Sedimentation to Consolidation 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.

Outline Introduction Literature Review Sedimentation to consolidation Summary and future work

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

Motivation Fundamental Researches: 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.

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

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

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

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

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

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)

Sedimentation

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

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

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

Consolidation (1/2)

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

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

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

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

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.

Experimental Setup

Experiment Focus Kaolinite, 6180 at fresh water and salt water 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

Preliminary Results

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

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

Preliminary Results ABS Data Backscatter

Backscatter

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

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 Thank you! Please Comment

Thank You Please Comment

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

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

Experimental Setup

Preliminary Results