Report prepared as part of course CEE 542 Soil and Site Improvement Winter 2014 Semester Instructor Professor Dimitrios Zekkos Department of Civil and Environmental Engineering University of Michigan ID: 791312
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Web-based Class Projecton Ground Improvement
Report prepared as part of course CEE 542: Soil and Site ImprovementWinter 2014 SemesterInstructor: Professor Dimitrios ZekkosDepartment of Civil and Environmental Engineering University of Michigan
Prefabricated Vertical Drains
Prepared by:
Jenna Scorza
Greg Fox
With the Support of:
Slide2Prefabricated Vertical DrainsGreg Fox & Jenna Scorza
Slide3IntroductionExpediting
consolidation of slow draining soilsShorten pore water travel distanceCoupled with surchargeHorizontal flow
Slide4History1920s: sand drain patented
1930s: band-shaped vertical drain made of cardboard core and paper filter jacket1980s: plastic PVD introduced and replaced predecessors
Slide5Features
Channeled plastic core wrapped with geotextileCore:Support for filter fabricProvide longitudinal flow pathsResistance to stretching and bucklingJacket:Acts as filter
Slide6FeaturesEquivalent Diameter
Hanso 1979Rixner 1986Oblong shape, theories available derived for circular shapeMany equations have been suggestedDifferent assumptions = different results
Slide7FeaturesIndependent EvaluationBy Richard P.
Lomg & Alvaro CovoAnalog Field PlotterElectrical potential to hydraulic headElectrical current to flow of waterResults agree with Suits et al. 1986
Flow Net for Flow to Oblong Drain from Circular Surface
Slide8BenefitsDecrease primary consolidation time period
Decrease surcharge required for precompressionIncrease rate of strength gain and stabilityCompared to Sand DrainsEconomic competitivenessLess soil disturbanceImproved speed and simplicity of installationFeasible nonvertical orientation and underwater installation
Slide9Disadvantages
Pre-excavation may be needed for very dense or stiff fillsGround distrubance may not be tolerable in sensitive soilsWinter ConsiderationsFrost line 3ft depth in MidWestFrost can reduce drain dischargeBuild up pack pressureRetard settlement developmentLead to false premise that primary consolidation has reached an end
Slide10Suitable Soils
Implemented in soils that are moderately to highly compressible under static loadingInorganic silts and clays of low to moderate sensitivityOrganic layersDecomposed peatClayey and silty sandsDredge spoilsVarved cohesive deposits
Slide11Installation
Steel mandrel encasing wick drainDriven with vibrating (or static) force by stitcherDrain anchored at desired depth, mandrel removedWick drain cut at surface Depth and Width of drains selected based on soil stratigraphy and project specifications
Slide12Depth and Width of InstallationDrain should be extended into any available pervious soil layer below
preconsolidation stress margin to assure discharge of waterDrains should be distributed across the entire footprint of an embankment and a small distance beyond
Slide13Design of Drains
Coefficient of Consolidation for Horizontal Drainage, chch = (kh / kv)*cvc
v from 1-D consolidation testCoefficient of Permeability for Horizontal Seepage, khkh / kv
~ 1 (conservative estimate)lab/field testing Coefficient of Permeability in Horizontal Direction of Disturbed Soil, kskh/
ks ~ 1~5varies with soil sensitivityDrain Influence ZoneD = 1.13s (Square)
D = 1.05s (Triangular)
Slide14Effectiveness of PVDs
Water Flow into DrainHydraulic ConductivitySmear ZoneDischarge CapacityDesignInstallationCloggingBending/KinkingBiological Degradation
Slide15Water Flow into DrainHydraulic Conductivity
k of surrounding soil will control water flow into drain
Slide16Water Flow into DrainSmear Zone Development
Results from Installation of drains Mandrel to clamp drainAnchor PlateKeep drain in place Prevent soil entering through bottom of drain
Slide17Water Flow into DrainSmear Zone Idealization
Slide18Water Flow into DrainSmear Zone Generalities
Larger Mandrel = Larger Smear ZoneShape of Mandrel affects shape of smear zoneSquare/Circular Mandrel = square/circular zoneRectangular mandrel = ellipsoidal zoneOuter boundary of zone range 4~18 times mandrel radiusRatio of hydraulic conductivity of undisturbed soil to smear zone ranges from 1~5
Slide19Discharge CapacityDesign & Installation
DesignCross Sectional Area - core available for flowGeosynthetic materials usedInstallationPresents critical case for the mechanical properties of drainASTM Grab, Puncture Tests
Slide20Discharge CapacityClogging & Biological Activity
CloggingFilter - Apparent Opening Size (AOS)Larger drain channel = less cloggingBiological ActivityDepending on duration of project
Slide21Discharge CapacityBending/Kinking of Drain
Consolidation of soil results in bending and/or kinking of drainWhether drain bends or kinks depends onFlexibility of drain (more flexibility leads to greater reduction in discharge capacity)Modulus of surrounding soil
Slide22Discharge CapacityBending/Kinking of Drain
Slide23Discharge CapacityBending/Kinking of Drain
Slide24Recent Development & Future of PVDs
Recent DevelopmentUse of electronics for quality controlDepth, Installation Force, GPS coordinates, date/time info.Necessity of such equipment depends on projectFuturePrecision of targeted geosynthetic functionUnderstanding of smear zone and drain deformation are largest areas for improvement
Slide25Questions?
Slide26More Information
More detailed technical information on this project can be found at:http://www.geoengineer.org/education/web-based-class-projects/select-topics-in-ground-improvement