1. SOFT SOIL (PROBLEMS & STABILISATION METHOD) Session 2 - 7
Course : S Ground Improvement Method
Year : 2010
SOFT SOIL (PROBLEMS & STABILISATION METHOD) Session 2 - 7

2. Stabilization Methods:
COURSE 2
Content:
Soft Soil Problems
Stabilization Methods:
Preloading & Vertical Drain
Stone Column
Dynamic Compaction
Chemical Stabilization
Reinforcement
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3. SOFT SOIL PROBLEMS LOW BEARING CAPACITY HIGH SETTLEMENT LIQUEFACTION
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4. SOFT SOIL PROBLEMS
LOW BEARING CAPACITY
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5. SOFT SOIL PROBLEMS
SETTLEMENT
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6. SOFT SOIL PROBLEMS
LIQUEFACTION
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7. STABILIZATION METHOD PRELOADING & VERTICAL DRAIN
Encountered problems on fine grained soft soil are low strength, and high compressibility
Preloading by surcharge embankment applied to reduce compressibility and increases soil strength
Fine grained soil possessed very low permeability that consolidation process takes very long time 
Vertical drains provide drainage paths to reach the surface
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8. PRELOADING & VERTICAL DRAIN
BASIC PRINCIPLE
Surcharge
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9. PRELOADING & VERTICAL DRAIN
BASIC PRINCIPLE
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10. VERTICAL DRAIN DESIGN
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11. VERTICAL DRAIN DESIGN
D = 1.05 S
D = 1.13 S
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12. VERTICAL DRAIN INSTALLATION
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13. VERTICAL DRAIN + VACUUM
Vacuum load can reach greater than 80kPa (equals to 4 – 5 m height preloading fills with g = 17 – 18 kN/m3)
Rapidly decreases excess pore water pressure
Inward lateral movement
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14. VACUUM CONSOLIDATION
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15. CONVENTIONAL VD VS VACUUM CONSOLIDATION
CONVENTIONAL VERTICAL DRAIN
VACUUM CONSOLIDATION
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16. STABILIZATION METHOD VIBRO COMPACTION
Compaction of loose granular soils by penetration of a vibratory probe or vibroflot.
Should combine with sand/stone column if applied in fine grained soil
Affected area by the compaction energy : m
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17. STABILIZATION METHOD
STONE COLUMN
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18. STONE COLUMN DESIGN BEARING CAPACITY SINGLE STONE COLUMN
Formula 1 
Allowable Bearing Capacity
FS = Factor of Safety = 3
Formula 2 
Formula 3 
Where:
v = vertical stress in stone column
hs = passive resistance of surrounding soil (the effect of loading shall be considered)
v’ = effective friction angle of stone column (35o – 40o)
cu = undrained cohesion of surrounding soil
PL = Pressuremeter limit presssure
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19. STONE COLUMN DESIGN
Available design methods with respect to settlement:
(1) Equilibrium Method
(2) Priebe’s Method
(3) Granular Wall Method
(4) Greenwood Method
(5) Incremental Method and
(6) Finite Element Method
Derived from unit cell idealisation, stone column is modelled to be a concentric body in a composite soil mass.
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20. STONE COLUMN DESIGN
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21. STONE COLUMN NOTES
Typical design values per column in range of 200 to 300 kN/column
Young modulus of stone column in range of 40 to 70 Mpa
The settlement of single stone column under design load usually in range of 5 to 10 mm
The maximum settlement of sotne column group is 100mm
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22. STONE COLUMN INSTALLATION
vibrator makes a hole in the weak ground
hole backfilled
..and compacted
Densely compacted stone column
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23. STONE COLUMN INSTALLATION
WET METHOD
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24. STONE COLUMN INSTALLATION
DRY METHOD (TOP-FEED METHOD)
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25. STONE COLUMN INSTALLATION
DRY METHOD (BOTTOM-FEED METHOD)
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26. STONE COLUMN INSTALLATION
BOREHOLE METHOD (RAMMED COLUMN)
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27. VIBROFLOTATION
Vibro Compaction Method by using a self vibrating probe or a vibroflot
Vibroflot (vibrating unit) Length = 2 – 3 m Diameter = 0.3 – 0.5 m Mass = 2 tonnes
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28. VIBROFLOTATION
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29. VIBROFLOTATION INSTALLATION
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30. STABILIZATION METHOD DYNAMIC COMPACTION
A method of improving the ground using that involves very high energy waves by hammering the earth
Pounders weighing 15 to 40 tons are released in free fall from a height of 10 to 40 m.
