mining and Metallurgy, Tarbiat Modares University, Iran
چکیده [English]

Summary
This papers focuses on the permeability of rock joint under direct shear tests and a comprehensive study was made to numerically evaluate the hydro-mechanical behavior of rock joints.
 
Introduction
Rock mass permeability is a key parameter in rock engineering projects such as repositories for radioactive waste, dam foundations, excavation of tunnels and caverns, geothermal energy plants, oil and gas production, etc. Due to the stiffer rock matrix, most parts of rock mass permeability are related to the joints and discontinuities. Further, shear and normal stress, shear and normal deformation, joint roughness and etc. affect rock joint permeability. Therefore interaction between stress and permeability is a crucial factor during different stages of reservoir’s life such as: assessment, productivity and management.
 
Methodology and Approaches
In the present paper, it is intended to consider the permeability of rock discontinuity in direct shear test. For this purpose, a distinct element code is used to develop numerical modeling of the direct shear test. UDEC has the capability to perform the analysis of fluid flow through the fractures and voids of a system of impermeable blocks. Steady-state pore pressures can be assigned to zones within deformable blocks and boundary conditions may be applied in terms of fluid pressures or by defining an impervious boundary. The fluid-flow calculation can also be run either coupled or uncoupled with the mechanical stress calculation. A fully coupled mechanical-hydraulic analysis is performed in which fracture conductivity is dependent on deformation, and conversely, joint fluid pressures affect the mechanical computations. Two main experimental stress conditions under which the shear force of rock joints can be determined, are the Constant Normal Load condition, CNL, and the Constant Normal Stiffness condition, CNS. The numerical model was calibrated with experimental tests and it was tried to confirm the validity of the developed model. Finally, a sensitivity analysis was made to investigate the effect of mechanical rock joint parameters and properties of fluid on the flow rate of discontinuities.
 
Results and Conclusions
Variation of shear stress and rock joint transmissivity with shear displacement compared in the both numerical model and experimental test and it is shown that the results of numerical modeling have a good agreement with results of experimental models from literature. Numerical analyses revealed that with increasing the shear displacement, increases hydraulic aperture and flow rate of discontinuities. Also it is revealed that joint roughness coefficient has a direct relation with flow rate of discontinuity. 

کلیدواژه‌ها [English]

  • Hydro-mechanical couple
  • shear displacement
  • permeability
  • Barton-Bandis
  • Distinct element method
[1] Zhang, L. (2013). Aspects of rock permeability. Frontiers of structural and civil engineering, 7(2), 102-116.
[2] Nishiyama, S., Ohnishi, Y., Ito, H., & Yano, T. (2014). Mechanical and hydraulic behavior of a rock fracture under shear deformation. Earth, planets and space, 66(1), 1-17.
[3] Park, H., Osada, M., Matsushita, T., Takahashi, M., & Ito, K. (2013). Development of coupled shear-flow-visualization apparatus and data analysis. International journal of rock mechanics and mining sciences, 63, 72-81.
[4] Baghbanan, A., & Jing, L. (2008). Stress effects on permeability in a fractured rock mass with correlated fracture length and aperture. International journal of rock mechanics and mining sciences, 45(8), 1320-1334.
[5] Koyama, T. (2007). Stress, flow and particle transport in rock fractures. PhD thesis, KTH University.
[6] Gale, J., Mac Leod, R., & Le Messurier, P. (1990). Site characterization and validation-Measurement of flow rate, solute velocities and aperture variation in natural fractures as a function of normal and shear stress, stage III, Technical report of Swedish Nuclear Fuel and Waste Management Co.
[7] Esaki, T., Du, S., Mitani, Y., Ikusada, K., & Jing, L. (1999). Development of a shear-flow test apparatus and determination of coupled properties for a single rock joint. International journal of rock mechanics and mining sciences, 36(5), 641-650.
[8] Yeo, I. D., De Freitas, M. H., & Zimmerman, R. W. (1998). Effect of shear displacement on the aperture and permeability of a rock fracture. International journal of rock mechanics and mining sciences, 35(8), 1051-1070.
[9] Lee, H. S., & Cho, T. F. (2002). Hydraulic characteristics of rough fractures in linear flow under normal and shear load. Rock mechanics and rock engineering, 35(4), 299-318.
[10] Mitani, Y., Esaki, T., Sharifzadeh, M., & Vallier, F. (2003). Shear-flow coupling properties of a Rock Joint and its modelling by geographic information system (GIS). 10th ISRM congress, sandton, South Africa.
[11] Olsson, R., & Barton, N. (2001). An improved model for hydromechanical coupling during shearing of rock joints. International journal of rock mechanics and mining sciences, 38(3), 317-329.
[12] Jiang, Y., Xiao, J., Tanabashi, Y., & Mizokami, T. (2004). Development of an automated servo-controlled direct shear apparatus applying a constant normal stiffness condition. International journal of rock mechanics and mining sciences, 41(2), 275-286.
[13] Barton, N., Bandis, S., & Bakhtar, K. (1985). Strength, deformation and conductivity coupling of rock joints. International journal of rock mechanics and mining sciences & geomechanics. Vol. 22, No. 3, pp. 121-140).
[14] Barton, N., Bandis, S., & Bakhtar, K. (1986). Strength, deformation and conductivity coupling of rock joints. Publikasjon-Norges geotekniske gnstitutt, (162), 1-20.
[15] Zimmerman, R. W., & Bodvarsson, G. S. (1996). Hydraulic conductivity of rock fractures. Transport in porous media, 23(1), 1-30.
[16] Smart, B. G. D., Somerville, J. M., Edlman, K., & Jones, C. (2001). Stress sensitivity of fractured reservoirs. Journal of petroleum science and engineering, 29(1), 29-37.
[17] Brady, B. H., & Brown, E. T. (2013). Rock mechanics for underground mining. Springer science & business media.