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PEC EPE Geological study materials
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PEC EPE Geological practice questions

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Question 1Geological Engineering

In the context of geological engineering for energy projects, which rock type is classified as an igneous rock formed by the cooling of magma or lava?

  1. Limestone
  2. Shale
  3. Basalt Correct answer.
  4. Marble

Explanation

Igneous rocks form from the cooling and solidification of molten material, and basalt is a common extrusive igneous rock. Limestone and shale are sedimentary, while marble is a metamorphic rock derived from limestone.

Question 2Geological Engineering

Which type of unconformity is present when sedimentary layers are deposited on top of eroded igneous or metamorphic basement rock?

  1. Nonconformity Correct answer.
  2. Paraconformity
  3. Angular unconformity
  4. Disconformity

Explanation

A nonconformity is defined by sedimentary strata resting directly on older igneous or metamorphic rocks, indicating a period of erosion of the crystalline basement. Angular unconformities involve tilted lower beds, while disconformities and paraconformities involve parallel sedimentary layers.

Question 3Geological Engineering

A rock sample has a measured mass of 540 g and a bulk volume of 200 cm³. What is its bulk density?

  1. 3.20 g/cm³
  2. 2.70 g/cm³ Correct answer.
  3. 1.85 g/cm³
  4. 2.45 g/cm³

Explanation

Bulk density equals mass divided by volume, so 540 g divided by 200 cm³ gives 2.70 g/cm³. This value is typical for rocks such as limestone or quartz-rich sandstone.

Question 4Geological Engineering

Which geophysical method is most directly used to measure the electrical resistivity of subsurface formations for groundwater and contamination studies?

  1. Ground-penetrating radar
  2. Electrical resistivity tomography Correct answer.
  3. Seismic reflection
  4. Magnetic surveying

Explanation

Electrical resistivity tomography injects current into the ground and measures potential differences to image subsurface resistivity distributions. Seismic methods measure elastic wave properties, radar measures dielectric contrasts, and magnetic surveys measure magnetic susceptibility.

Question 5Geological Engineering

In a geological engineering site investigation, which in-situ test provides a direct measurement of the undrained shear strength of soft clay?

  1. Plate load test
  2. Vane shear test Correct answer.
  3. Cone penetration test with pore pressure measurement
  4. Standard penetration test

Explanation

The vane shear test rotates a four-bladed vane in cohesive soil to measure torque and derive undrained shear strength directly. The SPT and CPT give correlations, while the plate load test evaluates bearing capacity and settlement rather than undrained strength.

Question 6Geological Engineering

Which type of fault is characterized by the hanging wall moving down relative to the footwall due to extensional stress?

  1. Strike-slip fault
  2. Reverse fault
  3. Normal fault Correct answer.
  4. Thrust fault

Explanation

A normal fault forms under extension, with the hanging wall dropping relative to the footwall. Reverse and thrust faults form under compression with the hanging wall moving up, and strike-slip faults involve lateral displacement.

Question 7Geological Engineering

Which mineral property is defined as the tendency of a mineral to break along planes of weak atomic bonding, producing smooth planar surfaces?

  1. Streak
  2. Fracture
  3. Cleavage Correct answer.
  4. Hardness

Explanation

Cleavage is the tendency to break along crystallographic planes determined by weaker atomic bonds, producing flat, reflective surfaces. Fracture describes irregular breakage, hardness measures scratch resistance, and streak refers to powdered color.

Question 8Geological Engineering

Which drilling technique is most appropriate for obtaining continuous, relatively undisturbed core samples in competent rock for geological engineering design?

  1. Rotary air drilling
  2. Percussion cable-tool drilling
  3. Diamond core drilling Correct answer.
  4. Auger drilling

Explanation

Diamond core drilling uses a rotating annular bit with diamond abrasives to cut cylindrical rock cores, providing continuous samples for logging and testing. Air rotary and cable-tool methods produce cuttings, and auger drilling is limited to shallow unconsolidated soils.

Question 9Geological Engineering

A confined sandstone aquifer has a porosity of 0.20 and a formation thickness of 25 m. Using a storage coefficient of 5×10⁻⁴, what volume of water is released per square meter of aquifer when the potentiometric head declines by 10 m?

