SOIL MECHANICS FINAL EXAM QUESTIONS AND ANSWERS]-
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1. In a three-phase soil system, what does the degree of saturation ($S$) represent as a
percentage?
A. The ratio of the volume of air to the total volume of voids
B. The ratio of the volume of water to the total volume of voids
C. The ratio of the weight of water to the dry weight of soil solids
D. The ratio of the volume of voids to the total volume of the soil mass
Answer: B
The degree of saturation is explicitly defined as the ratio of the volume of water occupying the
void space to the total volume of voids, expressed as a percentage ranging from 0%
(completely dry) to 100% (fully saturated).
2. A saturated soil sample has a water content of 25% and a specific gravity of soil solids
($G_s$) of 2.70. What is the void ratio ($e$) of this soil?
A. 0.675
B. 0.925
C. 1.080
D. 0.250
Answer: A
Using the fundamental phase relationship equation Multiplying 0.25 by 2.70 yields 0.675.
3. Which laboratory test is standardly used to determine the grain size distribution of fine-
grained soils passing the No. 200 sieve through sedimentation?
A. Sieve Analysis Test
B. Hydrometer Analysis Test
C. Direct Shear Test
D. Standard Proctor Test
Answer: B
Hydrometer analysis applies Stokes' law of sedimentation to measure the terminal settling
velocity of soil particles suspended in water, enabling the determination of particle sizes
smaller than 0.075 mm.
,4. What does a uniformity coefficient ($C_u$) greater than 6 combined with a coefficient of
curvature ($Cc$) between 1 and 3 indicate for a gravelly soil?
A. The soil is poorly graded with uniform particle sizes.
B. The soil is well-graded, possessing a wide and continuous range of particle sizes.
C. The soil contains a high percentage of expansive clay minerals.
D. The soil is gap-graded with missing intermediate particle dimensions.
Answer: B
In accordance with the Unified Soil Classification System (USCS), a gravel is classified as
well-graded (GW) only if $C_u > 4$ (or 6 for sands) and $Cc$ falls strictly between 1 and 3.
5. What is the liquid limit ($LL$) of a fine-grained soil conceptually defined as in soil
mechanics?
A. The minimum moisture content at which a soil can be rolled into threads 3 mm in diameter
without crumbling.
B. The arbitrary boundary moisture content separating the plastic state from the liquid state,
determined as the water content at which a standard groove closes after 25 drops in a Casagrande
cup.
C. The moisture content below which no further volume reduction occurs during drying.
D. The maximum water content a soil can hold before liquefaction occurs under static loads.
Answer: B
The liquid limit represents the conventional water content boundary where soil changes from
plastic behavior to liquid behavior, measured via the standard 25-blow Casagrande drop test.
6. A geotechnical engineer calculates the plasticity index ($PI$) of a clay sample to be 22.
According to standard Atterberg limits correlations, how is this soil classified regarding its
plasticity?
A. Low plasticity
B. Medium to high plasticity
C. Non-plastic silt
D. Organic liquid slurry
Answer: B
Plasticity index ($PI = LL - PL$) quantifies the range of moisture over which soil remains
plastic. A PI of 22 indicates medium to high plasticity clay requiring careful settlement and
swelling evaluations.
7. Under the Unified Soil Classification System (USCS), what symbol designates an
inorganic clay of high plasticity?
,A. CL
B. CH
C. ML
D. OH
Answer: B
The letter 'C' denotes clay, and 'H' denotes high plasticity (liquid limit greater than 50),
making 'CH' the designation for high-plasticity fat clays.
8. According to Darcy's law for laminar flow through porous media, what parameters
govern the rate of discharge ($q$)?
A. Hydraulic conductivity, cross-sectional area, and hydraulic gradient
B. Void ratio, degree of saturation, and dry unit weight
C. Effective stress, cohesion, and internal friction angle
D. Preconsolidation pressure and compression index
Answer: A
Darcy's law is expressed as $q = k \cdot i \cdot A$, where $k$ is hydraulic conductivity, $i$ is
the hydraulic gradient, and $A$ is the cross-sectional area perpendicular to flow.
9. In a flownet used for two-dimensional seepage analysis, what is the geometric
relationship between equipotential lines and flow lines?
A. They intersect at acute angles of 45 degrees.
B. They intersect each other at right angles (90 degrees).
C. They run perfectly parallel to one another throughout the soil mass.
D. They are concentric circles sharing a common origin.
Answer: B
Orthogonality is a fundamental rule of flownets; flow lines and equipotential lines must
intersect everywhere at 90-degree angles to form a valid curvilinear square grid network.
