Question $3$:

A tunnel with a rectangular cross$-$section has been excavated horizontally in a

north easterly direction at a width of $5$ m and height of $3$ m and on a bearing of $68$

to true North. A joint is visible at floor level in the North Western wall of the tunnel

$6$ m back from the face of the tunnel. The joint reaches the roof of the tunnel at

the $1$ m from the face of the tunnel. It is also visible in the roof and intersects the

face $2$ m from the north western wall.

What is the apparent dip angle of the joint in the wall and what is the true dip

angle and dip direction of the joint?

What potential instability mechanisms might arise as the tunnel face is

advanced? Use diagrams and detailed notes for each step.