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Anaheim Hills LandslideAnaheim Hills Landslide
‘‘Avenida de Santiago’Avenida de Santiago’
January 17th 1993January 17th 1993
IntroductionIntroduction Southern California, Southern California,
the Orange Countythe Orange County Winter storms cause Winter storms cause
widespread slope widespread slope failuresfailures
Disrupt infrastructureDisrupt infrastructure Excess rainwater Excess rainwater
causes rising causes rising groundwater levelsgroundwater levels
Re-activates ancient Re-activates ancient landslidelandslide
‘‘Avenida de Santiago’ Avenida de Santiago’ most high profilemost high profile
Why did it occur?Why did it occur?
1.1. North-facing North-facing hillside hillside topographytopography
2.2. GeologyGeology
3.3. Rising Rising GroundwaterGroundwater
4.4. Human errorHuman error
GeologyGeology Northward dipping sectionNorthward dipping section
• Sandstone and Siltstone (Puente Formation)Sandstone and Siltstone (Puente Formation)• Miocene ageMiocene age
Bedding dips 7Bedding dips 7°° to 25 to 25° to North° to North Strikes range NE to NWStrikes range NE to NW Failure in Puente FormationFailure in Puente Formation
• Parallel to beddingParallel to bedding SandstoneSandstone
• Medium to Coarse grainedMedium to Coarse grained• Poor cementedPoor cemented• WeakWeak• Inter bedded with SiltstoneInter bedded with Siltstone
GeologyGeology
Compressional uplift of tertiary Compressional uplift of tertiary sedimentary section due to blind sedimentary section due to blind thrust faultsthrust faults
San Andreas faultSan Andreas fault• Strike slips and thrust faultsStrike slips and thrust faults• Multiple earthquakesMultiple earthquakes• Late Quaternary time contributes to Late Quaternary time contributes to
landslidelandslide
WeatherWeather Intense rainfall December 1992 and Intense rainfall December 1992 and
January 1993January 1993• Equal to average annual rainfall (38cm)Equal to average annual rainfall (38cm)
Raised groundwater level in landslide Raised groundwater level in landslide massmass
Human ErrorHuman Error
Early Geotechnical InvestigationEarly Geotechnical Investigation• No groundwater evaluationNo groundwater evaluation
PiezometerPiezometer
• Poor borehole investigationsPoor borehole investigations Few widely spaced and shallowFew widely spaced and shallow
Responsive, not proactiveResponsive, not proactive• Local authorities authorised Geological Local authorities authorised Geological
Investigation upon observation of cracksInvestigation upon observation of cracks Neglected evidence of previous landslidesNeglected evidence of previous landslides
The LandslideThe Landslide
Soil Slumps and Soil Slumps and Soil Block slides Soil Block slides move at 2/3cm per move at 2/3cm per dayday
TranslationalTranslational• 400m wide x 600m 400m wide x 600m
longlong After management After management
solutions slide solutions slide deemed stationary deemed stationary by mid-April 1993by mid-April 1993
The LandslideThe Landslide
Cracks and Fissures developed at headCracks and Fissures developed at head Compressional features damaged infrastructure Compressional features damaged infrastructure
lower down slopelower down slope Immediate Engineering implicationsImmediate Engineering implications
Geotechnical InvestigationGeotechnical Investigation
Geotechnical InvestigationGeotechnical Investigation
Ridge Top Graben at LD-3 source of landslideRidge Top Graben at LD-3 source of landslide Slip occurs at Sandstone bedrock as identified by Slip occurs at Sandstone bedrock as identified by
borehole logsborehole logs
Engineering Prevention StrategiesEngineering Prevention Strategies
Dewatering to control groundwater levelDewatering to control groundwater level Removal and recompaction of potentially Removal and recompaction of potentially
compressible soilscompressible soils Complete or partial removal of ancient Complete or partial removal of ancient
landslideslandslides Stabilisation of potentially unstable cut Stabilisation of potentially unstable cut
slopesslopes• Case study $2.9 million for one house!Case study $2.9 million for one house!
Specific structure foundation designsSpecific structure foundation designs
DewateringDewatering
GHAD final solutionGHAD final solution 30 million gallons 30 million gallons
water per yearwater per year Dewatering wells and Dewatering wells and
horizontal drainshorizontal drains Lower and control Lower and control
groundwater levelsgroundwater levels Substantially Substantially
improved stability of improved stability of landslide masslandslide mass
Constantly monitoredConstantly monitored
ConclusionConclusion Re-activation of Ridge-Re-activation of Ridge-
Top Graben by seismic Top Graben by seismic shaking & rising shaking & rising groundwatergroundwater
Dewatering is a ‘stop Dewatering is a ‘stop gap’gap’
$3.5 million budget$3.5 million budget Constant road Constant road
resurfacingresurfacing New fissures appeared New fissures appeared
in 1998in 1998 Escape route planEscape route plan