web-based class project on ground improvement
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Web-based Class Project on Ground Improvement. Vibroflotation. Prepared by:. 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. - PowerPoint PPT PresentationTRANSCRIPT
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Web-based Class Project
on Ground Improvement
Report prepared as part of course CEE 542: Soil and Site Improvement
Winter 2014 SemesterInstructor: Professor Dimitrios Zekkos
Department of Civil and Environmental Engineering University of Michigan
VibroflotationPrepared by:
Yanet Zepeda Ian McCreery
With the Support of:
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Vibroflotation
Ian McCreery & Yanet Zepedahttp://www.cyes.es/images/obras/69/imagenes/max/00105%20AMPLIACION%20DARSENA%20SUR%20PTO%20VLC%201.JPG
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Overview❏ Introduction❏ Applicability❏ Equipment & Construction❏ Design❏ Cost❏ Case Study: Success❏ Case Study: Failure
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IntroductionVibroflotation utilizes horizontal vibrations in conjunction with
fluid to reduce the interparticle friction of the surrounding soil.
http://www.polbud-pomorze.ru/en/vibroflotation/
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IntroductionDuring vibration material falls into a denser state.Result: Increase in strength and a reduction in compressibility.
Densification of soil during vibroflotation (Bauer Maschinen GmbH, 2012)
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IntroductionUses:❏ Reduce potential settlement❏ Seismic liquefaction mitigation
Common for:❏ Off-shore projects❏ Land made of reclaimed soil❏ Hydraulic fills
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ApplicabilityMost coarse-grained soils with a fines content of less than 10%
are considered acceptable.
Ideally, loose soils below the water table.
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ApplicabilityProblem with Cohesive Soils:Fills voids between larger particles and immobilizes the material
due to positive pore water pressures; this inhibits the ability of the granules to move into a denser state.
http://www.vibromenard.co.uk/techniques/vibro-compaction/
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Applicability
The orange area represents the grain size distribution of soils suitable for vibroflotation (Bauer Maschinen GmbH, 2012)
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Equipment❏ Composed of vibroflot and follow-up pipe❏ Capabilities vary by manufacturer❏ About 12 feet in total length❏ Weigh about 10,000 to 20,000 lbs
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Equipment❏ Electric or hydraulically powered motor to
rotate a mass❏ Centrifugal force generated: 43,000 to
70,000 lbs❏ 2 Jets
❏ Bottom❏ Upper
http://i00.i.aliimg.com/photo/v0/240334132/VFA200_Hydraulic_Vibroflot.jpg
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Construction Procedures❏ Reach depths up to 150 feet❏ Densification achieved 5 to 15 radially from vibroflot
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Construction Procedures❏ VF trial❏ Soil penetration❏ Densification at desired
depth❏ Retract probe to next
location❏ Backfill
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Construction Procedures❏ Vibroflot Starving❏ Quality Control
❏ Penetration Depth❏ Penetration Rate❏ Withdrawal Rate❏ Probe Location❏ Power Peak❏ Operating Frequency❏ Post-Operation Density Checks
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DesignDensity goal set in terms of relative density
Spacing Patterns: Square, Triangular, Line
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CostHighly Variable
Croton Dam Case Study (1999)
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Cost
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Case Study: SuccessSeabird Naval Base at Karwar in
Indian state of Karnataka.
Construction of 3 mile long breakwater structure.
Project Seabird (Sharma, 2004)
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Case Study: SuccessExisting seabed was composed of clay and soft silt, it was
dredged to a depth of nearly 20 feet with hydraulic sand fill.
Problem:CPT’s revealed need for compaction of top 13 feet to reduce
settlement and mitigate liquefaction
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Case Study: Success35 acres selected for compactionFour 49 foot long vibrators suspended from a crane situated on a
barge
Project Seabird setup (Raju et al., 2003)
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Case Study: SuccessResults & Conclusion:CPTs performed every 164 feet along the breakwater structure.
The 13 feet of compacted fill achieved a twofold to threefold increase in penetration resistance compared to the uncompacted values.
Vibro flotation densified the hydraulic fill beneath the breakwater structure successfully.
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Case Study: FailureThermalito Afterbay in Northern
California
8 mile long embankment, 39 foot height
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Case Study: FailureAugust of 1975 an earthquake of magnitude 5.7 revealed an
active fault that had not been previously detected.
Department of Water Resources evaluated the embankments resistance to liquefaction under a 6.5 magnitude earthquake.
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Case Study: FailureAnalysis predicted that the silty sand layers in the foundation of
the embankment would liquefy entirely under these seismic conditions.
Densification of these silty sand layers was necessary to mitigate liquefaction risks.
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Case Study: FailureFoundation made of layers of different soils including clay, silt,
sand and gravel.
Surface layer throughout most of the embankment was composed of a clay and silt layer several feet thick.
Silty sand layers contain a median of 15 percent fines, with 30 percent of the samples containing more than 20 percent fines
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Case Study: FailureVibroflotation testing
program implemented
Thermalito Bay worksites table (Harder et. al., 1984)
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Case Study: FailureVibroflot was not used to penetrate the clay and silt surface
layer, here pre-drilling was used until silty sand layer reached then holes were backfilled before vibroflot was inserted.
An equilateral triangular spacing scheme was utilized with spacings ranging from 6.5 feet to 9.5 feet.
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Case Study: FailureResults for Worksite 2.
No appreciable improvement.
Same for Worksite 1.
Thermalito Bay CPT and SPT results (Harder et. al., 1984)
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Case Study: FailureConclusion:Vibroflotation is not an effective method for the densification of
silty sands below a cohesive soil cap.
The failure of vibroflotation as a technique in this case is most likely due to the relatively high fines content of 15 percent in the silty sand layer.
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ConclusionsVibroflotation is a successful and cost effective technique used to densify
loose coarse-grained soils
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Questions
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More InformationMore detailed technical information on this project can be found at:
http://www.geoengineer.org/education/web-based-class-projects/select-topics-in-ground-improvement