6 Compaction
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Transcript of 6 Compaction
William J. Likos, Ph.D.
Department of Civil and Environmental Engineering
University of Wisconsin-Madison
GLE/CEE 330 Lecture Notes
Soil Mechanics
Compaction and Ground Improvement
Ground Improvement Methods
“Reinforcement”
• Stone Columns• Soil Nails• Deep Soil Nailing• Micropiles (Mini-piles)• Jet Grouting• Ground Anchors• Geosynthetics• Fiber Reinforcement• Lime Columns• Mechanically Stabilized
Earth (MSE)• Biological (e.g. roots)
• Compaction• Preload/Surcharge• Electro-osmosis• Compaction grouting• Blasting• Deep dynamic
compaction
• Cement• Lime Admixtures• Dewatering• Heating/Freezing• Vitrification• Biotreatment
(after Shaefer, 1997)
“Improvement” “Treatment”
Could also add “Replacement”(often not cost effective)
Some Reinforcement Methods
Jet Grouting
(Menard)
Soil Nailing
(Atlas Copco)
Fiber Reinforced Soil
Some Improvement Methods
Deep Dynamic
Compaction
Compaction
Grouting
(UC Davis)
Surcharge
with
Drainage
Some Treatment Methods
Lime Treatment
Ground
Freezing
(Max Bogl)
Microbial
Treatment
(J. Dejong)
Compaction
• Densify soil by reducing volume of voids (Vv = Va + Vw)
• We primarily reduce the volume of air (Va)
• Compaction ≠ Consolidation !!!!!• Consolidation is compression from loss of water squeezed out over time resulting from applied load.
Objectives of Compaction:(1) Decrease settlements
(2) Increase shear strength
(3) Decrease permeability
Loose
Dense
Adjust w and
Compact
High n
High e
Low n
Low e
Vv
Vs
Vt
Vs
Vt
Vv
Adding water to reach
“optimum water content
Compaction MethodsCoarse-grained soils Fine-grained soils
• Hand-operated vibration plates
• Motorized vibratory rollers
• Free-falling weight; dynamic compaction (low frequency vibration)
•Falling weight and hammers
•Kneading compactors
•Static loading and press
•Hand-operated tampers
•Sheepsfoot rollers
•Rubber-tired rollers
Labo
rato
ryF
ield
Vibration
•Vibrating hammer (BS)
(Holtz and Kovacs, 1981; Head, 1992)
Kneading
(Das, 2000)
• Sandy (non-cohesive) soils• 100% coverage• Contact pressure = 300-400 kN/m2
• Static or vibratory• “Proof” rolling (smooth surface)
Smooth-Wheeled Roller
• Sandy or clayey soils• 70 – 80 % coverage• Contact pressure = 600-700 kN/m2
• Combination of pressure and kneading• Articulated wheels find “soft spots”
(Das, 2000)
Pneumatic Rubber-Tired Roller
• Small projections for kneading action• Clayey or silty soils• Contact pressure = 1400-7000 kN/m2
(Das, 2000)
Sheepsfoot Roller
• Retaining wall backfills• Foundation backfills• Compaction close to existing structures• Usually vibratory
(Das, 2000)
Portable Compactors
Intelligent Compaction
Feedback on vibratory
compaction
(Coduto, 1999)
Applicability for Soil Types
Proctor Compaction Curve
Zero air void curve
(ZAV)
Water content w (%)
Dry
den
sity
d
(Mg/
m3 )
Dry
den
sity
d
(lb/f
t3 )Line of optimums
Modified Proctor
Standard Proctor
Holtz and Kovacs, 1981
d max
wopt
16
•The peak point of the compaction curve•The peak point of the compaction curve is the point with the maximum dry density d max. Corresponding to the maximum dry density d max is a water content known as the optimum water content wopt (also known as the optimum moisture content, OMC). Note that the maximum dry density is only a maximum for a specific compactive effort and method of compaction. This does not necessarily reflect the maximum dry density that can be obtained in the field.
•Zero air voids curve•The curve represents the fully saturated condition (S = 100 %). (It cannot be reached by compaction)
•Line of optimums•A line drawn through the peak points of several compaction curves at different compactive efforts for the same soil will be almost parallel to a 100 % S curve, it is called the line of optimums
SwGG
e
G
s
wswsd
11
swGSeRecall:
Holtz and Kovacs, 1981
Zero Air Voids (ZAV) Curve
Standard Proctor test equipment
Das, 1998
Laboratory Compaction Procedures
(1) Several samples of the same soil, but at different water contents, are compacted according to the compaction test specifications.
(2) The total or wet density and the actual water content of each compacted sample are measured.
