Hybrid Drain Geosynthetics for fine-grain soil improvements

1. Consolidation pressure (p=20,50,100,200,400 kPa) H Drain face PWP-3 PWP-2 PWP-1 u 150mm diameter Kanto loam slurry Drain layer Hybrid Drain Geosynthetics for fine-grain soil improvements ChandanGhosh Prof. & Head [Geohazards] National Inst. of Disaster Management Ministry of Home Affairs, Govt. of India

2. Large strain slurry consolidation • Do slurry behave similar to normal soil? • Do PWP in slurry different from normal Terzaghi soil? • Can internal PWP be measured? • Do k, Cv, Cc, mv are constant with consolidation pressure? • Permeability –direct and from Consolidation theory differ much?

3. Typical application/troubles!!様々な工法や問題 Important!!! Drain flow capacity

4. Load types Clogging…flow capacity changes under confinement Problem domain Local/problematic soils Time dep. Sett.? Drain/reinforcement

5. Geosynthetics as drain • Drain – clogging and efficiency in flow under pressure • In-plane and x-plane flow be measured? • Index properties of geosynthetics • International codal practice • Evaluation of clogging – from slurry stage • Drain efficiency – hybrid drain system

6. AIM of present research To assess nature of clogging and flow capacity of drains confined in fine-grained soil To recommend suitable drain system for field application

7. Research needs Use of synthetic materials for improving fine-grained soils Flow capacity of synthetic drains placed in-situ Assessment of clogging and its prevention Recommending design flow capacity of drains based on available hydraulic index test data

8. Nonwoven cover Woven fabric Geocomposite-A GC-A Nonwoven –A NW-A Nonwoven –B NW-B Nonwoven –C NW-C Geosyntheticsused

9. In-plane flow X-plane flow Grain size distribution

10. Geosynthetic clogged by Kanto loam Clogging mechanism

11. Consolidation of soil – ideal vs natural • Can we measure excess PWP directly? • Can excess PWP exceeds applied load increment? • What if load increment ratio varies from 0.5 to 3? • What if applied pressure is increased in steps or in one go - say from p=0 to 400kPa? • How Excess PWP varies with Hor with r? • How different is “k” – if measured in a large specimen?

12. AIM • what happens inside slurry when loaded upto 400kPa • How different are all parameters? • Drained water and settlement – how are they related? • To check soil bevaviour and looking into gap – theory and practice

13. Leh cloud burst - 2010 • Slurry formation • Mud slides • Prevention of mud slides • Measuring in-plane flow and drain efficiency using a large dia consolidation apparatus • Measuring internal PWP during test • Validation of consolidation theory

14. HIGHLY POPULATED COMMERCIAL AREA NEW BUS STAND SONAM NORBOO MEMORIAL HOSPITAL BSNL OFFICE

15. Cloud burst at Leh, 4-5 Aug 2010 Boundary Wall of DIHAR Broken by slurry

16. Apparatus developed Basis of developing experimental methods

17. Silty clay slurry Compacting sand base Setting PWP tips Geocomposite as boundary drain filter 220 mm 150mm (d) (a) (c) (b) Blinding of Geocomposite filter Silty clay Airpressure regulator (f) Silty clay sample Particle blinding PWP-3 PWP-1 PWP-2 Data logger (g) (e) Test procedure

18. Consolidation pressure Kanto loam slurry Soil slurry Drain pipe Drain layer Drain (120x50mm) Flow tests in drains placed within Kanto loam and silty clay during consolidation

19. 4mm thick 5.5mm thick 2.7mm thick 6.2mm thick Double layer drain and in-situ state Geocomposite-A GC-A Nonwoven –A NW-A Nonwoven –B NW-B Nonwoven –C NW-C Various in-plane flow tests carried at in-situ Test situation – double layer drain system

20. Toyoura sand Various drains tested in-situ during consolidation of slurry

21. Status of drains after test

22. Permeability factor – in-situ • Permeability factor = ‘k’-no clog drain/’k’- soil • Permeability factor >105, which is satisfactory • With increasing pressure this factor increases, which • is also a good indication

23. Consolidation pressure Kanto loam slurry Soil slurry Drain pipe Drain layer Drain (120x50mm) Flow tests in drains placed within Kanto loam and silty clay during consolidation

24. Average in-plane flow capacity平均水平流動量 • Flow in HYBRID drain is the highest • Without sand mat flow is the low, NWC drain is the lowest • Confining pressure causes 70 to 80% reduction in GC drain

25. Clogging of drains • How to evaluate clogging? • How to remove clogging of drains? – ultrasonic removal • Hybrid drains – combination of geotextile and sand mat

26. Nonwoven cover Kanto loam Silty clay Inner woven part Clogging of geocomposite

27. Large dia – 1D consolidation • Can PWP be measured directly? • Slurry and normal soil states – at 50 kPa • Variation of internal excess PWP – with height ? • Do excess PWP attains 100% immediately after applied pressure? • Direct and indirect permeability – are they same? • k, p, mv, Cc, Cv – are these constant with p? • Can we measure Drained water during consolidation?

28. Kanto loam slurry Drain layer Consolidation from slurry stage • Kanto loam – slurry (is there a relation between LL and slurry water content?) • Why p=50 kPa?- transition from slurry to Terzaghi soil

29. At p=400kPa (dia =150mm, H=57mm)

30. Kanto loam – local soil and silty clay - commercial

32. Excess pore water pressure ratio (u/del p) Vertical strain of slurry sample

33. t50 at p=400kPa

34. Is there a unique transitional stage at p=50kPa?

40. mv, Cv, k – are not constant

43. With more “p”, u/p reduces

44. Excess PWP (p=20 to 400kPa)

45. Consolidation pressure (p=50 kPa) H50 Drain face PWP-3 PWP-2 PWP-1 u 150mm diameter

46. PWP inside specimen

47. Consolidation pressure (p=50 kPa) H50 Drain face PWP-3 PWP-2 PWP-1 u 150mm diameter

48. Excess PWP is more than net increase in “p”