Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 1
UNIVERSIDAD DE GRAN CANARIADredging Technology
Ir. Bernard MalherbeProject Development DirectorJan De Nul Group
Hydraulic Dredging: horizontal transportPart 1: Transport of dredged mixtures
trough pipes (2009/2010)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 2
Why Dredging ?
Scope of Works of Dredging:
– Realize or Improve or Maintain Nautical Accessibility for Ships to Ports, Fairways,…: CapitalDredging and Maintenance Dredging
– Reclaim New Land for housing, industrial development– Coastal Protection: restaure beach & dune system, dykes,..– Seabed preparation for offshore infrastructures : pipelines, cables, GBS platforms, scour-protection,
windmill-farms,…– Morphological compensations linked to maritime works– Sanitation of contaminated sediments
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 3
Figure 1-4:Evolution of Maximum Size of Maritime Vessel
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
500000
1930 1940 1950 1960 1970 1980 1990 2000 2010
Year into Operation
DW
T C
arry
ing
Cap
acity
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Bulkcarriers DWT Container Carriers TEU
ECONOMY OF SCALE : EVER INCREASING SHIP’S SIZES
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 4
Annual Maintenance Dredging vs Anual Cargo Troughput
36.6 59.7Lisboa
Nant es St Nazaire
Bordeaux
Hamburg
Ant werp
Rot t erdam
Zeebrugge
Hai Phong
Bremen&Bremerhaf en
0
5
10
15
20
25
0 50 100 150 200 250 300 350
Cargo Troughput (Mt/year)
ANNUAL MAINTENANCE DREDGING CAN BE A SIGNIFICANT COST-ITEM IN THE OVERALL PORT’S
ECONOMIC BALANCE
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 5
Dredging & Reclamation: itDredging & Reclamation: it ’’s all about soil and dredgerss all about soil and dredgers
The CSD “JFJ De Nul”cutter dredger with worldstlargest cutter-power
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 6
Dredging equipment: Hydraulic dredgers: Trailing Suction Hopper Dredger (TSHD)
Cutter Suction Dredger (CSD)Mechanical dredgers: Backhoe Dredger (BHD)
BHDCSDTSHD
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 7
Evolution of Cutter Suction Dredging FleetEvolution of Cutter Suction Dredging Fleet
CSD ‘Leonardo da Vinci’
CSD ‘Ortelius’
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 8
Evolution of Trailing Suction Hopper Dredging FleetEvolution of Trailing Suction Hopper Dredging Fleet
'C s::
Evolution of Trailing Suction Hopper Dredgers: Jan De Nul Fleet
5oooo ,--------------------------------------------------------------------------,25o
~OOO+----------------------------j~~~~~~~3!~
40000+----------------------------------- ----------~"'---I-__+ 200
~ 35000+-------------------------------------~= E
M = S 30000+-------------------------------------------------------~~~----~--~=--+150! ~ O ~ ~ s:: g. 25000 "51 o ~ ~ e "~ 20000 100 § 5 E "¡¡¡
~ 15000 ~ a. ~
10000 --~~~"'-------------------------------------------------+50
5000 ~~~~;;~~~::::::~----------------------------------------------_J O+-------~------_.------_,--------._------,_------~------_,------_.--------,_------+O
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
I - Hopper Capacity 1m3) - Vessel Length LOA (m) - Maximum Dredging Depth 1m)
tq:pr ...... ', -, -~ ~,.".-... ~ ..... 1fM9I"II
s ... ""pipo:_
........ -........ --~. lWI ... l_....¡
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 9
Dredging Tools: mechanical rupture of cohesion of soil + hydraulic jetting & erosion-transport
3 methods
BucketCutterheadDraghead
BHDCSDTSHD
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 10
Soil-cutting tools
Cutterheads fitted with Pickpoints (left) or Cutter-Teeth (right)
Draghead fith with Trailer-Teeth
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 11
Transport of dredged material
Transport over sea : 3
Side castingBargeHopper
BHDCSDTSHD
Pipeline
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 12
Transport of dredged material
Transport over land : 3 methods
PipelineTrestlesDumptrucks
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 13
Hydraulisch Transport with pipelines offers many advantages:
• Continu process, fit for huge quantities & productivities: 20.000 to 100.000 m3/day
• Swift mobilisation & readyness• Limited maintenance• Limited Personnel
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 14
Dredging & Transport Distance: influence on Unit Price
Example of Unit Price of Dredging as a function of One-Way Distance
0
5
10
15
20
0 5 10 15 20 25One-Way Sailing Distance Dredging to Disposal (km)
Uni
t Pric
e E
uros
/m3
in-s
itu
Trailer Suction Hopper Dredger
Cutter Dredger w ith 2 boosters & pipeline
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 15
Principles of hydraulic transport of dredged material
• Disrupted soil or rock Disrupted soil or rock –– individual particles, heavy suspensions or fragments individual particles, heavy suspensions or fragments –– are mixed with are mixed with water to form a slurry (typical densities: 1,15 to 1 ,50)water to form a slurry (typical densities: 1,15 to 1 ,50)
