ASBOG Engineering Geology 5 — Questions and Answers
Question 1: The Seed-Idriss simplified procedure for evaluating liquefaction potential uses which two key parameters derived from SPT data?
- N60 and liquid limit
- Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR) (Correct answer)
- Relative density and confining stress
- Friction angle and cohesion
Correct answer: Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR)
The simplified procedure compares the CSR imposed by the earthquake to the CRR of the soil (derived from corrected SPT blow counts) to determine the factor of safety against liquefaction.
Question 2: Which type of landslide is characterized by a curved, concave-up failure surface and backward rotation of the slide mass?
- Translational slide
- Rotational slide (slump) (Correct answer)
- Debris flow
- Topple
Correct answer: Rotational slide (slump)
A rotational slide (slump) moves along a spoon-shaped, concave-up failure surface, causing the head of the slide to tilt backward relative to the original slope.
Question 3: Schmidt hammer rebound values are used in engineering geology primarily to estimate:
- Rock mass permeability
- Uniaxial compressive strength of intact rock (Correct answer)
- Joint roughness coefficient (JRC)
- Rock Quality Designation (RQD)
Correct answer: Uniaxial compressive strength of intact rock
The Schmidt hammer measures surface rebound, which correlates empirically with the uniaxial compressive strength (UCS) and Young's modulus of intact rock.
Question 4: Which process is primarily responsible for creating a glacial U-shaped valley?
- Stream incision and lateral erosion
- Glacial abrasion and plucking widening valley walls (Correct answer)
- Mass wasting along vertical joints
- Differential chemical weathering of valley walls
Correct answer: Glacial abrasion and plucking widening valley walls
Glacial ice erodes valley walls and floor by abrasion and plucking, transforming the original V-shaped stream valley into a characteristic U-shaped trough.
Question 5: The 'rock bolt factor of safety' in a tunneling context is typically defined as the ratio of:
- Bolt tensile strength to bolt shear strength
- Pull-out capacity to applied load on the bolt (Correct answer)
- Rock mass rating to joint spacing
- Grout bond length to bolt free length
Correct answer: Pull-out capacity to applied load on the bolt
The factor of safety for a rock bolt equals the ultimate pull-out resistance (from grout bond and anchor) divided by the actual tensile load the bolt must carry.
Question 6: Which sedimentary structure is the most reliable indicator of the original 'way-up' (younging direction) in deformed strata?
- Bedding-plane parting
- Graded bedding (Correct answer)
- Joint spacing
- Cleavage refraction
Correct answer: Graded bedding
Graded bedding shows coarse grains at the base grading to fine grains at the top of each bed, reliably indicating the up direction at the time of deposition.
Question 7: During a geotechnical site investigation for a dam foundation on a river, which condition would most require detailed evaluation of internal erosion (piping) potential?
- Highly over-consolidated clay foundation
- Heterogeneous alluvial deposits with contrasting permeability layers (Correct answer)
- Massive granite bedrock with tight joints
- Dry desert sand with high relative density
Correct answer: Heterogeneous alluvial deposits with contrasting permeability layers
Heterogeneous alluvium with adjacent high- and low-permeability layers creates preferential seepage paths where hydraulic gradients can concentrate and progressively erode fine particles (piping).
ASBOG Engineering Geology 5
The Seed-Idriss simplified procedure for evaluating liquefaction potential uses which two key parameters derived from SPT data?