  1. 0.05 m³
  2. 5.0 m³
  3. 0.005 m³ Correct answer.
  4. 0.5 m³

Explanation

The storage coefficient is the volume released per unit area per unit head decline, so 5×10⁻⁴ × 10 m equals 0.005 m³ per square meter. Porosity and thickness affect total storage but not this direct calculation of released volume.

Question 10Geological Engineering

In slope stability analysis using the infinite slope model for a dry cohesionless soil, the factor of safety is best expressed as which ratio?

  1. (γ z cos β) / c
  2. tan φ / tan β Correct answer.
  3. tan β / tan φ
  4. c / (γ z sin β cos β)

Explanation

For an infinite dry cohesionless slope, the factor of safety reduces to the ratio of the tangent of the friction angle to the tangent of the slope angle. When the slope angle is less than the friction angle, the slope is stable.

Question 11Geological Engineering

Which seismic wave type is a compressional body wave that travels fastest through rock and is the first to arrive at a seismograph?

  1. Rayleigh wave
  2. S-wave
  3. Love wave
  4. P-wave Correct answer.

Explanation

P-waves are longitudinal compressional waves and travel faster than shear waves, so they arrive first. S-waves are transverse, and Love and Rayleigh waves are slower surface waves.

Question 12Geological Engineering

In a sedimentary basin analysis, which feature indicates a transgressive systems tract?

  1. Prograding deltaic clinoforms
  2. Aggradational coastal plain deposits
  3. Retrogradational parasequence stacking Correct answer.
  4. Incised valley fill above a sequence boundary

Explanation

Transgressive systems tracts are characterized by retrogradational stacking as shorelines migrate landward and accommodation increases. Progradational clinoforms indicate regression, and incised valley fills typically mark lowstand conditions.

Question 13Geological Engineering

Which soil parameter is determined from the liquid and plastic limits of a fine-grained soil?

  1. Permeability
  2. Coefficient of consolidation
  3. Relative density
  4. Plasticity index Correct answer.

Explanation

The plasticity index is the difference between the liquid limit and the plastic limit and quantifies the range of water content over which the soil behaves plastically. Consolidation, permeability, and relative density require other tests.

Question 14Geological Engineering

A rock mass classification system that uses the parameters RQD, number of joint sets, joint roughness, joint alteration, groundwater conditions, and stress reduction factor is which of the following?

  1. GSI (Geological Strength Index)
  2. RMR (Rock Mass Rating)
  3. Q-system Correct answer.
  4. SPT (Standard Penetration Test)

Explanation

The Q-system uses six parameters including RQD, joint set number, roughness, alteration, water, and stress reduction to classify rock mass quality. RMR uses different parameters including strength and spacing, GSI is based on structure and surface conditions, and SPT is a soil test.

Question 15Geological Engineering

Which geological hazard is most commonly triggered by the rapid loss of shear strength in loose, saturated sands during earthquake shaking?

  1. Rockfall
  2. Expansive soil swelling
  3. Subsidence
  4. Liquefaction Correct answer.

Explanation

Liquefaction occurs when cyclic earthquake loading increases pore pressure in loose saturated sands, reducing effective stress and shear strength. Rockfall, subsidence, and expansive swelling have different mechanisms unrelated to cyclic pore pressure buildup.

Question 16Geological Engineering

In a geological cross-section, a fold whose limbs dip away from a central axis and whose oldest rocks are exposed in the core is which type of fold?

  1. Anticline Correct answer.
  2. Syncline
  3. Isoclinal fold
  4. Monocline

Explanation

An anticline has limbs dipping away from the axis and exposes older rocks in the core. A syncline has limbs dipping toward the axis with younger rocks in the core, and a monocline is a single-step flexure.

Question 17Geological Engineering

Which geophysical technique is best suited for detecting a buried fault zone at depths of several hundred meters by imaging contrasts in seismic velocity and density?

