Tainan Hydraulics Laboratory, National Cheng Kung Univ. 1
Cohesive sediment dynamics under water waveSedimentation to Consolidation
Wen-Yang Hsu, Hwung-Hweng Hwung, Ray-Yeng Yang, Igor V. Shugan
Tainan Hydraulics Laboratory
National Cheng-Kung Univ.
Tainan, TAIWAN.
2009 Sediment Transport Symposium
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Outline
• Introduction
• Literature Review
• Sedimentation to consolidation
• Summary and future work
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Ch. 1
• Introduction
– Motivation
– Problem Identification
– Objectives
• Literature Review
• Sedimentation to consolidation
• Summary and future work
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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.
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Problem Identification (1/2)
CBS: concentrated benthic suspension2002, Fine sediment dynamics in the marine environment
Fluid mud
Consolidating bed
CBS
Dilute suspension
settling
depositionentrainment
entrainment
erosion
settling
deposition
erosion
liquefaction
hindered settling
consolidation
hindered settling
erosion
Concentration
FOLW
WAVEFlow velocity u (z,t)Concentration Φ (z,t)
Non-Newtonian Fluid
Newtonian Fluid
P SM
Fluid mud
Consolidating bed
CBS
Dilute suspension
settling
depositionentrainment
entrainment
erosion
settling
deposition
erosion
liquefaction
hindered settling
consolidation
hindered settling
erosion
Concentration
FOLW
WAVEFlow velocity u (z,t)Concentration Φ (z,t)
Non-Newtonian Fluid
Newtonian Fluid
P SM
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Problem Identification (2/2)
Flu
x
Concentration
gelcr
Gravitational settling
Hindered settling
Consolidation
Effect of permeability
Effect of effective stress
bed
Flu
x
Concentration
gelcr
Gravitational settling
Hindered settling
Consolidation
Effect of permeability
Effect of effective stress
bed
Dynamic response of fluid mud layer
Suspension
Settling Process
Stationary Suspension Consolidating
BedSettled Bed
RedispersionResuspension
Resuspension
Flow
Suspension
Settling Process
Stationary Suspension Consolidating
BedSettled Bed
RedispersionResuspension
Resuspension
Flow
Sedimentation to Consolidation
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Objectives
• Sedimentation– Settling function, transition region, dispersion
effects
• Consolidation– Effective stress, temporal variation of interface
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Ch. 2
• Introduction• Literature Review
– Properties of mud
– Sedimentation and consolidation
– Wave-mud interaction
• Sedimentation to consolidation• Summary and future work
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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
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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)
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Sedimentation
Propose a nonlinear relationship between settling velocity and concentration by using ADV approachMaa2007
Deals with settling of highly concentrated sediments by theory.Dankers2007
Using image system to measure floc size spectra and then calculate settling velocity.Manning2006
Using OBS sensors to measure net flux within a finite volume. And mass conservation is used to estimate settling velocity .
You2004
model the flocculation behavior and propose a new formula for hindered settlingWinterwerp2002
Using ADV to measure both the current and concentration. With advantage of not change ambient condition but rooms for improvement in data quality
Fugate etc.2002
LISST-100 laser particle sizerfor estimating floc size, density and settling velocityMikkelsen2001
The measurement results may also be different significantly because of the different sampling methodsEisma1997
Propose a conceptual model of floc size on the basis that flocculation is mostly determined by concentration and shear stress due to turbulence.
Dyer1989
Measurement of in-situ settling velocity by a tube. Observation of water-sand interfaceOwen1976
First theoretical analysis for sedimentation of highly concentrated suspensions. Settling velocity is determined by the local concentration only. Position of shock wave could be estimated.
Kynch1952
Subject and ApproachAtthorsYear
Propose a nonlinear relationship between settling velocity and concentration by using ADV approachMaa2007
Deals with settling of highly concentrated sediments by theory.Dankers2007
Using image system to measure floc size spectra and then calculate settling velocity.Manning2006
Using OBS sensors to measure net flux within a finite volume. And mass conservation is used to estimate settling velocity .
You2004
model the flocculation behavior and propose a new formula for hindered settlingWinterwerp2002
Using ADV to measure both the current and concentration. With advantage of not change ambient condition but rooms for improvement in data quality
Fugate etc.2002
LISST-100 laser particle sizerfor estimating floc size, density and settling velocityMikkelsen2001
The measurement results may also be different significantly because of the different sampling methodsEisma1997
Propose a conceptual model of floc size on the basis that flocculation is mostly determined by concentration and shear stress due to turbulence.
Dyer1989
Measurement of in-situ settling velocity by a tube. Observation of water-sand interfaceOwen1976
First theoretical analysis for sedimentation of highly concentrated suspensions. Settling velocity is determined by the local concentration only. Position of shock wave could be estimated.
Kynch1952
Subject and ApproachAtthorsYear
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Sedimentation (1/3)
• Kynch(1952):
• Assume that the settling velocity depends only on the local concentration.
