©JUSTTRACY EXAM SOLUTIONS
19/11/2024 3:50pm
Soil Mechanics Modified Exam
Questions And Improved Responses
What is the sieve number that is used to separate fine sand from medium sand? 40
What is the grain size diameter (in mm) that is the dividing line between fines and sand
particles sizes? 0.075
TF: The diffuse double layer is the basic structure of each clay particle, and these clay
particle diffuse double layers are the 2 different mineral sheets bonded together False. The
diffuse double layer is the region of attracted positive ions in solution and the negatively
charged surface of the clay
The plastic limit test involves rolling out a soil thread until it just breaks into smaller pieces
when thread is what diameter? 1/8 inch
List the 4 conditions necessary for Liquefaction to occur in a natural sand deposit Loose soil,
fine sand, below GWT, earthquakes
TF: A clay soil is considered to be at its liquid limit when the slot closes for 1/2 inch of its
length at 35 drops of the brass cup False. 25 drops
TF: All the clay soils exhibit the same behavior and shear strength when at their Liquid Limit,
even if one clay has LL=130% and another clay has LL=25% True
List the three most common clay minerals that were discussed in class Montmorillonite,
Kaolinite, Illite
Which common clay mineral has the most potential for shrink and swell when water content
changes? Montmorillonite
What is the name of the lab test that is used to determine the grain size distribution of the
particles of fine soil, that pass through the No. 200 sieve? Hydrometer Analysis
TF: Clay soils usually have a void ratio that is greater than 1.0, but not sand. True
Which of the following 4 USCS classified soils would be best for use as an impervious cap
over a landfill, that must provide: impermeability, resistance to shrink-swell, and relative ease
of compaction CL
If a sand soil has a void ratio value of 0.30, then what term best describes its density?
Very dense
What is the symbol for porosity? n
What is the symbol for void ratio? e
What is the equation for the degree of saturation? s=(Vw/Vv)*100%
What is the equation for the degree of water content? w=(Ww/Ws)*100%
, ©JUSTTRACY EXAM SOLUTIONS
19/11/2024 3:50pm
What is the equation for the specific gravity? s=(Ws/(Vs*Gammaw)
A soil with 4% fines, and 51% passing the No. 4 sieve, with a Cu=5.2 and Cc=1.5 will be
classified as which of the following? GW
In the USCS system, write the three words that describe a soil classified as ML soil?
Low plasticity silt
TF: In working with a "performance" specification, only the required percent compaction is
specified, but often the allowable range of moisture content is also specified True
Make a sketch to the right of the soil fabric that results from compacting clay soil that is dry
of optimum w.c. Particles are more spread out. Higher permeability and the particles
stick together better
ASTM test specification says that all the soil of a sample being tested in the lab Proctor test
must pass through a No. 4 sieve if the 4-inch diameter compaction mold is to be used. If
larger soil particles are present, what mold size must be used? 6 inch
TF: To achieve good degree of compaction throughout the lift thickness of a clayey soil, the
thickness of loose placed fill before compaction should not exceed about 8-10 inches
True
TF: The sheepsfoot roller is most often used to compact plastic clay soils because the small
peg-like feet apply the high stresses needed to shear through the clay and manipulate the clay
soils into denser condition True
What should be the water content of clay soil being compacted for a landfill liner or as core
of an earth-fill dam, both of which need to have very slow permeability? Wet of Optimum
TF: The optimum moisture content of a clay soil is usually substantially lower than that for a
well graded granular soil False. Clay is substantially higher than a well graded granular
soil
What are the details of the Modified Proctor compaction test that is done in a lab? Hammer
weight, Hammer drop weight, number of soil layers, number of drops on each layer 10
lb, 18 in, 5, 25
TF: When clean, well graded sand and gravel soil is being compacted using a vibratory
smooth-drum roller, the density test should be conducted at a depth of at least 5-inches below
the compacted surface to avoid the loosening that occurs due to the intense vibrations the
roller applies True
What is the effect of increased compactive effort, on the same soil? That is, using the
Modified Proctor test instead of the Standard Proctor Increased max dry unit weight
and decreased optimum moisture content
What is the best compaction equipment to use for a well-graded coarse to fine sand with very
little silt? Smooth Steel Drum Vibratory Roller
What is the best compaction equipment to use for low plasticity sandy clay soil with 25%
silt? Self-propelled pad foot-type of sheepsfoot roller