  1. Very low frequency electromagnetics
  2. Thermal infrared imaging
  3. Seismic refraction tomography Correct answer.
  4. Self-potential surveying

Explanation

Seismic refraction tomography images velocity variations with depth and can resolve fault zones where velocity contrasts exist. VLF and self-potential methods target shallow conductivity or electrochemical contrasts, and thermal infrared imaging is a remote surface technique.

Question 18Geological Engineering

Which criterion is used to assess the potential for brittle failure of rock around an underground excavation using the ratio of maximum tangential stress to uniaxial compressive strength?

  1. Brittle failure index Correct answer.
  2. Mohr-Coulomb criterion
  3. Hoek-Brown criterion
  4. Barton-Bandis criterion

Explanation

The brittle failure index compares the maximum tangential stress at the excavation boundary to the uniaxial compressive strength to estimate spalling and brittle failure potential. Hoek-Brown and Mohr-Coulomb are strength criteria, and Barton-Bandis describes joint behavior.

Question 19Geological Engineering

A confined aquifer has a transmissivity of 500 m²/day and a storativity of 0.0005. A pumping well is located 200 m from an observation well. Using the Theis method, which parameter must be estimated first to determine the dimensionless well function argument?

  1. Hydraulic conductivity
  2. Porosity
  3. Storativity and transmissivity with time and distance Correct answer.
  4. Specific yield

Explanation

The Theis solution uses the argument u = r²S/(4Tt), which requires storativity, transmissivity, radial distance, and time. Specific yield applies to unconfined aquifers, and porosity alone does not enter the Theis well function.

Question 20Geological Engineering

In a geological engineering report, which factor most directly controls the bearing capacity of a shallow foundation on a dense sand?

  1. Liquid limit of the sand
  2. Angle of internal friction and foundation width Correct answer.
  3. Atterberg limits of the sand
  4. Plasticity index of the sand

Explanation

Bearing capacity of dense sand is governed primarily by the angle of internal friction and foundation geometry, including width and embedment depth. Atterberg limits and plasticity indices apply to fine-grained cohesive soils.

Question 21Geological Engineering

Which geological setting is most favorable for the accumulation of hydrocarbons in a structural trap?

  1. A deeply weathered granite outcrop with no seal
  2. A broad anticlinal fold with an overlying impermeable seal Correct answer.
  3. An unconfined alluvial fan
  4. A homoclinal dipping aquifer open at the surface

Explanation

A structural trap requires a reservoir, a seal, and a closure configuration, which an anticline with an impermeable caprock provides. Open or unconfined settings lack the sealing and trapping geometry needed for accumulation.

Question 22Geological Engineering

In an active subduction zone, which earthquake mechanism typically produces the largest tsunamis?

  1. Volcanic tremor
  2. Shallow strike-slip faulting
  3. Shallow megathrust faulting with seafloor uplift Correct answer.
  4. Deep-focus normal faulting

Explanation

Large tsunamis are generated by shallow megathrust earthquakes that vertically displace the seafloor over a broad area. Strike-slip motion displaces the seafloor horizontally, deep earthquakes produce little seafloor deformation, and volcanic tremor is low-energy.

Question 23Geological Engineering

A rock core sample has a dry mass of 400 g, a saturated surface-dry mass of 440 g, and a submerged mass of 260 g. What is the apparent porosity of the sample?

  1. 40 percent
  2. 10 percent
  3. 30 percent
  4. 20 percent Correct answer.

Explanation

Apparent porosity equals the saturated mass minus dry mass divided by the saturated mass minus submerged mass, so (440−400)/(440−260) = 40/180 ≈ 22 percent, closest to the 20 percent option. The calculation uses water-saturated mass change as a proxy for pore volume.

Question 24Geological Engineering

In a finite element analysis of a deep tunnel in a viscoelastic rock mass, which time-dependent parameter most strongly governs the long-term convergence of the excavation?

  1. Bulk density
  2. Creep compliance or viscosity Correct answer.
  3. Thermal expansion coefficient
  4. Poisson's ratio

Explanation

Long-term convergence in viscoelastic rock is controlled by creep compliance or viscosity, which define how strain accumulates under sustained stress. Poisson's ratio, density, and thermal expansion affect elastic or thermal response but not time-dependent creep directly.

