This document discusses different methods for ground improvement (GI), including mechanical, hydraulic, and chemical modification techniques. Mechanical modification techniques aim to densify soils using external forces like compaction. Compaction increases soil strength and reduces compressibility, permeability, and liquefaction potential. Hydraulic modification techniques like dewatering and preloading are used to modify ground conditions by lowering the water table or accelerating consolidation. Preloading combined with vertical drains can shorten consolidation time in fine-grained soils. The document provides examples of different compaction and ground improvement equipment and methods.

1. CHAPTER 5
GROUND
IMPROVEMENT
(GI)

3. The need for engineered GI
• Avoid particular site
• Design the structure accordingly
• Remove & replace unsuitable soils
• Attempt to modify the existing ground

4. Ground Improvement
• the controlled
alteration of the
state, nature or
mass behaviour of
ground materials in
order to achieve an
intended satisfactory
response to existing
or projected
environmental and
engineering actions.

5. Classification of GI
GROUND
IMPROVEMENT
MECHANICAL
MODIFICATION
HYDRAULIC
MODIFICATION
CHEMICAL
MODIFICATION
MODIFICATION
BY
INCLUSION
Shallow
Compaction
Deep
Compaction
Dewatering Cement
Stone Column
&
Lime Column
Soil
Reinforcement
Preloading
&
Vertical Drain
Lime

6. Mechanical Modification
• Mechanical ground modification refers to
soil densification by external forces.
• mechanical modification is synonymous
with compaction.
• Compaction means densification of an
unsaturated soil by a reduction in the
volume of voids filled with air, while the
volume of solids and the water content
remain essentially the same.

7. What is compaction?
A simple ground improvement technique,
where the soil is densified through external
compactive effort.
+ water =
Compactive
effort

8. Compaction Curve
Water content
Dry
density
(
d
)
optimum
water content
d, max
Soil grains densely packed
- good strength and stiffness
- low permeability

9. Stabilization & Consolidation
• Stabilization
• an increase in
strength or a
reduction in the
deformation of a soil
mass
• caused by additives
• Consolidation
• soil mass is reduced
by the expulsion of
water.
• long-term application
of static loads or
electric forces to
saturated soils

10. Compaction
• Increase shear strength
• Reduce compressibility
• Reduce permeability
• Reduce liquefaction potential
• Control swelling and shrinking

11. Results of Poor Compaction

12. Shallow Compaction
• Shallow compaction in the field is
accomplished by rolling or vibrating
• Rolling is done with "sheepsfoot" drums,
round steel drums and rubber tired vehicle.
• Vibratory machines range in size from
small hand-propelled units to large motor-
driven machines

13. Applicability of compaction equipment

14. Pneumatic rubber-tired roller is
compacting clay soil

15. Vibratory steel-wheeled roller
compacting sand

16. Vibratory padded drum roller (similar to a
sheepsfoot roller)is compacting clay

17. Tamping-foot roller compacting
clay

18. Field Compaction
 for compacting very small areas
Vibrating Plates
 effective for granular soils

19. Field Compaction
 Provides deeper (2-3m) compaction. e.g., air field
Impact Roller

20. Laboratory Compaction Test
- to obtain the compaction curve and define the
optimum water content and maximum dry density for a
specific compactive effort.
hammer
Standard Proctor: Modified Proctor:
• 3 layers
• 25 blows per layer
• 5 layers
• 25 blows per layer
• 2.7 kg hammer
• 300 mm drop
• 4.9 kg hammer
• 450 mm drop
1000 ml compaction mould

21. Operational Aspects
of Shallow Compaction
• Operating frequency.
• Number of passes.
• Depth of layers.
• Special consideration for specific materials
• Applicability and production rate.