•• MixtureMixture --forming happens in forming happens in dragheaddraghead or or cutterheadcutterhead and is then sucked into the suction pipe, via and is then sucked into the suction pipe, via hydraulic depressionhydraulic depression
•• Mixture velocity and turbulence (Re > 4.000) preven t the mixtuMixture velocity and turbulence (Re > 4.000) preven t the mixtu re from settling downre from settling down
•• After discharge, turbulence decreases and particles are allowedAfter discharge, turbulence decreases and particles are allowed to settle downto settle down
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 16
Drawbacks of hydraulic transport
• Limited transport-distances: 2 tot 10 km• Differential settling: siltpockets• Increase of suspension load of transport-water: visual impact of turbidity• Wear of pipes
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 17
Hydraulic transport: practical application in dredging
Shipborne pipeline systems
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 18
Working principles of a TSHD and a CSD
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 19
Hydraulic transport via shipborne & external pipeline systems
TSHD reclaiming
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 20
Hydraulic transport via shipborne & external pipeline systems
TSHD reclaiming
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 21
Hydraulic transport via external pipelines
Floating & Land pipeline
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 22
Hydraulic transport via floating/land pipelines
Cutter-dredging and direct upland reclamation
CSD Leonardo da Vinci in Port Hedland, australia
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 23
Hydraulic transport & reclamation
ReclamationArea: dredged mixture with high solids concentrations
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 24
Hydraulic transport & reclamation
Discharge of transport-water over a weir-system at the outlet of a sedimentation basin
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 25
Beach restaurationdirect settling & open-water discharge
(Sylt, Germany),
Hydraulic transport & reclamation
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 26
Hydraulic Transport: Hydraulic-production computations
• cost-estimates for tender-preparation
• dimensioning of dredge-pumps and shipborne pipe systems for the design
of dredgers
• Dimensioning of jet-devices and nozzles for fluidisation of soil prior to
suction
• Control of performance of dredge-pumps
• Development of simulators
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 27
Horizontal Transport = transport of a mixture of (sea)water and particles
Clays
Sands
Gravels
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 28
Dredging operation: disruption of aquatic soils (rocks, sediments, …) + transport + disposal
Dredgeable Rocks
Hard Limestones, Arenites, Basalts…..
Limestones, Sandstones, .Tertiary Claystones, Mudstones, …Quaternary Calcarenites, cap-rocks, Corals,……
Hard Rocks(UCS 30 – 60 MPa)
Intermediate Hard Rocks(UCS = 12,5 – 30 MPa)
Soft Rocks(UCS < 12,5 MPa)
In hydraulic dredging the maximum allowable grain-size diameter of dredged soil is determined by the spherical aperture of the dredge pumps.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 29
Products of Rock Dredging by Cutter Suction Dredger
Cap-Rock dredged by CSD (Persian Gulf)
Tertiary Claystones dredged by CSD “JFJ DE Nul”(UCS = 11 MPa)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 30
Products of Rock Dredging by Backhoe Dredger
Coral Reef-Flat (UCS = 10 -15 MPa)
Basalt boulders (UCS = 32 -72 MPa)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 31
Products of Rock Dredging by Trailing Suction Hopper Dredger : Ripping mode (only applicable for large TSHD with high installed power, e.g. > 30.000 kW)
Coral Reef-Flat (UCS = 10- 23 MPa)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 32
Rock testing: UCS test result Contract: # EPC 2-04-P902 Borehole: #DK-BH-08 Sample: # 2 Depth, (m) 0,7-0,8 Job:
81.2 71.9 Weight (g) 914.0081.3 72.5 Area (sq.m) 0.00412881.2 73.1 Temperature (С) 168.1 7.3 Volume, (cm^3) 335.351
48 2.73 Machine #: МС-50032.32 2.62 Date: 4.03.05.83.98 0.2 Technician: Timchenko L.
82.00 1.0003.99
0.00 0.00 0.00 0.0 0.00 0.000000 0.004128 0.0000.50 0.50 0.50 42.0 42.00 0.615511 0.004154 10.1111.00 1.00 1.00 92.0 92.00 1.231022 0.004180 22.0111.50 1.50 1.50 168.0 168.00 1.846533 0.004206 39.9442.00 2.00 2.00 225.0 225.00 2.462043 0.004232 53.161
UCS = 53.161 MPaUCS* = 51.318 MPa
E*= 2.150 GPa E = 1.788 GPa 0.000 22.011
UCS* =
E*=
E =
Interval of Stress, (MPa)
UCS - corrected for sample L/D
E - corrected for sample L/D
Initial linear elastic modulus
Standard Test Method for Elastik Moduli of Intact Rock Core Specimens is Uniaxial comhression. (ASTM D 3148-96)
Load Constant, (kN/dv)Basalt
Load (kN) Axial Strain є1, %Corrected area, A' (sq.m)
Applied Stress, UCS (MPa)
Average Height (сm) Average Diameter (cm)
Unit wet weight (g/cm^3)
Type of failure:
Moisture content (%) Sample Description:
Unit dry weight (g/cm^3)Rate (mm/min)
Deformation (mm)
Dry weight + Tare (g)
Diameter #1 (mm) Diameter #2 (mm) Diameter #3 (mm)
Height #2 (mm) Height #3 (mm)
Height #1 (mm)
Nearshore Chihacheva Bay
Average Deformation (mm)
Load (Rdg.)
