Vibrocompaction, Vibroreplacement, and Vibrodisplacement

1
Vibrocompaction, Vibroreplacement, and
Vibrodisplacement

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

2
Outline of Presentation

• Introduction
• Installation Methods
• Theories and Design
• Quality Control

3
Introduction
4
Vibro Methods

• Vibrocompaction
• Densify insitu soil without removal and backfill
• Vibroreplacement
• Remove insitu soil backfilled with high-quality
  fill
• Vibrodisplacement
• - Displace soil backfilled with high-quality fill

5
Vibrocompaction

• Blasting
• Explode inside the ground
• Vibro-probe or Vibroflotation
• - Insert vibrating probes into the ground
• Vibro-drain
• Insert vibrating probes into the ground with
• a back-drain system

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Vibroreplacement

• Vibroflotation
• Insert vibrating probes into the ground, wash
• out insitu soil, and backfill high-quality fill
• Geopiers
• Augered into the ground backfilled with
• high-quality fill

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Vibrodisplacement

• Compaction sand pile
• Insert a casing into the ground and backfill
• sand inside the casing
• Bottom-fed stone column
• Insert vibrating probes into the ground and
• bottom-feed aggregates
• Vibro-concrete column
• Insert vibrating probes into the ground and
• bottom-feed low-strength concrete

8
Influence Factors of Effectiveness

• Soil type, especially its gradation and fine
• content
• Degree of saturation and water table location
• Initial relative density
• Initial in-situ stresses
• Initial soil structures, including the effects
  of
• age, cementation, etc
• Special characteristics of the method used

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Mechanism of Densification
For saturated cohesionless soils

• Breakdown of initial soil structure to a more
• stable packing arrangement
• Liquefaction under dynamic and cyclic
• loadings

For partially saturated cohesionless soils

• Collapse of soil structure and escape of gas
• from voids

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Installation Methods
11
Vibrocompaction
Woodward (2005)
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Sand Compaction Pile
Tanimoto (1973)
Courtesy of Fudo Construction, Inc.
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Casing Tip Movement
Tanimoto (1973)
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Special Valve for Pressured Air
Barksdale (1987)
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Casing Shoe
Barksdale (1987)
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Vibro Wing Machine
Massarsch and Fellenius (2005)
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Other Compaction Probes
Y probe
Terra probe
Vibro rod
18
Vibrocompaction
Woodward (2005)
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Suitability Number

• A rating system developed to judge the
  suitability of backfill
• material for vibro-compaction based on the
  settling rate of
• the backfill in water and project experience

Suitability Number
gt 50
0 - 10
10 - 20
20 - 30
30 - 40
Fair
Poor
Unsuitable
Rating
Excellent
Good
Brown (1977)
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Vibratory or Impact Compactability
Massarsch (1991)
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Performance Criteria

• For most vibrocompaction projects, the following
  performance
• criteria should be considered

• 60 relative density for floor slabs, flat
  bottom tanks,
• embankments
• 70 75 relative density for column footings,
  bridge footings
• 80 relative density for machinery and mat
  foundations

