List of top Geomechanics and Ground Control Questions

In an opencast coal mine, blast vibrations are measured at two locations, A and B simultaneously for a maximum charge per delay (Q) of 1200 kg as given.

Location	Distance from the blast face, D (m)	PPV (mm/s)
A	100	112.5
B	300	20.3

\(PPV=K[\frac{D}{\sqrt{Q}}]^{-B}\)
where, K and ẞ are site constants. The PPV in mm/s, at a distance of 200 m from the blast face, is (round off up to 2 decimals) 

Mohr-Coulomb envelop between shear stress, τ and normal stress, σ_n of a sandstone rock is given as
τ=7.5+0.84 o_n   (unit of stresses is MPa)
A sandstone sample is tested in triaxial mode with confining pressure of 5.0 MPa. The value of the shear stress, τ in MPa at the failure, is____.(round off up to 2 decimals)

A circular tunnel is constructed at a depth of 100 m. The average unit weight of overburden rock is 27.0 kN/m³. If the tangential stress measured at point A located at the horizontal boundary of the tunnel as shown, is 5.0 MPa, the tangential stress at point B in MPa, is____.(round off up to 2 decimals)

In a closed traverse, ABC, the bearings of two lines AB and BC are given.

Line	Length (m)	Bearing
AB	100	90°
BC	120	150°

The length, in m and bearing of line CA, in degree, respectively, are

The roof convergence data for 30 days at a monitoring station in a coal mine gallery is given.

Day	Convergence reading (mm)
0	0
5	4.7
10	11.3
16	19.6
22	28.8
30	34.8

The management decides on a Trigger Action Response Plan (TARP) if the following two premises occur simultaneously.
Premise 1: Rate of convergence exceeds 1.5 mm/day between two consecutive measurements. 
Premise 2: Rate of cumulative increase in convergence exceeds 1.0 mm/day. 
Identify the day on which TARP is enforced in that gallery. 

If the major (σ₁) and minor (σ₃) principal stresses for a rock element have a relationship as σ₃ = −\(\frac{1}{2}\) σ₁, the maximum shear stress is expressed by