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Sample Certificate in Rock Mechanics Exam Practice Questions
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1A 1.5 m drill run yields core pieces of the following lengths: 12 cm, 8 cm, 22 cm, 5 cm (fractured), 18 cm, 35 cm, and 10 cm. What is the Rock Quality Designation (RQD) for this drill run?
A.45%
B.65%
C.72%
D.85%
Explanation: RQD is calculated as the sum of sound core pieces equal to or greater than 10 cm divided by the total drill run length. Here, qualifying pieces are 12 cm, 22 cm, 18 cm, 35 cm, and 10 cm (total = 97 cm). Thus, RQD = (97 cm / 150 cm) * 100 = 64.67%, which rounds to 65%.
2Which five basic parameters are evaluated to obtain the basic Rock Mass Rating (RMR89) according to Bieniawski?
A.UCS, RQD, joint spacing, joint condition, and groundwater condition
B.Point load index, fracture frequency, friction angle, cohesion, and stress factor
C.UCS, stress reduction factor, joint roughness, aperture, and water inflow
D.Rock density, Young's modulus, Poisson's ratio, joint orientation, and RQD
Explanation: Bieniawski's basic RMR (RMR89) evaluates five fundamental parameters: Uniaxial Compressive Strength (UCS) of intact rock, Rock Quality Designation (RQD), spacing of discontinuities, condition of discontinuities, and groundwater conditions. An optional sixth adjustment is made for joint orientation relative to the excavation.
3In Barton's Q-system equation Q = (RQD / Jn) * (Jr / Ja) * (Jw / SRF), what physical aspect of the rock mass does the quotient (RQD / Jn) represent?
A.Inter-block shear strength
B.Relative block size
C.Active stress state
D.Water pressure ratio
Explanation: In the Q-system, the parameter ratio (RQD / Jn) represents the relative block size of the rock mass. (Jr / Ja) represents the inter-block shear strength, and (Jw / SRF) represents the active stress state.
4A underground drive in norite exhibits RQD = 80%, joint set number Jn = 9 (three joint sets), joint roughness Jr = 2 (smooth undulating), joint alteration Ja = 1 (unaltered), joint water reduction Jw = 1 (dry), and stress reduction factor SRF = 2.5 (medium stress). Calculate the rock mass Q value.
A.7.1
B.17.8
C.3.55
D.71.1
Explanation: Using Barton's equation Q = (RQD / Jn) * (Jr / Ja) * (Jw / SRF): (80 / 9) * (2 / 1) * (1 / 2.5) = 8.889 * 2 * 0.4 = 7.11. The rock mass is classified as Fair quality.
5According to Hoek and Brown, the Geological Strength Index (GSI) is primarily estimated from which two visual geological observations?
A.Intact rock hardness and groundwater discharge rate
B.Rock mass structure (interlocking of rock blocks) and surface condition of discontinuities
C.Drilling rate index and uniaxial compressive strength
D.Joint aperture width and seismic wave velocity
Explanation: GSI is estimated visually using charts based on two main geological axes: rock mass structure (ranging from intact/massive to blocky, disintegrated, or laminated) and surface condition of discontinuities (ranging from very good/rough unweathered to very poor/slickensided clay-coated).
6For standard 50 mm diameter core (Is(50)), what empirical multiplier is most commonly used in hard rock mining to estimate intact Uniaxial Compressive Strength (UCS) from point load strength?
A.10 - 12
B.14 - 16
C.20 - 25
D.35 - 40
Explanation: For standard 50 mm core (Is(50)), intact Uniaxial Compressive Strength is empirically estimated as UCS = C * Is(50), where C typically ranges between 20 and 25 for most hard igneous and metamorphic rocks (such as Witwatersrand quartzites and Bushveld pyroxenites).
7A diametral point load test conducted on a 50 mm diameter quartzite core yields a failure load P of 40 kN. Assuming De^2 = 0.0025 m^2 and an empirical conversion factor C = 24, calculate the estimated UCS of the rock sample.
A.160 MPa
B.384 MPa
C.240 MPa
D.96 MPa
Explanation: Point load index Is(50) = P / De^2 = 40 kN / 0.0025 m^2 = 16,000 kN/m^2 = 16.0 MPa. The estimated intact UCS is UCS = C * Is(50) = 24 * 16.0 MPa = 384 MPa.
8In a series of triaxial tests on intact Bushveld norite, the linear Mohr-Coulomb failure envelope yields a cohesion (c) of 25 MPa and an internal friction angle (phi) of 40 degrees. What is the uniaxial compressive strength (UCS) predicted by this Mohr-Coulomb envelope?
A.53.6 MPa
B.107.2 MPa
C.67.0 MPa
D.125.0 MPa
Explanation: Under Mohr-Coulomb theory, UCS = (2 * c * cos(phi)) / (1 - sin(phi)). For phi = 40 deg: cos(40 deg) = 0.7660, sin(40 deg) = 0.6428. Thus UCS = (2 * 25 * 0.7660) / (1 - 0.6428) = 38.30 / 0.3572 = 107.2 MPa.
9The Slake Durability Index test (Id2) is specifically performed to evaluate which rock mass behavior?
A.Resistance of rock to shear along pre-existing joint planes
B.Resistance of argillaceous rocks to weathering and disintegration when subjected to two cycles of wetting and drying
C.Dynamic fracture toughness under impact loading from blasting
D.Long-term creep rate under sustained high compressive stress
Explanation: The Slake Durability Index (ISRM standard test) evaluates the resistance of mudstones, shales, and other argillaceous rocks to slaking and disintegration when subjected to standard 10-minute wetting and drying rotation cycles in a mesh drum.
10For an undisturbed rock mass (D = 0) with GSI = 60 and intact parameter mi = 15, calculate the Hoek-Brown rock mass parameter mb using mb = mi * exp((GSI - 100) / 28).
A.1.25
B.3.59
C.7.50
D.15.00
Explanation: mb = mi * exp((GSI - 100) / 28) = 15 * exp((60 - 100) / 28) = 15 * exp(-40 / 28) = 15 * exp(-1.42857) = 15 * 0.23965 = 3.59. This scales the intact material parameter mi down to reflect jointing.
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