# Q Calculator and Q' Calculator

The tunneling Quality Index (Q) gives a description of the rock mass stability of an underground opening in jointed rock masses. This aids in the determination of tunnel support requirements. The numerical value of the index Q varies on a logarithmic scale from 0.001 to a maximum of 1,000. High Q-values indicates good stability and low values means poor stability. Q is based on 6 parameters and is calculated using the following equation: RQD = Degree of jointing (Rock Quality Designation) Jn = Number of joint sets Jr = Joint roughness number Ja = Joint alteration number Jw = Joint water reduction factor SRF = Stress Reduction Factor

The actual Q value can only be observed in the excavation itself. The Q value attained by other methods will be more uncertain. Generally, the number of joint sets may be underestimated from drill cores. Jw and SRF may be inaccurate without actual observations on site. This is generally when Q’ is used. Q’ omits the Jw and SRF parameters.