(3) Plot the dry unit weight gd versus water contents w for each compacted sample. The curve is called as a compaction curve.
wV
Wd
t
t
1,
Report (gd)max and wopt
Laboratory Compaction Procedures
Summary of Standard Proctor Compaction Test Specifications (ASTM D-698, AASHTO)
Das, 1998
Laboratory Compaction Procedures
Summary of Modified Proctor Compaction Test Specifications (ASTM D-698, AASHTO)
Das, 1998
Standard Proctor Test
12 in height of drop
5.5 lb hammer
25 blows/layer
3 layers
Mold size: 1/30 ft3
Energy 12,375 ft·lb/ft3
Modified Proctor Test
18 in height of drop
10 lb hammer
25 blows/layer
5 layers
Mold size: 1/30 ft3
Energy 56,250 ft·lb/ft3
23
)ft/lbft375,12(m/kJ7.592
m10944.0
)layer/blows25)(layers3)(m3048.0)(s/m81.9(kg495.2E
33
33
2
Volume of mold
Number of blows per
layer
Number of layers
Weight of hammer
Height of drop of
hammer
E =For
standard Proctor test
Effects of Soil Type
24Holtz and Kovacs, 1981; Das, 1998
Suitability of Soil Types for Construction
Type Strength Compressibility Permeability Interaction with Water
Uses Problems
Gravel High Low V. High No effect Pavement bases
Filters
Prone to caving Small clay content
affects propertiesSand High Low High Workable
over wide range
Wide range of uses
Fills (hydraulic)
Backfill
Poor at ground surface Prone to caving Prone to erosion
Low plasticity silts/clays
Low High Low Lose strength when wetted
Fills Prone to frost heave Collapse potential
High plasticity silts/clays
Low High V. Low Lose strength when wetted
Landfill covers/liners
Poor workability (sticky)
Swell/shrink potential
Organics Low High - - Landscaping Typically removed
Compaction and Soil Fabric
• Fabric – orientation and arrangement of particles (clay); has influence on soil behavior
•Soil fabric tends to be more flocculated (random) for compaction dry of optimum.
•Soil fabric tends to be more dispersed (oriented) for compaction wet of optimum.
Lambe and Whitman, 1979
Flocculated
Dispersed
Clay particles are plate-like
(e.g., kaolinite)
Engineering Behavior - Permeability
• Increasing the water content results in a decrease in permeability on the dry side of the optimum moisture content and a slight increase in permeability on the wet side of optimum.
• Increasing the compactive effort reduces the permeability since it both increases the dry density, thereby reducing the voids available for flow, and increases the orientation of particles.
From Lambe and Whitman, 1979; Holtz and Kovacs, 1981
Engineering Behavior - Strength
Samples compacted dry of optimum tend to be more rigid and stronger than samples compacted wet of optimum
From Lambe and Whitman, 1979
s1
s3
s1 – s3
Engineering Properties - Summary
29Holtz and Kovacs, 1981; Das, 1998 29
Dry side Wet side
Permeability
Compressibility
Swelling
Strength
Structure Flocculated Dispersed
More permeable
More compressible in high pressure
range
More compressible in low pressure
range
Higher
*Shrinks more
Less permeable
Higher
Lower
Field Quality Control
• Dry density and water content correlate well with the engineering properties, and thus they are convenient construction control parameters.
• Since the objective of compaction is to stabilize soils and improve their engineering behavior, it is important to keep in mind the desired engineering properties of the fill, not just its dry density and water content. This point is often lost in the earthwork construction control.
From Holtz and Kovacs, 1981
Quality Control – Relative Compaction
From Holtz and Kovacs, 1981
Control
(1) Relative compaction
(2) Water content (dry side or wet side)
100% saturation
Water content w %
wopt
Dry
de
nsi
ty, g
d
gd max
Line of optimums
90% R.C.
a c
Increase compaction
energy
b
%100..max
laboratoryd
fielddCR
QA/QC MethodsMethods
(a) Sand cone
(b) Balloon
(c) Oil (or water) method
Calculations
• Measure Wt, Vt
• Get gd field and w
• Compare d field with d max-lab and calculate relative compaction R.C.
(a)
(b)
(c)
QA/QC MethodsHoltz and Kovacs, 1981
Nuclear density meter
(a) Direct transmission
(b) Backscatter
(c) Air gap
(a)
(b)
(c)
Principles
DensityGamma radiation is scattered by the soil particles and the amount of scatter is proportional to the total density of the material. Gamma radiation is typically provided by radium or a radioactive isotope of cesium.
Water contentWater content can be determined based on neutron scattering by hydrogen atoms. Typical neutron sources are americium-beryllium isotopes.
“Borrow Pit” Problem
Borrow pit
Sandy Soil
w = 15%
e = 0.69
Compacted
Embankment
yd = 18 kN/m3
30 m X 1.5 m X 1000 m
Truck
Transport
(10 m3/truck)
volume