Heather Drive Heather Drive Landslide UtahLandslide Utah

James von der FechtJames von der FechtSimon PennockSimon Pennock

IntroductionIntroduction

• Heather Drive is in the city of Layton, UtahHeather Drive is in the city of Layton, Utah

Utah’s GeologyUtah’s Geology

• Landslides are common across the StateLandslides are common across the State

• Layton’s Location -Layton’s Location -• Soft, silty and clayey materialSoft, silty and clayey material• Near the Wasatch FaultNear the Wasatch Fault

• Utah has a very complex and Utah has a very complex and distinctive Geologydistinctive Geology

Lake Bonneville

• Quaternary Period Lake, present during Pleistocene Epoch

• Delta covered where Layton is now situated

• Sands and gravels deposited along the shoreline and at river delta

Geological History

• Lake has since receded

• Cause of Layton’s ground conditions

• Took place August 2001

The Heather Drive LandslideThe Heather Drive Landslide

• Landslide area ≈ 350m wide and 150m long• Land affected situated on a relatively gentle (20-28%) slope

• Caused by a reactivation of a prehistoric landslide

• Preceded by several smaller reactivations in Layton from 1997 onwards

• Main scarp formed measured up to 2.9m in height

• 6 houses damaged on Heather Drive - • 3 destroyed• 3 partially recoverable

Impacts of the LandslideImpacts of the Landslide

• Economic cost approximately $1million -• Loss of homes• Re-routing of Utilities• Other costs incurred by Layton City

Landslides Across UtahLandslides Across Utah• Types LandslidesTypes Landslides

• DebrisDebris• SlidesSlides• FallsFalls

• CausesCauses• RainfallRainfall• SnowfallSnowfall• IrrigationIrrigation

• SeasonalSeasonal• March, April, MayMarch, April, May• July and AugustJuly and August

• FrequencyFrequency• Regular small scale Regular small scale

landslideslandslides

ProblemProblem• Debris FlowDebris Flow

• CausesCauses• Heavy Heavy

precipitationprecipitation• Channel scourChannel scour• Slope gradientSlope gradient

ProblemProblem• Circular SlipCircular Slip

• CausesCauses• Poor drainagePoor drainage• Dynamic Dynamic

loadingloading• Excavation at Excavation at

toetoe

ProblemProblem• Rock FallRock Fall

• CausesCauses• Poor drainagePoor drainage• UndercuttingUndercutting

• Stress changeStress change• Separation of Separation of

materialsmaterials

Alternative Engineering Alternative Engineering ApproachesApproaches

• DrainageDrainage• ττ = c’ + = c’ + σσnn

’ ’ tan tan ФФ• Where Where σσ’ = ’ = σσ - - υυ

• Minimise irrigationMinimise irrigation• FarmingFarming

• Avoid excavation near Avoid excavation near the base of a landslidethe base of a landslide

• Re-profilingRe-profiling• Urban areaUrban area

Alternative Engineering Alternative Engineering ApproachesApproaches

• Soil stabilisationSoil stabilisation• PinningPinning• VegetationVegetation

• TreesTrees• EducationEducation

• PlannersPlanners• New geological mapsNew geological maps

Solution AdoptedSolution Adopted

• MonitoringMonitoring• Main scarpMain scarp

• EducationEducation• Sharing informationSharing information• Detailed response Detailed response

planplan

ConclusionConclusion• Many types of landslide common in Utah• Heather Drive typical landslide case

• Layton incurred over $1million costs

• Landslides due to underlying geology and rainfall

• Landslides cost Utah millions of dollars per year