Geotechnical Engineering Exam 2
UPDATED QUESTIONS AND CORRECT
ANSWERS
What is a flow net? How is it drawn? Explain the difference between flow lines and equipotential
lines in your answer. - CORRECT ANSWER A flow net it used to calculate seepage before
software. It consists of two sets of perpendicular lines that create a curvilinear grid. Lines that connect
equal pressure are drawn, and flow lines are drawn perpendicular and form squares.The flow line is
the predicted path that water follows. The equipotential lines connect points of equal pressure (or
head).
What do engineers do to calculate Darcy's law (seepage) in two dimensions? - CORRECT
ANSWER Engineers use software that simulate ground water flowing down.This use to be
done with flow nets, but they are less accurate and take longer.
Explain why piping failures occur rapidly based on the loss of material. - CORRECT
ANSWER Soil has friction. Water gets in between particles and undoes the friction. As soil
iscarried away, the seepage path gets shorter, so the gradient goes up. The increasing seepage creates
more erosion.
Explain the critical zone - CORRECT ANSWER The permeable layer retains water, and this
water moves downward. Once the water reaches the bottom of the sheet pile, there is a critical zone
where there is no stress, and the strength decreases. Water then flows up the other side and brings
particles with it to cause failure.
Which type of geosynthetic is most likely to be composed of expanded polystyrene? - CORRECT
ANSWER geofoam
Which of the following is a primary issue that must be addressed in the design of a geosynthetic
filter? - CORRECT ANSWER Clogging
The typical application of geonet is filtration. - CORRECT ANSWER false, it's typically used
for drainage
Which of the following defines permittivity? - CORRECT ANSWER k/t
, Transmissivity is the in-plane permeability of a geosynthetic. - CORRECT ANSWER true
Which of the following is a typical application for a non-woven geotextile? - CORRECT
ANSWER Nonwoven geotextiles are often used for filtration, and protection (e.g., against
erosion).
Which type of geosynthetic is most likely to be used to reinforce soil for a mechanically stabilized
earth retaining wall? - CORRECT ANSWER geogrid
If a particular geonet is used as a drain beneath 20 ft of fill, it will have the same transmissivity as the
same geonet used as a drain beneath 5 ft of the same fill. - CORRECT ANSWER The geonet
under 20 ft of fill experiences a higher stress, or pressure than the geonet under 5 ft of fill. The high
stress means the transmissivity should be less beneath 20 ft of fill compared to 5 ft of fill.
Which test(s) are used to evaluate geosynthetic-soil interaction properties? - CORRECT
ANSWER interface shear test and pullout test
Creep is not important in the mechanical properties of geosynthetics. - CORRECT
ANSWER Creep is very important for polymer materials, of which geosynthetics are made.
They can creep significantly over time, which is essential to understand for design with geosynthetics.
Geosynthetic materiala - CORRECT ANSWER high density polyethylene (HDPE)
Low density polyethylene (LDPE)
Polypropylene (PP)
Expanded polystyrene (ESP, common)
Categories - CORRECT ANSWER geotextile (woven/non-woven)
Geogrid
Geonet
Geomembrane
Geofoam
Geocell
UPDATED QUESTIONS AND CORRECT
ANSWERS
What is a flow net? How is it drawn? Explain the difference between flow lines and equipotential
lines in your answer. - CORRECT ANSWER A flow net it used to calculate seepage before
software. It consists of two sets of perpendicular lines that create a curvilinear grid. Lines that connect
equal pressure are drawn, and flow lines are drawn perpendicular and form squares.The flow line is
the predicted path that water follows. The equipotential lines connect points of equal pressure (or
head).
What do engineers do to calculate Darcy's law (seepage) in two dimensions? - CORRECT
ANSWER Engineers use software that simulate ground water flowing down.This use to be
done with flow nets, but they are less accurate and take longer.
Explain why piping failures occur rapidly based on the loss of material. - CORRECT
ANSWER Soil has friction. Water gets in between particles and undoes the friction. As soil
iscarried away, the seepage path gets shorter, so the gradient goes up. The increasing seepage creates
more erosion.
Explain the critical zone - CORRECT ANSWER The permeable layer retains water, and this
water moves downward. Once the water reaches the bottom of the sheet pile, there is a critical zone
where there is no stress, and the strength decreases. Water then flows up the other side and brings
particles with it to cause failure.
Which type of geosynthetic is most likely to be composed of expanded polystyrene? - CORRECT
ANSWER geofoam
Which of the following is a primary issue that must be addressed in the design of a geosynthetic
filter? - CORRECT ANSWER Clogging
The typical application of geonet is filtration. - CORRECT ANSWER false, it's typically used
for drainage
Which of the following defines permittivity? - CORRECT ANSWER k/t
, Transmissivity is the in-plane permeability of a geosynthetic. - CORRECT ANSWER true
Which of the following is a typical application for a non-woven geotextile? - CORRECT
ANSWER Nonwoven geotextiles are often used for filtration, and protection (e.g., against
erosion).
Which type of geosynthetic is most likely to be used to reinforce soil for a mechanically stabilized
earth retaining wall? - CORRECT ANSWER geogrid
If a particular geonet is used as a drain beneath 20 ft of fill, it will have the same transmissivity as the
same geonet used as a drain beneath 5 ft of the same fill. - CORRECT ANSWER The geonet
under 20 ft of fill experiences a higher stress, or pressure than the geonet under 5 ft of fill. The high
stress means the transmissivity should be less beneath 20 ft of fill compared to 5 ft of fill.
Which test(s) are used to evaluate geosynthetic-soil interaction properties? - CORRECT
ANSWER interface shear test and pullout test
Creep is not important in the mechanical properties of geosynthetics. - CORRECT
ANSWER Creep is very important for polymer materials, of which geosynthetics are made.
They can creep significantly over time, which is essential to understand for design with geosynthetics.
Geosynthetic materiala - CORRECT ANSWER high density polyethylene (HDPE)
Low density polyethylene (LDPE)
Polypropylene (PP)
Expanded polystyrene (ESP, common)
Categories - CORRECT ANSWER geotextile (woven/non-woven)
Geogrid
Geonet
Geomembrane
Geofoam
Geocell