10. How is the seepage pressure ($j$) per unit volume exerted by flowing water on a soil
skeleton calculated?
A. $j = i \cdot \gamma_w$
B. $j = \sigma \cdot tan(\phi)$
C. $j = c + \sigma' \cdot tan(\phi)$
D. $j = \gamma_d \cdot G_s$
Answer: A
, Seepage pressure represents the frictional drag exerted by percolating water on soil particles,
equal to the hydraulic gradient ($i$) multiplied by the unit weight of water ($\gamma_w$).
11. What condition occurs when the upward seepage force in a soil mass equals the
submerged unit weight of the soil, resulting in a complete loss of effective stress and shear
strength?
A. Consolidation settlement
B. Soil liquefaction and quick condition (boiling)
C. Capillary fringe saturation
D. Secondary compression creep
Answer: B
A quick condition or hydraulic boiling occurs when upward flow creates a seepage pressure
equal to buoyant unit weight, causing effective stress to drop to zero and soil to lose load-
bearing capacity.
12. What is the primary physical definition of effective stress ($\sigma'$) in a saturated soil
mass according to Terzaghi's principle?
A. The total normal force acting across any cross-sectional area divided by the total area.
B. The intergranular stress transmitted directly through particle-to-particle contact points,
calculated as total stress minus pore water pressure ($\sigma' = \sigma - u$).
C. The hydrostatic pressure exerted by stationary groundwater table levels.
D. The shear resistance mobilized along a potential sliding failure plane.
Answer: B
Terzaghi's effective stress principle establishes that all measurable effects of a change in
stress, such as shear strength and compression, are due to changes in effective stress ($\sigma'
= \sigma - u$).
13. A soil layer has a total vertical stress of 200 kPa and a groundwater table located at the
ground surface. If the depth is 10 meters, what is the effective vertical stress at that depth?
(Assume unit weight of water is 9.81 kN/m³)
A. 200 kPa
B. 101.9 kPa
C. 98.1 kPa
D. 298.1 kPa
Answer: B
COMPLETE STUDY GUIDE | PRACTICE QUESTIONS AND
ANSWERS-RATIONALES | EXAM PREP | DOWNLOAD INSTANT
PDF | GUARANTEED PASS || LATEST EXAM 2026-2027
1. In a three-phase soil system, what does the degree of saturation ($S$) represent as a
percentage?
A. The ratio of the volume of air to the total volume of voids
B. The ratio of the volume of water to the total volume of voids
C. The ratio of the weight of water to the dry weight of soil solids
D. The ratio of the volume of voids to the total volume of the soil mass
Answer: B
The degree of saturation is explicitly defined as the ratio of the volume of water occupying the
void space to the total volume of voids, expressed as a percentage ranging from 0%
(completely dry) to 100% (fully saturated).
2. A saturated soil sample has a water content of 25% and a specific gravity of soil solids
($G_s$) of 2.70. What is the void ratio ($e$) of this soil?
A. 0.675
B. 0.925
C. 1.080
D. 0.250
Answer: A
Using the fundamental phase relationship equation Multiplying 0.25 by 2.70 yields 0.675.
3. Which laboratory test is standardly used to determine the grain size distribution of fine-
grained soils passing the No. 200 sieve through sedimentation?
A. Sieve Analysis Test
B. Hydrometer Analysis Test
C. Direct Shear Test
D. Standard Proctor Test
Answer: B
Hydrometer analysis applies Stokes' law of sedimentation to measure the terminal settling
velocity of soil particles suspended in water, enabling the determination of particle sizes
smaller than 0.075 mm.
,4. What does a uniformity coefficient ($C_u$) greater than 6 combined with a coefficient of
curvature ($Cc$) between 1 and 3 indicate for a gravelly soil?
A. The soil is poorly graded with uniform particle sizes.
B. The soil is well-graded, possessing a wide and continuous range of particle sizes.
C. The soil contains a high percentage of expansive clay minerals.
D. The soil is gap-graded with missing intermediate particle dimensions.
Answer: B
In accordance with the Unified Soil Classification System (USCS), a gravel is classified as
well-graded (GW) only if $C_u > 4$ (or 6 for sands) and $Cc$ falls strictly between 1 and 3.
5. What is the liquid limit ($LL$) of a fine-grained soil conceptually defined as in soil
mechanics?