FHWA NHI-04-001 (2004)
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Effectiveness of Vibrocompaction
Hayward Baker
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Relative Density vs. Tributary Area
Relative Density (Percent)
Site Surface Area Per Compaction Probe (ft2)
Hayward Baker
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Vibro-Drain
Hodge (1998)
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Vibro-Drain
Hodge (1998)
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Vibro-Drain Induced Settlement
Hodge (1998)
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Vibroflotation/Stone Columns
28
Vibroreplacement Top Feed
Hayward Baker
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(No Transcript)
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(No Transcript)
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Exposed Columns
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Vibroreplacement
Woodward (2005)
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Effectiveness of Vibroreplacement
Hayward Baker
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Stone Columns
Woodward (2005)
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Geopier Construction
36
Geopier Construction
37
Geopier Construction
Well-graded stone tampered in thin lifts
Beleved tamper increases lateral pressures
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Geopiers
39
Geopiers under Footing
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Vibro Concrete Column
Hayward Baker
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Vibro Concrete Column
42
Vibro Concrete Column
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Vibro Concrete Column
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Theories and Design
45
Failure Modes
(2-3)d
Shear failure
d
Bulging failure
Punching failure
46
Suitability of Stone Columnsin Soft Clay
Undrained shear strength gt 15 kPa
47
Theoretical Solution for Bearing Capacity
?c
?s
h
?p 45o ?p/2
?p
?
r0
Ultimate bearing capacity
Brauns (1978)
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Bearing Capacity of Single Column
?s 0
If ?p 38o, ?p 64o and ? 61o
Brauns (1978)
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General Bearing Capacity Formula for Single
Column
cu (kPa)
Soil type
K
Kp K
References
4.0 3.0 6.4 5.0 5.0 - -
25.2 15.8-18.8 20.8 20.0 25.0 14.0-24.0 12.2-15.2
Hughes Withers(1974) Mokashi et al
(1976) Brauns (1978) Mori (1979) Broms (1979) Han
(1992) Guo Qian (1990)
Clay Clay Clay Clay Clay Clay Clay
19.4 19.0 - 20.0 - 15.0-40.0 -
Recommended
Ye et al. (1994)
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Area Replacement Ratio
d
Contributory area, A
Ac
As
s
A Ac As
Area replacement ratio, as
as Ac / A
Equilateral triangular pattern
Square pattern
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Typical Diameter and Area Replacement Ratio
Typical diameter of stone columns 2 to 3
feet VCC columns diameter 20 inches, base and
top 30 inches
Typical area replacement ratio 10 to 30
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Volume of Backfill
Assume full displacement
A
A
Vf
Backfill
Void
Vv
Void
Vv
V0
V1
Vs
Solids
Solids
Vs
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Required Column Spacing
Volume of backfill
Spacing for square pattern
Spacing for triangular pattern
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Equal Stress vs. Equal Strain
?c
?s
?c
?s
?s
Ec
Ec
Es
(a) Equal strain
?c
?s
?c
?s
?s
Ec
Ec
Es
(b) Equal stress
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Stress Concentration
?c
?s
?
Ec
Ec
Es
Es gt Ec
Stress concentration ratio
Stress reduction factor
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Stress Concentration Ratio
Stress
?c2
?c3
?c4
?c1
?s4
?s3
?s2
?s1
Strain
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Stress Concentration Ratio
Stress concentration ratio, n
1.0
0
Strain
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Stress Concentration Ratio
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Equivalent Modulus
?c
?s
?
?
Ec
Es
Equivalent modulus
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Settlement Reduction Factor
Settlement of untreated ground
Settlement of treated ground
If assume mv mv
Settlement reduction factor
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Improvement Factor
1/
Hayward Baker
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Model for Ideal Vertical Drains
de1.06s (triangular pattern of drains,
sspacing) de1.13s (square pattern of drains)
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Partial Differential Equation for Axisymmetric
Flow
General
Vertical flow
Terzaghis 1D consolidation theory
Horizontal flow
Barrons consolidation theory
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Overall Rate of Consolidation (Carillo, 1942)
Ur rate of consolidation due to radial flow
Uv rate of consolidation due to vertical flow
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Barrons Solution
Average rate of consolidation due to radial flow
Diameter ratio
Time factor in radial flow
cr - coefficient of consolidation due to radial
flow dc and de diameters of a drain well and
its influence zone, respectively t time period
for consolidation
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Model for Free-Draining Stone Columns
de
p
Drainage surface
rc
z
H
Stone column
2H
kv
kh
r
Drainage surface
re
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Han and Yes Solution
Average rate of consolidation due to radial flow
Diameter ratio
Time factor in radial flow
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Degree of Consolidation
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Comparison
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Degree of Consolidation due to Vertical Drain
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Degree of Consolidation due to Radial Drain
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Dissipation of Excess Pore Pressure
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Stress Variations with Time
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Smear and Well Resistance Effects
de
p
Drainage surface
rs
rc
z
H
Drain well
2H
ks
kc
r
Drainage surface
re
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Hansbos Solution
Average rate of consolidation due to radial flow
Diameter ratio of smeared zone to drain well
ds Diameter of smeared zone
kr - radial permeability of undisturbed
surrounding soil
ks - radial permeability of smeared soil H
longest drainage distance due to vertical flow z
depth in the ground at which the rate of
consolidation is computed
Discharge capacity of drain well
kc - permeability of drain well
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Han and Yes Solution
Average rate of consolidation due to radial flow
Time factor in radial flow
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Effect of Well Resistance
Han and Ye (2002)
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Effect of Smear
Han and Ye (2002)
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Stability Analysis
Aboshi et al. (1979)
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Stability Analysis
typically, 0.4 to 0.6
Priebe (1978)
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Stability Analysis
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Soil Densification Effect
SPT N value
Clay
Depth
Sand
Treated
Test point
Untreated
Silt
83
SPT N Value mid-way between Sand Piles
84
SPT N Value at the Center of Sand Piles
85
Effect of Fine Content on SPT N Value
Saito (1977)
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Effect of Grain Size on SPT N Value
87
Uniform Cyclic Shear Stress
?v the total stress, rd stress reduction
factor
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Stress Reduction Factor
Seed Idriss (1971)
89

Cyclic Stress Ratio (CSR)
Cyclic stress ratio (CSR) is defined as
90
Factor of Safety against Liquefaction
 
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Required Factor of Safety against Liquefaction
 
Martin and Lew (1999)
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Magnitude Correction Factors
Magnitude, M
CSRM/CSRM7.5
5 ¼ 6 6 ¾ 7 ½ 8 ½
1.50 1.32 1.13 1.00 0.89
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Effect of Fine Contents
Seed et al. (1975)
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Zone of Liquefaction
95
Process of Earthquake-Induced Settlement
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Settlement of Saturated Sands after Earthquake
Settlement
evi volumetric strain
Hi liquefiable soil thickness
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Relation between Relative Settlement and Ground
Improvement Method
- Relative Settlement (cm) -
ltUnimproved Areagt
Relative settlement?0
- Ground Improvement Method -
ltImproved Areagt
Courtesy of Fudo Construction, Inc.
98
The 1995 Hyogo-Ken Nambu Earthquake
Outline of the Earthquake ?Occurrence time
01/17/95 ? Magnitude M7.2 ? Source Depth 20km
cracks and sand boils were observed
ltUnimproved Areagt
Courtesy of Fudo Construction, Inc.
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Effectiveness at Leisure Facilities by Sand
Compaction Piles - the 1995 Hyogo-Ken Nambu
Earthquake
No Damage was observed
ltImproved Areagt
Courtesy of Fudo Construction, Inc.
100
Extent of Improvement
Improved area
Liquefaction
l
L
L 2/3 l and 5m lt L lt 10m
JGS (1998)
101
Quality Control
102
Quality Control Method

• SPT/DCP tests into the columns and surrounding
  soil
• CPT tests into the surrounding soil
• Plate load tests
• Geophysical methods

103
Dynamic Cone Penetration Test
Geopier
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Plate Load Test
Geopier
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Plate Load Tests

• Untreated ground
• Single column
• Composite ground
• Group columns

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Plate Load Tests
Single column
Composite ground
Group columns
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Single Column Load Test
White et al. (2007)
108
Group Column Load Tests
White et al. (2007)