22. Deep Compaction
• Precompression
• Explosion
• Heavy damping
• Vibration
• Compaction grouting

23. Dynamic Compaction
- pounding the ground by a heavy weight
Suitable for granular soils, land fills
and karst terrain with sink holes.
Crater created by the impact
Pounder (Tamper)
solution cavities in
limestone
(to be backfilled)

24. Dynamic Compaction
Pounder (Tamper)
Mass = 5-30 tonne
Drop = 10-30 m

25. Dynamic Compaction

26. Vibroflotation
Vibroflot (vibrating unit)
Length = 2 – 3 m
Diameter = 0.3 – 0.5 m
Mass = 2 tonnes
Practiced in several forms:
 vibro–compaction
 stone columns
 vibro-replacement
Suitable for granular soils
(lowered into the ground
and vibrated)

27. Vibroflotation

28. Vibroflotation

29. Vibroflotation

30. Vibroflotation

31. Vibroflotation

32. Vibroflotation

33. Stone Columns
vibrator makes a
hole in the weak
ground
hole backfilled ..and compacted Densely compacted
stone column

34. Blasting
Aftermath of blasting
Fireworks?
For densifying granular soils

35. Earthmoving Equipment
Large Excavator (see minivan on left for scale)

36. Volumetric Measure
• Bank cubic yard - 1 cubic yard (cy) of
material as it lies in the natural state,
bcy
• Loose cubic yard - 1 cy of material after it
has been disturbed by a loading
process, lcy
• Compacted cubic yard - 1 cy of material in
the compacted state, also referred to as
a net in-place cubic yard, ccy

37. Volumetric Measure

38. Shrinkage factor = compacted dry unit weight
bank dry unit weight
Swell factor = loose dry unit weight
bank dry unit weight

39. EXAMPLE
An earth fill, when completed, will occupy a net
volume of 142,950 m3. The borrow material that
will be used to construct this fill is a stiff clay. In its
"bank" condition, the borrow material has a wet
unit weight, 20.28 kN/m3, a water content w % of
16.5%, and an in-place void ratio (e) of 0.620. The
fill will be constructed in layers of 20.32 cm depth,
loose measure, and compacted to a dry unit
weight d 17.92 kN/m3 at a water content of 18.3%.

40.   3
3
/
1775
/
41
.
17
165
.
0
1
28
.
20
1
m
kg
or
m
kN
w
borrow
d 






  3
3
/
1827
/
92
.
17 m
kg
or
m
kN
fill
d 


41. Compaction Control Test
compacted ground
d,field = ?
wfield = ?
Compaction
specifications
Compare!
w
d

42. Compaction Control Test
Sand Cone Balloon Dens meter Shelby Tube Nuclear Gauge
Advantages
* Large sample
* Accurate
* Large sample
* Direct reading obtained
* Open graded material
* Fast
* Deep sample
* Under pipe haunches
* Fast
* Easy to redo
* More tests (statistical
reliability)
Disadvantages
* Many steps
* Large area required
* Slow
* Halt Equipment
* Tempting to accept flukes
* Slow
* Balloon breakage
* Awkward
* Small Sample
* No gravel
* Sample not always
retained
* No sample
* Radiation
* Moisture suspect
* Encourages amateurs
Errors
* Void under plate
* Sand bulking
* Sand compacted
* Soil pumping
* Surface not level
* Soil pumping
* Void under plate
* Overdrive
* Rocks in path
* Plastic soil
*Miscalibrated
* Rocks in path
* Surface prep required
* Backscatter
Cost * Low * Moderate * Low * High

43. HYDRAULIC MODIFICATION
• dewatering - modifying ground by lowering
the water table, redirecting seepage, or
simply reducing its water content
• In coarse-grained soils, dewatering can be
achieved
• In fine-grained soils dewatering becomes
synonymous with forced consolidation.

44. WHY??
• to provide a dry working area, such as in
excavations for building foundations, dams,
and tunnels
• to stabilize constructed or natural slopes
• to reduce lateral pressures on foundations or
retaining structures
• to reduce the compressibility of granular soils
• to increase the bearing capacity of foundations

45. PRELOADING TECHNIQUES
• The simplest solution
of preloading is a
preload, e. g. by
means of an
embankment.
• The temporary
surcharge can be
removed when the
settlements exceeds
the predicted final
• settlement

46. How to force consolidation
process
Precompression
Sand Drain
Prefabricated Vertical
Drain

49. PRELOADING + SURCHARGE
• To shorten the
consolidation time,
vertical drains are
installed together with
preloading
• the vertical drain
installation reduces
the length of the
drainage path and,
• accelerates the
consolidation process

51. Effect of Smear and Drain
Resistance
• Disturbance of the soil adjacent to the
drain is likely to decrease its permeability
and thus slow down the consolidation
process