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ESTIMATING THE INFLUENCE OF SURFACE CHARACTERISTICS OF ROCK JOINTS ON SHEAR BEHAVIOR Graduate school of Science and Technology, Nagasaki University Y.Tasaku, Y.Jiang, Y.Tanahashi, B.Li

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・ The dependency of mechanical behavior on boundary conditions. ・ The relationship between the mechanical behavior and the surface characteristics are evaluated. The deformation behavior and stability of underground structures depend principally on the shear strength of discontinuities in rock masses. Direct shear test Measurement and evaluation of joint surface Introduction The shear strength is generally dominated by surface characteristics of rock joints. The development of deep underground space has received high attention

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Rock slope (non- reinforcement) Constant normal load condition Free σ n ＝ Constant τ Constant normal load (CNL) condition

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Constant normal stiffness (CNS) condition Joint Constraint from rock masses Deep underground Change of normal stress σ n ≠Constant τ Constant normal stiffness (CNS) condition

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Digital-controlled shear test apparatus Horizontal Jack Vertical Jack Specimen

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Structure of surface measurement system Laser displacement meter Computer for control and record X-Y positioning table

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・ Mix ratio(weight ratio) plaster ： water ： retardant =1 ： 0.2 ： ・ Unconfined compressive strength σ n0 =32.0MPa (middle hard rock) Specimen Natural surfaces Possible to analyze the substantial fractal dimension ・ Dimension (mm) 200×100×100

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Test cases J１J１ J2 J3 (Large asperity in the center and smooth surface) (Many small asperities) (Specimen of previous study with very smooth surface)

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Test cases ・ Initial normal stress σ n0 : 1MPa, 2MPa (50 ～ 100 ｍ ), 5MPa (about 250 ｍ ) Each of J1 and J2 has 9 cases; 18 cases at all ・ Normal stiffness: k n J1 is 1GPa/m and 7GPa/m J2 is 1GPa/m and 3GPa/m, ・ Control condition Constant normal load (CNL) condition and constant normal stiffness (CNS) condition

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Result of shear test (J1,σ n0 =2MPa) CNL condition CNS condition(k n =3GPa/m) CNS condition(k n =7GPa/m)

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Surface of specimen before and after shear (J1,σ n0 =2MPa) Before shear After shear on CNL condition After shear on CNS condition ( k n =3GPa/m) (mm)

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Evaluation method of surface roughness by projective covering method Projective covering cell Fracture surface δ : length of a mesh A T (δ): Total area A T0 (δ): Apparent area (2 ＜ D s ＜ 3)

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Transition of fractal dimension CNL CNS(k n =1GPa/m ） Before shearing CNS （ k n =3GPa/m ） J2

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Statistical parameter of two dimensions N: Total number of measuring points along the profiles y i ： ith value of height ⊿ x ： Minute distance to direction x Z 2 is the average slope of asperity

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Transition of Z 2 CNL CNS(k n =3GPa/m ） Before shearing CNS （ k n =7GPa/m ） J2

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Maximum shear stress τ ： Maximum shear stress σ n0 ： Initial normal stress JRC ： Joint roughness coefficient JCS ： Joint wall compressive strength φ b ： Inter friction of joint Maximum shear stress: (Barton 、 1977) Two dimensional indicator Suggestion equation ‘a’ and ‘b’ are obtained from the relationship between JRC and D s on experience. Actual rock joint is three dimensional

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Comparison of the Barton’s empirical equation with proposed equation Barton’s empirical equation σ n0 (MPa)125 J1 J2 J3 σ n0 (MPa)125 J1 J2 J3 Proposed equation Base line

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Conclusion Shear behavior of rock joint Constraint from rock blocks Surface characteristics of joint The relation of Initial normal stress and surface roughness （ about CNL ） Influence Confirmation of validity Proposed equation It is possible to predict the shear behavior by D s

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END

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自然の岩石を供試 体として用いる 圧裂試験 表面のケースの充実 D s を用いて、せん断特 性を正確に予測

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D s とピークせん断応力との関係 表面 2 （ D s =2.0279) 表面 1 （ D s = ） 表面 3 （ D s =2.008 ） 破線：理論値

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JRC 値は以下の式 (Tse 、 1979 ） JRC 値と Z 2

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せん断応力の比較 (σ no =2MPa) 表面 1 表面 2 CNL 制御 CNS 制御 (k n =3GPa/m) 表面 1 表面 2

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