ASBOG Engineering Geology 2 — Questions and Answers
Question 1: Which index property is most directly used to assess the liquefaction potential of a sandy soil?
- Plasticity Index
- Relative density (Correct answer)
- Compression index
- Shrinkage limit
Correct answer: Relative density
Relative density (Dr) controls how loosely or densely sand is packed, which directly governs its susceptibility to liquefaction under cyclic loading.
Question 2: A rock mass with three mutually perpendicular joint sets has a maximum block volume defined by spacing S1, S2, and S3. What is the block volume?
- S1 + S2 + S3
- S1 × S2 × S3 (Correct answer)
- (S1 × S2 × S3) / 2
- π × S1 × S2 × S3 / 6
Correct answer: S1 × S2 × S3
For three orthogonal joint sets, the intact block is a rectangular parallelepiped with volume equal to the product of the three spacings.
Question 3: Which geophysical method is best suited for detecting a buried paleochannel filled with saturated sand beneath a clay layer?
- Gravity survey
- Ground-penetrating radar
- Seismic refraction
- Electrical resistivity tomography (Correct answer)
Correct answer: Electrical resistivity tomography
Electrical resistivity tomography (ERT) can differentiate between the conductive clay and the more resistive or differently resistive saturated sand in the paleochannel.
Question 4: During a slope stability analysis, a tension crack filled with water increases the driving force primarily by:
- Reducing the weight of the sliding mass
- Adding hydrostatic pressure on the failure plane (Correct answer)
- Increasing the friction angle of the soil
- Decreasing pore water pressure at the toe
Correct answer: Adding hydrostatic pressure on the failure plane
Water in a tension crack exerts hydrostatic pressure directed into the slope, which increases the net driving force on the potential failure surface.
Question 5: The Standard Penetration Test (SPT) N-value correction for overburden stress is called the:
- Energy ratio correction (Er)
- Normalized blow count (N60)
- Overburden correction factor (CN) (Correct answer)
- Borehole diameter correction
Correct answer: Overburden correction factor (CN)
The overburden correction factor CN adjusts raw SPT N-values to a reference effective stress of 1 atm so results from different depths can be compared.
Question 6: Which classification system uses the Rock Quality Designation (RQD), joint spacing, joint condition, groundwater, and orientation of discontinuities to rate a rock mass?
- Q-system (NGI)
- Rock Mass Rating (RMR) (Correct answer)
- Geological Strength Index (GSI)
- Point Load Index classification
Correct answer: Rock Mass Rating (RMR)
Bieniawski's Rock Mass Rating (RMR) system sums ratings for UCS, RQD, joint spacing, joint condition, groundwater, and a joint orientation adjustment.
Question 7: A Newmark displacement analysis is used in seismic slope stability to estimate:
- The factor of safety under static loading
- Permanent slope displacement during an earthquake (Correct answer)
- Pore pressure buildup in saturated soils
- Maximum ground acceleration at bedrock
Correct answer: Permanent slope displacement during an earthquake
Newmark's sliding block method integrates accelerations that exceed the yield acceleration to estimate the permanent displacement a slope experiences during seismic shaking.
ASBOG Engineering Geology 2
Which index property is most directly used to assess the liquefaction potential of a sandy soil?