Tare: # Tare weight (g) Wet weight + Tare (g)
Borehole # DK-BH-08 Sample #: 2 Depth: 0,7-0,8 m
Axial Strain є1, %
App
lied
Str
ess,
UC
S (
MP
a)
Results of Unconfined Compression Test
0.000
10.000
20.000
30.000
40.000
50.000
60.000
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 33
Basic Rock-Mechanical Characteristics for Rock-Dredging
Ductile Rocks
Brittle Rocks
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 34
Dredging of Rock: Blasting or Rock-Cutter-Dredging ? A matter of rock and cuttingpower.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 35
Mineralogy of Rocks: Calcirudite ( UCS = 13 MPa)
Calcirudite:
C : Calcite
D: Dolomite
A: Aragonite (Shell-fragments)
Q: Quartz
Polarizing Microscope Photograph
A
Q
D
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 36
Mineralogy of Rocks: Granite ( UCS = 95 MPa)
Macro-Cristalline Pink Granite(Magmatic Intrusive Rock):
Q : Quartz
Fp: Feldspars Plagioclase
Fk: Feldspars Orthoclase
M: Muscovite (Mica)
Z: Zircon
Polarizing Microscope Photograph
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 37
Rock Mechanics for Dredging: examples
40509060Rock-Quality DesignationRQD (%)
4050150100Rock-Strength DeviceRSD (MPa)
15 - 3060 - 8080 - 10050 - 90Shore Hardness
10 - 1505 - 10300150Abrasivity Index FPMs
591916Puncture Resistance Is50 (MPa)
40160220180Uniaxial CompressionStrength UCS (MPa)
SandstoneLimestonePorphyreBasaltParameter
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 38
Dredging operation: disruption of aquatic soils (sediments, rocks,…) + transport + disposal
Sediments: mainly 3 types
2 mm < d5063 µm < d50 < 2 mmd50 < 63 µm
Granular sediments: gravel,
boulders ,…Granular sediments: SandCohesive sediments: Clay &
Silts
In hydraulic dredging the maximum allowable grain-size diameter of dredged soil is determined by the spherical aperture of the dredge pumps.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 39
Geotechnical characteristics of some common sediments
15
20
85
97
97
SandContent > 0,063mm(%)
882.161.861626Well-graded sand
2.322.12920Glacial till
1.27
2.09
1,89
Volume-massSat (tds/m3)
0.4319584Mud (silt-clay)
65 - 851,501934Uniform densesand
< 351,433246Uniform loosesand
Relative DensityDr (%)
Volume-massDry (tds/m3)
Water Contentw (%)
Porosityn (%)
Sediment Type
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 40
Geotechnical properties of soils in the horizontal transport process of mixtures
Cobbles, boulders, gravels,…
• Main in-situ geotechnical properties (before dredging)– Grain-size distribution, including d50 (median particle-size),
dmf (determining particle-size = (d10+ d20+…d90)/9), sorting degree,…
– Angularity and grain-form– Angle of Internal Friction,– Specific volume-mass,ρs of individual particles
• Quartzite: 2,660 kg/m3• Basalt : 2,900 kg/m3• Claystone :2,300 kg/m3
• Main mixture properties (during transport)
– Grain-size distribution
– Angularity, abrasivity,..
– Specifiv volume-mass
�Critical velocity
� Wear
� Equilibrium slope
� Settling velocity
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 41
Grain-Size distribution of dredged gravel
63mm
.r:f¡: me
~ "'" ~ 90
~
~ "" ~ 70
•
e 100.000
r--.
m "\ \ '\
\ \ , '"
, m ,
I.~ ~
t-.. "-
l' "<; m "-
, l' mm
-........ .:bj 3 m
"'00 0,2 10 mm 0.100 0.010
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 42
Granular sediments: gravels and sands
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 43
Basic Geotechnics of granular sediments and soils: sands. Dredging is a rapid deformation-process ( xx m/sec) versus the evacuation velocity of excess pore-water pressure ( < 10 – 3 m/sec)>> Undrained Conditions
Relative Density (%) >> Degree of Compaction of granular soil
ρd - ρdmin
Dr = ------------------------- x 100 (%) and Drcrit (Casagrande) : no volume-changeρdmax – ρdmin Dr > Drcrit >> Dilatancy
Dr < Drcrit >> ContractancyWith: Dr < 25 % : very loosely packed
Dr : 50 – 75 %: densely packedρdmax: determined by Modified Proctor Test
Cohesion, c (kPa)– Fine sand (d50 = 0,200 mm) : c = 4 kPa– Very coarse sand (d50 = 0,900 mm): c = 0,8 kPa
Angle of Internal Friction, φ (degrees)– Angular sand-grains (river sand) : φ= 38°– Spherical sand-grains (eolian sand) : φ= 25°
Permeability Coefficient, k (m/sec)– Fine sand : k = 10 – 5 m/sec– Very coarse sand : k = 10 -3 m/sec
Shell-fragment content
Critical erosion velocity (at large flow velocities (> 3 m/sec)At low flow velocities : cfr ShieldsAt high flow velocities: cfr van Rhee
(Drawings after Lübling, 2004)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 44
Grain-size distributions of dredged materials in Western Scheldt
Grain-size distribution of Western Scheldt estuary sediments
100.00
90.00
80.00
l. ¡¡p . -- -•
ti + BAl
F. Fredefik - " - " -" " -1- --" -• ... " , - . "
... 70.00 1- - , • ....
