This presentation will provide the reader with all the necessary information regarding ground improvement techniques for both cohesive and non-cohesive soils with comparison among few. It also carries some practical examples of ground improvement.

1. PROBLEMATIC SOILS

2. What is Problematic Soil?
Problematic soils are those soils which need some treatment before
or after construction of foundation.
These soils exhibit properties which are undesirable to any
foundation, i.e., excessive movement.
These soils must be identified in the field before construction is
planned.

3. Types of Problematic Soils:
Expensive soils:
Expand when water is added and shrink when dry out.
Collapsing soils:
stable under load while dry, large decrease in bulk volume while
saturated under the same load. (50 to 90 % silt particles)
Sanitary landfills:
Settle over a long period of time.
Peat deposits:
Rotten/Dead plant deposits.
Glacial deposits:

4. Identification of Problematic Soils:
The ability to identify problematic soils is of exceptional value to
constructors and geotechnical engineers.
Identification is done both by experience and testing.
Swelling and Plasticity Index:
Either Swelling test or PI to estimate the magnitude of possible
swell in a clay.
Liquid and Plastic Limits:
LL and PL values also help to identify type of problematic soils.

5. Identification of Problematic Soils:
Swell Test:
Liquid and Plastic Limits:
Plasticity Index Potential Volume Change
Over 35 Very High
22 – 48 High
12 – 32 Medium
LL 30 – 60 %
PL 20 – 25 %
Collapsing Soil

6. Cause Of failure in Problematic Soils:
 Type of Geo-material:
Expensive soils, collapsing soils, peat deposits etc.
Geo-Material Potential Problems
Soft clay Low strength, high compressibility, low permeability
Silt High liquefaction, high erodibility, low strength
Expensive soil Large volume change
Dredged material High water content, low strength
Solid waste Non-uniformity, high degradation potential
Organic soil Large creep formation, high compressibility
Bio-based by product Low strength, high degradation potential

7. Cause Of failure in Problematic Soils:
Man Made Conditions:
Excavation, tunnelling, pile driving, and rapid drawdown of
surface water, elevation of surface water.
Natural Conditions:
• Presence of problematic soil materials
• High groundwater table
• Inclined bedrock
• Steep natural slopes

8. Cause Of failure in Problematic Soils:
 Geo-technical Problems:
Geo-technical
Problems
Possible Causes
Bearing failure High applied pressure & low shear strength
Large differential
settlement
High permeability & high compressibility
Hydro-compression Collapsible soil & saturation
Instability (sliding,
slope failure)
Steep slope & soft foundation soil
Liquefaction Earthquake, loose silt & high water table

9. Ground Improvement
Methods and Classification

10. Ground Improvement Techniques:
Introduction:
The solution to problematic soils is to use certain methods which can
improve the strength and quality of geo-materials.
Modern ground improvement methods were developed since the
1920s.
At present more then 50 ground improvement techniques.

11. Ground Improvement Techniques:
Historical Background:
vertical sand drains, In 1925,
Use of cotton fabric as reinforcement. In 1926
Vibro-compaction method in 1937.
Prefabricated vertical drains (PVD) in 1947.
Henri Vidal, Reinforcement for retaining walls in France.
Louis Menardl, Dynamic compaction technique in France.
In 1986, J. P. Giroud, geo-synthetics.

12. Classification:
Different criteria to classify ground improvement techniques.
Foundation Type
• Deep foundation.
• Shallow foundation.
Soil Type
• Fine grained soil.
• Granular soil.
• Cohesive & Non-cohesive soil.
Function performed
• Densification, replacement, drainage, consolidation etc.

13. Frequently used Techniques:
Densification
• Rapid Impact Compaction
• Vibro-compaction
Replacement
• Deep soil exchange
Use of Admixtures
• grouting
Thermal Treatment
Piling Technique

14. Selection of Ground Improvement Techniques:
Selection of suitable ground improvement technique is based
on following parameters;
Structural conditions
Geotechnical conditions:
Environmental constraints
Construction conditions
Reliability and Durability

15. Selection of Ground Improvement Techniques:

16. Selection Procedure:
Selection of best suited improvement technique is a very
important task.
A standard selection procedure is followed.

17. Selection Procedure:

18. Future Trends:
Following future trends in ground improvement are in
focus now-a-days;
Combination of technologies.
Smart automated improvement technologies.
Use of recycled materials.
performance-based specifications.
Advancement in bio-synthetics.

19. IMPROVEMENT TECHNIQUES

20. Rapid Impact Compaction (RIC)
 Developed for treating miscellaneous fills up to depths of about 4 m.
 It is an intermediate compaction method between conventional
shallow compaction and deep dynamic compaction.

21. Details
 It densifies soil material by repeatedly dropping a hydraulic hammer
mounted on an excavator at a fast rate.
 Weight of hammer is typically 5–12 tons, which is dropped freely
from a height of 1.2 m.
 It is dropped on a circular steel foot with a diameter of 1.0–1.5 m.

22. Drawback in RIC
 The technique is generally not very effective in low permeability
saturated soils.
 The key limitation for this technology is that the depth of
improvement is smaller.