Question 25Geological Engineering

A 30 m thick confined aquifer has a hydraulic conductivity of 10 m/day and a storativity of 1×10⁻⁴. A well pumps at 2000 m³/day. Using the Theis approximation, which parameter combination best determines the drawdown at 100 m after 1 day?

  1. u = r²S/(4Tt) with T = 10 m²/day
  2. u = r²S/(4Tt) with T = 300 m²/day Correct answer.
  3. u = rS/(4Tt) with T = 300 m²/day
  4. u = 4Tt/(r²S) with T = 300 m²/day

Explanation

Transmissivity equals hydraulic conductivity times thickness, 10 m/day × 30 m = 300 m²/day, and the Theis argument is u = r²S/(4Tt). Using the correct formula and transmissivity gives the drawdown through the exponential integral.

Question 26Geological Engineering

In a geological engineering site investigation, which in-situ test is most suitable for estimating the undrained shear strength of a soft clay layer at a depth of 10 m?

  1. Cone penetration test (CPT)
  2. Vane shear test (VST) Correct answer.
  3. Seismic refraction survey
  4. Standard penetration test (SPT)

Explanation

The vane shear test directly measures the undrained shear strength of cohesive soils by rotating a four-bladed vane in the ground. It is particularly suited for soft to medium clays where sample disturbance is a concern. SPT and CPT provide correlations, but VST gives a direct measurement.

Question 27Geological Engineering

Which type of unconformity is characterized by sedimentary rocks overlying igneous or metamorphic rocks, with the erosional surface cutting across the crystalline fabric?

  1. Disconformity
  2. Nonconformity Correct answer.
  3. Angular unconformity
  4. Paraconformity

Explanation

A nonconformity is an unconformity where sedimentary strata overlie igneous or metamorphic rocks. The erosion surface truncates the crystalline rocks, which formed at depth and were later exposed. Angular unconformities involve tilted sedimentary layers below, while disconformities and paraconformities involve parallel sedimentary strata.

Question 28Geological Engineering

Which geophysical method is most effective for mapping the depth to the water table in a granular aquifer where a strong electrical conductivity contrast exists between the unsaturated and saturated zones?

  1. Magnetic survey
  2. Ground-penetrating radar (GPR)
  3. Electrical resistivity tomography (ERT) Correct answer.
  4. Gravity survey

Explanation

ERT measures subsurface electrical resistivity, which is highly sensitive to water content and pore fluid conductivity. The saturated zone typically has lower resistivity than the unsaturated zone, making ERT well suited for water table mapping. GPR can also detect the water table but is limited by clay content and depth.

Question 29Geological Engineering

Which metamorphic rock is typically formed from the metamorphism of limestone and is composed predominantly of calcite?

  1. Slate
  2. Quartzite
  3. Marble Correct answer.
  4. Schist

Explanation

Marble forms when limestone or dolostone is subjected to heat and pressure, recrystallizing the calcite into a dense, interlocking mosaic. Quartzite derives from quartz sandstone, slate from shale, and schist from a variety of protoliths under higher-grade metamorphism.

Question 30Geological Engineering

In a rock mass, the ratio of the uniaxial compressive strength of intact rock to the major principal stress at failure is used to assess the onset of brittle failure. This ratio is known as the:

  1. Spalling limit
  2. Rock Mass Rating (RMR)
  3. Brittleness index Correct answer.
  4. Geological Strength Index (GSI)

Explanation

The brittleness index, often expressed as the ratio of intact rock strength to the maximum principal stress, indicates the likelihood of brittle failure such as spalling or rockburst. GSI and RMR are classification systems, and the spalling limit is a threshold value used in some criteria.

Question 31Geological Engineering

Which type of aquifer is bounded above by a confining layer that restricts the vertical movement of water, causing the water level in a well to rise above the top of the aquifer?

  1. Unconfined aquifer
  2. Perched aquifer
  3. Leaky aquifer
  4. Confined aquifer Correct answer.

Explanation

A confined aquifer is overlain by a low-permeability confining layer, so the water within it is under pressure greater than atmospheric. When a well penetrates the aquifer, the water level rises to the potentiometric surface, which may be above the aquifer top. Unconfined aquifers have a water table at atmospheric pressure.

