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Anaheim Hills Landslide. ‘Avenida de Santiago’ January 17th 1993. Introduction. Southern California, the Orange County Winter storms cause widespread slope failures Disrupt infrastructure Excess rainwater causes rising groundwater levels Re-activates ancient landslide

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anaheim hills landslide

Anaheim Hills Landslide

‘Avenida de Santiago’

January 17th 1993

introduction
Introduction
  • Southern California, the Orange County
  • Winter storms cause widespread slope failures
  • Disrupt infrastructure
  • Excess rainwater causes rising groundwater levels
  • Re-activates ancient landslide
  • ‘Avenida de Santiago’ most high profile
why did it occur
Why did it occur?
  • North-facing hillside topography
  • Geology
  • Rising Groundwater
  • Human error
geology
Geology
  • Northward dipping section
    • Sandstone and Siltstone (Puente Formation)
    • Miocene age
  • Bedding dips 7° to 25° to North
  • Strikes range NE to NW
  • Failure in Puente Formation
    • Parallel to bedding
  • Sandstone
    • Medium to Coarse grained
    • Poor cemented
    • Weak
    • Inter bedded with Siltstone
geology1
Geology
  • Compressional uplift of tertiary sedimentary section due to blind thrust faults
  • San Andreas fault
    • Strike slips and thrust faults
    • Multiple earthquakes
    • Late Quaternary time contributes to landslide
weather
Weather
  • Intense rainfall December 1992 and January 1993
    • Equal to average annual rainfall (38cm)
  • Raised groundwater level in landslide mass
human error
Human Error
  • Early Geotechnical Investigation
    • No groundwater evaluation
      • Piezometer
    • Poor borehole investigations
      • Few widely spaced and shallow
  • Responsive, not proactive
    • Local authorities authorised Geological Investigation upon observation of cracks
  • Neglected evidence of previous landslides
the landslide
The Landslide
  • Soil Slumps and Soil Block slides move at 2/3cm per day
  • Translational
    • 400m wide x 600m long
  • After management solutions slide deemed stationary by mid-April 1993
the landslide1
The Landslide
  • Cracks and Fissures developed at head
  • Compressional features damaged infrastructure lower down slope
  • Immediate Engineering implications
geotechnical investigation1
Geotechnical Investigation
  • Ridge Top Graben at LD-3 source of landslide
  • Slip occurs at Sandstone bedrock as identified by borehole logs
engineering prevention strategies
Engineering Prevention Strategies
  • Dewatering to control groundwater level
  • Removal and recompaction of potentially compressible soils
  • Complete or partial removal of ancient landslides
  • Stabilisation of potentially unstable cut slopes
    • Case study $2.9 million for one house!
  • Specific structure foundation designs
dewatering
Dewatering
  • GHAD final solution
  • 30 million gallons water per year
  • Dewatering wells and horizontal drains
  • Lower and control groundwater levels
  • Substantially improved stability of landslide mass
  • Constantly monitored
conclusion
Conclusion
  • Re-activation of Ridge-Top Graben by seismic shaking & rising groundwater
  • Dewatering is a ‘stop gap’
  • $3.5 million budget
  • Constant road resurfacing
  • New fissures appeared in 1998
  • Escape route plan
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