Analysis of Stone Column
- 1. ANALYSIS OF STONE COLUMN Prepared by SUHAS MOHIDEEN (Student ID: 10401920) School of Engineering Edith Cowan University Supervisor Dr. Sanjay Kumar Shukla
- 2. Brief Introduction Stone column is a ground improvement method Origin in Germany (1950s) It is constructed by well compacted coarse aggregates installed in the ground to serve various purposes such as reinforcement, densification and drainage
- 3. Objectives Analyse Single Stone Column’s Bearing Capacity, Mitigation of Excess pore water pressure & Drain Capacity Analyse Road Embankment supported by Stone column Analyse Group of Stone Column Investigate the application of Geosynthetics
- 4. Applicable Soil Types Soft Cohesive Soils Granular Soils with High Fines Organic Soils Marine/Alluvial Clays Liquefiable Soils
- 5. Plaxis Software Plaxis Software is a finite element analysis software used in this project to analyse the stone column Plaxis is used worldwide by top engineering companies and institutions in the civil and geotechnical engineering industry Developed by University of Delft, Holland in 1980s Models can be created as plain strain or Axisymmetric
- 6. Applied Load Dynamic Load(kPa) 10 Frequency (Hz) 20 Amplitude (kPa) 20 Static (kPa) 50 Stone Column Dimensions Diameter(m) 0.8 Length (m) 5 Friction angle 38 degree Single Stone Column Figure 1: Load Calculation in Plaxis for Stone Column
- 7. Single Stone Column Deformed Mesh Figure 2: Untreated soil Figure 3: Unit cell Stone column RESULTS Untreated soil : 4.823*10-3 m Unit cell stone column: 0.9664* 10-3m
- 8. Single Stone Column Mitigating Excess Pore Water Pressure Figure 4: Untreated soil Figure 5: Unit cell Stone column RESULTS Untreated soil : 0.4030kN/m2 Unit cell stone column: 0.0714 kN/m2
- 9. Single Stone Column Change in Ground Water Level Stone Column dropped Ground water table to -2m elevation due to its drain capacity Consolidation calculation type selected for 7 days interval in Plaxis Software Figure 6: Ground Water Table Level
- 10. Road Embankment supported by stone Column Surface Load Road Embankments Stone columns Load Dynamic Load (kPa) 120 Frequency (Hz) 20 Amplitude (kPa) 20 Static (kPa) 50 Geogrid Elastic EA= 18 kN/m Geotextile Elastic EA= 2.1 kN/m Stone Column Dimensions Total 5 number of stone column Diameter(m) 1.2 Length (m) 5.5 Friction angle 41 degree Figure 7: Road Embankment supported by 5 Stone Columns
- 11. Figure 7: Road Embankment on untreated soil Figure 8: Road Embankment supported by Stone Columns Road Embankment Supported by Stone Column Total Displacement
- 12. Figure 8: Excess Pore Water pressure under Road Embankment on untreated soil Figure 9: Excess Pore Water pressure under Road Embankment supporting stone column Road Embankment Supported by Stone Column Excess Pore Water Pressure
- 13. Figure 10: Total principal strain under Road Embankment supported by stone column Figure 11: Total principal strain under Road Embankment supported by stone column applied geosynthetics Geotextile Geogrid Road Embankment Supported by Stone Column Total Principal Strain
- 14. Group Of Stone Column Geosynthetic encased stone columns Load Static (kPa) 30 Geogrid Elastic EA= 18 kN/m Stone Column Dimensions Total 8 number of stone column Diameter(m) 1.25 Length (m) 5 Friction angle 40 degree Figure 12: Group of Stone Column
- 15. Figure 13: Total Displacement in untreated soil Figure 14: Total Displacement in Group of Stone column installed soil Group Of Stone Column Total Displacement
- 16. Group Of Stone Column Ground Water Head Discharge Figure 15: Ground Water Discharge in untreated soil Figure 16: Ground Water Discharge in Group of Stone column Installed soil
- 17. Numerical Calculations Design of Stone Column Using Hienz. J. Priebes Method Assumptions • The column is based on a rigid layer • The column material is uncompressible • The bulk density of column and soil is neglected
- 18. Numerical Calculations )1)(1(2 )2(2)3( 1 rSac rSr rr AK AA AA Basic Improvement Factor )1(4 )5( 10 rac r rr AK A AA Assuming Poisson's ratio=0.33, The Priebe (1995) formula can be simplified as Area Ratio typically values range from 0.10 to 0.40 2 e c e C r D D A A A Figure 17: Relation between the improvement factor (after Priebe, 1995)
- 19. For the friction angle Numerical Calculations C =360 rA =0.1 Function of frictional angle of stone column 36sin1 36sin1 sin1 sin1 C C acK =0.259 )1.01(259.0*4 )1.05( 1.01.010Therefore, =1.425 Settlement reduction factor 425.1 11 0 =0.70175
- 20. Area Ratio Internal friction angle of stone column 0.1 0.701754 0.654879 0.603974 0.2 0.510725 0.458295 0.40568 0.3 0.378215 0.331126 0.286041 0.4 0.280899 0.241955 0.205931 0.6 0.14771 0.124953 0.104592 0.8 0.060916 0.05114 0.042517 rA 0 36C 0 40C 0 44C 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 A A Settlement Reduction Factor Series1 Series2 Series3 0 40C 0 44C 0 36C rA Numerical Calculations Results Figure 18: Effect of friction angle on settlement reduction factor
- 21. Conclusions When the Ar ratio (dc/de) increases, the settlement rate of clay is increases. By reducing the Ar ratio, settlement of clay decrease with regarding to the full depth of stone column. The group of stone column capacity decreases by increasing the stone column centre-to-centre distance to S/D = 3or beyond this value. Consolidation rate is higher for larger diameter Geosythetic encased stone columns protect the stone column from forming Bulging failure
- 22. Thank you