Question 32Geological Engineering

Which of the following best describes the process of differential weathering in geological engineering?

  1. The transport of weathered material by wind and water.
  2. The mechanical fracturing of rock by tectonic stress.
  3. The uniform breakdown of rock due to chemical dissolution.
  4. The selective weathering of weaker minerals or rock units, leading to uneven topography. Correct answer.

Explanation

Differential weathering occurs when rock units or minerals weather at different rates because of variations in composition, hardness, or structure. This selective erosion produces uneven landforms such as ridges and valleys. It is distinct from uniform dissolution, tectonic fracturing, or erosion and transport.

Question 33Geological Engineering

In a geological engineering context, which parameter is used to quantify the degree of fracturing in a rock mass by measuring the percentage of intact core pieces longer than 100 mm in a drill run?

  1. Fracture frequency
  2. Joint roughness coefficient (JRC)
  3. Core recovery
  4. Rock Quality Designation (RQD) Correct answer.

Explanation

RQD is defined as the sum of lengths of intact core pieces longer than 100 mm divided by the total length of the core run, expressed as a percentage. It provides a quantitative measure of rock mass fracturing. Core recovery measures total recovered core, fracture frequency counts fractures per unit length, and JRC describes joint surface roughness.

Question 34Geological Engineering

A soil sample has a void ratio of 0.65 and a specific gravity of solids of 2.65. What is the porosity of the sample?

  1. 0.650
  2. 0.394 Correct answer.
  3. 0.253
  4. 0.606

Explanation

Porosity n is related to void ratio e by n = e / (1 + e). Substituting e = 0.65 gives n = 0.65 / 1.65 = 0.394. This calculation does not require the specific gravity of solids, which is used for other phase relationships.

Question 35Geological Engineering

In a slope stability analysis, the factor of safety against sliding along a planar failure surface in a rock slope is defined as the ratio of resisting forces to driving forces. Which parameter most directly increases the resisting force when the slope is fully drained?

  1. Slope height
  2. Cohesion along the failure plane Correct answer.
  3. Unit weight of the rock
  4. Groundwater table elevation

Explanation

For a drained planar failure, the resisting force includes cohesion times the failure plane area plus friction due to effective normal stress. Cohesion directly adds to the resisting force regardless of normal stress. Unit weight and slope height increase driving forces, and groundwater elevation reduces effective normal stress.

Question 36Geological Engineering

Which seismic hazard is characterized by the amplification of ground shaking in soft, low-velocity sediments relative to bedrock during an earthquake?

  1. Site amplification Correct answer.
  2. Liquefaction
  3. Surface rupture
  4. Tsunami

Explanation

Site amplification occurs when seismic waves travel from stiff bedrock into softer, lower-velocity sediments, causing an increase in shaking amplitude. This phenomenon is influenced by impedance contrasts and resonance within the sediment column. Liquefaction is a loss of shear strength in saturated sands, tsunamis are water waves, and surface rupture is fault displacement at the ground surface.

Question 37Geological Engineering

In a geological cross-section, a fault is identified where older rocks are juxtaposed against younger rocks, and the fault plane dips 60° toward the east. The hanging wall is on the east side. Which type of fault is this?

  1. Normal fault Correct answer.
  2. Strike-slip fault
  3. Thrust fault
  4. Reverse fault

Explanation

In a normal fault, the hanging wall moves down relative to the footwall due to extensional stress, placing older rocks in the footwall against younger rocks in the hanging wall. A reverse fault would have the hanging wall move up, and a thrust fault is a low-angle reverse fault. Strike-slip faults have predominantly horizontal movement.

Question 38Geological Engineering

A pumping test in a confined aquifer yields a drawdown of 2.5 m at a distance of 50 m from the pumping well after a long pumping period. If the transmissivity is 800 m²/day and the pumping rate is 1500 m³/day, what is the approximate storativity? Use the Theis nonequilibrium equation and assume u < 0.01 so that the approximation s = (Q/(4πT)) ln(2.25Tt/(r²S)) applies, with t = 1 day.

