MINE 303 - Final Exam with correct answers 2024

Early engineering works (1900s) assumed that rock was infinitely strong (T/F) - answer-True What is the name of the phenomenon, typical of very deep mining, that describes rock effectively "imploding" in the excavation? - answer-Rockburst Photo-elasticity was used in the early days of rock engineering to look at how stresses were redistributed around an excavation. In terms of mechanical behaviour of rock masses, what was the underlying assumption of that technique. - answer-Rock masses were considered as elastic media The behaviour of most engineering structures in rock are exclusively controlled by the strength of the intact rock (T/F) - answer-False What are two examples of disasters that happened in the period of that had a major impact on the development of rock mechanics. - answer-Malpasset dam collapse; Vajont rockslide Name three (3) rock mass classification systems widely used in today's rock engineering? - answer-Q Index (Barton et al., 1974) Geological Strength Index (GSI) Rock Mass Rating (RMR) system If the unit weight of rock is 26 kN/m3 then the vertical stress acting on an element of rock at a depth (z) of 200m would be: - answer-5.2MPa Human Uncertainty - answer-Subjectivity and measurement error, differing professional opinions Model Uncertainty - answer-Gaps in the scientific theory that is required to make predictions on the basis of causal inference Geological Uncertainty - answer-Unpredictability associated with the identification, characterisation and interpretation of the site geology and hydrogeology Parameter Uncertainty - answer-Absence of data for key parameters, spatial variability in rock/ soil properties, and scale effects (e.g. intact rock vs. rock mass properties) Rock engineering design generally requires the real problem to be idealised and simplified (T/F) - answer-True In order to reduce engineering risk, it is necessary to: - answer-Reduce data uncertainty and address the observed variability in a qualitative and quantitative manner. Consider both data uncertainty and data variability In rock engineering, design often has to be completed prior to developing access to rock exposures therefore: - answer-Geotechnical assumptions made at the beginning of a project need to be revised as the project is being developed Scanline mapping is an efficient method to collect discontinuity data since all the discontinuities within the selected rock outcrop are included in the mapping process (T/F) - answer-False JRC assessments (10cm scale) less than 10 are indicative of rough surfaces (T/F) - answer-False When collecting rock engineering data from rock exposures, every structural feature must be included in the survey (T/F) - answer-False When collecting rock engineering data from rock exposures, the proportion of the rock mass to be surveyed should be relative to the characteristics of the structural features being mapped (T/F) - answer-True When collecting rock engineering data from rock exposures, the proportion of the rock mass to be surveyed would be the same for all rock types (T/F) - answer-False When collecting rock engineering data from rock exposures, the proportion of the rock mass to be surveyed must be at least 10m2 (T/F) - answer-False Four (4) discontinuity parameters that can be directly obtained from mapping of the rock exposure: - answer-Fracture spacing Fracture aperture Orientation (Dip/ Dip Direction) Small scale roughness and large scale undulations Two (2) discontinuity parameters that cannot be directly obtained from mapping of the rock exposure: - answer-Fracture radius Block size Thirteen (13) steps for core logging: - answer-1. Piece core/ mark fractures 2. Separate the run if required 3. Assign core loss/ run depth/ length 4. Record recovery 5. Record RQD 6. Record fractured zones 7. Record # of fractures/ FOF/ # of fractured zones 8. Record DOB 9. Record hardness 10. Record DOA 11. Record JC 12. Add comments 13. Select samples for PLI Core logging is based on precise and reliable quantitative measurements of rock mass properties (T/F) - answer-False When preparing to log a core, piecing the core & marking fractures is the first step to be performed (T/F) - answer-True DOB is measured as soon as the core has been pieced together (T/F) - answer-False DOA is recorded before establishing JC ratings (T/F) - answer-True Samples for PLI testing are removed before measuring RQD (T/F) - answer-False With reference to core logging, counting induced and mechanical fractures as natural fractures will always provide a conservative approach for all rock engineering problems (T/F) - answer-False What is the RQD given: Hardness R1; core run length = 2m; natural fractures [40cm, 9cm, 15cm, 25cm, 30cm, 25cm, 8cm, length of loss of core 48cm] - answer-67.5% Approximate unit weight of marble - answer-27 kN/m3 Point load testing is used to determine the tensile strength of intact rock (T/F) - answer-False Calculate I_s