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~J <br />• <br />MainCressonSlopeEvaluation <br />Adrian6rown <br />7.1.4 Kink band failure parameters <br />Closely jointed rockmasses are subject to development of shear zones and "kink bands", where the <br />individual rock blocks which make up the rockmass shear, and/or rotated, and create a zone of weakness <br />within the rockmass. This zone of weakness can form the basis for slope failure. This phenomenon occurs <br />principally in very large slopes, but is capable of occurring in smaller slopes, such as the slopes proposed <br />at East Cresson. The Hoek and Bray parameters do not consider the possibility that a kink band might <br />form along the failure plane, reducing the strength of the rockmass. <br />To check for the feasibility of this phenomenon occurring, the empirical equation of Ladanyi and <br />Archambault (1970) is used: <br />ti = {6(1-a9)(v + tan ~) + a8rlo'b [~(1+n}-1]/n ~[1+n6/(rl6b)]}/[1-(1-a9) v tan ~] <br />where: i =shear strength <br />6 =normal stress <br />6b =block UCS (120 MPa = 17,400 psi) <br />• <br />L = (2/nr)^3 tan i <br />~ =number of rows in kink band (4 est) <br />i =angle of roughness planes (10° est) <br />~ =friction angle of material (39°) <br />v =dilation rate at peak shear strength = (1-6/6b)^K tan i <br />K = 5 for kink band (Hoek) <br />~1=degree of interlocking (0.5 for kink band) <br />n = UCS/Tensile strength (10 est) <br />Applying these values to the equation produces the results shown in Figure 19 and Figure 20. Based on <br />this evaluation, the angle of friction and cohesion which are computed for an approximately 700 foot high <br />slope are: <br />Wall Hei ht ft 700 <br />Normal stress a 4.9 <br />Effective Stress Cohesion a 0.3 <br />Effective Stress Cohesion si 41 <br />Effective Stress Friction An a 46 <br />• <br />The total stress which occurs at a depth of 700 feet is approximately 4.9 NIPa, or 700 psi. <br />1385D.980612 ~r <br />