A. The minimum moisture content at which a soil can be rolled into threads 3 mm in diameter
without crumbling.
B. The arbitrary boundary moisture content separating the plastic state from the liquid state,
determined as the water content at which a standard groove closes after 25 drops in a Casagrande
cup.
C. The moisture content below which no further volume reduction occurs during drying.
D. The maximum water content a soil can hold before liquefaction occurs under static loads.
Answer: B
The liquid limit represents the conventional water content boundary where soil changes from
plastic behavior to liquid behavior, measured via the standard 25-blow Casagrande drop test.
6. A geotechnical engineer calculates the plasticity index ($PI$) of a clay sample to be 22.
According to standard Atterberg limits correlations, how is this soil classified regarding its
plasticity?
A. Low plasticity
B. Medium to high plasticity
C. Non-plastic silt
D. Organic liquid slurry
Answer: B
Plasticity index ($PI = LL - PL$) quantifies the range of moisture over which soil remains
plastic. A PI of 22 indicates medium to high plasticity clay requiring careful settlement and
swelling evaluations.
7. Under the Unified Soil Classification System (USCS), what symbol designates an
inorganic clay of high plasticity?
,A. CL
B. CH
C. ML
D. OH
Answer: B
The letter 'C' denotes clay, and 'H' denotes high plasticity (liquid limit greater than 50),
making 'CH' the designation for high-plasticity fat clays.
8. According to Darcy's law for laminar flow through porous media, what parameters
govern the rate of discharge ($q$)?
A. Hydraulic conductivity, cross-sectional area, and hydraulic gradient
B. Void ratio, degree of saturation, and dry unit weight
C. Effective stress, cohesion, and internal friction angle
D. Preconsolidation pressure and compression index
Answer: A
Darcy's law is expressed as $q = k \cdot i \cdot A$, where $k$ is hydraulic conductivity, $i$ is
the hydraulic gradient, and $A$ is the cross-sectional area perpendicular to flow.
9. In a flownet used for two-dimensional seepage analysis, what is the geometric
relationship between equipotential lines and flow lines?
A. They intersect at acute angles of 45 degrees.
B. They intersect each other at right angles (90 degrees).
C. They run perfectly parallel to one another throughout the soil mass.
D. They are concentric circles sharing a common origin.
Answer: B
Orthogonality is a fundamental rule of flownets; flow lines and equipotential lines must
intersect everywhere at 90-degree angles to form a valid curvilinear square grid network.
10. How is the seepage pressure ($j$) per unit volume exerted by flowing water on a soil
skeleton calculated?
A. $j = i \cdot \gamma_w$
B. $j = \sigma \cdot tan(\phi)$
C. $j = c + \sigma' \cdot tan(\phi)$
D. $j = \gamma_d \cdot G_s$
Answer: A
, Seepage pressure represents the frictional drag exerted by percolating water on soil particles,
equal to the hydraulic gradient ($i$) multiplied by the unit weight of water ($\gamma_w$).
11. What condition occurs when the upward seepage force in a soil mass equals the
submerged unit weight of the soil, resulting in a complete loss of effective stress and shear
strength?
A. Consolidation settlement
B. Soil liquefaction and quick condition (boiling)
C. Capillary fringe saturation
D. Secondary compression creep
Answer: B
A quick condition or hydraulic boiling occurs when upward flow creates a seepage pressure
equal to buoyant unit weight, causing effective stress to drop to zero and soil to lose load-
bearing capacity.
12. What is the primary physical definition of effective stress ($\sigma'$) in a saturated soil
mass according to Terzaghi's principle?
A. The total normal force acting across any cross-sectional area divided by the total area.
B. The intergranular stress transmitted directly through particle-to-particle contact points,
calculated as total stress minus pore water pressure ($\sigma' = \sigma - u$).
C. The hydrostatic pressure exerted by stationary groundwater table levels.
D. The shear resistance mobilized along a potential sliding failure plane.
Answer: B
Terzaghi's effective stress principle establishes that all measurable effects of a change in
stress, such as shear strength and compression, are due to changes in effective stress ($\sigma'
= \sigma - u$).
13. A soil layer has a total vertical stress of 200 kPa and a groundwater table located at the
ground surface. If the depth is 10 meters, what is the effective vertical stress at that depth?
(Assume unit weight of water is 9.81 kN/m³)
A. 200 kPa
B. 101.9 kPa
C. 98.1 kPa
D. 298.1 kPa
Answer: B