for a diametral point load test on a core with a diameter of 35mm (load at failure is 12kN) I_s = P/D^2 - answer-I_s = [9 MPa, 10MPa] Considering a diametral point load test on a core with a diameter of 35mm (load at failure is 10 kN), what is true on the relationship of I_s to I_s(50) - answer-I_s I_s(50) The PLT is an attractive alternative to the Uniaxial Compression Strength (UCS) test (T/F) - answer-True UCS = 23*I_s(50) for all rock types (T/F) - answer-False UCS = K*I_s(50) where K increases as the core diameter increases (T/F) - answer-True UCS = K*I_s(50) where K=f(core diameter) (T/F) - answer-True A cylindrical specimen of elastic isotropic rock material was loaded in a triaxial cell with a confining pressure of 5 MN/m2 and an axial stress of 50 MN/m2. Strain gauges attached to the specimen indicated an axial strain of 850 microstrains with a lateral (extensile) strain of -80 microstrains. Use the data to calculate the Poisson ratio (v) of the material. - answer-v = 0.17 The Poisson ratio for an elastic rock material ranges between 0 and 1 (T/F) - answer-False (0 - 0.5) How many elastic constants are required to define the stress-strain relationships for a perfectly elastic isotropic rock material? - answer-2 Brittle failure implies a sudden loss of strength with associated very large but recoverable deformation (T/F) - answer-False Brittle failure implies a sudden loss of strength with little or no permanent (plastic) deformation (T/F) - answer-True Ductile failure implies that rock can sustain further permanent elastic deformation but the load bearing capacity will eventually reach zero (T/F) - answer-False Ductile failure implies that rock can sustain further permanent deformation without losing load-carrying capacity (T/F) - answer-True For foliated rock materials, the strengths measured from both UCS and Brazilian tests are independent of the foliation angle (T/F) - answer-False The Brazilian test provides a direct measurement of the tensile strength of the rock (T/F) - answer-False For foliated rock materials, the deformability modulus (E) measured in UCS tests is a function of the foliation angle (T/F) - answer-True Which of the followings are reasonable estimates of E and UCS for an igneous rock? 1. E = 40GPa, UCS = 100MPa 2. E = 22GPa, UCS = 55GPa 3. E = 20000MPa, UCS = 50MPa 4. E = 30MPa, UCS = 75MPa 5. E = 10GPa, UCS = 200MPa 6. E = 32GPa, UCS = 72000kPa - answer-1, 3, 6 How many UCS tests should be performed for the same rock material according to ASTM? - answer-At least 5 UCS tests carried out on the same rock material will always yield very similar values with an insignificant coefficient of variation (T/F) - answer-False Changing the loading rate will not influence the measured strength and deformations (T/F) - answer-False UCS tests carried out on the same rock material could yield a significant coefficient of variation (T/F) - answer-True Rock materials are natural materials therefore their properties are easily quantified with significant precision (T/F) - answer-False Changing the loading rate will influence the measured strength and deformations (T/F) - answer-True CHILE - answer-Continuous Homogenous Isotropic Linear Elastic DIANE - answer-Discontinuous Inhomogeneous Anisotropic Non-Elastic Knowledge of the magnitude and directions of both in-situ and induced stresses is important because: - answer-The strength of the rock in the rock surrounding the opening may be exceeded. When an opening is excavated, the stress field is locally disrupted and a new set of stresses are induced in the rock surrounding the opening. In the proximity of a normal fault, the stress ratio k would likely be: - answer-0 k 1 The horizontal stresses acting on an element of rock at a depth (z) below the surface are much more difficult to estimate than the vertical stresses (T/F) - answer-True The horizontal stresses acting on an element of rock at depth (z) below the surface are a function of the stresses resulting from the weight of the overlying strata and locked-in stresses of tectonic origin (T/F) - answer-True In the proximity of a thrust fault, the stress ratio k would likely b: - answer-k 1 Zones of compression would be represented by streamline crowding (T/F) - answer-True Zones of relaxation and/ or tension would be represented by streamline separation (T/F) - answer-True What are the main objectives that drive rock mass classification systems? - answer-1. Identification of significant parameters influencing rock mass behaviour. 2. Derivation of quantitative data for engineering design. 