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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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Introduction
Vibroflotation 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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Introduction
During 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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Introduction
Uses:❏ Reduce potential settlement❏ Seismic liquefaction mitigation
Common for:❏ Off-shore projects❏ Land made of reclaimed soil❏ Hydraulic fills
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Applicability
Most 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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Applicability
Problem 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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Design
Density goal set in terms of relative density
Spacing Patterns: Square, Triangular, Line
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Cost
Highly Variable
Croton Dam Case Study (1999)
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Cost
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Case Study: Success
Seabird 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: Success
Existing 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: Success
35 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: Success
Results & 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: Failure
Thermalito Afterbay in Northern California
8 mile long embankment, 39 foot height
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Case Study: Failure
August 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: Failure
Analysis 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: Failure
Foundation 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: Failure
Vibroflotation testing program implemented
Thermalito Bay worksites table (Harder et. al., 1984)
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Case Study: Failure
Vibroflot 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: Failure
Results 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: Failure
Conclusion: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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Conclusions
Vibroflotation is a successful and cost effective technique used to densify loose coarse-grained soils
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Questions
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More 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