This presentation summarizes two case studies of ground improvement projects in India. [1] Vibro-replacement was used to improve soils for a power plant, increasing density and liquefaction resistance as shown by dynamic cone penetration and load tests. [2] Dynamic compaction improved soils for a university, increasing SPT blow counts and reducing liquefaction susceptibility to 12m, allowing shallow foundations. In-situ testing before and after both projects verified the desired soil property improvements.

1. RaviRavi SundaramSundaram & Sanjay Gupta& Sanjay Gupta
Cengrs Geotechnica Pvt. Ltd.
Noida
A-100 Sector 63, Noida
Ph: (O): 0120-42067111 (M): 9810538095

2. Ground Improvement Process
Modification of soil properties to achieveModification of soil properties to achieve
improvementimprovement
Densification of loose soils
Mitigation of liquefaction potential
Strengthen soft clays
Increase safe bearing capacity
Reduce foundation settlement
Ensure that foundation behavior is
within the acceptable limits

3. Success of Ground Improvement Process
Identify target soil properties to beIdentify target soil properties to be
achieved after improvement, whatachieved after improvement, what
minimum value is acceptableminimum value is acceptable
InIn--situ testing is essential to ensuresitu testing is essential to ensure
that the desired improvement isthat the desired improvement is
achievedachieved
The soil characteristics afterThe soil characteristics after
improvement should be comparedimprovement should be compared
with the target soil propertieswith the target soil properties

4. This presentation covers
Two case studiesTwo case studies
Ground improvement for a Gas Based Power Plant inGround improvement for a Gas Based Power Plant in
North Delhi byNorth Delhi by VibroVibro--ReplacementReplacement
In-situ tests:
dynamic cone penetration tests, and
Load test on the stone columns
Ground Improvement for a university at GreaterGround Improvement for a university at Greater
NoidaNoida by Dynamic Compactionby Dynamic Compaction
In-situ tests:
Boreholes with SPT
Static Cone Penetration tests

5. VibroVibro--Replacement for a PowerReplacement for a Power
Plant in DelhiPlant in Delhi

6. Case Study-1: Vibro-Compaction
108 MW Gas Based Power Plant in north
Delhi
Facilities planned include STG, GTG, Steam
Turbine, Boiler, Chimney, Cooling Water
System, Switchyard, etc.
Alluvial Plains of River Yamuna
Earthquake Zone IV as per IS 1893-2002
Loose sands to 8 m depth prone to
liquefaction during major earthquakes

7. Site Layout Plan
15 boreholes – 30 m
depth
6 static cone
penetration tests(SCPT)
Spectral Analysis of
Surface Waves (SASW)
tests along 8 lines
3 cross-hole seismic
tests (CHST)

8. Typical Borehole Data
Loose surficial fill
to 0.5-2 m depth
Natural deposits
primarily fine
sand / silty sand
with intermediate
minor layers of
sandy silt
Groundwater at
5.2 – 6.4 m
depth

9. Static Cone Penetration Test

10. SASW and CHST

11. Design Profile

12. Liquefaction Assessment
Seed & Idris (1971) method – NEERI
Summary Report
Project area in Earthquake Zone IV
Maximum Credible Earthquake
Design Earthquake Magnitude: 6.7 on
Richter scale
Peak Ground Acceleration: 0.24g
Cyclic Resistance Ratio (CRR) determined
from SPT & SCPT

13. Liquefaction analysis results
A critical factor of safety of 1.2 was considered for the
analysis
Soils to a depth of 8.0 m are be susceptible to
liquefaction during earthquakes

14. Foundation System
Open foundations bearing on natural soils -
Not feasible
Critical or heavily loaded plant facilities –
STG, GTG, Steam Turbine, Boiler, Chimney
600600 mm diameter bored castmm diameter bored cast--inin--situsitu
piles extending well below thepiles extending well below the
liquefiable zoneliquefiable zone

15. Foundation System
Medium loaded plant facilities –
Cooling Tower,Cooling Tower,
ClariflocculatorsClariflocculators & other facilities of the& other facilities of the
Water Treatment system,Water Treatment system,
SwitchyardSwitchyard
Ground improvement doneGround improvement done
byby vibrovibro--replacement methodreplacement method

16. Vibro-Replacement Method
Dry Vibro Stone
columns
installed by bottom-
feed method
500 mm dia extending
to 10 m depth
Centre-to-centre
spacing: 1.5 m
Design Net Bearing
Pressure: 160 kPa

17. In-Situ Tests
Dynamic Cone Penetration Tests
(DCPT)
Evaluates extent of improvement
achieved with depth
Load Test on Stone Columns
Evaluates load-settlement behavior of
improved ground

18. Dynamic Cone Penetration Tests
After CompactionAfter Compaction
Blow Counts exceed 15
below 2 m depth
Substantial improvement
in penetration resistance
Medium dense to 4-5 m
depth
Dense below 5 m depth
Improved soils not likely
to liquefy during
earthquake

19. Load Test on Vibro-Columns

20. Plate size 1.51.5 m xm x
1.51.5 mm, square,
30 mm thick,
Loading intensity:
1st cycle – 240 kPa
2nd cycle – 500 kPa
Safe bearing pressure
> 160 kPa
Loading Intensity vs. Settlement