• ws=ws0 f(C)
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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
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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
z
CDCw zs
z
CD w C
z
[ ( )]( ) zs
CDC w w C z
t z z
CwCw s
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Consolidation (1/2)
Compressibiblitof ultra-soft soilBo 2008
Experiment and modlefor conslolidationbedBartholomeeusen2003
It demonstrates the transition from a fluid-supported suspension to a soil, characterisedby a change from a state in which pore pressures are equal to the vertical total stress, to a state defined by the existence of effective stress, at which pore pressures are less than the total vertical stress
Sills1998
There is no sharp boundary between sedimentation and consolidation, instead there is a transition zone.Been and Sills1981
Self-weight consolidation: Pore water is driven out of the focsand out of the space between the focs. Terzaghi1943
Subject and MethodologyAtthorsYear
Compressibiblitof ultra-soft soilBo 2008
Experiment and modlefor conslolidationbedBartholomeeusen2003
It demonstrates the transition from a fluid-supported suspension to a soil, characterisedby a change from a state in which pore pressures are equal to the vertical total stress, to a state defined by the existence of effective stress, at which pore pressures are less than the total vertical stress
Sills1998
There is no sharp boundary between sedimentation and consolidation, instead there is a transition zone.Been and Sills1981
Self-weight consolidation: Pore water is driven out of the focsand out of the space between the focs. Terzaghi1943
Subject and MethodologyAtthorsYear
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Consolidation (2/2)
• Hight (1987):– Transition point between suspension and soil
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Ch. 3
• Introduction• Literature Review • Sedimentation to consolidation
– Bed material test
– Settling behavior
– Consolidation Process
• Dynamic response of fluid mud • Summary and future work
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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 analysisComposition analysis– By X-Ray analysis
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Preliminary Result
Particle size, um
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
Cum
ulative %
0
10
20
30
40
50
60
70
80
90
100
2116180
圖1.
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
0 4 8 12 16S hear ra te (S -1)
0
20
40
60
Sh
ea
r st
ress
(P
a)
Desity=1.45 g/cm 3
Desity=1.40 g/cm 3
Desity=1.30 g/cm 3
Desity=1.20 g/cm 3
Desity=1.05 g/cm 3
Slope: viscosityInflection point: yield stress
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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.
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Experimental Setup
OBS: Optical Backscatter Sensor
ADV: Acoustic Doppler Velocimeter
ABS: Acoustic Backscatter Sensor
3cm OBS1
10cm OBS3
18cm OBS4
34cm OBS6
42cm OBS7
ABS Surface,55cm
Bottom
26cm OBS5, 16Mhz ADV
6cm OBS2
50cm OBS8
Mixing pumps
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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
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Preliminary Results
0 2000 4000 6000 8000SSC (m g /L )
0
0.05
0.1
0.15
0.2
0.25
ws
(mm
/se
c)
Salt w ater
F resh W ater
You (2004)
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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
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Experimental Setup
• Initial SSC would start from 1000 mg/L~100000mg/L
1cm P1
5cm P2
15cm P4
ABS Surface,50cm
Bottom
10cm P3
20cm P5
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Preliminary Results
time (min)
dis
tance f
rom
head
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
10
20
30
40
50
60 0
200
400
600
800
1000
time (min)
dis
tance f
rom
head
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
10
20
30
40
50
60 0
200
400
600
800
1000
time (min)
dis
tance f
rom
head
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
10
20
30
40
50
60 0
200
400
600
800
1000
time (min)
dis
tance f
rom
head
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
10
20
30
40
50
60 0
200
400
600
800
1000
0.5 MHz
1.0 MHz
2.0 MHz
4.0 MHz
ABS Data Backscatter
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time (min)
dis
tance f
rom
head
50 100 150 200
20
40
60 0
500
1000
time (min)
dis
tance f
rom
head
50 100 150 200
20
40
60 0
500
1000
time (min)
dis
tance f
rom
head
50 100 150 200
20
40
60 0
500
1000
time (min)
dis
tance f
rom
head
50 100 150 200
20
40
60 0
500
1000
0.5 MHz
1.0 MHz
2.0 MHz
4.0 MHz
Backscatter
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-2 .5 -2 -1.5 -1 -0.5 0 0.5Pre ssu re
0
20
40
60
80
He
igh
t (cm
)
ss e s
ss
e
s
u u u
effective stress
total stress
u hydrostatic pore water pressure
u excess pore water pressure
u seepage water pressure
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Expected Results
• Sedimentation– Settling function, effect of salinity and shock wave
mechanism• Consolidation
– Consolidation function, response of effective stress
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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
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Thank YouPlease Comment
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Ch. 4
• Introduction
• Literature Review
• Sedimentation to consolidation
• Dynamic response of fluid mud
• Summary and future work
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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
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Experimental Setup
0.60m
0.3m
25mWave maker
porous structures
Wave gauges
Dalsa 1M 28 Camera
PIV SystemSpot lights
Image acquisition system
ABS Surface,30cm
Pressure OBSWater
Suspension
Fluid Mud
Consolidation Bed
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Preliminary Results
3 4 5 6 7 8 9kw
0
0.2
0.4
0.6
0.8
b/H
i
h 1=4cm d=1.05g/cm 3
h 1=8cm d=1.05g/cm 3
h 1=4cm d=1.20g/cm 3
h 1=8cm d=1.20g/cm 3