tainan hydraulics laboratory, national cheng kung univ. 1 cohesive sediment dynamics under water...

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


Outline

• Introduction

• Literature Review

• Sedimentation to consolidation

• Summary and future work


Ch. 1

• Introduction

– Motivation

– Problem Identification

– Objectives





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.


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


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


Objectives

• Sedimentation– Settling function, transition region, dispersion

effects

• Consolidation– Effective stress, temporal variation of interface


Ch. 2

• Introduction• Literature Review

– 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

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


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)– Settling column

• Milkkelsen(2001)– Laser In Situ Scattering and Transmissometry

• Fennesy(1994)– Measurement of size floc by taking picture in a

dilute suspension


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


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


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 analysisComposition analysis– By X-Ray analysis


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


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

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


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


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)


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

1cm P1

5cm P2

15cm P4

ABS Surface,50cm

Bottom

10cm P3

20cm P5


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


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


-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


Expected Results

• Sedimentation– Settling function, effect of salinity and shock wave

mechanism• Consolidation

– Consolidation function, response of effective stress


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


Thank YouPlease Comment


Ch. 4

• Introduction



• Dynamic response of fluid mud



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

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


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

tainan hydraulics laboratory, national cheng kung univ. 1 cohesive sediment dynamics under water...

Documents