21. Liquefaction Mitigation
Untreated ground (before compaction) is
susceptible to liquefaction to 8 m depth
After compaction, Factor of Safety against
liquefaction > 1.2
Susceptibility to liquefactionSusceptibility to liquefaction
successfully mitigatedsuccessfully mitigated

22. Dynamic Compaction for aDynamic Compaction for a
University in GreaterUniversity in Greater NoidaNoida

23. Case StudyCase Study--2: Dynamic Compaction2: Dynamic Compaction
A major university
at Greater Noida,
UP
Covers an area of
about 500 acres
84,000 m2 of
constructed area,
30% green cover
Site in the flood
plains of the River
Yamuna, about 2
km from river

24. Vicinity Map

25. 25
Site Conditions
Loose alluvium - fine sand (Yamuna
Sand) met in project area
Site is in Earthquake Zone IV - IS
1893: 2002
Groundwater met at shallow depth
Every structure individually assessed
to evaluate liquefaction potential
Sand to 8-12 m depth is prone to
liquefaction during major earthquakes

26. Geotechnical Investigations
Over 600 boreholes and 150 SCPT’s
done all over the university area
Each structure assessed to evaluate
liquefaction potential
THIS PRESENTATIONTHIS PRESENTATION covers
geotechnical investigation before & after
improvement for
Boys Hostel 8.1KBoys Hostel 8.1K

27. Site Layout Plan – Boys Hostel No. 8.1KBoys Hostel No. 8.1K
Before
Improvement
4 BH – 15 m
1 SCPT – 15 m
After
Improvement
4 BH – 15 m
1 SCPT – 15 m

28. Typical Borehole Data
The soils at the
site classify
primarily as sandy
silt / clayey silt to
1.5~2 m depth,
underlain by fine
sand to 15 m depth
Fines content:3-
10 %
Groundwater at
3.5-4 m depth, may
rise to GL

29. Liquefaction Assessment
Seed & Idris (1971) method – NEERI
Summary Report
Project area in Earthquake Zone IV
Design Earthquake Magnitude: 6.7 on Richter
scale
Peak Ground Acceleration: 0.24g
Cyclic Resistance Ratio (CRR) determined
from SPT & SCPT
Fine sands to 8 m depth at Boy’s Hostel is
susceptible to earthquake during the design
earthquake

30. Foundation System
Open foundations bearing on natural
soils - Not feasible
Pile foundations - high foundation
cost and time of construction – Not
preferred by client
Solution - Ground improvementGround improvement
by dynamic compactionby dynamic compaction

31. Dynamic Compaction
Dropping a heavy weight
can compact loose sands
to substantial depth
Done on a grid pattern
Next cycle: Weight
dropped at intermediate
points
Effective for sands only
with little fines

32. Conceptual Illustration

33. Crane & Pounder
Conventional Crane
– TLC 955A
11.65 T pounder
falling from height
of 14 m
Energy: 1600 kN-m
Corresponding
depth of
improvement: 9 m

34. Compaction – 2 phases
1 week time lag in
between – to allow
pore pressures to
dissipate
1st Phase
4 x 4 m grids
2nd Phase staggered 2 m
No. of drops: 10 at each
grid point
Depth of the craters
formed: 1.0-1.5 m approx

35. Ironing Phase
Craters filled with GSB
Grade II material
Hammer weight: 11.65 T
Height of fall: 6 m
No. of drops: 5
Energy: 2114 kN-m
Area graded with 10
passes of 10 T vibratory
roller

36. In-Situ Tests
Standard Penetration Tests (SPT) in
boreholes
Static Cone Penetration Test (SCPT)
Compare SPT and qCompare SPT and qcc valuesvalues
before and after compactionbefore and after compaction
Assess Liquefaction PotentialAssess Liquefaction Potential
after densificationafter densification

37. SPT & SCPT before & after improvement

38. Extent of Improvement Achieved
After compaction, N>16After compaction, N>16--20, qc > 520, qc > 5
MPaMPa
Peak improvement: between 1 and 5 m
depth
Improvement below 10-11 m depth is
marginal

39. Liquefaction susceptibility analysis
before and after compaction
Before CompactionBefore Compaction
-- Liquefaction to 12 m depthLiquefaction to 12 m depth
After CompactionAfter Compaction
-- No LiquefactionNo Liquefaction
Susceptibility to liquefaction successfully mitigatedSusceptibility to liquefaction successfully mitigated

40. Liquefaction Mitigation
Untreated ground (before compaction) is
susceptible to liquefaction to 13 m depth
After compaction, Factor of Safety againstFactor of Safety against
liquefaction > 1liquefaction > 1
Foundation for the Boys Hostel building
8.1K: Isolated column footings withIsolated column footings with
interinter--connecting plinth beamsconnecting plinth beams
Net allowable bearing pressure:Net allowable bearing pressure:
175175 kPakPa

41. Concluding Remarks
Conducting in-situ tests is essential to verify
effectiveness of ground improvement
For reliable and effective improvement,
sufficient tests should be performed before
and after improvement
The testing should ensure that the target soil
properties are achieved
Mitigating liquefaction
Densification of loose soils
Desired Bearing Capacity

42. Thank You!