ª Œª Œ 27ƒ 4C Á 2007 7œ pp. 293~304 ª x mw - Shear Behavior Charateristics of Drilled Shaft - Rockmass Interface Using Direct Shear Test Under Constant Normal Stiffness Condition Á Á z Jeong, Sang SeomÁWoo, Sang YoonÁSeol, Hoon Il Abstract This paper described the theoretical shear strength function proposed to predict the shear behavior of pile-rock joint under constant normal stiffness condition. The quantified values of rock socket roughness were determined through previous studies and this study. Constant normal stiffness direct shear tests were carried out to quantify the shear behavior characteristics based on major influencing factors of shear behavior such as asperity angle, unconfined compressive strength, initial confining stress. Based on CNS test results, this paper proposed the shear strength function simulating the major influencing factors of shear behavior of pile-rock joint, including asperity angle, unconfined compressive strength and elastic compression displacement as well. The proposed function was verified by the CNS test result performed to artificial rocks molded to describe regular asperities, granite and gneiss. Through comparisons with the CNS test results, it is shown that the shear strength function by this study is in good estimation with the general trend observed by the tests. Through comparisons of the maximum shear strength between the domestic criterion of shaft resistance and shear strength function of this study, it was shown that the maximum shear strength by the function of this study considerably increased than the strength by the doemstic criterion along with the higher asperity angle and initial confining stress. Keywords : rock-socked drilled shafts, constant normal stiffness tests, bore hole roughness, pile-rock joint, shear strength function x k w,» x ü x ww e» yw - w (CNS) x ww e»,,» gj p q w. m r e» e» k w w ƒ w w, CNS x w wš. w» ü» mw - r, mw r e»» f»» l w j ùký. w : (CNS) x, e» y, e» ƒ,,», Hoek-Brown q», w 1. x ü x k w x w. w, Horvath (1983), O'Neill (1995), Seidel and Collingwood(2001), y (2003) x k e», p,»,, ty j w ùkù. x k w š w x k w öe * z Á Á w œ w m œw (E-mail : soj9081@yonsei.ac.kr) *( ) gr» q (E-mail : spzone@hanmail.net) *** z Á w w m œw (E-mail : geo_dr@yonsei.ac.kr) 27ƒ 4C 2007 7œ 293
