List of top Geomechanics and Ground Control Questions on Stress Measurement Techniques asked in GATE MN

The in-situ stresses are determined by the Flat-jack method by making three slots (P, Q, and R) on the wall (ABCD) of a mine gallery as shown. The in-situ stresses $ \sigma_P $, $ \sigma_Q $, and $ \sigma_R $ are determined at slot-P, slot-Q, and slot-R, respectively. If $ \sigma_P > \sigma_Q $, and $ \sigma_R = 0 $, the shear stress on the wall is

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.

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.

A triaxial test on a sandstone sample is conducted at a confining pressure of 10 MPa. The elastic axial and volumetric strains at axial stress of 50 MPa are recorded to be $ 4.2 \times 10^{-3} $ and $ 2.0 \times 10^{-3} $ respectively. The modulus of elasticity, in GPa, and Poisson’s ratio of the sample, respectively are closest to:

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:

The major ($ \sigma_1 $) and minor ($ \sigma_3 $) principal stresses and the maximum shear stress ($ \tau_{{max}} $) are related as $ |\tau_{{max}}| = \sigma_1 = - \sigma_3 $. The magnitude of normal stress on the plane where $ \tau_{{max}} $ acts is:

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 longwall face, the full seam thickness of 3 m is cut by a shearer with a web depth of 0.7 m. Hauling speed = 12 m/min. AFC trough cross-section = 0.4 m$^2$, loading coefficient = 0.7. Find the AFC speed (in m/s), rounded to one decimal place.

A 3-point borehole extensometer is installed to identify the location of a single discontinuity plane in a hanging wall rock by measuring deformations at three locations as shown in the figure. The absolute readings of deformations measured on two different dates are listed in the table. Based on the measured data the most likely inference is

Identify the WRONG statement: Break-even stripping ratio

A square pattern of blasting is shown in the figure. For the case of simultaneous blast, identify the zone of no fragmentation.