Slope stability

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Slope stability

• Quantitative assessment of the INITIATION of some
  mass wasting processes
• Nice way to illustrate body and surface forces
  and frictional failure
• Practical use

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Small earthflow in roadcut in North Dakota
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Recent shallow landslides on the east side of I-5
near Castaic.
http//landslides.usgs.gov/recent/socal_reconn/ima
ges/photo17.jpg
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http//landslides.usgs.gov/recent/socal_reconn/pho
to8.php
Abundant recent shallow landslides west of I-5
near Santa Clarita.
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Small, recent shallow landslides in older scars
from previous years, east of I-5 in Orange
County.
Landslide in the Hollywood Hills northwest of Los
Angeles.
http//landslides.usgs.gov/recent/socal_reconn/pho
to14.php
http//landslides.usgs.gov/recent/socal_reconn/pho
to15.php
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Recent failure of the south bank of the Santa
Clara River.
http//landslides.usgs.gov
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Deep seated
Shallow
http//www.ecy.wa.gov/programs/sea/landslides/abou
t/shallow.html
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Landslide stability analysis

• Basically a force balance between driving and
  resisting forces evaluated on the potential
  failure plane.
• Evaluated as a ratio of driving to resisting
  forces

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Derive stress components

• Act along an inclined plane covered by
  unconsolidated material

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Given a column of wet debris (part of a slide
mass) of unit width and depth and height h, what
is the stress acting along its base?
Red is corrected part of derivation
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2) Shear strength resistance of material to
shear stresses generated by gravity
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3) Analysis of slope stability
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Effect of water in the slide -Load is accounted
for in bulk density
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Apply coulomb equation to stability analysis
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Factor of safety example
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Factor of safety examples
From last page FS factor_of_safety(c_prime, h,
theta, vr, rho_r, m, phi)
factor_of_Safety(11900, 6, 10, 0.6, 2670,
1, 8) rho_b 2002 FS 0.9895 Slope goes up FS
factor_of_safety(c_prime, h, theta, vr, rho_r,
m, phi) factor_of_Safety(11900, 6,
20, 0.6, 2670, 1, 8) rho_b 2002 FS
0.5075 Diminish saturation, safety goes up FS
factor_of_safety(c_prime, h, theta, vr, rho_r, m,
phi) factor_of_Safety(11900, 6,
10, 0.6, 2670, 0.5, 8) rho_b 1802 FS
1.2320 Increase internal friction safety goes
up FS factor_of_safety(c_prime, h, theta, vr,
rho_r, m, phi) factor_of_Safety(11900,
6, 10, 0.6, 2670, 1, 16) rho_b 2002 FS
1.4044
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Vary saturation FS factor_of_safety(c_prime,
h, theta, vr, rho_r, m, phi)
factor_of_Safety(11900, 6, 10, 0.6, 2670, m, 8)
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Vary failure surface slope FS
factor_of_safety(c_prime, h, theta, vr, rho_r, m,
phi) factor_of_Safety(11900, 6, theta,
0.6, 2670, 1, 8)
FS 1 at 10
FS 0.51 at 20
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