19/11/2024 3:50pm
Soil Mechanics Modified Exam
Questions And Improved Responses
What is the sieve number that is used to separate fine sand from medium sand? 40
What is the grain size diameter (in mm) that is the dividing line between fines and sand
particles sizes? 0.075
TF: The diffuse double layer is the basic structure of each clay particle, and these clay
particle diffuse double layers are the 2 different mineral sheets bonded together False. The
diffuse double layer is the region of attracted positive ions in solution and the negatively
charged surface of the clay
The plastic limit test involves rolling out a soil thread until it just breaks into smaller pieces
when thread is what diameter? 1/8 inch
List the 4 conditions necessary for Liquefaction to occur in a natural sand deposit Loose soil,
fine sand, below GWT, earthquakes
TF: A clay soil is considered to be at its liquid limit when the slot closes for 1/2 inch of its
length at 35 drops of the brass cup False. 25 drops
TF: All the clay soils exhibit the same behavior and shear strength when at their Liquid Limit,
even if one clay has LL=130% and another clay has LL=25% True
List the three most common clay minerals that were discussed in class Montmorillonite,
Kaolinite, Illite
Which common clay mineral has the most potential for shrink and swell when water content
changes? Montmorillonite
What is the name of the lab test that is used to determine the grain size distribution of the
particles of fine soil, that pass through the No. 200 sieve? Hydrometer Analysis
TF: Clay soils usually have a void ratio that is greater than 1.0, but not sand. True
Which of the following 4 USCS classified soils would be best for use as an impervious cap
over a landfill, that must provide: impermeability, resistance to shrink-swell, and relative ease
of compaction CL
If a sand soil has a void ratio value of 0.30, then what term best describes its density?
Very dense
What is the symbol for porosity? n
What is the symbol for void ratio? e
What is the equation for the degree of saturation? s=(Vw/Vv)*100%
What is the equation for the degree of water content? w=(Ww/Ws)*100%
, ©JUSTTRACY EXAM SOLUTIONS
19/11/2024 3:50pm
What is the equation for the specific gravity? s=(Ws/(Vs*Gammaw)
A soil with 4% fines, and 51% passing the No. 4 sieve, with a Cu=5.2 and Cc=1.5 will be
classified as which of the following? GW
In the USCS system, write the three words that describe a soil classified as ML soil?
Low plasticity silt
TF: In working with a "performance" specification, only the required percent compaction is
specified, but often the allowable range of moisture content is also specified True
Make a sketch to the right of the soil fabric that results from compacting clay soil that is dry
of optimum w.c. Particles are more spread out. Higher permeability and the particles
stick together better
ASTM test specification says that all the soil of a sample being tested in the lab Proctor test
must pass through a No. 4 sieve if the 4-inch diameter compaction mold is to be used. If
larger soil particles are present, what mold size must be used? 6 inch
TF: To achieve good degree of compaction throughout the lift thickness of a clayey soil, the
thickness of loose placed fill before compaction should not exceed about 8-10 inches
True
TF: The sheepsfoot roller is most often used to compact plastic clay soils because the small
peg-like feet apply the high stresses needed to shear through the clay and manipulate the clay
soils into denser condition True
What should be the water content of clay soil being compacted for a landfill liner or as core
of an earth-fill dam, both of which need to have very slow permeability? Wet of Optimum
TF: The optimum moisture content of a clay soil is usually substantially lower than that for a
well graded granular soil False. Clay is substantially higher than a well graded granular
soil
What are the details of the Modified Proctor compaction test that is done in a lab? Hammer
weight, Hammer drop weight, number of soil layers, number of drops on each layer 10
lb, 18 in, 5, 25
TF: When clean, well graded sand and gravel soil is being compacted using a vibratory
smooth-drum roller, the density test should be conducted at a depth of at least 5-inches below
the compacted surface to avoid the loosening that occurs due to the intense vibrations the
roller applies True
What is the effect of increased compactive effort, on the same soil? That is, using the
Modified Proctor test instead of the Standard Proctor Increased max dry unit weight
and decreased optimum moisture content
What is the best compaction equipment to use for a well-graded coarse to fine sand with very
little silt? Smooth Steel Drum Vibratory Roller
What is the best compaction equipment to use for low plasticity sandy clay soil with 25%
silt? Self-propelled pad foot-type of sheepsfoot roller
