SCHEDULE

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SCHEDULE
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OUTLINE

• In Class Exam 2
• Landsliding
• Types
• Mechanics
• Sensitivity
• Probability

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MIDTERM 2a

• Mean 14.4
• Range 5-30.5
• Class performance is now where previous classes
  were by finals

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MIDTERM 2a

• Which is most difficult?
• 1/4 description
• 1/4 coverages
• 1/4 functions
• 1/4 code

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Landslide Type Deep-Seated

• Large
• Gradual
• Lithologic Control
• Groundwater Control

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Landslide Type Shallow Rapid

• Small
• Rapid
• Root Control
• Saturation Control

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Landslide Mechanics

• Factor of Safety
• Ratio of Forces
• FSresisting/initiating
• FSlt1 landslide
• FSgt1 no landslide

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Landslide Mechanics

• qo is the surcharging weight of the vegetation
• ? is the angle of the slope
• ? is the friction angle of the soil
• C is the soil cohesion
• Cr is the root reinforcement
• h is the soil thickness
• z is the saturated thickness
• gw is the unit weight of water
• gs is the unit weight of saturated soil

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Stability Calculation
slope_grid
q0_grid
z
phi_grid
gw
Cr_grid
gs_grid
h_grid
C_grid
FS_grid
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Computational Process
literature
Stand cover
dem
Soil cover
Grids of Slope, Cohesion, friction...
FS_grid
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Example

• Using
• q010-40 psf
• C0 psf
• Cr100-200psf
• phi35-40 deg
• gs150 pcf
• gw72 pcf

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Problem 1

• Equation usually doesnt predict cells that slid,
  but predicts sliding in cells that didnt.
• Reasons
• uncertainty in parameters
• uncertainty in process
• Solution Pseudo probability
• FS is only correlated with landsliding

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Problem 2

• Parameters are uncertain/variable
• Solution
• Model uncertainty in each parameter, i.e.
  Cohesion might be within range (3-10 kPa)
• 1. Choose a value for each parameter
• 2. Calculate FS
• 3. Repeat
• 4. Calculate fraction of times FSlt1

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Problem 3

• How do you model soil saturation?
• Solution
• Assume steady state rainfall
• QinQout
• qwdPfa
• Pcdc(qw)/fa
• where dc is the critical value of z that makes
  FS1
• zgth never slides
• zlt0 always slides

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Problem 4

• Isnt this all too complicated to use?
• Solution
• Map hazard ratings (low/moderate/high)

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Problem 5

• What are the consequences of management?
• Solution
• Observe fraction cells that slid with each mgt
• Assume similar fraction for future mgt
• Map/calculate resulting landsliding

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Example

• If we map the topography as high/mod/low
• And map management as road/cut/none
• We can make a 3x3 table of hazard/mgt
• We can calculate fraction of cells in each zone
  that have slid
• We can what if on other road harvest plans