Most suitable for granular soil
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31. DYNAMIC COMPACTION
Cost effective method for: - sand densification - soil compaction - ground compaction - land fill treatment - unconsolidated fill or soil treatment
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32. DYNAMIC COMPACTION
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33. DYNAMIC COMPACTION
For design, suitability assessment, and determination of optimum field operation parameters rely mainly on :
Empirical Equations
Field Pilot Tests
Past experiences
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34. DYNAMIC COMPACTION
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35. DYNAMIC COMPACTION DESIGN
Effective Depth Improved
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36. DYNAMIC COMPACTION DESIGN
Applied Energy
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37. DYNAMIC COMPACTION DESIGN
Design Chart
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38. DYNAMIC COMPACTION DESIGN
Design Procedure
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39. DYNAMIC COMPACTION MECHANISM
IN COHESIONLESS SOIL
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40. DYNAMIC COMPACTION NOTES
Important notes for deep compaction
(1) Effective depth will not exceed 15 m in practice (Lukas, 1986).
(2) Depth of compaction (D) is proportional to the square root of the impact energy (Metric
Ton*Meter) /drop. Different relations have been proposed.
D = (W*h)1/2 for cohesive material (Menard and Broise, 1975)
D = 0.5 (W*h)1/2 for cohesionless material (Leonards et al., 1980)
Actually, D = 0.3~0.7 (W*h)1/2 from field observation. Use a higher value for loose soils.
(3) Maximum improvement occurs within a zone between 1/3 to 1/2 the depth of compaction.
(4) If a line is attached from the crane to the weight, the efficiency of the energy reduces by 20%
(Lukas, 1986).
(5) The ground water has to be at least 2 m below existing ground or 0.6 m below the bottom of
craters.
(6) An area of 5,000 to 10,000 m2 is required to be economical.
(7) Vibration and noise (115 to 120 dB at source) may be a concern to the nearby developments.
Figure 1.3 shows the estimated vibration velocity due to the compaction (Lukas, 1986).
(8) Minimum 34 ~ 50 m clearance from any structure.
(9) The number of repeated drop on the same spot should be limited to drops (Lukas, 1986)
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41. STABILIZATION METHOD CHEMICAL STABILIZATION INJECTION GROUTING
DEEP SOIL MIXING
JET GROUTING
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42. CHEMICAL STABILIZATION
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43. INJECTION GROUTING
1. install grout pipes using drilling or driving techniques.
2. The mortar-like grout, injected under certain pressure through the pipes.
The grout pipe is then lifted some distance (0.3 to 1.5 m), and the injection process is repeated.
3. Grouting can stiffen and strengthen the soil layer by in creasing its density, and acting as a reinforcement.
Grouting may also be used to re-level a structure that has been damaged by differential settlements.
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44. DEEP SOIL MIXING
Soil Mixing is the mechanical blending of the in situ soil with cementitious materials.
Strengthen soft and wet cohesive soils in a very short time period
Treatment is possible up to depths of 30 m
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45. DEEP SOIL MIXING
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46. JET GROUTING
Uses high kinetic energy (20-60 MPa) liquid spurt (jet) for chopping up the ground around and mixing it with binding agent.
Can be used for treating most soil types
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47. JET GROUTING TYPES
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48. JET GROUTING
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49. CHEMICAL STABILIZATION – RESULT
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50. STABILIZATION METHOD
REINFORCEMENT
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51. REINFORCEMENT
BASIC PRINCIPLE
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52. REINFORCEMENT MATERIAL
GEOSYNTHETIC
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