Page 107 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides
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Chapter 7 Tunneling Hazards 79
FIGURE 7.5 Monogram for prediction of tunnel stability. (From Bhasin and Grimstad, 1996)
sy > strength ¼ qcmass þ PO A=2 ¼ q0cmass ð7:14Þ
where sy is the tangential stress and qcmass is the uniaxial compressive strength (UCS)
of the rock mass, Po is in situ stress along the tunnel axis, and A is the rock parameter
proportional to friction (Chapter 13). Practically, Eq. (7.14) can be written as follows for
a circular tunnel under a hydrostatic stress field:
2 P > qcmass þ P Á A=2 ð7:15Þ
where P is the magnitude of the overburden pressure. Therefore, it may be noted that
squeezing may not occur in hard rocks with a high value of parameter A.
