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Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
Stone columns -  an overview(Ground improvement)
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Stone columns - an overview(Ground improvement)

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  • 1. Stone Columns: An Overview by S.V. Abhishek & V. Tarachand Department of Civil Engineering College of Engineering (A) Andhra University Visakhapatnam
  • 2.  Amongst Stone Columns various techniques for improving in-situ ground conditions, stone columns are probably the most versatile, due to their ability to perform a variety of important geotechnical functions.  Origin Germany (1950s)  In India, the use of stone columns began in the early 1970s.  Load bearing columns of well compacted coarse aggregate installed in the ground to serve various purposes such as reinforcement, densification and drainage.
  • 3. Applicable Soil Types Soft, Non-Compactible, Weak Soils Granular Soils with High Fines Content (in excess of 15%) Organic Soils Marine/Alluvial Clays Liquefiable Soils Waste Fills Reclaimed Fly Ash/Pond Ash Ponds
  • 4. Functions  Improve the bearing capacity of weak soils.  Carry high shear stresses by acting as stiff elements and hence increase the stability of embankments founded on soft ground.  Facilitate radial drainage (by acting as vertical drains) and dissipate rapidly the excess pore water pressure leading to acceleration of consolidation process and reduced post-construction settlements.  Mitigate the potential for liquefaction and damage by preventing build up of high pore pressure, providing a drainage path and increasing the strength and stiffness of the ground.
  • 5. Due to high angle of internal friction and stiffness of stone column when compared to that of in-situ weak soil, majority of applied load is transferred to stone column. As a result, less load is transferred to surrounding weak soil which leads to reduction in settlement.
  • 6. Installation Patterns Area of Influence = (√3/2)S2 De = 1.05S Area of Influence = S2 De = 1.13S Time required for consolidation is directly proportional to square of the drainage path.
  • 7. Load Carrying Mechanism Lateral earth pressure/radial confining stress against bulging from surrounding soil. Surface resistance or frictional resistance developed between the column material and surrounding weak soil acting upwards within the critical length. Passive resistance mobilized by column material. Load carrying capacity of stone columns = 100 to 400 kN. Note: End bearing is not considered in estimation of load carrying capacity because load carrying mechanism is local perimeter shear.
  • 8. Estimation of Load Carrying Capacity  Assumed that foundation loads are carried only by the stone columns with no contribution from the intermediate ground. K p (4c + σ 'r )  Hughes & Withers (1974) qa = F.S. where, qa = allowable bearing capacity of stone column Kp = coefficient of passive earth pressure = tan2(45+φ/2) c = cohesion of soil σr’ = average effective radial stress over a depth of ‘4d’ where ‘d’ is the diameter of the column F.S. = factor of safety = 1.5 to 3.0
  • 9. Settlement Control  Stone columns should extend through weak soil to harder firm strata to control settlements.  Provision of stone columns does not reduce the entire consolidation settlement. The reduction depends on the spacing of stone columns (generally 2.0 to 3.0 m c/c over the site).  Maximum percentage reduction of settlement is 75%.
  • 10. Drainage Function of Stone Columns  Load carrying capacity of stone columns is generated by the top section of the column which extends to about 4 times the diameter of the stone column.  The length below 4d allows for radial drainage and acceleration of settlements.  To retain continuity of drainage path, it is necessary to provide a 150 mm thick drainage blanket on top of the stone columns.
  • 11. Failure Mechanism (IS: 15284 Part 1 – 2003)
  • 12. Installation Techniques 1. Rammed Stone Column Technique 2. Vibro-Replacement Wet Top-Feed Method Dry Bottom-Feed Method
  • 13. Rammed Stone Column by Cased Borehole Method (Datye and Nagaraju, 1975)
  • 14. Vibro-Replacement The Depth Vibrator Principle: Extension Tube Coupling Air or Water Supply Motor Excentric Weight Tip
  • 15. Depth Vibrator (Courtesy of Keller Group) Air Chamber and Lock Extension Tube Flexible Coupling Electric Motor Stone Feeder Pipe Eccentric Weight Top-Feed Vibrator Bottom-Feed Vibrator
  • 16. Wet Top-Feed Method (Courtesy of Keller Group)
  • 17. Dry Bottom-Feed Method with Leader Supported Rig (Courtesy of Keller Group)
  • 18. Vibrocat (Courtesy of Keller Group)
  • 19. Dry Bottom-Feed Crane Hung System (Courtesy of Keller Group)
  • 20. Quality Control - Production Monitoring On-board M4 Computer: Depth, Compaction, Length of Pull, Re-penetration, Increase in Power Consumption, Column Diameter
  • 21. Stone Column after Installation
  • 22. Post-Installation Quality Control (Load Test)
  • 23. Applications in Civil Engineering  Rail and Road Embankments  Bridge Approaches and Abutments  Offshore Bridge Abutments  Airport Runways and Taxiways  Storage Tanks (LNG, Crude Oil, LPG etc)  Power Plants
  • 24. Ipoh-Rawang Electrified Double Track (Malaysia)
  • 25. Ipoh-Rawang Electrified Double Track (Malaysia)
  • 26. KVMRT Kajang Maintenance Depot (Malaysia)
  • 27. Bridge Approaches and Abutments Putrajaya, Malaysia
  • 28. Putrajaya Bridge Approach Embankment R.C. Structure RL +32.0 Top of Bridge Deck Water Lev. RL +21.5 Embankment RL +12.0 Pile cap Stone columns Bored piles Stone columns
  • 29. Offshore Bridge Abutments Johor Bahru, Malaysia
  • 30. Airport Runways and Taxiways Alor Setar Airport Project, Malaysia
  • 31. Storage Tanks Hazira LNG Terminal, Gujarat
  • 32. Case History of Highway Embankment on Stone Column Treated Ground in Queensland, Australia (Oh et al. 2007)
  • 33. Subsoil Properties
  • 34. 520 mm Untreated 495 mm SC @ 3m c/c SC @ 2m c/c 390 mm
  • 35. Lateral Displacement Profiles
  • 36. Conclusions Stone Columns are one of the most versatile techniques for engineering the ground.  They can be installed to improve a variety of ground conditions through several variants of the technique such as rammed stone columns and vibro-replacement (wet top-feed and dry bottomfeed methods).  The in-situ ground is improved by reinforcement, densification and drainage functions performed by the stone columns.  From the case history, the embankment treated with stone columns spaced at 2 m centre to centre experienced the least settlement and lateral displacement when compared to the other cases. 
  • 37. Acknowledgments Prof. M.R. Madhav Professor Emeritus, JNTU Visiting Professor, IIT Hyderabad Dr. V.R. Raju Managing Director Keller Asia
  • 38. Earthquake Rose Thank You

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