  1. 9.6×10⁻⁴
  2. 1.2×10⁻⁴ Correct answer.
  3. 4.8×10⁻⁴
  4. 2.4×10⁻⁴

Explanation

Rearranging the approximation for storativity: S = (2.25 T t)/(r²) exp(-4πT s / Q). Substituting T=800 m²/day, t=1 day, r=50 m, s=2.5 m, Q=1500 m³/day gives S ≈ 1.2×10⁻⁴. This is a typical storativity value for a confined aquifer.

Question 39Geological Engineering

Which geological material is most prone to karst development, leading to sinkholes and ground subsidence?

  1. Shale
  2. Limestone Correct answer.
  3. Granite
  4. Basalt

Explanation

Karst landscapes form from the dissolution of soluble rocks, primarily limestone and dolomite, by slightly acidic water. This dissolution creates voids and conduits that can lead to sinkholes and subsidence. Granite and basalt are igneous and largely insoluble, while shale has low solubility and high clay content.

Question 40Geological Engineering

In a rock mass classification system, the Geological Strength Index (GSI) is used to estimate the reduced rock mass strength. Which two parameters are primarily used to determine GSI?

  1. Uniaxial compressive strength and density
  2. Rock type and weathering grade
  3. Joint set number and joint roughness
  4. Blockiness and joint surface condition Correct answer.

Explanation

GSI is determined from the structure of the rock mass (blockiness, ranging from intact to disintegrated) and the condition of joint surfaces (roughness, weathering, infilling). These two factors are plotted on a chart to obtain a GSI value. Other parameters like joint set number are part of RMR, not GSI directly.

Question 41Geological Engineering

A retaining wall is to be designed for a dry cohesionless backfill with a unit weight of 18 kN/m³ and an angle of internal friction of 30°. Using Rankine's theory, what is the active earth pressure coefficient?

  1. 1.00
  2. 0.50
  3. 3.00
  4. 0.33 Correct answer.

Explanation

Rankine's active earth pressure coefficient for a horizontal backfill is K_a = (1 - sin φ)/(1 + sin φ). For φ = 30°, sin 30° = 0.5, so K_a = (1 - 0.5)/(1 + 0.5) = 0.33. This coefficient is used to calculate lateral earth pressure.

Question 42Geological Engineering

Which of the following best explains why the SPT blow count (N-value) can be misleading in gravelly soils?

  1. The SPT is not standardized for gravelly soils and should always be replaced by CPT.
  2. Gravel particles increase pore water pressure during driving, lowering N-values.
  3. Gravel particles may cause the sampler to jam, leading to artificially high N-values. Correct answer.
  4. Gravelly soils always have high fines content, reducing penetration resistance.

Explanation

In gravelly soils, large particles can obstruct the split-spoon sampler, causing it to jam and producing abnormally high blow counts that do not reflect the true density. This can lead to an overestimation of soil strength. The other options misstate the behavior of gravel during SPT.

Question 43Geological Engineering

In a sedimentary basin, which trap style is formed by the upward movement of a ductile unit, such as salt, that arches overlying strata to create a structural closure?

  1. Stratigraphic trap
  2. Anticlinal trap
  3. Fault trap
  4. Salt dome trap Correct answer.

Explanation

A salt dome trap forms when salt flows upward due to density contrast, arching the overlying sedimentary layers and creating a structural high where hydrocarbons can accumulate. Anticlinal traps are formed by folding without necessarily involving salt, and fault traps rely on fault displacement.

Question 44Geological Engineering

A rock core has a diameter of 50 mm and a length of 100 mm. In a uniaxial compression test, the peak axial load is 200 kN. What is the uniaxial compressive strength of the rock?

  1. 50.9 MPa
  2. 101.9 MPa Correct answer.
  3. 203.7 MPa
  4. 25.5 MPa

Explanation

The cross-sectional area of the core is π*(0.025 m)² = 0.0019635 m². The stress is load divided by area: 200,000 N / 0.0019635 m² ≈ 101.9 MPa. This is a typical calculation for intact rock strength.

