Cohesive sediment dynamics under water wave Sedimentation to Consolidation

1. 2009 Sediment Transport Symposium Cohesive sediment dynamics under water wave Sedimentation to Consolidation Wen-Yang Hsu, Hwung-Hweng Hwung, Ray-Yeng Yang, Igor V. Shugan Tainan Hydraulics Laboratory National Cheng-Kung Univ. Tainan, TAIWAN.

2. Outline • Introduction • Literature Review • Sedimentation to consolidation • Summary and future work

3. Ch. 1 • Introduction • Motivation • Problem Identification • Objectives • Literature Review • Sedimentation to consolidation • Summary and future work

4. Motivation • Cohesive Sediment Dynamics in Marine Environment • Fundamental Researches: Wave-mud interaction, fine sediment transport • Engineering Problems: Coastal protection, land reclamation, dredging of deepwater navigational channels, water quality management and military application.

5. Problem Identification (1/2) 2002, Fine sediment dynamics in the marine environment CBS: concentrated benthic suspension

6. Problem Identification (2/2) Sedimentation to Consolidation Dynamic response of fluid mud layer

7. Objectives • Sedimentation • Settling function, transition region, dispersion effects • Consolidation • Effective stress, temporal variation of interface

8. Ch. 2 • Introduction • Literature Review • Properties of mud • Sedimentation and consolidation • Wave-mud interaction • Sedimentation to consolidation • Summary and future work

9. Properties of mud • Bio-physical-chemical Properties • Composition:clay, silt, water, organic and inorganic maters • Size:smaller than 63 μm ( clay <4 μm , silt <63μm) • Structure:fragile, non-spherical • Molecular Electrons:attractive force and repulsive force Brady, N.C. and R.R. Weil, 1999, The nature and properties of soil, Prentice-Hall,Upper Saddel River, NJ Kaolinite Illite, Chlorite

10. Behavior of mud • Plasticity: is the ability of a clay mass to undergo deformation before breaking. • Cohesion:is the ability of a material to stick or adhere together. • Flocculation:occurs when two particles collide and stick together and effected by three agents: • Brown Motion (Dyer, 1986) • Turbulent Shear (Hunt, 1986) • Differential Settling (Van Leussen, 1994)

11. Sedimentation

12. Sedimentation (1/3) • Kynch(1952): • Assume that the settling velocity depends only on the local concentration. • ws=ws0 f(C)

13. Sedimentation (2/3) • Owen (1976) • Settling column • Milkkelsen(2001) • Laser In Situ Scattering and Transmissometry • Fennesy(1994) • Measurement of size floc by taking picture in a dilute suspension

14. Sedimentation (3/3) • Fugate (2002) • Vertical 1-D equation of conservation of sediment mass in thewater column • Steady state at slack tides at a fixed point • Similarity of Fick’s law • Balance between gravitational settling and diffusive dispersion

15. Consolidation (1/2)

16. Consolidation (2/2) • Hight (1987): • Transition point between suspension and soil

17. Ch. 3 • Introduction • Literature Review • Sedimentation to consolidation • Bed material test • Settling behavior • Consolidation Process • Dynamic response of fluid mud • Summary and future work

18. Bed Material Test • Selection of sediments • Kaolinite, 6180, 211… • Size distribution and specific density • d50, dry density • Rheological property • Viscosity, yield stress,creep behavior • Composition analysis • By X-Ray analysis

19. Preliminary Result Clay(<4um): 28 % Silt(4~63um): 67 % Fine sand (125~250um): 5% D50=10.8um Clay components (<2um) Kaolinite (69%), Illite (30%) with a small fraction of SiO2 Slope: viscosity Inflection point: yield stress

20. Settling behavior • From gravitational settling to hindered settling • Discuss significant factors which would change the floc size, density, and then, settling velocity. • Establish settling function as a background information.

21. Experimental Setup

22. Experiment Focus • Different sediment and ambient water condition • Kaolinite, 6180 at fresh water and salt water • Range of concentration • 100mg/L~20000mg/L (intense data around transition region) • Diffusive dispersion effect and mechanisms of shock waves • The relations between diffusion and no-shock waves • ABS and ADV calibration for converting backscatter signal to SSC • Measurement of settling velocity • Tracing shock wave, mass conservation, ADV approach

23. Preliminary Results

24. From settling to consolidation process • Formation of lutocline, fluid mud and consolidating bed • Transition region between sedimentation and solid bottom will be major subject. • Time function, distribution of concentration and stress should be important background for mud motion

25. Experimental Setup • Initial SSC would start from 1000 mg/L~100000mg/L

26. ABS Data Backscatter Preliminary Results

27. Backscatter

29. Expected Results • Sedimentation • Settling function, effect of salinity and shock wave mechanism • Consolidation • Consolidation function, response of effective stress

30. Thank you! Please Comment Thank You! Please Comment Team: H.-H. Hwung (Principal Investigator) J. P.-Y. Maa I. V. Shugan R.-Y. Yang C.-M. Liu H.-C. Hsu Y. Chang W.-Y. Hsu H.-L. Wu

31. Thank You Please Comment

34. Ch. 4 • Introduction • Literature Review • Sedimentation to consolidation • Dynamic response of fluid mud • Summary and future work

35. Dynamic response of fluid mud • Energy transformation and energy dissipation due to wave-mud interaction • Dynamic response of pressure, concentration, velocity and rheology property in mud layer. • Occurrence of resonance

36. Experimental Setup

37. Preliminary Results