w š w w ƒ v š. x k w» wù(baqulin, 1982; O'Neill, 1995; Kim, 1999), e», ty x ƒ, x, ü sw y r w w, ü x k w û» w ƒ v w.» x ü x ww e» yw, k CNS x w gj p q w. w, r e» k w w š w w w, ü x w k mw, mw» ü» w w, w y y w. 2. e» y, e» w CNS x w» w e» d y w. e» yw Barton(1977) JRC(joint roughness coefficient), s,»», v k w, e» y e» d j» j» w w š w w, v k (fractal) e» ƒ w m w Seidel and Harberfield(1995)ƒ w y w. y, 1 - w ¼ x(chord length, l a ) ƒ, x ƒ ³ s(gaussian)w y w. l k ³e e» v q (1) ùkü w ( r) ƒ ³e ƒxk e» y w., w ¼ x(l a ) e» yw, w l a» w. n 1 1 r = -- r n i = -- l n a sin θ i i = 1 n i = 1 ( ) Seidel Collingwood(2001) w x w mw e» ƒ f û, e» 0.9~16.2mm š šw. Nam(2004) m, z» (auger, core barrel) w œw e» v q mw d w yw. ü, y (2003) ü y, r 10 15z e» k w, e» s³ x ¼ (l a ) 50mm» yw., ü e» s³ 1~4mm ùkû.» k w x x ty e» k w, 2 v q (laser profile gauge) mw d (digitize)w z, Seidel and Harberfield (1995)ƒ w y w, ü e» y wì ww t 1 ùkü. e» y, ü e» 1. y e» x (Seidel and Harberfield, 1995) 2. e» d t 1. ü e» y (MPa) x ¼, l a (mm) e» (mm) e» ƒ (deg) š Seidel (2001) y (2003) Nam(2004) r (ty ) 5.0 1~6 1.1~6.9 50 r ( ) 50.3 1~7 1.1~8.0,,, r,, z y 100~150 r 30~130 75~77 5~10 1.7~16.2 1.9~18.9 50 10~70 0.9~-6.6 1.0~7.6 50 1~4 1.1~4.6 74 1~3.5 1.1~4.0 Clay Shale 2.1~12 Limestone 10 50 Driling bit Back- analysis RCD 3.6~5.3 4.1~6.1 Auger 4.7~5.8 5.4~6.7 Core Barrel 3.2~3.7 3.7~4.2 Auger 4.3~5.1 4.9~5.8 Core Barrel (1) 294 ª Œª Œ
1~7mm ƒ, e» ü sw ùkû. w e» s³ ƒ w x ¼ 50mm», e» (ƒ ) 1mm~16mm( ƒ 1.1~18.9 ) w, CNS x w. 3. CNS(Constant Normal Stiffness) x x e» y w (constant normal stiffness, CNS) x ww, gj p q w» w, k w w (, e»,» ) š w w w» w. x w CNS x mw w ƒ y w (Johnston, 1987; Indraratna, 1999; Seidal, 2001) ü x CNS x mw x k ü y w y (2004), CNS x m GSI(geological strength index) w Hoek-Brown q» w, w w z (2006). m ƒ r w CNS x 3 ùkù 3 yw. 1 k q (dilation) ù» ƒ (sticking), 2 ká w z, ñ (slip) ù q (dilation) w 3. y m r CNS x (Johnston, 1987) r t 2. r p x p q u (MPa) E intact (MPa) e» ƒ, ν i (deg) r 20.1 2720 0.30 gj p r 41.5 21000 0.30 ƒƒ, 3 j x k e» Áq w w x. 3.1 x e» z š w» w, CNS x x r w x ww w, r w e» ƒ ƒ r, œ š w r w x ww. x k w gj p r w w 40 MPa š p k w w, d w 12 t xw ùkû. r x» w y k x¼ 25mm, e» ƒ 4.6 o ( r=2mm), 9.1 o ( r=4 mm), 15.6 o ( r=7mm) ƒ ƒx ùe ƒ m, r¼ 175mm, s 100mm j». w, x w» w, e»» w 27 x ww, w x r gj p r, k, s p wì t 2 w ùkü. 3.2 x» w x w 27 z CNS x w z, x ùkü. 4 0.5MPa/mm,» 0.35MPa w e» ƒ 4.6 o, 9.1 o, 15.6 o r - (τ-w), - (d-w), - (τ-σ N ), - (d-σ N ) ùkü. 4(a) - (τ-w) ká ƒ e» ƒ ƒw f q (dilation) f ƒ(d-σ N ) w (τ-σ N ) ƒw». 5 e» ƒ 9.1 o (0.2, 0.5, 1.0MPa/mm) w ƒw ƒ ƒ, w f. e» ƒ w» q ( r), f ƒw ƒw.» w e»ƒ - (τ-σ N )» x, K N (MPa/mm)», s ini (MPa) 4.6, 9.1, 15.6 0.2, 0.5, 1.0 0.35, 0.70, 1.05 27ƒ 4C 2007 7œ 295
4. e» w( r, K N =0.5MPa/mm, σ ini =0.35MPa)», e»ƒ ƒ w - (τ-σ N )»»ƒ. e» x e» ƒw» (initial peak strength) z ká f ƒw. 6(a),»» ƒ x» k z ká w. e» ƒ k» w w. w x gj p r r Á w gj p k w, x» -gj p ùkù. ù 4 ùkü ñ» w CNS x w j» ƒ. 5. w( r, σ ini =0.35MPa, i = 9.1 o ) 296 4. w ƒ w 4.1 w z (2006) k w w w» w, w ƒ Hoek-Brown q» w. xk Hoek-Brown q» - ùký, x k t»w (2). 7 xk Mohr-Coulomb» ù ww CNS x x(nonlinear) xk tx. σ normal σ B tm f Aσ ci ------------------------------ = σ ci», m b, s, a, σ ci, σ tm (=-sσ ci /m b ), A B w. (2) ª Œª Œ