23. RIC Design Parameters
Design parameters for rapid impact compaction include:
o Type of soil material on field
o Ground water table
o Weight of impact hammer
o Height of drop
o Pattern of impact points
o Distance to nearby structures

24. Sequence of Work
 Excavation to foundation level, levelling and rolling.
 Pre-treatment DPT testing.
 First pass by RIC rig (70 blows), levelling and rolling.
 Level survey and DPT testing.
 Second pass by RIC rig (50 blows), levelling and rolling.

25. Sequence of Work (Cont’d)
 Level survey, post treatment DPT testing and PBT at 0.5 m and 1.0 m
below final treatment level.
Restoration of levels to underside of foundation level.
 Whilst ground improvement works were suspended.

26. Primary and Secondary Tamping

27. Practical Example
Sheffield (UK) – Improvement of an old ash fill site.
I. Non-engineered fill (made ground) consisting mainly of ash, clinker and slag had been
deposited.
II. Fill materials to be in a loose condition.
III. Significant compression and densification during treatment.

28. VIBRO COMPACTION
Vibro-compaction drives a vibrating probe into the ground.
 It generates lateral vibratory forces to rearrange particles into a
dense state.

29. Details
 In saturated cohesion-less soil material, due to excess pore water
pressure effective stresses reduces, so that the shear strength is
reduced.
 As a result, the rearrangement of particles becomes easier.
 In dry cohesion-less soil material, water can be injected to make the
compaction easier.
 Water or air is often used to assist the penetration and densification.
 Backfill is also used to improve the degree of densification.

30. Drawbacks
 This method is limited to cohesion-less soil material with a low clay
content (i.e., less than 3%).
Installation induces vibration and possible ground subsidence.

31. Design Parameters
 Soil material type, fine content, and percent of clay particles
Thickness and depth of problematic soil material
Depth of groundwater table
Initial void ratio or relative density of soil material
Target void ratio or relative density of soil material
Pattern and spacing of compaction

32. Working
 It induces lateral vibrations and vibratory forces.
The forces attenuate with an increase of the distance from the
compaction point.
Dynamic stresses induced by dynamic compaction destroy the
structure of granular soils.
Reduction in shear strength of soil.
Soil dilation and then densification.

33. Practical Example
JURONG Island in Singapore.
I. It is situated in Singapore with a 3,200 ha.
II. This is man-made island formed by joining several small islands through
extensive land reclamation works.
III. It consists of loose granular soil.
IV. Has layer thickness 20m to 35m.
V. Both single and twin vibro rigs were used.

35. Soil Improvement by Heating
 Heating a soil mass can improve the soil state by increasing its
strength.
 Higher the heat input per mass of soil being treated, the greater the
effect.
 Even small increase in temperature may cause strength increase in
fine grained soils.

36. Effect of Heat

37. Drawback
 This techniques can only be used when a large and inexpensive heat
source is located near the site.

38. Soil Improvement byCooling
 Remove heat from ground to reduce soil temperature below freezing
point.
 And then turn soil material into solid.
 Freezing of pore water acts as a cementing agent between the soil
particles.
 It causes significant increase in shear strength and permeability.

39. Application
 Suitable for saturated clay and sand.
 Used for temporary protection during excavation

40. Jet Grouting
 This method involves injecting concrete into the ground, under
pressure, to form a series of underground pillars of concrete bulbs.
This compacts the ground between the compact pillars.

41. Details
 It is an erosion-based system.
 Granular soils are considered the most erodible and plastic clays the
least.
 The technique hydraulically mixes soil with grout to create in situ
geometries of soil-crete.

42. Working
 Hydraulic Rotary drill is used to reach the design depth.
 At that point grout and sometimes water and air are pumped to the
drill rig.
This create a cementitious soil matrix called soil-crete.

43. Traditional Jet Grout Systems
 Single-fluid system:
 High-velocity cement slurry grout is used to erode and mix the soil.
This system is most effective in cohesion less soil.
 Double-fluid system:
The high-velocity cement slurry jet is surrounded with an air jet.
The shroud of air increases the erosion efficiency.
The double-fluid system is more effective in cohesive soils than the single-
fluid system.

44. Traditional Jet Grout Systems (Cont’d)
 Triple-fluid system:
A high-velocity water jet surrounded by an air jet is used to erode the soil.
A lower jet injects the cement slurry at a reduced pressure.
Separating the erosion process from the grouting process.
It results in higher quality soil-crete.
This system is the most effective system in cohesive soils.

45. Traditional Jet Grout Systems (Cont’d)

46. Applications
 Densification of granular soils
 Raising settled structures
 Settlement control
 Underpinning of existing foundations
 Excavation support
 Protection of existing structures during tunnelling
 Liquefaction mitigation
 Water control

47. Limitation and Drawback
 Quantity of grout is hard to estimate.
 Effectiveness of some applications cannot be predicted.
 Area of improvement is sometimes uncertain.
 Grouting may cause ground movement and distresses to existing
structures.
 Certain chemical grouts may contain toxicity and have adverse
impact to groundwater and underground environment.

48. Practical Example
 Teesta Low Dam, Hydro Power Plant at Kalijhora, West Bangal, India.
 Grout curtain in coffer dam.
 Safe excavation works and construction work
Soils consisted of a typical river bed material with boulders intermixed with silty sand.
permeability of the coffer dam ranges 10-3 to 10-4 m/sec and the target permeability
was 10-6 m/sec.