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3.4 Rock Quality <br />The in -situ strength and deformation properties of rocks are influenced by intact strength <br />(uniaxial compressive strength) and the condition of geologic discontinuities within the <br />rock mass volume of interest. A number of indices, from simple to sophisticated, have <br />been used by practitioners in rock engineering to characterize rock mass quality. A useful <br />parameter commonly used in geomechanics is RQD, which is the sum of all core pieces <br />greater than four inches divided by the total interval length. Table 3 presents a <br />relationship between RQD and rock quality suggested by Deere (1969). Another, more <br />sophisticated index (see section 3.5) is Rock Mass Rating (Bieniawski 1984). <br />Figures 10 through 12 present RQD results for TC- 03 -01, TC- 03 -02, and TC -03 -03, <br />including data statistics. On the average, rocks located near the Terror Creek are <br />classified as "Fair ". Within each hole, there are zones of rock classified as good to <br />0 <br />excellent, as well as occasional poor rocks. RQD values improve generally from TC -03- <br />01 toward the other holes in the corridor. • <br />n - <br />TC -03 -01 <br />n.a. =so>r <br />0 <br />E <br />E <br />i <br />0 10 20 30 Q 50 60 r0 60 0 100 <br />Rock Duality Designation, <br />Figure 10. Histogram frequency diagram for RQD values for TC- 03 -01. • <br />Maleki Technologies, Inc. Page 21 <br />