Geotechnical Characterization of soft clays of the Godavari_Delta

1. IGCIGC--2011 Kochi2011 Kochi
Sanjay Gupta, Ravi Sundaram,
Sorabh Gupta
CENGRS GEOTECHNICA PVT. LTD.CENGRS GEOTECHNICA PVT. LTD.
Noida

2. IGCIGC--2011 Kochi2011 Kochi
Godavari Delta
Coastal Andhra Pradesh - East and
West Godavari Districts
Third largest delta in the country
Godavari and its distributaries form a
symmetrical delta
Geomorphology: Bay-Estuary Lagoon
complex

3. IGCIGC--2011 Kochi2011 Kochi
In the Godavari Delta
Soft clays met to substantial depth
High Moisture content – close to liquid
limit
Low Shear Strength
High Salinity
Shallow water table
Challenge to geotechnical engineer

4. IGCIGC--2011 Kochi2011 Kochi
Vicinity Map
Project Site

5. IGCIGC--2011 Kochi2011 Kochi
Site Location
PROJECT SITEPROJECT SITE

6. IGCIGC--2011 Kochi2011 Kochi
Onshore Gas Terminal
Low lying, close to sea-coast, has fish
ponds & marshy soils
Facilities Planned:
Captive Power Plant
Cooling Tower
Gas Dehydration Unit
Nitrogen Plant
Admn building & associated units

7. IGCIGC--2011 Kochi2011 Kochi
Geotechnical Investigations – 2
stages
Preliminary Investigation to evaluate soil
characteristics
24 boreholes, 16 SCPT, 4 ERT
Preloading by placing 4-4.5 m dredged
sand and installing PVD to 12 m depth
Second Stage investigation: 7-8 months
after installing PVD
47 BH, 18 SCPT, 3 CHST, 4 ERT

8. IGCIGC--2011 Kochi2011 Kochi
Layout Plan - Geotechnical
Investigation

9. IGCIGC--2011 Kochi2011 Kochi
Installation of PVD
PVD to 12 m depth; spacing: 1.5PVD to 12 m depth; spacing: 1.5--2 m2 m
PVD

10. IGCIGC--2011 Kochi2011 Kochi
Stratigraphy

11. IGCIGC--2011 Kochi2011 Kochi
Contours of Depth of Cemented
Sand Stratum

12. IGCIGC--2011 Kochi2011 Kochi
SPT & SCPT Profile
Improvement MarginalImprovement Marginal after 7after 7--8 months8 months –– May take more time??May take more time??

13. IGCIGC--2011 Kochi2011 Kochi
Design Profile

14. IGCIGC--2011 Kochi2011 Kochi
Engineering Properties
(Post Improvement)
Depth,Depth,
mm
Strata DescriptionStrata Description
SPT NSPT N--
valuesvalues
qqcc MPaMPa
qquuuu
KN/mKN/m22 φφ°°
00--44 Dredged Sand (Fill)Dredged Sand (Fill) 55--4040 22--1616 2828--3535
55--1010 Soft Silty ClaySoft Silty Clay 22--88 11--22 3030--6060
1010--1313
Silty SandSilty Sand
(discontinuous)(discontinuous)
55--2020 22--1515 2929--3434
1313--2525 Firm Silty ClayFirm Silty Clay 44--1212 11--33 4040--100100
2525--4444 Stiff Silty ClayStiff Silty Clay 1010--2828 6060--160160
4444--5555 Cemented SandCemented Sand 5050--100+100+ 3232--4040

15. IGCIGC--2011 Kochi2011 Kochi
Corrosivity
Low Electrical Resistivity – 0.5-2.1
ohm-m
High corrosion potential for buried
metallic pipelines / utility lines
Salinity: Chlorides > 20,000 ppm in
groundwater
Potential for corrosion of embedded
reinforcement steel in concrete

16. IGCIGC--2011 Kochi2011 Kochi
Dynamic Characteristics
CROSSHOLECROSSHOLE
SEISMIC TESTSEISMIC TEST
Test at 3 locations
1 source hole & 2
receiver holes

17. IGCIGC--2011 Kochi2011 Kochi
P & S Wave Velocities
Vs: 80-150 m /s
Vp: 1400-1800
m/s, wave vel
in water
So Vp
interpreted,
assuming μ

18. IGCIGC--2011 Kochi2011 Kochi
Dynamic Shear & Young’s modulus

19. IGCIGC--2011 Kochi2011 Kochi
Dynamic Parameters Cu, Cτ, Cψ, Cφ

20. IGCIGC--2011 Kochi2011 Kochi
Foundation System
Driven Precast Piles installed
350 mm square piles driven 1-1.5 m into
the underlying cemented sand met below
45 m depth
M-30 grade concrete with corrosion
resistant steel (CRS) – piles precast at site
End bearing mobilized in sand stratum
Negative Skin Friction considered in the
soft clay to about 25 m depth due to low
N-values and very low shear strength

21. IGCIGC--2011 Kochi2011 Kochi
Design Pile Capacities
Compression : 420 kN
Pullout : 210 kN
Factor of Safety : 2.5
Lateral : 34 kN
for 5 mm deflection of pile head

22. IGCIGC--2011 Kochi2011 Kochi
Pile Load Test
Vertical Load TestVertical Load Test Lateral Load TestLateral Load Test

23. IGCIGC--2011 Kochi2011 Kochi
Concluding Remarks
In the Godavari delta, soft clays in the
coastal belt extend to substantial depth,
underlain by cemented sand
Characterized by low electrical resistivity,
high salinity
The improvement 7-8 months after
installing PVD is marginal
Driven Precast Pile seated in the deep-
seated sand is a suitable foundation option

24. IGCIGC--2011 Kochi2011 Kochi
Thank You!Thank You!
CENGRS GEOTECHNICA PVT LTDCENGRS GEOTECHNICA PVT LTD