modern foundation tech. (compiled)

1. Modern Foundation
Techniques
&
Ground Improvement
Techniques

2. Why ground improvement
required…..??

8. Need for engineered ground
improvement
Concerns
• Mechanical properties are not adequate
• Swelling and shrinkage
• Collapsible soils
• Soft soils
• Organic soils and peaty soils
• Sands and gravelly deposits.
• Foundations on dumps and sanitary landfills
• Handling dredged materials
• Handling hazardous materials in contact with soils
• Use of old mine pits

9. Leaning tower of Pisa

10. Effect of Swelling

11. Effect of shrinkage
Swelling and shrinking soils exist in many areas in India, Large
tracts of Maharashtra, Andhra, Deccan plateau, Chennai

12. Collapsible soils
Collapse occurs due to saturation, loss of cementation bonds, specific clay
structure and areas in some areas in Rajasthan and in some counties abroad this is
prevalent.

13. Failure of slope

14. Effects of liquefaction

15. Definition……
Ground Improvement refers to a technique
that improves the engineering properties of the
soil mass treated.
Usually, the properties that are modified are
shear strength, stiffness and permeability.
Ground improvement has developed into a
sophisticated tool to support foundations for a
wide variety of structures.

16. Need for engineered ground
improvement
Strategies
• When a project encounters difficult foundation
• conditions, possible alternative solutions are
• Avoid the particular site
• Design the planned structure (flexible/rigid) accordingly
• Remove and replace unsuitable soils
• Attempt to modify existing ground
• Enable cost effective foundation design
• Reduce the effects of contaminated soils
• Ensure sustainability in construction projects using ground
improvement techniques

17. Ground Improvement Techniques
for different soil types
Ground improvement can be done through
various mechanisms
• Compaction
• Dewatering
• Reinforcement
• Admixtures or grouting

18. Classification of ground modification
techniques
• Mechanical modification
• Hydraulic modification
• Physical and chemical modification
• Modification by inclusion and confinement
• Combination of the above

19. Ground Improvement Techniques:
On the basis of mechanism by which they improve the
engineering properties of soil, the most of common of
these can be divided into the following major
categories. These are
Densification Techniques.
Reinforcement Techniques.
Stabilization Techniques.
Miscellaneous Methods.
Apart from the methods listed above, there are some
other simple methods like removal and replacement of
soil. In this paper these are discussed first before
taking up above techniques.

20. Removal and Replacement of Soil:
One of the oldest and simplest soil improvement
methods is to simply excavate the unsuitable soil
and replace them with compacted fill. This
method is often used when the problem the soil
is that it is too loose. In that case, the same soils
used to build the fill, except now it has a higher
unit weight (because of compaction) and thus has
been better engineering properties. This is a
common way to remediate problems with
collapsible soils.

21. Removal and replacement is generally
practical only above the ground water table.
Earthwork operations become more difficult
when the soil is very wet, even when the free
water pumped out, and thus are generally
avoided unless absolutely necessary.
Clay
Newly added
murum
Clay
Clay
Removed
Murum

22. Pre-compression of Soil:
• It is also called “Pre-loading”
• It requires only conventional equipment earthmoving
equipment, which is readily available. No special or
proprietary equipment is needed.
• Any grading contractor can perform the work
• The results can be effectively monitored by using
appropriate instrumentation and ground level surveys.
• The method has a long track record of success.

23. • The cost is comparatively low, so long as soil for
preloading is readily available. However, there also are
disadvantages.
• The surcharge fill generally must extend horizontally at
least 10m beyond the perimeter of the planned
construction. This may not possible for confined sites.
• The transport of large quantities of soil onto the sites
may not be practical, or may have unacceptable
environmental impacts (i.e., dust, noise, traffic) on the
adjacent areas.
• The surcharge must remain in place for months or
years, thus delay in construction.

25. Densification Techniques:
The strength and stiffness of the soil is higher
when the particles are packed in a dense
configuration than they are packed loosely. As a
result, densification is one of the most effective
and commonly used means of improving soil
characteristics. This can be approaches in
following ways.

26. Vibro Techniques:
Vibro techniques use probes that are vibrated
through soil deposit in a grid pattern to
densify the soil over the entire area of
thickness of the deposit. These are classified
in to the following methods. These are

27. 1Vibro Compaction:
Vibro Compaction is a method for compacting
deep granular soils by repeatedly inserting a
vibratory probe. It is also known as VIBRO
DENSIFICATION.
By inserting depth vibrations, the vibrations
are produced by rotating a heavy eccentric
weight with the help of an electrical motor with
in the vibrator. The vibratory energy is used to
rearrange the granular particles in a denser state.
Penetration of the vibro is typically aided by
water jetting at the tip of the probe.

28. The Vibro-Compaction Process

29. Some of advantages and disadvantages of
this method are given below.
• It is often an economical alternative to deep
foundations, especially when considering the
added liquefaction protection in seismic ares.
• It is most effective in granular soils
• It cannot be sued in cohesive soils.

30. Vibro Flotation:
In vibro floatation a torpedo like probe (the vibro
float) suspended by a crane is used to density a soil
deposit. Vibro floats usually 12 to 18 inch in diameter
and about 10 to 16 ft long, contain weights mounted
eccentrically on a central shaft driven by electric or
hydraulic power.
The vibro float is initially lowered to the bottom of
the deposit by a combination of vibration and water or
air jetting through ports in its pointed nose cone. The
vibro float is then incrementally with drawn in 2 to 3 ft
intervals at an over all rate of about 1ft/min to loosen
the soil above the vibro float temporarily and aid in its
with drawl. The vibrations produce a localized zone of
temporary liquefaction that causes the soil surrounding
the vibro float to densify.

