Unsaturated Soil Mechanics in
Geotechnical Practice Questions &
Answers
What is the Definition of Phase? - answer 1) Must have different Material Properties
2) Must have Definite Boundary Surface
What size of soil grain is the limit that differs it from course grained and fine grained
soil? - answer 0.075 mm
Define State Variable (give 2 examples) - answer The non material variables
required for the characterization of the system (e.g., stress and strain)
Define Constitutive Relation (Give 3 Examples) - answer The relationship between
different state variables through material properties (e.g., Darcy's law, and M-C failure
criterion, Bishop's Effective Stress).
Define Soil Compaction - answer The soil compaction aims to improve the density of
unsaturated soil used by the construction of geotechnical structure
Define Soil Consolidation - answer is a type of soil deformation induced by water
drainage. The soil associated with the consolidation process is in a fully saturated state.
What is the Soil Water Characteristic Curve (SWCC)? - answer The relationship
between water content and matric suction
What are the functions of SWCC? - answer 1) Water Retention Capacity
a)absorption: (water content is low), particle size affects this
b)capillary effect: (water content is high) pore size affects it
2) Predict material Properties
ex) K = K(S) = K(ua - uw)
What Quantities are used to describe SWCC? - answer 1) AEV: Matric Suction
a) Large Soil Pores
b) Small soil pores
2) Residual Water Content
What are the methods to determine SWCC?
(Or What is the hysteresis in SWCC?) - answer 1) Drying Path (Desorption Process)
, 2) Wetting Path (Sorption Process)
What factors can contribute to the hysteresis in SWCC? - answer a) Non uniformity
of soil Pores:
When the matric suction is the same, the soil can hold more water in the dry path
b) Contact Angle Effect:
When the water content is same, soil can have a higher matric suction in the drying path
c) Entrapped air in sorption process (Wetting Path)
d) Differential Changes in soil structure in drying and wetting path
drying path - Volume contraction
wetting path - Volume expansion
What are the features of the Filter Paper Technique?
(Or how do you determine soil suction through filter paper?) - answer 1) Measure
Total suction(Non-Contact) and Matric suction (Contact)
2) Indirect Measurement Method
3) Break Point
a) Absorption (Low Water Content)
b) Capillary Effect (High Water Content)
4) Time consuming
Why is the HAE ceramic needed to measure the matric suction? - answer It prevents
the air from entering the measuring system
What are the features of HAE ceramics? - answer 1) small pore size
2) AEV high
What is the major limitation of tensiometer for the measurement of matric suction? -
answer It is not possible to measure a negative pore water pressure which is less
than -100 kPa
What are the features of Axis Translation Technique? - answer 1) Pore air and water
pressure are increased, water content and matric suction is kept constant
2) Air pressure system needed to increase pore air pressure
3) HAE ceramic required
Geotechnical Practice Questions &
Answers
What is the Definition of Phase? - answer 1) Must have different Material Properties
2) Must have Definite Boundary Surface
What size of soil grain is the limit that differs it from course grained and fine grained
soil? - answer 0.075 mm
Define State Variable (give 2 examples) - answer The non material variables
required for the characterization of the system (e.g., stress and strain)
Define Constitutive Relation (Give 3 Examples) - answer The relationship between
different state variables through material properties (e.g., Darcy's law, and M-C failure
criterion, Bishop's Effective Stress).
Define Soil Compaction - answer The soil compaction aims to improve the density of
unsaturated soil used by the construction of geotechnical structure
Define Soil Consolidation - answer is a type of soil deformation induced by water
drainage. The soil associated with the consolidation process is in a fully saturated state.
What is the Soil Water Characteristic Curve (SWCC)? - answer The relationship
between water content and matric suction
What are the functions of SWCC? - answer 1) Water Retention Capacity
a)absorption: (water content is low), particle size affects this
b)capillary effect: (water content is high) pore size affects it
2) Predict material Properties
ex) K = K(S) = K(ua - uw)
What Quantities are used to describe SWCC? - answer 1) AEV: Matric Suction
a) Large Soil Pores
b) Small soil pores
2) Residual Water Content
What are the methods to determine SWCC?
(Or What is the hysteresis in SWCC?) - answer 1) Drying Path (Desorption Process)
, 2) Wetting Path (Sorption Process)
What factors can contribute to the hysteresis in SWCC? - answer a) Non uniformity
of soil Pores:
When the matric suction is the same, the soil can hold more water in the dry path
b) Contact Angle Effect:
When the water content is same, soil can have a higher matric suction in the drying path
c) Entrapped air in sorption process (Wetting Path)
d) Differential Changes in soil structure in drying and wetting path
drying path - Volume contraction
wetting path - Volume expansion
What are the features of the Filter Paper Technique?
(Or how do you determine soil suction through filter paper?) - answer 1) Measure
Total suction(Non-Contact) and Matric suction (Contact)
2) Indirect Measurement Method
3) Break Point
a) Absorption (Low Water Content)
b) Capillary Effect (High Water Content)
4) Time consuming
Why is the HAE ceramic needed to measure the matric suction? - answer It prevents
the air from entering the measuring system
What are the features of HAE ceramics? - answer 1) small pore size
2) AEV high
What is the major limitation of tensiometer for the measurement of matric suction? -
answer It is not possible to measure a negative pore water pressure which is less
than -100 kPa
What are the features of Axis Translation Technique? - answer 1) Pore air and water
pressure are increased, water content and matric suction is kept constant
2) Air pressure system needed to increase pore air pressure
3) HAE ceramic required