IJI Kallosluis - /. ,
f 60.00
• ., 50.00 E
t - - , Hanswe ert --- - ,
, U
• , , ~ 40.00 ---~ -
• L
• 30.00
Walsoorden t r ' - -- <-
20.00 1, .-1
10.00 • • :.:.; l '
0.00 , . -"
10 1
850 71 0 500 355 250 180 125 00 63 ,
.... :_-_._- ,_ :_--_\
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 45
Basic Geotechnics : Mohr’s Circle describing the stress conditions in soils
Total Stress :
ՇՇՇՇ = = = = σσσσnnnn . Tan . Tan . Tan . Tan φφφφ + C+ C+ C+ C
Effective Stress ::::
ՇՇՇՇ’ = (σn- u) . Tan φ’ + CՇՇՇՇ = (Undrained) Shear-Strengthσn = total Normal Stressu = pore-water pressureφ = angle of Internal FrictionC = cohesion
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 46
Basic Geotechnics : Mohr’s Circle describing the stress conditions in soils
Granular Soils: sands• low C & ՇՇՇՇ = increasing withdepth
• high φ
Cohesive Soils: clays
• high C & ՇՇՇՇ =~=~=~=~ C
• low φ
σn
ՇՇՇՇ
c
φ
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 47
Basic geotechnics: vertical and horizontal stresses
Active & Passive Horizontal Soil Pressure cfr Rankine:In dredging, overburden normal stressesare (generally) low:
• >> low horizontal soil pressure…and equilibrium inflow slope , θ, is generallyclose to φ ρs
2
tg θ = tg φ x -----------------------------
( ρs2 + ρw. (ρs- ρd) )
• angle (π /4 +/- φ’/2) is determining the optimal cutting angle
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 48
Erosion-sensitivity of sand at large flow velocities (cfr Bischop et al, 2009)
.. oS ~ e O .¡;; e w
0,100
0,010
0,001
0,000 0,0
Experimental d.lta VS. modal calculations
-,
, ,
, .,: , , • , , ~ •• , , • ,
~' ./ .&
/' ' ./ ~~
/ /.1 'r" •
, • I
•
0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4 ,5
Flow velocity [mIs]
Fig, 9: Erosion rates for Zwin'94-experiment
• 45 degrees side slope angle
• 60 degrees side slope angle
• 70 degrees side slope angle --van Rijn 185 mu --van Rijn 315 mu
- van Rhee-simplified 185 um - van Rhee-simplffied 315 um
¡
1 g
5,0
= .'
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 49
Cohesive Soils in hydraulic transport : Clays, Silts, Muds,…
Undrained Shear-Strength, cu (kPa)
Liquidity Index (non-dimension)
Yield Stress, Շy (Pa)
Dynamic Viscosity, η (Pasec)
Thixotropy (Pasec or Watt)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 50
Determining for Cohesive soils:
• water-content (w) and Atterberg limits(SL, PL, LL)
• Plasticity-Index : PI = LL – PL
(PI = high >Clay; PI = low > Silt)
• Liquidity Index: LI = (w-PL)/(LL-PL)
• Activityt : A = PI / (% < 0,075mm)
(A < 0,75 Inactive; A 0,75-1,25: Normal; A > 1,25: Active)
• Shear-strength and Cohesion
• Stress-Strain behaviour
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 51
Cohesive sediments dredged and lagooned
After filling at ρsat = 1,32 t/m3 After 1 month: consolidation & dessication
ρsat = 1,60 t/m3
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 52
Cohesive Soils in hydraulic transport : indicative values
-0,95
0
2,5
LiquidityIndexIn-SituLI si
-0,580500Montmorillonite(swelling clay)
450100Illite (most common clay)
12,53050Kaolinite(weathering of granite)
LiquidityIndex As slurryLI m
wP(Casagrande’s
PlasticityLimit)
wL(Casagrande’s
Flow Limit)
Type of clay
> 150Hard
75 - 150Stiff
40 - 75Firm
< 40Soft
Undrained ShearStrength , cu
(kPa)
Description
In cohesive sediments, the φ is very low, not to say sometimes
close to 0. This means that shear-strengths of cohesive sediments
are determined by c, the cohesion(which is intrinsic at σn =0. But c is observed to increase slightly
with depth in loose cohesivemuds due to consolidation
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 53
Cohesive soils & sediments: Undrained Shear Strength and Liquidity Index
" u
.., 1.0
Q.II
O'.e
Q1
" ~.4 • v S 00.5 .. ~ 0 .4 ... :i o_~ ..J
O'.L
0.1
()
-Q,I
-o ~
LL
.L
A,~ jrjclql soj l M'1<1 ... U
-~' ~~-t-±-t~t-------~----~--~~~~~~~------~~--~~-.~~~~~~~------~~--~~~~~ '" . , , I'.i .1 /(11 ... 1, 2;J. '" !5 fI 1 S, !II j(J 2(I, !O 4 0!iOo I!O JO l1O;)tOCJ 2: 001 !OC 400 i!O:O
U~drQII\.~ S~.Of· Slf'. n ~t~ é u • ~ Pa
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 54
Frictional Behaviour of Fluids in Flow
• Water and individual particles: slurry transport– Reynold’s Number– Determining parameters:
• dynamic viscosity of transport fluid (termperature, salinity,…)• Volumetric mass of fluid (kg / m3 or kgds/m3)• Particle dimensions determining Critical speed and Slip-Factor• Velocity, vs Critical Speed
• Viscuous flow of cohesive particles: Non-NewtonianBingham fluids– Hedström Number & Reynold’s Number– Determining parameters:
• Dynamic viscosity of suspension (temperature, salinity, volumetric mass, sand-content)
• Initial rigidity Շy (or Yield Stress Շo)• Thixotropy
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 55
Stress-Strain behaviour of Newtonian and Non-Newtonian Fluids
Newtonian : Water
Bingham Plastic:
Pseudoplastic:
Dilatant:
Cohesive sediment suspensions,sludge, paint, blood, ketchup
latex, paper pulp,.