Question 45Geological Engineering

In the context of earthquake-induced slope failure, which factor most strongly controls the susceptibility of a slope to seismically induced landslides?

  1. The regional metamorphic grade of the bedrock
  2. The color of the slope-forming materials
  3. The slope angle and the presence of weak, saturated materials Correct answer.
  4. The age of the slope-forming materials

Explanation

Seismically induced landslides are most likely on steep slopes underlain by weak, saturated, or cohesionless materials that can lose strength during shaking. Slope angle directly affects driving stress, and saturation can lead to liquefaction or increased pore pressures. Color, metamorphic grade, and age are not direct controls.

Question 46Geological Engineering

Which geophysical method relies on measuring variations in the Earth's gravitational field to detect subsurface density contrasts, such as a buried salt dome or a cavity?

  1. Seismic reflection
  2. Magnetic survey
  3. Electrical resistivity
  4. Gravity survey Correct answer.

Explanation

Gravity surveys measure small variations in the gravitational acceleration caused by differences in subsurface density. A salt dome, which is less dense than surrounding rock, or a cavity produces a measurable gravity anomaly. Seismic reflection images acoustic impedance contrasts, magnetic surveys measure magnetic susceptibility, and resistivity measures electrical conductivity.

Question 47Geological Engineering

In a finite element analysis of a tunnel excavated in a rock mass subjected to high horizontal stress, the zone of maximum compressive stress concentration typically develops at which location around the opening?

  1. At the sidewalls Correct answer.
  2. At the face of the tunnel
  3. Uniformly around the entire periphery
  4. At the crown and invert

Explanation

For a circular tunnel in a hydrostatic stress field, the tangential stress is uniform, but when horizontal stress is much higher than vertical, the maximum compressive stress concentration occurs at the sidewalls (springline). This can lead to spalling or rockburst on the walls. The crown and invert experience lower tangential stress in this case.

Question 48Geological Engineering

A confined aquifer has a hydraulic conductivity of 5 m/day and a thickness of 20 m. The potentiometric surface is 30 m above the top of the aquifer. What is the transmissivity of the aquifer?

  1. 150 m²/day
  2. 600 m²/day
  3. 3000 m²/day
  4. 100 m²/day Correct answer.

Explanation

Transmissivity T is the product of hydraulic conductivity K and aquifer thickness b: T = K × b. Here, T = 5 m/day × 20 m = 100 m²/day. The potentiometric surface elevation does not affect transmissivity, which is a property of the aquifer.

Question 49Geological Engineering

In a geological engineering site investigation, a seismic refraction survey is performed over a two-layer subsurface. The P-wave velocity of the upper layer is 800 m/s and of the lower layer is 2500 m/s. The crossover distance is 20 m. What is the approximate depth to the interface?

  1. 7.5 m Correct answer.
  2. 15.0 m
  3. 10.0 m
  4. 5.0 m

Explanation

For a two-layer case, the depth to the interface can be estimated from the crossover distance x_c using the formula z = (x_c/2) * sqrt((V2 - V1)/(V2 + V1)). Substituting V1=800, V2=2500, x_c=20 gives z ≈ 10 * sqrt(1700/3300) ≈ 10 * 0.718 ≈ 7.2 m, closest to 7.5 m. This is a standard refraction interpretation.

Question 50Geological Engineering

A rock slope is intersected by a persistent joint set that dips at 45° out of the slope face, while the slope face dips at 70°. The joint friction angle is 30° and the joint cohesion is zero. Under dry conditions, which statement is correct regarding the potential for planar sliding?

  1. Sliding is possible only if the slope height exceeds 50 m.
  2. Sliding is impossible because the joint dips less than the slope.
  3. Sliding is impossible because the joint dip is less than the friction angle.
  4. Sliding is possible because the joint dip exceeds the friction angle and daylights in the slope face. Correct answer.

Explanation

For planar sliding on a joint, the joint must daylight in the slope face (joint dip < slope dip) and the joint dip must exceed the friction angle for sliding to occur under dry conditions with zero cohesion. Here, 45° < 70° and 45° > 30°, so sliding is kinematically and frictionally possible. Slope height does not control the onset of sliding in this simple criterion.