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Vibro Compaction

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Vibro Compaction Vibro Compaction, also known as VibroflotationTM, is used to densify clean, cohesionless soils. The action of the vibrator, usually accompanied by ... – PowerPoint PPT presentation

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Title: Vibro Compaction


1
Vibro Compaction
Vibro Compaction, also known as VibroflotationTM,
is used to densify clean, cohesionless soils. The
action of the vibrator, usually accompanied by
water jetting, reduces the inter-granular forces
between the soil particles, allowing them to move
into a denser configuration, typically achieving
a relative density of 70 to 85 percent.
Compaction is achieved above and below the water
table.
2
Vibro CompactionProcess
3
Vibro CompactionProfile of Sand Grains
Volume reduction due to densification of
non-cohesive soils may result in surface
settlement of 5 to 15 of the treated depth.
4
Vibro Compaction Design Considerations
  • The design approach for Vibro technologies will
    generally be governed by one or more of the three
    major categories of site improvement
  • Shear resistance increase
  • Settlement control
  • Liquefaction lateral spreading mitigation

5
Vibro CompactionRange of Treatable Soils
6
Vibro Compaction Design Requirements
  • Design of the Vibro program requires information
    on
  • Total loads (structure, surcharge, live, wind and
    seismic)
  • Soil type (variation, stratigraphy, groundwater
    location)
  • Type of footing/slab design
  • Structural settlement tolerance
  • Site restrictions and limitations
  • To address the above issues, the Vibro program is
    designed such that the zone of influence of the
    vibratory probe ensures the necessary soil
    densification and/or reinforcement.

7
Vibro CompactionDensification Results
8
Vibro CompactionExpected Results
9
Vibro Compaction Design Steps
  • 1. Perform site investigation
  • Soil gradation important
  • 2. Calculate performance with existing soil
    conditions
  • Problem understood
  • 3. Establish compaction requirements
  • Sufficient densification to reduce settlement
    and/or prevent liquefaction
  • 4. Develop appropriate Vibro Compaction approach
  • Treat entire site or just footing?
  • 5. Establish testing criteria
  • Relative density, SPT, CPT, PMT, etc.

10
Vibro Compaction Increased Bearing Capacity
  • Bearing capacity is a function of the soils
    shear strength which is derived from the soils
    angle of internal friction (f) and/or cohesion
    (c). The Vibro systems increase the allowable
    bearing capacity by increasing the effective f
    angle.
  • Vibro Compaction densifies cohesionless granular
    soils, thus increasing the angle of internal
    friction directly. The allowable bearing capacity
    is calculated with conventional procedures using
    the improved angle.

11
Vibro Compaction Reduced Settlement
  • Settlement is a function of the soils modulus
    and consolidation character. Vibro systems
    decrease the settlement that will occur beneath a
    proposed foundation by either directly increasing
    the in situ soils modulus value and/or by
    constructing high modulus Vibro stone columns in
    a grid pattern beneath the planned foundation.
  • Vibro Compaction densifies cohesionless granular
    soils, thus increasing the soils modulus value
    directly. The settlement is calculated with
    conventional procedures using the improved
    modulus value.

12
Vibro Compaction Quality Control
  • Compaction point locations
  • Resistance level as measured by amp meter
    (vibrator draws
  • more current in denser soils)
  • Quantity of fill added or reduction in site level

13
Vibro Compaction Acceptance Testing
  • Standard Penetration Test (SPT)
  • Cone Penetrometer Test (CPT)
  • Pressuremeter Test (PMT)
  • Dilatometer Test (DMT)
  • Load test

14
Vibro CompactionBenefits
  • Increases bearing capacity and reduces foundation
    size
  • Reduces foundation settlement
  • Mitigates liquefaction potential
  • Permits construction on granular fills

15
Vibro Replacement Stone Columns extends the range
of soils that can be improved by vibratory
techniques to include cohesive soils.
Densification and/or reinforcement of the soil
with compacted granular columns or stone
columns is accomplished.
Vibro ReplacementStone Columns
16
Vibro ReplacementStone Columns
  • Cohesive, mixed and layered soils generally do
    not densify easily when subjected to vibration
    alone. The Vibro Replacement Stone Columns
    technique was developed specifically for these
    soils, effectively extending the range of soil
    types that can be improved with the deep
    vibratory process.
  • With Vibro Replacement Stone Columns, columns of
    dense, crushed stone are designed to increase
    bearing capacity, reduce settlement, aid
    densification and mitigate the potential for
    liquefaction, and improve shear resistance.

17
Vibro ReplacementStone Column Process
18
Vibro ReplacementStone Column Construction
  • The two primary methods of Vibro Stone Column
    construction are
  • Wet, Top Feed Method (Replacement and
    Displacement)
  • In this technique, jetting water is used to
    remove soft material, stabilize the probe hole,
    and ensure that the stone backfill reaches the
    tip of the vibrator. This is the most commonly
    used and most cost-efficient of the deep
    vibratory methods. However, handling of the spoil
    generated by the process may make this method
    more difficult to use on confined sites or in
    environmentally sensitive areas.

