1. Compaction and Ground Improvement
GLE/CEE 330 Lecture Notes
Soil Mechanics
William J. Likos, Ph.D. Department of Civil and Environmental Engineering University of Wisconsin-Madison

2. Ground Improvement Methods
“Reinforcement”
“Improvement”
“Treatment”
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
Could also add “Replacement”
(often not cost effective)
(after Shaefer, 1997)

3. Some Reinforcement Methods
Jet Grouting
Soil Nailing
Fiber Reinforced Soil
(Atlas Copco)
(Menard)

4. Some Improvement Methods
Deep Dynamic Compaction
Compaction Grouting
Surcharge with Drainage
(UC Davis)

5. Some Treatment Methods
Microbial
Treatment
Lime Treatment
Ground Freezing
(Max Bogl)
(J. Dejong)

6. Compaction Objectives of 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:
Decrease settlements
Increase shear strength
Decrease permeability

7. Adding water to reach “optimum water content
Loose Vv Vt
Adding water to reach “optimum water content
High n
High e Vs
Adjust w and
Compact Vv Vt Vs
Low n
Low e
Dense

8. (Holtz and Kovacs, 1981; Head, 1992)
Compaction Methods
Coarse-grained soils
Fine-grained soils
Vibration
Kneading
Falling weight and hammers
Kneading compactors
Static loading and press
Vibrating hammer (BS)
Laboratory
Hand-operated vibration plates
Motorized vibratory rollers
Free-falling weight; dynamic compaction (low frequency vibration)
Hand-operated tampers
Sheepsfoot rollers
Rubber-tired rollers
Field
(Holtz and Kovacs, 1981; Head, 1992)

9. Smooth-Wheeled Roller
Sandy (non-cohesive) soils
100% coverage
Contact pressure = kN/m2
Static or vibratory
“Proof” rolling (smooth surface)
(Das, 2000)

10. Pneumatic Rubber-Tired Roller
Sandy or clayey soils
70 – 80 % coverage
Contact pressure = kN/m2
Combination of pressure and kneading
Articulated wheels find “soft spots”
(Das, 2000)

11. Sheepsfoot Roller Small projections for kneading action
Clayey or silty soils
Contact pressure = kN/m2
(Das, 2000)

12. Portable Compactors Retaining wall backfills Foundation backfills
Compaction close to existing structures
Usually vibratory
(Das, 2000)

13. Intelligent Compaction Feedback on vibratory compaction

14. Applicability for Soil Types
(Coduto, 1999)

15. Proctor Compaction Curve
Line of optimums
Zero air void curve (ZAV)
d max
Dry density d (Mg/m3)
Dry density d (lb/ft3)
Modified Proctor
Standard Proctor
wopt
Water content w (%)
Holtz and Kovacs, 1981

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

17. Zero Air Voids (ZAV) Curve
Recall:
Holtz and Kovacs, 1981

18. Laboratory Compaction Procedures
Standard Proctor test equipment
Das, 1998

19. Report (gd)max and wopt
Several samples of the same soil, but at different water contents, are compacted according to the compaction test specifications.
The total or wet density and the actual water content of each compacted sample are measured.
Plot the dry unit weight gd versus water contents w for each compacted sample. The curve is called as a compaction curve.
Report (gd)max and wopt

21. Laboratory Compaction Procedures
Summary of Standard Proctor Compaction Test Specifications (ASTM D-698, AASHTO)
Das, 1998

22. Laboratory Compaction Procedures
Summary of Modified Proctor Compaction Test Specifications (ASTM D-698, AASHTO)
Das, 1998

23. For 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
Volume of mold
Number of blows per layer
Number of layers
Weight of hammer
Height of drop of hammer 
E =
For standard Proctor test

24. Effects of Soil Type
Holtz and Kovacs, 1981; Das, 1998

25. Suitability of Soil Types for Construction
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 properties
Sand
Workable over wide range
Wide range of uses
Fills (hydraulic)
Backfill
Poor at ground surface
Prone to erosion
Low plasticity silts/clays
Lose strength when wetted
Fills
Prone to frost heave
Collapse potential
High plasticity silts/clays
V. Low
Landfill covers/liners
Poor workability (sticky)
Swell/shrink potential
Organics -
Landscaping
Typically removed

26. Compaction and Soil Fabric
Clay particles are plate-like
(e.g., kaolinite)
Flocculated
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.
Dispersed
Lambe and Whitman, 1979

27. 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

28. Engineering Behavior - Strength
s1 – s3
Samples compacted dry of optimum tend to be more rigid and stronger than samples compacted wet of optimum s3
From Lambe and Whitman, 1979

29. Engineering Properties - Summary
Dry side
Wet side
Structure
Flocculated
Dispersed
Permeability
More permeable
Less permeable
Compressibility
More compressible in high pressure range
More compressible in low pressure range
Swelling
Higher
*Shrinks more
Strength
Higher
Lower
Holtz and Kovacs, 1981; Das, 1998 29

30. 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

31. Quality Control – Relative Compaction
100% saturation
Control
(1) Relative compaction
(2) Water content (dry side or wet side)
Line of optimums
gd max
90% R.C.
Dry density, gd   
Increase compaction energy
wopt a b c
From Holtz and Kovacs, 1981
Water content w %

32. QA/QC Methods (a) Sand cone (b) Balloon (a) (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.
(b)
(c)

33. QA/QC Methods (a) Direct transmission (a) (b) Backscatter (c) Air gap
Holtz and Kovacs, 1981
QA/QC Methods
Nuclear density meter
(a) Direct transmission
(b) Backscatter
(c) Air gap
(a)
Principles
Density
Gamma 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 content
Water content can be determined based on neutron scattering by hydrogen atoms. Typical neutron sources are americium-beryllium isotopes.
(b)
(c)

34. “Borrow Pit” Problem volume Compacted Embankment Borrow pit Truck
Transport
(10 m3/truck)
30 m X 1.5 m X 1000 m
Sandy Soil
w = 15%
e = 0.69
yd = 18 kN/m3