SEISMIC SLOPE STABILITY - 1906eqconf.org1906eqconf.org/tutorials/EQHazMapGrndShaking_McCrink.pdf ·...
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SEISMIC SLOPE STABILITY Tim McCrink Seismic Hazards Mapping Program California Geological Survey 100 th Anniversary Earthquake Conference Commemorating the 1906 San Francisco Earthquake April 18 – 22, 2006
Transcript of SEISMIC SLOPE STABILITY - 1906eqconf.org1906eqconf.org/tutorials/EQHazMapGrndShaking_McCrink.pdf ·...
SEISMIC SLOPE STABILITY
Tim McCrinkSeismic Hazards Mapping Program
California Geological Survey
100th Anniversary Earthquake Conference Commemorating the 1906 San Francisco Earthquake
April 18 – 22, 2006
Topics Covered
• CGS Earthquake-Induced Landslide Zones
• Site-Specific Seismic Slope Stability Analyses
CALIFORNIA GEOLOGICAL SURVEY
EARTHQUAKE-INDUCED LANDSLIDE ZONES OF REQUIRED
INVESTIGATION
LANDSLIDE ZONES - MAPPING APPROACH SUMMARY
• INPUT DATA:– GEOTECHNICAL SHEAR TEST DATA– GEOLOGIC MAP DATA– DIGITAL TERRAIN DATA– DESIGN SEISMIC DATA
• METHODOLOGY:– INFINITE-SLOPE FAILURE MODEL– NEWMARK DISPLACEMENT ANALYSIS
ZONE MAPPING CRITERIA
• ANALYTICALLY DETERMINED – HAZARD POTENTIAL CRITERIA - NEWMARK
DISPLACEMENTS:• VERY LOW - < 5 cm• LOW - > 5 cm to < 15 cm• MODERATE - > 15 cm to < 30 cm• HIGH - > 30 cm
• EXISTING LANDSLIDE AREAS, INCLUDING EARTHQUAKE-TRIGGERED SLOPE FAILURES
Landslide Inventory
Shear Strength Groups
Geologic Stratigraphy
Geologic Structure
Digital Terrain
PSHA Data
Dip Gradient
Dip Azimuth
Slope Gradient
Slope Azimuth
Strong Motion Record
Hazard Potential Matrix
Dip-Slope Map
Slope Gradient
Geologic Material Strength Map
Landslide Hazard
Potential Map,
Zone MapZone Map
GENERALIZED WORK FLOWShear Strength Data
Shear Strength Groups
Ay vs. Disp.
Stability Analyses
GEOTECHNICAL SHEAR TEST DATA
• SHEAR TEST SOURCES
• CRITERIA FOR COLLECTION
• DATA PROCESSING
Material Strength by Geologic Unit
0 10 20 30 40 50 60Angle of Internal Friction (phi)
0
5
10
15C
ount
Coarse-Grained
Fine-Grained
Chatsworth Formation (Kc)
Strength Groups
Slope Stability Analysis
• Static Conditions:– FS = R/D = Wcos α tan φ / Wsin α = tan φ / tan α
• Dynamic Conditions:– ay = (FS - 1)g sin α (Newmark’s Equation)
W
kh(t)W
W
Rs Rd
Ns = W cos α Nd
α α
STATIC CONDITIONS DYNAMIC CONDITIONS
INFINITE SLOPE MODEL
1967-1981 USGS DEM SHADED RELIEF
1998 RADAR DEM SHADED RELIEF
DIGITAL TERRAIN DATA
Slope Gradient Map
GEOLOGIC MAP INFORMATION
• STRATIGRAPHIC INFORMATION
• GEOLOGIC STRUCTURE INFORMATION
• LANDSLIDE INVENTORY INFORMATION
GEOLOGIC MATERIAL STRENGTH MAP=
+
+
Stratigraphic InformationGEOLOGIC MAP:
Geologic Structure Information
• STRIKE AND DIP MEASUREMENTS
• FOLD AXES
GEOLOGIC MAP:
Adverse Bedding Map
Geologic Structure Information
Landslide Inventories
• EXISTING LANDSLIDES
• KNOWN EARTHQUAKE-INDUCED SLOPE FAILURES
GEOLOGIC MAP:
GEOLOGIC MATERIAL STRENGTH MAP
DESIGN SEISMIC DATA
• REPRESENTATIVE STRONG-MOTION RECORD(S)
• STRONG-MOTION RECORD SELECTION
PERMANENT SLOPE DISPLACEMENTS FROM EARTHQUAKE GROUND
MOTION
DISPLACEMENT vs. YIELD ACCELERATION
0.1
1.0
10.0
100.0
1000.0
DIS
PLA
CE
ME
NT
(cm
)
0.01 0.1 1 YIELD ACCELERATION (g)
NEWMARK DISPLACEMENTvs. YIELD ACCELERATION
30 cm
15 cm
5 cm
0.076
0.129
0.232
USC STATION #14 - Channel 3
H M L VL
HAZARD POTENTIAL MATRIX
Very Low Low Moderate High1 (36) 0 to 46% 47 to 52% 53 to 57% > 57%
2 (33) 0 to 39% 40 to 46% 47 to 49% > 49%
3 (30) 0 to 31% 32 to 37% 38 to 42% > 42%
4 (25) 0 to 22% 23 to 27% 28 to 31% > 31%
5 (16) - 0 to 2% 3 to 8% > 8%
MINDEGO HILL QUADRANGLE HAZARD POTENTIAL MATRIX
Geologic Material
Strength Group (Average Phi)
HAZARD POTENTIAL
(% Slope)
