Course
Year
: S0892 - Ground Improvement Method
: 2010
INTRODUCTION
Session 1
GENERAL
SCOPE OF THE COURSE
• Introduction (Geotechnical problems)
• Soft Soil (Problems and stabilization methods)
• Slope Stabilization
• Unique Soil, basic principle and improvement method
• Case study of Ground Improvement
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GENERAL
Grading Policy
• Home Work ………........................
• Mid Semester Test ……………….
• Final Test …..................................
TOTAL .....................
20%
30%
50%
100%
Note:
• Appropriate changes to this grading policy may be made with
student consent.
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REFERENCE TEXTBOOK
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REFERENCE TEXTBOOK
SUPPORTING
TEXTBOOK
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COURSE 1
Content:
• Introduction
• Geotechnical Problems
• Remedial/Improvement Methods
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INTRODUCTION
TYPICAL POOR SOIL
COARSE GRAINED MATERIAL
• Loose sands:
– Often found in land reclamation projects and are placed by man.
– Often dredged and are relatively clean (< 10% fines).
– Typical CPT cone tip resistance (qc) values of 4–6 MPa or SPT N
values of 4 to 7.
• Loose silty sands:
– Often alluvial deposits and are often layered with alternate layers having
higher fines contents.
– Compactable, but to a lesser degree than clean sands and may need
some additional material such as coarse aggregate.
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INTRODUCTION
TYPICAL POOR SOIL
FINE GRAINED MATERIAL
• Soft and “ultra soft” silts:
– Very low undrained shear strength
• Soft : cu values in the range of 10 to 20 kPa
• Ultra soft : cu values in the range of 4 to 10 kPa
– Low plasticities and relatively high permeabilities.
– Consolidate quickly and do not settle in the long term.
• Soft and very soft marine clays:
–
–
–
–
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Low shear strengths
Low permeabilities (k approximately 1 × 10-8 to 1 × 10-9 m/s).
Plasticities tend to be high (Plasticity Index greater than 50 to 60%).
Standard Penetration Tests tend to give blow counts of 0-2 even at
large depths.
– Because of the very low permeabilities, these soils consolidate over a
long period of time and also tend to exhibit secondary compression.
INTRODUCTION
TYPICAL POOR SOIL
FINE GRAINED MATERIAL
• Organics soils, peats:
– Usually identified in the field by visual inspection or by the smell of
decayed wood or plant matter.
– Generally, a soil is considered to be peat if the organic content is
greater than 75%.
– Organic soils and peats are among the most difficult soils to improve
since they tend to settle in the long term due to creeping and
decomposition of the organic matter.
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SOFT & ULTRA SOFT SILT
- Cu = 5 – 20 kPa
- Low Plasticity
- High Permeability
- Cv = 5 – 10 m2/year
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SOFT & VERY SOFT MARINE CLAY
- Cu = 0 – 20 kPa
- High Plasticity
- Low Permeability
- Cv = 0.5 – 1 m2/year
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GEOTECHNICAL PROBLEMS
•
•
•
•
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LOW BEARING CAPACITY
HIGH SETTLEMENT
LIQUEFACTION
UNSTABLE
GEOTECHNICAL PROBLEMS
LOW BEARING CAPACITY
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GEOTECHNICAL PROBLEMS
SETTLEMENT
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GEOTECHNICAL PROBLEMS
LIQUEFACTION
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GEOTECHNICAL PROBLEMS
UNSTABLE SOIL
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IMPROVEMENT METHOD
APPLICABLE
GRAIN
SIZE
RANGES
FOR DIFFERENT
STABILIZATION METHODS
APPLICABLE GRAIN
SIZE RANGES
FOR
DIFFERENT STABILIZATION
METHODS
GRAVEL
SAND
SILT
CLAY
VIBRO-COMPACTION
VIBRO-DISPLACEMENT COMPACTION
PARTICULATE GROUT
CHEMICAL GROUT
DISPLACEMENT GROUT
PRELOADING
DYNAMIC CONSOLIDATION
(HEAVY TAMPING)
ELECTRO-OSMOSIS
REINFORCEMENT
THERMAL TREATMENT
REMOVE AND REPLACE
PREW ETTING
10
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1.0
0.1
0.01
0.001
PARTICLESIZE
SIZE [m m ] [mm]
PARTICLE
James K. Mitchell, "Stabilization of Soils for Foundations of Structures", University of California, Berkeley, 1976
0.0001
IMPROVEMENT METHOD
GROUND
IMPROVEMENT
CONSOLIDATION
DENSIFICATION
CHEMICAL
DENSIFICATION
REINFORCEMENT
VERTICAL DRAIN
+ SURCHARGE
VIBRO
COMPACTION
DEEP SOIL
MIXING
GEOSYNTHETICS
VACUUM
CONSOLIDATION
DYNAMIC
COMPACTION
JET GROUTING
STONE COLUMN
COMPACTION
GROUTING
INJECTION
GROUTING
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PRINCIPLE OF GROUND IMPROVEMENT
• DENSIFICATION  rearrangement of soil particles
• CONSOLIDATION  drainage and reduction of voids
• CHEMICAL MODIFICATION  hardening by addition of
binders
• DISPLACE & REINFORCE  pushing unstable soils
aside, installing stiffer
elements
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