quicksand
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 56
Rheology of cohesive-sediment suspensions: initial rigidity, dynamicviscosity and thixotropy (after Malherbe, 1987)
Shear Stress
(Poi
A.INDIRECT MEASU
't; INITIAL "'GtDrn
RESS • STRAIN ANALYSIS
Sheor Rote I.el: ... , •
Shear
(Po)
8 .DIRECT MEASUREMENT
't", IN "'Al IIGtDlTV
STRESS • nME RELATION AT CONSTANT LOW
'SHEAR RATE (VAN E-TEST)
FIGURE 5 Typical rheograms of mud Zeebrugge) together with the defillition rigidity and dynamic viscosity.
Time' mini
(harbour of of initial
'1..-----
40
INtTtAL A.GIDITV U-., DVNAMtC VtBCaStTV (P ••• c' VDLUME MAsa OF .EDIMENT'~/m3J CDNCENTRATIDN CKg/m3, Mue CONTENT ,,, e 63 micron' "O·C
, , , , , I I , . , '
30 .. • ... ,,: , , " . , J " ,
J •• ,&16 :,: , 1 , ", , , I • 7D.B" , , I "", , I ',J; l' , l. .,
20 ./ 1 1:: i! I I l ' 1 142,D"
1 I I l' " • 1~D" 1 I , .... &" 1, I
, 1 ,.J:'" I , I I I 4~" , I 1 I 11 J' I
, I ,'7,; 1
, I " I '1 " , , ", le' , 10 I , ")" " ,
, ' J, I " 3&.D" 1 " / I I l' I I , I l· .aptJ/
100" I I l ' I , I
:~~i~':L ~~~~;i;~~~~;;~~¿:}~t~.4-~,~;¡;¡ _____ "'-1-4 ------ - --- -_. o , ~Yr- ~;;lj:;j.~~~! :
O .-..... : ...... ~:~*--'-f:.~. 1I :: :
o 100 100 400 lOO 700
1.150
Ts gIl
1.400 ~slt
FIGURE 6 : Results of rheologic investigations on mud out of the harbour of Zeebrugge. Relation between the initial rigidity, the density and tlle sand-content of the mudo The figure illustrates a1so the "rheologic behaviour transition", R.T.
17
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 57
Rheology will determine erosion-sensitivity (expressed as u*crit) for cohesive sediments (B Malherbe PhD thesis)
" .. ". x 16 2
" 7r
,t .p
.. ,a So"'. .. _,-...-"_", von _' _ _ _ _
"un"nt "homln¡
,.
.. ~ gOlv" n
I-/"~ • l4: O
O ,
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 58
Rheology determines the equilibrium inflow slope of cohesive sediments
Equilibrium Inflow Slopes of Cohesive Sediments (Mud Zeebrugge) as a function of Yield Stress or Initial Rigidity
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
Initial Rigidity Ty (Pa)
Slo
pe F
acto
r (m
)
Equilibrium Slope Under Water Equilibrium Slope Above Water
1
m
θ
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 59
Rheology determines the Flow behaviourof Non-Newtonian Bingham Fluids in pipes
Bingham fluids exhibit Newtonian behavior after the shear stress exceeds ՇՇՇՇo or ՇՇՇՇyyyy. In the central region a “plug” of unsheared fluid or suspension occurs.
(ref University of Texas, Austin).
Unsheared plug Core
Sheared Annulus
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 60
Flow behaviour of Non-Newtonian Bingham Fluids
Unsheared Core
crr ≤ ( )20
2 cc
cz rRr
uu −==∞µ
τ
crr > ( )
−
+−=∞
012
ττµ R
rrRu rz
z
Sheared Annular Region
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 61
Frictional losses of fluids in pipelines: affinities with Friction Cfct & Volume-Mass
Applies to any type of fluid – Newtonian, Pseudo-Plastic, Bingham, Dilatant,…- under any flow conditions
2..
2V
D
Lpf ρλ=∆
General equation describing frictional head losses of fluids/suspensions in pipes
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 62
Laminar Bingham Fluid Flow: determination of friction factor
( )
−+= 73
4
Re..3Re.61.
Re
16
BPBPBP
HeHe
λλ
20
2 ..
