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Building a-University_on_liquiable_soils

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Building a-University_on_liquiable_soils

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Building a-University_on_liquiable_soils

  1. 1. BUILDING A UNIVERSITY ON LIQUEFIABLE SOILS USING DYNAMIC COMPACTION Ravi Sundaram, Sanjay Gupta, Sorabh Gupta CENGRS GEOTECHNICA PVT. LTD.
  2. 2. Project Details Gautam Budh University at Greater Noida, Uttar Pradesh Covers an area of about 511 acres 84 000 m2 of constructed area 30% green84,000 m2 of constructed area, 30% green cover Site in the flood plains of the River Yamuna, about 2 km from river 2
  3. 3. Vicinity Map 3
  4. 4. The Project 2007.. 4
  5. 5. The Project Today.. 5
  6. 6. .. And what it will be. 6
  7. 7. Site Conditions Site is in Earthquake Zone IV - IS 1893: 2002 Loose alluvium - fine sand (Yamuna Sand) Groundwater met at shallow depth S d t 8 12 d th i t li f tiSand to 8-12 m depth is prone to liquefaction Ground Improvement by Dynamic Compaction carried out for all buildings planned at site Each structure was individually assessed 7
  8. 8. Benefits achieved Dynamic compaction successfully mitigated liquefaction potential Greater stability during earthquake Need for piling was eliminated and the buildings were supported on open foundations Substantial savings achieved – foundation cost was less than 50% of what would be required if piling was done Savings also achieved in time required to complete foundation construction 8
  9. 9. Investigations Before CompactionInvestigations Before Compaction 9
  10. 10. Investigations After CompactionInvestigations After Compaction 10
  11. 11. Plethora of Data.. Over 700 boreholes and 200 static cone penetration t t l t d i thtests completed in the University area over a period of 3 years 11
  12. 12. This Paper Presents.. Ground Improvement by DYNAMIC COMPACTIONDYNAMIC COMPACTION done for FACULTY BLOCKFACULTY BLOCK ill t ti l f th kill t ti l f th kas an illustrative example of the workas an illustrative example of the work done and extent of improvementdone and extent of improvement achievedachieved The need for piling was eliminatedThe need for piling was eliminated resulting in substantial savingsresulting in substantial savings 12
  13. 13. Faculty Block Location 13
  14. 14. Scope of Work- Faculty Block At Faculty Block: Before Compaction: 4 boreholes – 15 m 1 SCPT After Compaction: 4 boreholes – 15 m 1 SCPT 14
  15. 15. Before Compaction 15
  16. 16. After Compaction 16
  17. 17. Borehole Data – Before Compaction SPT values typically 10-15 to 8 m depth Fines content:Fines content: 5-10 % Groundwater at 4- 5 m depth, may rise to GL 17
  18. 18. Liquefaction Assessment Seed & Idriss (1971) method – NCEER Summary Report Cyclic Stress Ratio (CSR) Maximum Credible Earthquake (MCE) Design Earthquake Magnitude: 6.7 Peak Ground Acceleration: 0.24g 18
  19. 19. Liquefaction Assessment Cyclic Resistance Ratio (CRR) determined from SPT & SCPT As per the analysis, the fine sands to 8 m depth at the Faculty Block are susceptible todepth at the Faculty Block are susceptible to liquefaction in the event of the design earthquake 19
  20. 20. Dynamic Compaction Dropping a heavy weight can compact loose sands to substantial depth Effective for sands only Done on a grid pattern 20
  21. 21. Conceptual Illustration The maximum depth of improvement (Df) at the project site was estimated using Mitchell & Katti, 1981: WHD WHD where n = modification factor (taken as 0.7) W = weight of pounder, and H = height of drop WHnD = WHnD = 21
  22. 22. Compaction Details Conventional Crane – TLC 955A Compaction in 3 Phases: 2 Compaction Phases and2 Compaction Phases and Ironing Phase 1 week time lag in between – to allow pore pressures to dissipate 22
  23. 23. Compaction Phase Area divided into 4 x 4 m grids 11.65 T pounder falling from height of 14 m 10 drops at each grid point10 drops at each grid point Energy Imparted: 1600 kN-m Corresponding depth of improvement: 9 m 2nd Phase staggered 2 m 23
  24. 24. Ironing Phase Craters filled with GSB Grade II material Hammer weight: 11.65 T Height of fall: 6 mHeight of fall: 6 m No. of drops: 5 Energy: 2114 kN-m Area graded with 10 passes of 10 T vibratory roller 24
  25. 25. SPT before compaction 25
  26. 26. SPT before & after compaction 75 % Improvement to about 4 m depth 25~30 % Improvement to about 10 m depth 26
  27. 27. SPT & SCPT before & after compaction 75 % Improvement to 4 m depth 25~30 % Improvement to 10 m depth 27
  28. 28. SPT & SCPT before & after compaction 50-170 % Improvement to 4 m depth 25~50 % Improvement to 10 m depth 28
  29. 29. Extent of Improvement Achieved After Compaction, N>20, qc > 50 MPa Peak Improvement: Between 1 and 5 m depthdepth Improvement below 10 m depth is marginal 29
  30. 30. CRR Evaluation (Before Compaction) 30
  31. 31. CRR Evaluation (After Compaction) After Compaction, CRR > CSRAfter Compaction, CRR > CSR 31
  32. 32. FOS against Liquefaction (based on SPT & SCPT) fiableZoneLiquef No LiquefactionLiquefaction to 8m depth Before Compaction After Compaction 32
  33. 33. Liquefaction Mitigation Untreated ground (before compaction) is susceptible to liquefaction to 8 m depth After compaction, Factor of Safety against liquefaction > 1liquefaction > 1 Susceptibility to liquefactionSusceptibility to liquefaction successfully mitigatedsuccessfully mitigated 33
  34. 34. Foundation Selection For unimproved ground, pile foundations transferring the loads below the liquefiable zone would be necessary. Pile lengths would be on the order of 15 to 20 m Open foundations on improved ground: IsolatedOpen foundations on improved ground: Isolated footings with connecting beam Design Net Bearing Pressure: 175 kPa175 kPa RESULTED IN SUBSTANTIAL SAVINGSRESULTED IN SUBSTANTIAL SAVINGS IN COST AND CONSTRUCTION TIMEIN COST AND CONSTRUCTION TIME 34
  35. 35. Concluding Remarks Case Study demonstrates successful mitigation of liquefaction potential by use of dynamic compaction Successful in areas of loose clean sandsSuccessful in areas of loose clean sands Field trials are necessary to confirm feasibility Sufficient in-situ testing before and after improvement should be done to confirm efficacy of the improvement 35
  36. 36. Thank You!Thank You! 36

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