1. Soft Soil Engineering (Class note) Junhwan Lee School of Civil and Environmental Engineering Yonsei University

2. Outline Ch. 1. Introduction to soft soil engineering Ch. 2
Outline Ch. 1 Introduction to soft soil engineering Ch. 2 Geological and geotechnical characteristics Ch. 3 Soil exploration and characterization Ch. 4 Settlement analysis Ch. 5 Strength analysis Ch. 6 Ground improvement Ch. 7 Monitoring and construction management Ch. 8 Design example

3. wn Natural water content (wn) gives: Profiling and Check on Soil Type
wn + AL  Strength
 Consolidation/Swelling
  wn + t + Gs  Degree of Saturation (S)
 Storage quality

4. t Total unit weight (t) gives: Total stress (v) = t  depth
Effective stress (’v) = v – u
Testing Method:
Soft Clay  Trim by Wire Saw
Stiff Clay  Trim by Knife
Sand (clean)  Estimate  from SPT N

5. Atterberg Limits (AL) ALs give: Upper & Lower limits of Plastic State
ALs + wn (LI)  Indication of Strength
 Consolidation/Swelling
Problem:
LL - Short mixing time, Improper equipment
calibration (height, base type)
PL - No 3 mm – resulting in high PL

6. ALs and wn
Soil profiles and indication of strength

7. Sieve Analysis Purpose:
Soil Classification - e.g., gravel, sand, silt/clay
Size distribution of Coarse grained material
Drainage condition  Permeability  Density
Testing Method:
WET SIEVE: Weigh Dry Soil  Wash through #200 Sieve  Dry  Sieve  Weigh  Give Particle Size Distribution

8. Soil Anisotopy Cause Resultant Deposition - Orientation
Stress Induced - OCR
Flow/Consolidation Anisotropy
Strength Anisotropy
Stress-Strain Anisotropy

9. Steady State Condition CRS-V Theory
Compression Curves
Steady State Condition
CRS-V Theory

10. Testing Methods
Oedometer test
Rowe-cell tests

11. Preconsolidation pressure Distribution of pore pressure
Issues
Preconsolidation pressure
Distribution of pore pressure

12. Vertical Drain Methods
PVD
Rate of consolidation

13. Issues
Preconsolidation pressure
Distribution of pore pressure