19
Vibro ReplacementTop-Feed Construction Method
20
Vibro Replacement
  • Dry, Bottom Feed Method (Displacement)
  • This technique uses the same vibrator probes as
    standard Vibro Replacement Stone Columns, but
    with the addition of a hopper and supply tube to
    feed the stone backfill directly to the tip of
    the vibrator. Bottom Feed Vibro Replacement is a
    completely dry operation where the vibrator
    remains in the ground during the construction
    process. The elimination of flushing water in
    turn eliminates the generation of spoil,
    extending the range of sites that can be treated.
    Treatment is possible up to a depth of 80 feet
    and is not inhibited by the presence of
    groundwater.

21
Vibro ReplacementBottom-Feed Construction Method
22
Vibro Replacement Design Steps
  • 1. Perform site investigation
  • Soil type, gradation, consolidation, and
    strength important
  • 2. Calculate predicted improvement
  • Problem understood
  • 3. Establish requirements of ground improvement
  • What settlements, factor of safety, etc., are
    allowable
  • 4. Design Vibro Replacement scheme
  • Number of stone columns and/or performance
    requirements required to achieve desired results
  • 5. Establish testing criteria
  • Load test, SPT, area of stone columns

23
Vibro Replacement Important Parameters
  • Ground conditions
  • Relative density
  • Degree of saturation
  • Permeation

24
Vibro ReplacementDesign Considerations
  • The design approach for Vibro technologies will
    generally be governed by one or more of the three
    major categories of site improvement
  • Shear resistance increase
  • Settlement control
  • Liquefaction lateral spreading mitigation

25
Vibro ReplacementDesign Considerations
26
Vibro ReplacementDesign Requirements
  • Design of the Vibro program requires information
    on
  • Total loads (structure, surcharge, live, wind and
    seismic)
  • Soil type (variation, stratigraphy, groundwater
    location)
  • Type of footing/slab design
  • Structural settlement tolerance
  • Site restrictions and limitations
  • To address the above issues, the Vibro program is
    designed such
  • that the zone of influence of the vibratory probe
    ensures the
  • necessary soil densification and/or reinforcement.

27
Vibro CompactionDensification Results
28
Vibro ReplacementExpected Results
29
Vibro Replacement Increased Bearing Capacity
Vibro Replacement constructs dense, Vibro stone
columns in the zone requiring improvement. The
allowable bearing capacity can be calculated by a
variety of methods, such as the one developed by
Priebe in The Design of Vibro Replacement,
Ground Engineering, December 1995. If any of the
in situ soils are granular, their improved value
should also be accounted for in the design.
30
Vibro Replacement Reduced Settlement
  • Vibro Replacement constructs high modulus dense
    Vibro stone columns in the zone requiring
    improvement. The anticipated settlement can be
    evaluated by a variety of methods, such as the
    Priebe method.
  • This method provides an improvement factor based
    on the stone columns angle of internal friction
    and the percentage of the treatment zone replaced
    by stone (area replacement ratio).
  • In addition, if any of the in situ soils are
    granular, their improved parameters should also
    be included in the design.

31
Vibro ReplacementReduced Settlement
Method to estimate settlement reduction using
stone columns in cohesive soils
32
Vibro ReplacementLiquefaction Prevention
  • Seismic motion causes pore pressure to increase.
    When the pore pressure increases to equal
    interstitial grain-to-grain stresses,
    liquefaction is initiated. The soil then loses
    shear strength, resulting in bearing failures and
    slope instability, followed by large deformations
    (horizontal and vertical)
  • Site improvement by densification has proven to
    be the most effective solution. Densification
    will increase interstitial stresses, thus
    preventing liquefaction and settlement
  • Densification is required to preclude excessive
    settlements and offers the most secure remedy to
    multiple ground accelerations (aftershocks)

33
Vibro ReplacementEmbankment Subgrade Improvement
  • Vibro stone columns increase the slope stability
    safety factor especially when they attract
    sufficient loading to increase shearing
    resistance. The shear strength of treated soil
    depends on the shear strength of the untreated
    soil, the transverse shear strength of the
    columns, the area replacement ratio and the load
    conditions.

34
Vibro ReplacementTypical Arrangement of Stone
Columns
35
Vibro Replacement Quality Control
  • Production Monitoring
  • Quantity and quality of backfill added
  • Vibrator amperage draw
  • Treatment depth
  • Post-Construction Testing
  • Standard Penetration Testing (SPT)
  • Cone Penetrometer Testing (CPT)
  • Dilatometer Testing (DMT)
  • Load Testing
  • Shear Wave Velocity Profiling

36
Vibro Replacement Benefits
  • Permits shallow footing construction
  • Reduces foundation settlement
  • Increases bearing capacity, allowing reduction in
    footing size
  • Mitigates liquefaction potential
  • Prevents earthquake-induced lateral spreading
  • Provides slope stabilization
  • Permits construction on fills

37
Dynamic Compaction
Weights of 10 to 30 tons Drop heights of 50 to
100 ft Impact grids of 7 x 7 ft to 20 x 20 ft
38
Dynamic Compaction
39
Dynamic Compaction
40
Dynamic Compaction
41
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