6.» w( r, i= 4.6 o, K N =0.5MPa/mm) z (2006) CNS x k Hoek-Brown q» w,, e», w x k w š (3) w, 7 CNS x x - ( ) x xk( ) ùký. f = f = f = B sσ ci ( σ ini ) -------- m b Aσ ci ----------------------------------- σ ci wz ( ) ---------- w st (w(z) w st ) sσ ci ( σ ini + K ( n wz ( ) w ) st tani) -------- m b Aσ ci ----------------------------------------------------------------------------------- σ ci f ( max z) (3a) (w st <w(z) w max ) (3b) (w max <w(z)) (3c)», σ ci =, σ normal = -, σ tm = =-sσ ci /m b, σ ini =», A=1, B=GSI( 8 ), i= e» ƒ, s, m b = Hoek-Brown B, w= -, w st = k xw =0.5~2mm, w max = xw, K N = w. 4.2 k š w w z (2006) CNS x k z, k ƒ ƒ (4) w. r = ( wz )tani ( ) w st», w st = k xw (mm)», i = r e» ƒ ( o ) w. w CNS x, (4) mw w x mw ƒ û w. ƒ r k sww» š q. w k w» w, ³e ƒx e» ƒ y r 9 ùkü. r n w sn ¼ s ƒ r¼ L T, r s³ Ì D ƒ. Seidal and Harberfield(2002) w xi σ i ƒ ƒw, w xj w k, δ ji (5)., w, I ji x L i w ü ƒ, w 0. w w 1 tx. r e š w, L j w L i w w w I ij I ji. L i ƒw w w L k ¾ y w, (6). (4) 7. y( z, 2006) δ ji = σ i D I ji -------- E (5) 27ƒ 4C 2007 7œ 297
그림 8. 지질강도지수(Geologcal Strength Index, GSI)(Hoek 등, 1995) 이고 δ=δ =δ 이 되므로, 변위영향계수는 다음의 식 (7)과 같 게 되며, 모든 현에서의 최종 1차압축량, δ는 다음의 식 (8) 과 같이 제안될 수 있다(Seidel and Harberfield, 2002). i i+k 그림 9. 일반화된 암석시편의 거칠기 단면 i + k Iij δj D δi = ------------i k E (6) i+k Iij = i k Iji = 1 i k (7) σi D δ = δi = -------E (8) 따라서, CNS 직접전단시험시, 수직변위가 관찰되는 탄소 성 구간에서의 수직변위의 증가량은 다음의 식 (9)와 같다. 만일 동일한 수직응력이 모든 현에 가해진다면, δ=δ =δ i j j 298 ( σ + σ ) D r = ( w( z) w )tani δ = ( w( z ) w ) tani -------------------------------n st st E ini (9) 大韓土木學會論文集
w,, K n ƒ w ƒ ( σ n =K n r), r k š ƒ (10). r gj p r k w (11) ùký. σ n tani wz ( ) w st --- E = K n ----------------------------------------------------- D 1 + K n --- E ( ) σ ini D (10) w, B r e» w t 3 ƒ ùkû. t 3. w w T m Y r 1.2 115.0 Asperity angle, i( ) -0.01-7.8 q u (kpa) 5.0E-06 17.8 i * q u -1.5E-07-3.6 (w st <w(z) w max ) (11) (11) r Ì, D d w w ù, x d ƒ w, k x w w, Z w w. w k x w w k œ w x œ y (expansion of an infinite cylindrical cavity, Boresi, 1965) w. œ y w, (K N ) (12) k (E m ), s (ν m ), (r) ùký. σ N E m K = --------- = -------------------- r r( 1 + ) ν m (12) ƒw, w k ƒ w, Hooke e w (13) ñ. K σ E m = -- = ------ Z (13)» E m k, ν m s. (12) (13) l e w, Zƒ w. Z = r 1 + ν m ( ) (14)» z (2006) (11) B ty k ùkü GSI w ù, r p GSI d š r k y (2004) r ƒ û r ty ³» GSI B w. y (2004) ww