∞
=µ
τρDHe
∞
=µρ VD
BP
..Re
Hedström Number
(Non-linear)
Reynolds Number
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 63
Turbulent Bingham Fluid Flow: determination of friction factor
( )He .146.01.378,1
Re10
.109.2
193.0
5−−
−
+−=
=x
BPa
ea
λλ
λ
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 64
Hydraulic Transport: physics of the system
1. Pipeline characteristic (Discharge (Q)/Head (H) relationship)- homogeneous fluid in straight pipe- Soil-water mixtures in straight pipes- special head-losses: bends, narrowings,…- vertical and inclined pipes
2. Pump-characteristic (Discharge (Q)/ Head (H) relationship)
- Pumptypes
- Characteristic for homogeneous fluids
- Characteristic for soil-water mixtures
3. Driving system
- Modification of pump-characteristic
- for diesel-elec, direct diesel,… driving
4. Working area of whole system: driving system, pump, pipeline and mixture
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 65
Hydraulic Transport: the Pump – Drive – Pipeline FitDescription via Q – H relationships
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 66
Hydraulic Transport: Pipeline Hydraulic Characteristic
Basic Assumptions:• Horizontal cylindric pipeline: no bends, valves,…• Homogeneous incompressible fluid: perfect suspension, no
segregation, no gases,…• Newtonian fluid: (almost) linear realationship between shear stress
and strain• Uniform flow: no velocity profiles between wall and center-line• Constant flow velocity
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 67
Hydraulisch Transport: Pipeline characteristic
• Law of mass-conservation:
• Law of momentum-conservation:
outoutinin AVmAVm .... ρρ =
∆p/L = 4.ՇՇՇՇ0 / D (Navier-Stokes) ∆p f = ( α.ρ. v2/2 + λ.L/D. ρ.v²/2 + ξ .ρ.v2/2) (Darcy-Weisbach)with λλλλ=f (Re, He, k/D) ( head-loss coefficient due to friction: see previous slides)
foutin ppp ∆+=
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 68
Hydraulic Transport: Pipeline characteristic
• Law of energy-conservation: Law of Bernouilli
Cstghvp =++ ρρ 2
2
1
Pressure Energy
Kinetic Energy
Potential Energy
This physical law expresses the whole process: the pump-d rive plant adds energyto the mixture by increasing velocity: this Kinetic Energy is then oscillatingconstantly within the system between Kinetic Energy (mixture velocity), Pressureenergy (pressure) and Potential energy (elevation). Velocity, pressure and elevation are thus the main parameters of the dredging process .
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 69
Hydraulic Transport: Pipeline characteristic
Integration of the 3 physical Laws yields:
Applied to:
• Succession of pipes with various diameters:
• Special losses with dedicated ξ coefficient for bends, valves, etc..:
outoutinin ghvD
Lvpghvp ρρλρρρ +++=++ 222
2
1.
2
1
2
1
222
12
2
1.
2
1
2
1ghv
D
Lvpghvp iioutoutinin ρρλρρρ +++=++ ∑
22222
12
2
1
2
1...
2
1.
2
1
2
1ghvv
D
Lvvpghvp iiiioutoutinin ρρξρλραρρρ +++++=++ ∑∑
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 70
Hydraulic Transport: pipeline characteristic
22222
12
2
1
2
1...
2
1.
2
1
2
1ghvv
D
Lvvpghvp iiiioutoutinin ρρξρλραρρρ +++++=++ ∑∑
In the dredging process the geometry/elevation of the pipeline is generallyfixed and known, i.e. not variable during the process. Kinetic Energy and Pressure Energy are the components that can be controlled. They can betransformed into pressure, by dividing the terms by ρ.g.
dynamic pressure and the static pressure (manometric head)
These terms together express the HeadLosses, ∆H, due to friction in the pipelineand in special pipe-components: note the same character as a dynamic pressure!
Entry-losses Straight pipe friction-losses
Bend, valve,..friction-losses
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 71
Special resistances for specific pipeline components:
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 72
Hydraulic Transport: Pressure Equations
outiiioutoutinin ghvvD
Lvvpghvp ρρξρλραρρρ +++++=++ ∑∑ 2222
12
2
1
2
1...
2
1.
2
1
2
1
Entry-losses
Straight pipe friction-losses
Bend, valve,..friction-losses
Pressure Line:
))./(().(....2
1.
2
1...
2
1..
2
1).(. 2222
mwswmwimimiimmpumpzmzvac vLiSktgvvD
Lvvhhgghp ρρρρρρξρλραρρρ −−−−−−−−−= ∑∑
Suction Line:
Special losses for non-cohesive particles (cfr
Führböter)
Führböter
0
0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2 2.5 3
dmf [mm]
Skt
[-]
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 73
Hydraulic Transport: Graphical representation of pipeline-characteristic
- Relationship is of the following kind : caQH += ²
aQ² = Head Lossesdue to friction
c = geometric elevation head
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 74
Suction characteristic for a horizontal pipeline
p0pin
pz
pp
p0 = patm
p in = patm – (1 + αααα)0.5 ρρρρm v²
Pz = patm – (1 + αααα + λλλλ L/D)0.5 ρρρρm v²
Pp = patm – (1 + αααα + λλλλ L/D)0.5 ρρρρm v² + ∆∆∆∆p
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 75
Suction characteristic for a dredge pipeline in operation:
p0 pin
pz
pp
p0 = patm + ρρρρw g h z
p in = patm + ρρρρw g h z – (1 + αααα)0.5 ρρρρm v²
patm
hz
hp
pz = patm + ρρρρw g h z – ρρρρm g (hz-hp) - (1 + αααα + ξ + λλλλ Li/D). 0.5. ρρρρm .v² - ρw.g.Skt.Li.(ρ m-ρw)/((ρs-ρw).v)
pp = patm + ρρρρw g hz – ρρρρm g (hz-hp) – (1 + αααα + ξ + λλλλ Li/D)0.5 ρρρρm v² - ρw.g.Skt.Li.(ρ m-ρw)/((ρs-ρw).v) + ∆p
Li
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 76
Hydraulic Transport: Forces on particles in water
Forces exterted on particle:
1. Gravitational force
2. Buoyancy force (Archimedes)
3. Flow-resistance forces• Wall-friction• Drag-resistance
gVF ssg ρ=
gVF swB ρ=
stwDD AvCF ²2
1 ρ=
FB
Fg
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 77
Hydraulic Transport: Forces on particles in water
4. Lift-forces due to velocity gradients, particle geometry,….
stwLL AvCF ²2
1 ρ=
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 78
Hydraulic Transport: free-fall velocity of particles in water
1 í
0.001
•
• • • •
0.01
o
o ,-" ,-" • , , , ,-r' o . -¡.~ · l· • nff : "-""
Specific Sand & Grave' Fal. Velod!)' in slill Water (18'1::) CIr Jan De Hui Group
, o o-o-, o
o o ..
