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Building a mega-power plant on liquefiable sands


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Building a mega-power plant on liquefiable sands

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Building a mega-power plant on liquefiable sands

  2. 2. Project Site Site located in northwest Punjab -On the banks of River Beas -At Goindwal Sahib
  3. 3. 500 MW Thermal Power Plant Covers area of over 500 acres Facilities planned Power House Boiler Chimney ESP Cooling Towers This paper presents data from BOILERBOILER -- II
  4. 4. Scope of Geotechnical Investigation 71 boreholes – 30 m depth 9 static Cone Penetration tests 13 trial pits 6 cross-hole seismic tests 4 field CBR 2 field permeability tests 19 electrical resistivity tests
  5. 5. Regional Geology Alluvial Deposits of Indo-Gangetic Alluvium River deposits of Beas and its tributaries Pleistocene to Recent Deposits
  6. 6. Site Stratigraphy – Boiler-I Clean sand to 30 m depth Design water table at GLDesign water table at GL
  7. 7. SPT Profile N<10 to 3-5 m depth N = 11-16 to 10 m depth N = 17-27 to 15 m depth N = 32 to 51 to 24 m depth N = 55 to 77 to 30 m depth
  8. 8. CPT (qc) Profile qc=25-70 kg/cm2 to 3-5 m depth qc=33-67 kg/cm2 to 10 m depth qc=70-120 kg/cm2 to 12 m depth Refusal at14~15 m depth
  9. 9. Shear Wave Velocity Vs Profile Vs<200~200 m/s to 10 m depth; gradually increases with depth
  10. 10. Detailed Liquefaction Analysis Youd & Idriss (2001) – NCEER Summary Report Cyclic Stress Ratio (CSR) Cyclic Resistance Ratio (CRR) Factor of Safety = CRR / CSR Earthquake Magnitude: 6.7 on Richter Scale6.7 on Richter Scale Peak ground acceleration, aamaxmax = 0.24 g= 0.24 g
  11. 11. CSR, CRR, Factor of Safety Sand in Boiler-I liquefiable to 10 m depth Depth of Liquefiable Zone: 9-11.5 m for various facilities
  12. 12. Engineering Solutions Ground Improvement by Vibro- Compaction For Medium to heavily loaded facilities Pile Foundations (RCC bored cast- in-situ piles) extending well below the liquefiable zone For very heavily loaded facilities such as TG & Chimney
  13. 13. Vibro-Compaction in progress Courtesy KellerCourtesy Keller
  14. 14. Cone tip resistance .. before & after BoilerBoiler--II CPT comparison beforeCPT comparison before and after compactionand after compaction Analysis of postAnalysis of post-- compaction datacompaction data confirmed thatconfirmed that liquefaction potentialliquefaction potential has been successfullyhas been successfully mitigatedmitigated
  15. 15. Plate Load Tests … before & after BoilerBoiler--II PLT before and afterPLT before and after compactioncompaction Plate Size: 60 x 60 cmPlate Size: 60 x 60 cm Results indicateResults indicate substantial reduction insubstantial reduction in settlementsettlement
  16. 16. Foundations on improved ground After vibroAfter vibro--compaction, soils atcompaction, soils at founding level compacted using afounding level compacted using a 10 ton roller10 ton roller Raft Foundation at 2 m depthRaft Foundation at 2 m depth Design Net Allowable bearingDesign Net Allowable bearing Pressure =Pressure = 220 kPa220 kPa Permissible total settlement = 25 mmPermissible total settlement = 25 mm
  17. 17. Pile Foundations RCC bored cast-in-situ piles for very heavily loaded facilities – TG, Chimney Static pile capacity analysis done ignoring skin friction in liquefiable zone
  18. 18. Computed Capacities – Bored Piles Pile Dia, mm Pile length below COL, m Safe Compressive Capacity, Tons Compression Uplift 600 20 83 27 23 95 33 26 108 39 Cut-off-level: 3.5 m below GL
  19. 19. Concluding Remarks Design and construction of the power plant facilities done after detailed investigations studies to assess liquefaction potential Analysis indicated liquefaction to 10 m depth at Boiler-1
  20. 20. Concluding Remarks Ground improvement by vibro- compaction successfully mitigated liquefaction potential Piles extending sufficiently below the likely zone of liquefaction used to transfer structural loads safely