CE 261
2nd Semester 2020-2021
Module 1
• Mohr Circle and the Pole Method are graphical methods whose main
purpose to help visualize the magnitudes and direction of stresses for
a given plane, as well as independently check computations made
using the formulas/expressions for computing stresses along a given
reference frame.
• Be familiar with initial and final Mohr Circles associated with different
shear strength tests.
• For undrained tests, there is an total and effective stress Mohr Circle.
Module 2
• Be familiar with the standard plots associated with different basic
tests.
• Test results within a test series a plotted together within a single
graphs.
• Some graphs with a common ordinate (independent variable) are
normally plotted one on top of another.
• There are three different failure criteria for triaxial tests
• Maximum principal stress ratio
• Maximum deviator stress
• Maximum strain
Module 3
• Skempton’s Pore pressure parameters: and
•
• There are two conventions for stress paths:
• MIT: , , and
• Cambridge: , , and where .
Module 3
• For triaxial test (CL):
• Drained stress path is a 1H:1V (MIT)/ 1H:3V (Cambridge) straight line.
• Horizontal distance between corresponding points on the TSP and ESP
is equal to the pore pressure at the point in the test.
• A 1H:1V line drawn tangent to the (MIT) ESP corresponds to point of
maximum pore pressure.
• For soils with no cohesion, a line tangent to the ESP passing through
the origin corresponds to the point of maximum PSR.
Module 4
• There are four sources of friction in coarse grained soil (assuming
samples if fully saturated):
• Particle sliding
• Expansion/Dilation
• Particle rearrangement/reorientation
• Particle crushing
• Dense versus loose behavior are differentiated by:
• Dilation versus contraction, as well as the presence or absence of strain
softening under drained loading.
• Negative versus positive pore pressures during undrained loading.
Module 4
• The dense versus loose behavior is dependent on the combination of
the initial void ratio and the confining pressure.
• Consequently, is not dependent only on void ratio, but also on the
confining pressure.
Module 5
• Taylor’s method requires the computation of the from test data. In
the program ds_taylor.exe, the derivative is computed using finite
difference approximation.
• First point:
• Last point:
• All other points:
Module 5
• A similar approach is used for subsequent methods for drained triaxial
tests.
• The correction is not applied if the sample undergoes a contraction
instead of a dilation.
• For samples undergoing strain softening, there is a peak angle of
internal friction and a residual angle of internal friction . For a given
confining pressure, the peak angle of internal friction varies with the
initial void ratio. However, the residual angle of internal friction is
independent of the initial void ratio.
Module 5
• For a given confining pressure , a dense sample dilates and a loose
sample contracts until it reaches the critical void ratio . The
relationship between is referred to a the critical state line.
• In theory, samples shear without undergoing any volumetric strain in
the critical state .
• Experimentally, there are very slight differences from the state when
the sample shears within any volumetric strain (constant volume),
and the residual state .
Module 5
• Taylor’s method requires the computation of the from test data. In
the program ds_taylor.exe, the derivative is computed using finite
difference approximation.
• First point:
• Last point:
• All other points:
