Transcript Vibroflotation - Geoengineer.org

Web-based Class Project
on Ground Improvement
Vibroflotation
Prepared by:
Yanet Zepeda
Ian McCreery
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
With the Support of:
Vibroflotation
http://www.cyes.es/images/obras/69/imagenes/max/00105%20AMPLIACION%20DARSENA%20SUR%20PTO%20VLC%201.JPG
Ian McCreery & Yanet Zepeda
Overview
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Introduction
Applicability
Equipment & Construction
Design
Cost
Case Study: Success
Case Study: Failure
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/
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)
Introduction
Uses:
❏ Reduce potential settlement
❏ Seismic liquefaction mitigation
Common for:
❏ Off-shore projects
❏ Land made of reclaimed soil
❏ Hydraulic fills
Applicability
Most coarse-grained soils with a fines content of less than 10%
are considered acceptable.
Ideally, loose soils below the water table.
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/
Applicability
The orange area represents the grain size distribution of soils suitable for vibroflotation (Bauer Maschinen GmbH, 2012)
Equipment
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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
Equipment
❏ Electric or hydraulically powered motor to
rotate a mass
❏ Centrifugal force generated: 43,000 to
70,000 lbs
❏ 2 Jets
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Bottom
❏ Upper
http://i00.i.aliimg.com/photo/v0/24033
4132/VFA200_Hydraulic_Vibroflot.jpg
Construction Procedures
❏ Reach depths up to 150 feet
❏ Densification achieved 5 to 15 radially from vibroflot
Construction Procedures
❏ VF trial
❏ Soil penetration
❏ Densification at desired
depth
❏ Retract probe to next
location
❏ Backfill
Construction Procedures
❏ Vibroflot Starving
❏ Quality Control
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Penetration Depth
Penetration Rate
Withdrawal Rate
Probe Location
Power Peak
Operating Frequency
Post-Operation Density Checks
Design
Density goal set in terms of relative density
Spacing Patterns: Square, Triangular, Line
Cost
Highly Variable
Croton Dam Case Study (1999)
Cost
Case Study: Success
Seabird Naval Base at Karwar in
Indian state of Karnataka.
Construction of 3 mile long
breakwater structure.
Project Seabird (Sharma, 2004)
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
Case Study: Success
35 acres selected for compaction
Four 49 foot long vibrators suspended from a crane situated on a
barge
Project Seabird setup (Raju et al., 2003)
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.
Case Study: Failure
Thermalito Afterbay in Northern
California
8 mile long embankment, 39 foot
height
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.
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.
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
Case Study: Failure
Vibroflotation testing
program implemented
Thermalito Bay worksites table (Harder et. al., 1984)
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.
Case Study: Failure
Results for Worksite 2.
No appreciable
improvement.
Same for Worksite 1.
Thermalito Bay CPT and SPT results (Harder et. al., 1984)
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.
Conclusions
Vibroflotation is a successful and cost effective technique used to densify
loose coarse-grained soils
Questions
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-groundimprovement