3. Provide methods to compare geological conditions at different sites. Jn depends on the number of mapped joint sets and for 3 joint sets, Jn = 9 (T/F) - answer-True Jn depends on the number of mapped joint sets and for 2 joint sets, Jn = 4 (T/F) - answer-True Jn depends on the number of mapped joint sets and for 4 joint sets, Jn = 16 (T/F) - answer-False 4 or more joint sets: Jn = 15 Jn depends on the number of mapped joint sets and for 1 joint sets, Jn = 2 (T/F) - answer-True Jr 1 for rough joint surfaces (T/F) - answer-True Can Jr, Jn, Jw, or Ja = 0 ? - answer-No The Equivalent Dimension (De) for a temporary mine opening is smaller than the De for a permanent mine opening (T/F) - answer-True The Excavation Support Ratio (ESR) for a temporary opening would be larger than the ESR for a permanent opening (T/F) - answer-True GSI does not directly include water or stress conditions, which are accounted for in stress and stability analyses using the Hoek-Brown criterion (T/F) - answer-True GSI directly considers water or stress conditions (T/F) - answer-False GSI provides a number that combined with the intact rock properties can be used for estimating the reduction in rock mass strength for different geological conditions (T/F) - answer-True GSI includes an evaluation of the uniaxial compressive strength of the intact rock pieces (T/F) - answer-False The mechanical behaviour of a fractured rock mass is strongly affected by the properties and geometry of the existing discontinuities because: - answer-1. The presence of discontinuities controls the mechanical response of the rock mass 2. Discontinuities are characterised by a much lower strength compared to the intact rock matrix Joint roughness increases the shear strength of a joint surface (T/F) - answer-True The undulations and asperities on a natural joint surface have a significant influence on its shear behaviour (T/F) - answer-True Joint roughness is represented as an angle (i) such that the overall friction angle of the joint surface (f) is equation to (f_b - i) where f_b is the basic friction angle (T/F) - answer-False Joint roughness is site specific and scale dependent (T/F) - answer-True For joint surfaces (wall-to-wall contact, no infill material), at high normal stress, the cohesion parameter would increase as the roughness and the strength of the joint surfaces increases (T/F) - answer-True For joint surfaces separated by a 5mm thick clay layer (no wall-to-wall contact when sheared), the cohesion parameter would be the cohesion of the fill material (T/F) - answer-True The cohesion parameter represents a cohesive strength that is independent of joint roughness (T/F) - answer-False For joint surfaces (wall-to-wall contact, no infill material) the cohesion parameter would provide additional strength to withstand tensile forces acting normal to the joint surfaces (T/F) - answer-False What is an empirical system used to measure the roughness of a natural discontinuity? - answer-JRC Under what conditions would the Barton-Bandis equation lose its validity? - answer-Normal stress equals zero Which would be the maximum value of normal stress that could be used in the Barton-Bandis equation for it to remain valid? - answer-Normal Stress = Joint Compressive Strength For a given amplitude (in mm), JRC _10cm JRC_100cm (T/F) - answer-True When using Mohr-Coulomb, the cohesion parameter for a rock mass is the summation of the cohesion of the intact rock and the cohesion of the joint surfaces (T/F) - answer-False The Mohr-Coulomb failure envelope corresponds to a condition of shear stress at failure (T/F) - answer-True An increase in pore pressure would cause both s1 and s3 to decrease by an amount equal to the pore pressure (T/F) - answer-True An increase in s3 is predominantly detrimental to stability (T/F) - answer-False Which are the parameters required to define the stress path that a rock sample would undergo due to changes in the applied stresses? - answer-Maximum shear stress (t) and average principal stress (s) The excavation of a tunnel or slope would cause a reduction of s3 in proximity of the tunnel face or slope face (T/F) - answer-True Which of the following is a required input for the Hoek-Brown failure criterion? 1. Mi 2. UCS 3. GSI 4. Mb 5. RQD 6. Ei - answer-1,2,3 For intact rock, the mi parameter in the Hoek-Brown criterion is a function of the ratio between UCS and tensile strength (T/F) - answer-True For intact rock, mi = mb, s = 1, a = 0.5, and D is assumed to be 0 (T/F) - answer-True When GSI = 100 (intact rock), the equations for mb and s are independent of the value assigned to D (T/F) - answer-True In a standard triaxial test, a rock sample is subjected to a stress ratio (k) such that: - answer-Initially k = 1, then k decreases as s1 increases Rock mass strength is a scale dependent property and rock mass strength increases with sample size (T/F) - answer-False D is a factor which depends on the degree of disturbance due to blast damage and stress relaxation (T/F) - answer-True Applying the blast damage factor D to the entire rock mass provides conservative results (T/F) - answer-False The Hoek-Brown criterion assumes: - answer-Heavily jointed rock masses Isotropic conditions What are factors influencing the strength and deformability of a rock? - answer-Frequency/ mechanical properties of discontinuities Ratio of s1 to sc