A 500 MW thermal power plant was constructed on the banks of the River Beas in northwest Punjab. Geotechnical investigations found clean sand down to 30 m depth, with liquefaction potential to 10 m depth under the boiler facilities. Vibro-compaction was used to improve the ground and mitigate liquefaction. Cone penetration tests and plate load tests before and after confirmed the ground improvement. Raft and pile foundations extending below the liquefiable zone were used for heavily loaded structures like the boiler, turbine generator, and chimney. Pile capacities were computed ignoring skin friction in the liquefiable zone. The detailed investigations and ground improvement works successfully addressed the liquefaction hazards.

1. Sanjay Gupta
Ravi Sundaram
Sorabh Gupta
CENGRS GEOTECHNICA PVT. LTDCENGRS GEOTECHNICA PVT. LTD

2. Project Site
Site located
in northwest
Punjab
-On the banks
of River Beas
-At Goindwal
Sahib

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. 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. Regional Geology
Alluvial Deposits of Indo-Gangetic
Alluvium
River deposits of Beas and its
tributaries
Pleistocene to Recent Deposits

6. Site Stratigraphy – Boiler-I
Clean sand to 30 m depth
Design water table at GLDesign water table at GL

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. 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. Shear Wave Velocity Vs Profile
Vs<200~200 m/s
to 10 m depth;
gradually
increases with
depth

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. 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. 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. Vibro-Compaction in progress
Courtesy KellerCourtesy Keller

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. 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. 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. 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. 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. 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. 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

21. CENGRS GEOTECHNICA PVT. LTDCENGRS GEOTECHNICA PVT. LTD