CNS x l w w, e» ƒ, š T m eƒ 3.6~17.8 w e š 2 j» ƒ š w. m w B (15) w. B = 0.01i + 5.0 10 6 q u 1.5 10 7 iq u + 1.2 (15)», i : ¼ 50mm w w e» ƒ ( o ) t 4. x r w e», q u : (kpa) 5. CNS x CNS x w mw, w r e»,,» w w gj p ùký k w. yw w, CNS x ww x w w w. w k r t 4. r k NXj» w ww, k š»»» w. y (2003) ww r(r ) w t 4 ùkü, r r m i Marinos and Hoek(2001) w» k ƒƒ w. t 4 eƒ w CNS x w 10~14 ùkü. r,, e» ƒ( ),» w ww, r, e» ƒ,, ww Material Type q u (MPa) E(MPa) m i r Ì(mm) B Gypsum plaster 15 550 16 75 1.12~1.26 Gneiss 17~89 61000 28 51 1.17~1.60 27ƒ 4C 2007 7œ 299
. 46z CNS x w w ù, x w. 10 11 r w CNS x w, ƒ x š, š, š w., w ( e»,,», k ) w wš, CNS x ewš š q. p, k ƒ r, š» w k w d ƒ w ùkû. w, r e» ƒ ƒ j ù CNS ƒ j, x e sƒ wš, CNS x, r e» ƒ j ù CNS j f š, ƒ j r k e» q w ƒ f» w j w e» q ¾ š w w» q. 12~14 r(r ) w w CNS x w ùkü. r r w k ƒ f ƒ k ùkû š w., r e»ƒ ³ewš r ³ w w ƒ x w r w w», w d ƒ ù, k k w, r w w w š wš q w. l, w w gj p- r e»,,,» w w dƒ w. 10. w CNS x ( r, K N =0.2MPa/mm, σ ini =1.05MPa) 300 ª Œª Œ
11. w CNS x ( r, i=4.6 o, K N =0.5MPa/mm) 12. w CNS x (r, i=10 o, K N =3.0MPa/mm) 6. w p w w x mw, w w ƒ w y w. y (2004) w w 27ƒ 4C 2007 7œ 301
13. w CNS x (r, q u =2MPa, i=5 ) ü x k,» ü» w (τ max ) mw ww.»» w (2003) x k w NAVFAC DM-7.2 (1986)» wš.» g j p x l (16) w. f i = ( 2.3~3) q u f i = ( 3~4) q u 14. w CNS x (r, K N =0.32MPa/mm, q u =17MPa) ( > 40cm) ( <40cm) (16a) (16b)», f i : w», q u : gj p 302» w (2001) ü x k, w» w (17) Canadian Foundation Engineering Manual(1992) (w œ, 2002). q s ---- b q u = ---- p a q s p a 0.5 = 0.05f c ' (f c '=q u ) (17a) (f c '<q u ) (17b)», q s : w, p a :», q u : g, b: x (=1.42(Rowe and Armitage, 1984), =0.63(Carter and Kulhawy, 1988)), f c ': gj p. ü» l 15 w ùkü. 15, ƒ š w»» w e»» j w ùkû. l»» ª Œª Œ
x r q u (MPa) r 20.1 15. ü» ( r, q u =20.1MPa) t 5. (MPa) x K N =0.5MPa/mm σ ini =1.05MPa i=9.1 K N =0.5MPa/mm»» (2003)» (2002) i=4.6 o 1.16 i=9.1 o 1.69 i=15.6 o 2.46 0.38 0.89 σ ini =0.35MPa 1.97 σ ini =0.70MPa 2.25 σ ini =1.05MPa 2.46» ùkû y w ù, e»» f»» l j z(»» 270%~640%)w ùkû.» ww t 5 ùkü.,» ü» w.» ü» ƒ š wš», e»» w w w w. 7.» x ü x mw e» y ww, x w, gj p w. m w w w w w, ü x, mw k w. mw. 1. e» y w, v l e» ƒ w m k y w š, e» ü m ¼ (l a ) 50mm, e» ƒ 1.1 o ~18.9 o w. 2. w CNS x, gj p j k, ká, š (triple curve) xk ùký. k (sticking zone)» j ƒwš ká (dilation zone) e»,, ƒ j ƒw ùkû. w,» k» w, z ká e» w. 3.» ü» (»» w, 2003;», 2002) mw, mw» ü» e»» j.» ü» ƒ š wš», w w w w w y w. š x z,,, w k(2006) e» š w 27ƒ 4C 2007 7œ 303
