$2\mathrm{.}1$ Barton's Q $($Tunnelling Quality Index$)$ is evaluated by the formula:

$Q=\frac{RQD}{J_n}\frac{J_r}{J_a}\frac{J_w}{SRF}$

Describe the meaning of each of the six variables in the $Q-$Index formula and describe their influence on tunnel stability.

$2\mathrm{.}2$ Calculate the RQD of a $4\mathrm{.}95m$ core run where all the joints intersected by the borehole are spaced exactly $11cm$ apart. What would the RQD have been if all the joints were spaced $9cm$ apart? Discuss.

$2\mathrm{.}3$ Which strength criterion is commonly used when assessing the strength of in$-$situ rock that is transected by many closely$-$spaced joint sets at multiple angles? Discuss the limitations of this criterion.

$2\mathrm{.}4$ Barton and Choubey developed the following equation to calculate shear strength on a plane:

$={}_{n}tan\{{}_b+JRClo{g}_{10}(JC\frac{S}{{}_n})\}$

Define and describe each of the four parameters required as input. What significance is there with an increasing ${}_n?$