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Janucn.v 1 .5, 008 Pqg 21 <br />Ruck properties were adjusted using the Hoek-Brown method" to account for natural <br />fracturing of the rock mass and disturbance induced by the landslide movement. The method <br />makes use of the Geologic Strength Index (GSI), which is essentially the same as RMRs,). The <br />generalized strength criterion relates principal stresses to each other at failure according to <br />Equation 2. <br />( }a <br />rrj =rr3 +c*c,l rnh-/' +SJ (E:qn. 2) <br />l (T U <br />where nib, S, and (r are a functions of the material constant, in,, and GSI, as given by Equation Z. <br />nib = mi x cw/) GS1 - 100 <br />28-14D , <br />erp GS1 - 1001 (Eqn. 3) <br />9-3D <br />a + I (e-G,Sl: 15 _ e-20 3 <br />2 ? <br />D is the disturbance factor which ranges between 0-1 where I is very disturbed rock. For this <br />work, D = 0 was assumed for all rock below the slide plane and 1) varied between 0-0.5 for <br />rocks within the landslide depending on loss of core and geologist comments in the logs. The <br />instantaneous uniaxial compressive strength, a, is obtained by setting a, = 0 in Equation 2 and <br />the tensile strength is obtained by setting at = e73 = a, in Equation 2, which result in F.quatiun 4. <br />ac. = CT u <br />UXS <br />S x rru (Eqn. 4) <br />7rnr = rrr = - <br />nib <br />The rock mass modulus ofdcibrmation is given by Equation 5. <br />E1- ?? ?TCr x0(GLS-10,'40) (Eqn. 5) <br />1(1(1 <br />Equation 2 is a non-linear relation between a, and a;. Equivalent linear Mohr-Coulomb <br />strength parameters cohesion, C,,,,, and friction, ?,n,, fi)r the rock mass were used as input for the <br />stabilitv analyses. The equivalent linear parameters were computed by fitting an average linear <br />relationship to the curve generated by solving Equation 2 for a range of minor principal stress <br />values defined by a, <- a3 <a3ma\. The relation for c•,,,, and O,,,, are given by Equation 6. <br />Hoek E., C. Carranza-Torres and B. CorkUnl (2002), "Hoek-Brown Failure Criterion 2002 Edition;' 51/r ;Noah <br />Ilneric•an RotI Alet-hanics SlwipoPiun7 uncl I'rh Tunneling .4Ssoc•iarion of ('una I ('onJi rente 1'. I/l,VS-J:I(', <br />p. 267-271. http: ?www.rocscience.com librarylpdf RL I .pdt, <br />Agapito Associates, Inc.