x k w w, w œwz p, w œwz, Vol. 22, No 7. y, y, w³, «x (2003) ü x k f e» w, w œwz»w z, w œwz, pp. 431-438. y, y(2004) d x k» š, 2001 w œ 2 š. w œ (2002) x k». w œwz(2003)»» w. Baquelin, F., Frand, R., and Jezequel, J. F. (1977) Prameters for friction piles in marine soils, 2nd International Conference in Numerical Methods for Offshore Piling, Austin, April, 1982. Barton, N. and Choubey, V. (1997) The shear strength of rock joints in theory and practice, Rock Mech., Vol. 10, pp. 1-54. Boresi, A. P. (1965) Elasticity in Engineering Mechanics. Prentice- Hall, Englewood Cliffs, N.J. Carter, J. P. and Kulhawy, F. H. (1988) Analysis and Design of Drilled Shaft Foundations Socketed Piles, Ph.D. dissertation, Department of Civil Engineering, Monash University, Melbourne, Australia. Hoek, E., Kaiser, P.K., and Bawden. W.F. (1995) Support of Underground Excavations in Hard Rock. Rotterdam:Balkema. Horvath, R. G., Kenny. T. C., and Kozicki, P. (1983), Method of improving the performance of drilled piers in weak rock, Canadian Geotechnical Journal, Vol. 20, pp. 758-772. Indraratna, B., Haque, A., and Aziz, N., (1999) Shear behavior of idealized in filled joints under constant normal stiffness, Geotechnique, Vol. 49, No. 3, pp. 331-355. Johnston, I. W., Lam, T. S. K. and Williams, A. F. (1987) Constant normal stiffness direct shear testing for socketed pile design in weak rock, Geotechnique, Vol. 37, No. 1, pp. 83-89. Kim, S. I., Jeong, S. S., Cho, S. H. and Park, I. J. (1999) Shear load transter characeteristics of drilled shafts in weathered rocks, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, pp. 999-1010. Marinos, P. and Hoek, E. (2001) Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Bulletin of the Engineering Geology & the Environment (IAEG), Vol. 60, pp. 85-92. Nam, M. S., (2004) Improved Design for Drilled Shafts in Rock, University of Houston, Dissertation. O'Neill, M. W., Townsend, F. C., Hanssan, K. M., Buller, A. and Chan, P. S. (1995) Load Transfer for Drilled Shafts in Intermediate Geomatrials, FHWA-RD-95-XXX Draft report U.S. Department of Transportation. Rowe, R. K. and Armitage, H. H. (1984) The design of piles socketed into weak rock, Report GEOT-11-84, University of Western Ontario, London, Ont. Seidel J. P, Harberfield C. M. (1995) Towards an understanding of Joint Roughness, Rock Mechanics and Rock Engineering Journal, Vol. 28, No. 2, pp. 69-92. Seidel, J. P. and Collingwood, B. (2001) A new socket roughness factor for prediction of rock socket shaft resistance, Canadian Geotechnical Journal, Vol. 38, No. 1, pp. 138-153. Seidel J P. and Harberfield C M. (2002) A theoretical model for rock joints subjected to constant normal stiffness direct shear, Int. J. Rock Mech. Min. Sci., Vol. 39, No. 5, pp. 539-553. ( : 2007.5.17/ : 2007.6.15/ : 2007.6.15) 304 ª Œª Œ