31. Principle of the technique
• Vibro floating is most effective in clear granular soils
with the contents less than 20% and clay contents
below 3%
• Vibro flotation has been used successfully to density
soils to deep [this of up to 115ft]

32. Dynamic Compaction:
Dynamic Compaction is normally used under the following
circumstances:
• To increase in-situ density and this way improve the
bearing capacity and consolidation characteristics of soils
(or waste materials) to allow conventional foundation and
surface bed construction to be carried out. The technique
typically improves the in-situ soils such that allowable
bearing pressures of up to 250 kpa can be used with
foundation settlements of the order of 10 to 20 mm.
• To increase in-situ density and in this way improve in-situ
permeability and/or reduce liquefaction potential.

33. What soils are suitable:
Most soil types can be improved, including
silts and some clays. The most commonly
treated soils are old fills and granular virgin soils.
Soils below the water table are routinely treated.
However, careful control has to be used to allow
dissipation of excess pore pressures created
during the weight dropping.

34. Blasting:
Blasting is most effective in loose sands that
contain less than 20% silt and less than 5%
clay.
Although blasting is quite economical, it is
limited by several considerations, as it
produces strong vibrations that may damage
near by structures or produce significant
ground movements.

35. Reinforcement Techniques:
In some cases it is possible to improve the
strength and stiffness of a existing soils
deposit by installing discrete inclusions that
reinforce the soil. These inclusions may consist
of structural materials, such as steel, concrete
or timber and geomaterials such as densified
gravel.

36. Compaction Piles:
Compaction piles improve the seismic performance of a soil
by three different mechanisms. First the flexural strength
of piles themselves provides resistance to soil movement
(reinforcement). Second, the vibrations and displacements
produced by their installation cause densification. Finally,
the installation process increses the lateral stress in the soil
surrounding the piles.
Compaction piles generally densify the soil with in a
distance of 7 to 12 pile diameters and consequently
installed in a grid pattern. Between compaction piles a
relative density of up to 75% to 80% are usually achieved.
Improvement can be obtained with reasonable economy to
depth of about 60 ft.

37. JET GROUTING

38. JET GROUTING
In jet grouting the soil is mixed with cement
grount injected horizontally under high pressure
in a previously drilled bore hole.
Jet grouting uses a special pipe equipped with
horizontal jets that inject grout into the soil at
high pressure. The pipes are first inserted to the
desired depth, then they are raised and rotated
while the injection is in progress, thus forming a
column of treated soil.
Because of high pressure, this method is usable
on a wide range of soil types.

39. Electro Osmasis and Electro Chemical
Hardening Method:
The electroosmasis process can be used to increase the
shear strength and reduce the compressibility of soft clayey
and silty soils beneath foundation. By introducing an
electrolyte such as calcium chloride at the anode, the base
exchange reaction between the iron anode and
surrounding soil is increased, resulting in the formation of
ferric hydroxides which bind the soil particles together.
However because cost of electric power and wastage of
electrodes, electroosmasis with or without electrochemical
hardening can be considered only for special situations
where the alternative of piling cannot be adopted.

40. METHODS FOR GROUND IMPROVEMENT
1. VERTICAL DRAINS
2. SOIL NAILING
3. STONE COLUMNS
4. VIBRO COMPACTION
5. DYNAMIC COMPACTION

41. VERTICAL DRAINS
 These consist of a column of pervious material placed in
cylindrical vertical holes at sufficiently close spaces.
 All drains should be connected at the ground surface to a
drainage blanket.
 Vertical drains accelerate consolidation by facilitating drainage
of pore water.
 Vertical drains are laid out in rows, staggered, or aligned to
form patterns of equilateral triangles or squares.
 Two types of drains are discussed below

42. A sand drain is a simple
process, employing a column
of at least 10 inches in width
augered into ground to be
surcharged & consolidated.
The column is then filled with
sand and connected to a
free-draining blanket of
granular soil.
SAND DRAINS

43. WICK DRAIN
• A wick drain is
usually about, 4
inches wide, 1/8-inch
thick which acts as a
high-permeability
conduit for water to
flow out of the soil
and to the surface.
• Most common
application of wick
drains is for
accelerating the
settlement rate of
compressible soils.

44. SOIL NAILING
• This ground reinforcement process uses steel tendons which
are drilled and grouted into the soil to create a composite mass.
• A shotcrete facing is typically applied.
• Soil Nailing is an in situ technique for reinforcing, stabilizing and
retaining excavations and deep cuts.

45. Shotcreteing

46. Holes are drilled though machine

47. Soil Nailing

48. Stone column
 Also known as vibro-replacement or vibro-displacement,
is a ground improvement process where vertical
columns of compacted aggregate are formed through the
soils to be improved.
 The vibrator first penetrates to the required depth by
vibration and air or water jetting or by vibration alone.
 Gravel is then added at the tip of the vibrator and
progressive raising and repenetration of the vibrator
results in the gravel being pushed into the surrounding
soil.
 The soil-column matrix results in an overall mass having
a high shear strength and a low compressibility.

49. Stone column

51. Vibro compaction
• It is a ground improvement process for densifying loose
sands to create stable foundation 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.

52. Crane Mounted Vibrator

53. Process of vibro compaction

54. Dynamic compaction
 Dynamic Compaction is the dropping of heavy weights on the
ground surface to densify the soils at depth.
 It involves the repeated dropping of large steel tampers by
means of crawler cranes.
 Tampers typically range from 6 to 20 tons and are dropped
from heights of about 40 to 80 feet.

55. MACHINE WITH TAMPER COMPACTION BY TAMPER