0.1 1 10
o o o
o o o
'o. o o
o , •
o o
.¡ ••• ~ . .¡ L •••••• '
"
. _ ..... __ . .. _ ... __ . • o
o jo.,.. jo •
, o , , , ,
o .+.-o o o
'0 .
o o
, , , ,
-, o .
o , . .•... ~.~ ..... .
«
• o o . . • . . . • • . . . . . . • o o , , , ,
~, o
" ••
o
o ,~
.
"
o o o ; o o
' .' + .¡ ' .'¡ .'
_ .. __ .-• •• + ••• ,"
. . . • • . •
o ,
•
, ' o
" "
o.,
0.01
0.001
0.0001
0.00001
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 79
Practical application: dumping of particles trough a vertical pipe
Non-visquous fluids: only local water-displacement around the particle compensatesfor the volumetric passage of the particle. The total Head remains constant
Visquous fluids : the particle drags an added mass of water during its fall and the upward compensating current gets resistance from the wall of the pipeand the stone. The water-head decreases in the pipe.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 80
............ '_ ........ ""...., .. J." Oo ..... DP cr. .. , ( __ ).
' .700 m
2.<00 ....
' .000"",
~ ,," ..... O H., ..... . OOmm -_....-. .... ....". .... ..,.,.. . .,..-m. ... ."..., __ ..~-'" -_." ............ ......-. ( ... _...,~,..., """'_
'0. '" m (_"""''''1 ,_ . .,..,.,_ ........
I""",,J ... . 0 .... . -- '"
, " , .• ,-"" " .2 m
' .' m (:'0.000 ""'J "-" m (''''00 _ 1
,",ro m'
,".' '''-h . "'" _N ., ..... ,. ro~
=
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 81
Hydraulic Transport: Application in Deep Sea Mining
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 82
Hydraulic Transport: Application in rock-dumping
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 83
Hydraulic Transport: Application in rock-transport, ballasting of GBS
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 84
Hydraulic Transport: Particles in flowing water inside a dredge pipe
During the hydraulic transport-process of a dredger:- the dredge-pump & drive plant, adds energy to the fluid by increasing
its Kinetic Energy, which is soon transformed into a combination of Kinetic energy (fluid velocity) and into Potential energy (pressure)
- By increasing the velocity, the turbulence within the fluid will increase, hence facilitating the keeping of particles in suspension
- Energy will not really be transmitted to the sand-particles, but- Particles are kept into suspension by turbulences and
(omnidirectional) turbulent forces- They will be dragged by dragforces (actual friction resistance)
caused by the moving fluid- The velocity of sand-particles is lower than the one of the moving
fluid: this phenomenon is called “slip” and depends upon the sizeof the particles, the concentration of solids inside the suspension, the viscosity, etc…
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 85
Hydraulic Transport: Hydraulic regimes of particles in flowing water
Mainly, 4 flow-regimes:
Stationary bed Sliding bed with Homogeneouspartial suspension suspension
Governing factors- Increasing velocity: more drag, more turbulence- Increasing viscosity (increasing concentration): more drag- Decreasing grain-size: smaller fall velocity- Decreasing pipe-diameter: higher velocity
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 86
Hydraulic Transport: Hydraulic regimes of particles in flowing water
Particular Case: Plug flow occurring mainly with cohesive sediments(mud-type) with high concentrations , viscosities and/or yieldstress
Plug
Sheared Annulus
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 87
Hydraulic Transport: Phenomenon and physics of Slip
Slip-velocity is dependent upon hydraulic regime
- Particle in suspension:
- Particle in sliding bed:
- Particle in vertical flow:
Factors governing slip:• Contact-surface between particle and fluid• Specific density of particles wrt fluid• Grain-size diameter
slîpws vvv −=
0≈slipv
wslip vv <<0
0≈slipv
0.4-0.65Boulders
0.65-0.85Gravel
0.7-0.9Coarse Sand
0.8-1Fine Sand
0,9 - 1Silt and Clay
Slipfactor ƒsSediment/soil
m
sS v
v=∫
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 88
Hydraulic Transport: Effect of Inclination of dredge-pipe on Slip
Inclined pipe: large Slip-factor
Vertical pipe: small Slip-factor
Horizontal pipe:
Intermediate Slip-factor, see prev tabe
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 89
Volume-Mass and Density: Concepts and Definitions
Volume-massρρρρ is the mass of a soil (kg) per volume-unit (m3). The unit of volume-mass is kg/m3.
The mass of a saturated soil is determined by:• The solid constituents - grains, rock-fragments, shells, organic
matter…- and their specific volume-mass• The liquid or gaseous constituents in the voids between the solids• The proportion (%) of these 3 different phase-constituents in 1 m3,
determined by void-ratio, compaction-degree,… and the gas-content in the fluid
Density is the volume-mass of a soil referred to the referencevolume-mass (fresh water at ρρρρ w = 1.000 kg/m3). Density is hence dimensionless.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 90
Facts and Figures about volume-mass
• Dry solid volume mass• Void-content n = volume of voids / total volume
typically is n = 40 – 60% for granular soils
• Specific volume-mass of solids: Quartz, Feldspars, Carbonate
• Typical values for sand are 1.100 – 1.500 kgds/m³
• Volume-mass of (water) saturated mixture
Typical values for sand are 1.800 – 2.000 kg/m³(variable according to shell-content, grain-size distribution, grain-shape, compaction-characteristics,..)
