
| Day | Convergence reading (mm) |
| 0 | 0 |
| 5 | 4.7 |
| 10 | 11.3 |
| 16 | 19.6 |
| 22 | 28.8 |
| 30 | 34.8 |
| Line | Length (m) | Bearing |
| AB | 100 | 90° |
| BC | 120 | 150° |
The length, in m and bearing of line CA, in degree, respectively, are
| Location | Distance from the blast face, D (m) | PPV (mm/s) |
| A | 100 | 112.5 |
| B | 300 | 20.3 |
In a Brazilian test, the front view of a homogeneous rock sample is shown in the figure. The failure initiates at the point, where the rock sample is subjected to stress. The failure initiates at the point marked as:

In a bord and pillar panel, a square pillar of size 35 m \( \times \) 35 m (centre to centre) is extracted to form four equal square-shaped stooks as shown. The width of each gallery and crosscut is 5 m. The height of the working seam is 3 m. The reduction in safety factor after pillar splitting by using Bieniawski’s pillar strength formula, in %, is _______ (rounded off to 2 decimal places).

Bieniawski's pillar strength formula is given by \( S_p = S_1 \left( 0.64 + 0.36 \frac{w}{h} \right) \), where \( S_1 \) is the strength of a 0.9 m\(^3\) coal block, \( w \) is the pillar width, and \( h \) is the mining height.