1. EVALUATION OF COUPLED SHEAR-FLOW BEHAVIOR OF SINGLE ROCK JOINTS R. Saho, Y. Jiang, Y.Tanabashi, B.Li Graduate School of science and technology Nagasaki University

2. Background of research In recent years, the development of deep underground spaces like radioactive waste disposal has received great attention in all countries operating nuclear power plants. These facilities positively utilize the isolability and impermeability of rock masses,which require the thoroughly understanding of the mechanical-hydraulic behaviors of rock fractures in rock mass. Geological disposal is the most promising option for a safe long-term management of radioactive waste as agreed by scientists and politicians.

3. Background Schematic cross-action of Yucca Mountain (America) and depiction of processes that are important to repository performance

4. Purpose of research Shear-flow coupling test Fluid flow in rock mass takes places predominantly through fractures. ・ A fracture normally undergoes stresses from two directions, normal stress and shear stress. ・ The void structures in the fracture change remarkably due to dilation and the relative displacement between the two joint walls especially for mated joints. Understanding the permeability property of rock fractures in shear process.

5. A new direct shear-flow test apparatus The shearing process could be applied on single rock joint under either CNL or CNS boundary conditions with the hydraulic tests at the same time. The weight of water flowing out of the fracture is measured by an electrical balance in real time. (2) (1)

6. Differential manometer measurement A new direct shear-flow test apparatus The water head can be accurately measured by using a differential manometer. (3)

7. A new direct shear-flow test apparatus (4) Visualization system for shear-flow test of rock joints. Normal load Digital Camera PC Acrylic board Shear load Joint surface Water Tank

8. Test on parallel-plate model Water head (h) aperture 2.0m, 1.0m, 0.5m 0.07mm, 0.14mm, 0.21mm, 0.28mm, 0.35mm A typical fracture contains isolated asperity regions where the two rock surface are in contact,surrounded by open regions where the two surface are separated by an aperture that may vary from point to point. A simple parallel- plates model was used in hydraulic tests by changing the arrangement and ratio of contact areas. The setting contact areas on two smooth parallel plates with uniform aperture,by changing the distribution case (case 1, case 2, case 3) and contact ratio (15%, 20%, 25%) to test the response of flow to the contacts.

9. Q: the volumetric flow g: the acceleration of gravity e: the hydraulic aperture : the kinematic viscosity of the fluid i: the hydraulic gradient Methodology to evaluate the hydraulic conductivity If considering the joint as composed of two smooth parallel plates and the flow to be steady, single phase, laminar and incompressible, the Darcy’s law may be written as: Where is usually called the “cubic law” Cubic law is exact only for smooth-wall fractures with uniform aperture. e L w flow

10. Experiment case3 2 1 case 25%20%15% Contact ratio (Contact area: )

11. h=0.5m h=2.0m h=1.0m deviation Cubic law Test results (Contact area20% ） A part of flow may have changed from the laminar flow to turbulent flow at large mechanical apertures. Experimental results distribute below the Cubic law

12. The arrangement of contact areas seems to have negligible influence on the flow through a fracture. Test results of different arrangements (Contact area20%) Case 1 Case 2 Case 3 Cubic law Case 1 Case 2 Case 3 Similar tendency

13. Test result of different contact ratios 15% 20% 25% Cubic law 15% 25% 20% Contact ratio have significant influence on the flow through a fracture. Contact ratio= contact area/fracture area

14. Surface view of specimen Joint 1Joint 2 Three shear-flow tests were carried out with boundary conditions: case 1: CNL(1) normal stress  n0  =1MPa case 2: CNL(2) normal stress  n0  =2MPa case 3: CNS normal stress  n0  =1MPa, normal stiffness k n =0.5GPa/m

15. Shear behaviours of rock joint Joint 1 Joint 2 Residual strength CNL( σ n0 =1MPa) CNL( σ n0 =2MPa) CNS( σ n0 =1MPa k n =0.5GPa/m) Peak shear stress Larger shear stresses are obtained under either higher normal stress or higher normal stiffness at the same initial normal stress.

16. Normal behaviours of rock joint Joint 1 Joint 2 CNL( σ n0 =1MPa) CNL( σ n0 =2MPa) CNS( σ n0 =1MPa k n =0.5GPa/m) Relation between shear displacement and normal displacement. Positive dilation is shown in the residual region and negative dilation is generated when a shear starts.

17. σ Conductivity versus shear displacement (CNL: σ n0 =2MPa) Joint 1Joint 2 High hydraulic gradient Middle hydraulic gradient Low hydraulic gradient Average of hydraulic gradient The conductivity decreases as hydraulic gradient increase. The values of the conductivities are greatly different.

18. σ Comparison of hydraulic aperture and mechanical aperture (CNL: σ n0 =2MPa) Joint 1 Joint 2 Hydraulic aperture Mechanical aperture The mechanical aperture and hydraulic aperture agrees well with each other. In the initial stage of shear, the apertures decrease remarkably and then increase as shearing.

19. Conclusions A newly-developed shear-flow test apparatus was used to carry out the tests on parallel-plate model and artificial rock joints. The contact ratio has a greater influence on the fluid flow than the arrangement of contact area. The rock joint dilates as the shear displacement progresses as well as the mechanical and hydraulic aperture. (1 ) (2 ) (3 ) Higher shear stress and dilation value could be obtained on a joint with greater roughness.

20. Future study (1) More shapes of contact area will be tested based on the parallel-plates model in the future study as well as improving the precise of the test apparatus. (2) Shear-flow coupling tests are required on more abundant rock fractures with different sizes under various boundary conditions. (3) Visual tracer test will be developed to find out more detailed information of the fluid flow though a rock fracture.

21. The end 謝 安 全 第 一