HAZARD POTENTIAL
EARTHQUAKE-INDUCED LANDSLIDE ZONES OF REQUIRED
INVESTIGATION
LANDSLIDE HAZARD ZONE METHOD LIMITATIONS
• NOT CONSISTENTLY IDENTIFIED:– SHATTERED RIDGES– RIDGE-TOP SPREADING– FAILURE OF FLAT AREAS ABOVE HEAD SCARPS– LANDSLIDE RUNOUT
• FRACTURE DENSITY OR ORIENTATION• OUT-DATED TERRAIN INFORMATION• TOPOGRAPHIC AMPLIFICATION, DIRECTIVITY
SITE-SPECIFIC SEISMIC SLOPE STABILITY
Seismic Slope StabilityElements
• Investigation:– Office – Field– Laboratory
• Analyses:– Seismic– Site Response– Stability
Site Investigation Considerations• Geology, Topography, Aerial Photo Analysis
– Existing Slope Failures– Ridge-Top Failures– Cliffs, Rock Fall– Lateral Spread Features– Nearby Active Faults
• Adverse Bedding / Discontinuity Conditions• Shear Wave Velocity
Material Strength For Dynamic Conditions
From Blake et al., 2002
Seismic Analysis Considerations
• Pseudo-Static Analysis– Peak Horizontal Ground Acceleration (PGA)– Magnitude (M)– Distance (r)
• Deformation Analyses– PGA, M, r– Duration (D5-95)– Mean Period of Ground Motion (Tm)– Strong Motion Time Histories
Pseudo-Static Slope Stability Analysis
Basic Concept
From Franklin & Chang 1977
Origin of the Seismic Coefficient Approach
• Terzaghi (1950)– Severe – 0.1– Violent – 0.25– Catastrophic – 0.5
• Seed (1979)– Use k = 0.15, FS => 1.15
• Hynes-Griffin & Franklin (1984)– Use k = 0.5 * PGA, FS => 1.0, 80% strengths
SP 117 Implementation Committee “Screening Analysis”
• k = feq x (PGAr / g)• FS = 1.0
• Assumptions:– Significant Displacements of 5 or 15 cm– Stiff Soil or Soft Bedrock– Relatively Thin Slide Mass (H <~ 20 m)– Ts/Tm <~ 0.5
Determining feq
Determining feq
Example Pseudo-Static Analysis
Static Analysis
FS = 2.2
Ground Motion Estimation - PGA
Ground Motion Estimation - M, r
Seismic Coefficient - 5cm Criteria
k = f eq * MHAr = 0.56 * 0.8 = 0.45
Seismic Coefficient - 15cm Criteria
K = 0.46 * 0.8 = 0.37
Pseudo-Static Analysis
FS = 0.93
Deformation Slope Stability Analysis
Types of Deformation Analyses
• Sliding Block Models
• Stress-Deformation Models
Sliding Block Model
From Kavazanjian, et al., 1997
Types of Sliding-Block Analyses
• Rigid-Block Analysis
• Decoupled Analysis
• Coupled Analysis
Selecting the Appropriate Sliding Block Analysis
From: Wartman, et al., 2003
Performing A Rigid Block Analysis
• Pseudo-Static Analysis - ky
• Select Appropriate Time Histories
• Double Integrate Time Histories to Determine Cumulative Displacements
Example Rigid Block Analysis
Determine Yield Coefficient
Select Earthquake Time Histories
Perform Displacement Calculations
What Do the Displacement Numbers Mean?
• Sliding Block Displacements Provide an Index of Probable Seismic Slope Performance– SP 117
• <10cm – Damage Unlikely• >10cm, <100cm – Serious Deformations• >100cm – Slopes Unstable
– Implementation Committee• Buildings - <5cm• Non Building Areas - <15cm• Strain Softening Materials
– Peak Strengths - <5cm– Residual Strengths - <15cm
Internet Resources For Seismic Slope Stability
• Landslide-Related Information at CGS:– http://www.consrv.ca.gov/cgs/geologic_hazards/la
ndslides/index.htm• Seismic Hazard Zone Maps From CGS:
– http://gmw.consrv.ca.gov/shmp/ • CGS Special Publication 117
– http://www.conservation.ca.gov/cgs/shzp/webdocs/sp117.pdf
Internet Resources For Seismic Slope Stability
• Interactive Ground Motion Estimates:– http://www.consrv.ca.gov/CGS/rghm/pshamap/pshamain
.html– http://earthquake.usgs.gov/hazmaps
• Implementation Committee Report:– http://www.scec.org/resources/catalog/hazardmitigation.
html#land
• Newmark Analysis Software:– http://earthquake.usgs.gov/resources/software/slope_perf
.php