³/7.265.2 mts −=ρ
sairsd nnn ρρρρ )1()1( −≅+−=
wssat nn ρρρ +−= )1(
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 91
Volume-mass and sediment-soil properties
Volume-mass of a sediment or soil expresses the packing of grains and will determine:
• Cohesion and shear- resistance• Relative compaction degree (granular soils)• Degree of consolidation (cohesive soil)• Void ratio
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 92
The first most important geotechnical equation in Dredging
:
R.~onsh ip between Dry Vo l ....... -mólss;md S;nurMed VoIurne-m;ass
~OO T"----------------------------------------------------' Pd = (P,a' - P ... ) x _p, __
( p, - P .. )
P .. - 10!5 q,'m.l (,u'In' .... id. Sal _ jO ' . ' " Y._ - " "CJ
p , _ , . , ' ,-oIu ......... -.; h. of • • e'"',.,'--__ -1
" ,..., ~ • >
j ,...,
'.00 +-----__ ------,_----__ ------,_----__ ------__ ----__ ------__ -----' • ..., . 00 1200 ,..., ,..., ,"'o
Dry VoIUITMI Mus (kg dsIm3)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 93
The second most important geotechnical equation in Dredging: the mechanisms of dilution and concentration
Principle of Continuity of solids = during the whole process of dredging – between in-situ, via dredged mixture to discharge and ultimately consolidation/compaction – the mass of solidsdoes not change. The only changes occurring are related tothe proportion of water & gases vs. solids.
Two exceptions:• During overflow: overflow losses induce the loss of fines to the
natural system. • During disposal: fines are dispersed (aquatic disposal) or
evacuated as fines over the weir
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 94
Continuity of mass of dry solids (cont)
M dsx = mass of dry soils/mixture-solids in stage xV = bulk volume of soil/mixtureρd = (ρsat – ρw) x _ρs___
( ρs – ρw)• ρw = 1025 kg/m3 (seawater with Sal = 30 0/00 and Temp = 15°C)• ρs = 2650 kg/m3 (specific volume-weight of Quartz)
M ds 1 . V1 = M ds 2 . V2 >> (ρρρρsat 1 –ρρρρw). V1 = (ρρρρsat 2 –ρρρρw) . V2
V1 (ρρρρsat2 –ρρρρw)
V2 (ρρρρsat1 –ρρρρw).Cf =
This simple formula transforms any soil-volume in any other volume, just on the basis of the bulk saturated volume-mass.
Cf is often called the ‘Concentration Factor’.
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 95
Dredging Volumes Control: what is measured ? And where ?
Production control can only rely on (online) measurements !!.
Bathy Survey
Vdel = Vin-situ in- Vin-situ out
In-situ (post dredging)
Topo survey
Vdel
Geotechnical survey
ρdel
On disposal
In hopper
Vdel
Suction & discharge tubes
Suction tube
V mixture
Suction tube
ρmixture
Onboard dredger
Bathy Survey
V in-situ in
Geotechnical surveyρin-situ
In-situ (pre-dredging)
Volume(m3)
PressureHeads(kPa)
Velocity(m/sec)
Volume-mass(kg/m3)
Site
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 96
Hydraulic Dredging Volumes during Transport: Notions of Apparent Concentration and Delivered concentration
Mwater
Msolids
In-SituρisVsi
MixtureρmVm
Dilution (bulking) Discharge (delivery)
Consolidation
DischargeρdelVdel
ConsolidatedρconVcon
Apparent Concentration Ca
Ca = Vm (also referred to as Cvi)
Vsi
Delivered Concentration Cdel
Cdel = Vdel (also referred to as Cvd)
Vsi
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 97
Hydraulic Discharges during Transport
The mixture- discharge, Qm, is defined as the sum of the (transport-) Water-Discharge, Qw, plus the Solids-Discharge , Qs. Discharge introduces the notion of unit-time: xx m3/sec.
However, the measuring gauges, monitor 2 parameters:• ρsat or ρbulk (radio-active transmission probe, measuring the
attenuation of γ -rays, interacting with large atoms)• vw or the velocity of the electrolytic fluid water (electro-magnetic
gauge)
Hence, no direct measurement is achieved of the Solids-Discharge, Qs,…which is ultimately what a dredger is only interested in. Sediment-particles in a moving fluidare known to “slip”, which means they are moving with a velocity slower or equal tothat of the fluid (see Slide 47). That’s why the Ca is called ‘apparent’.
Therefore, there is little other choice for the dredger than to assume a slip-factor , ƒs, for the transported sediment, and to calculate the Solids-Discharge from the Mixture-Discharge.
Qdel = ƒs . Qm = ƒs. vm.A . Ca A = section of dredging tube at the gauge
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 98
Hydraulic Discharges during Transport
In the equation above, all parameters are measured or known , except the slip-factor, ƒs.
But ƒs can , in some circumstances, be measured by feedback: when comparing the total integrated mixture volume, Vm over a given period, with the (topographical) measured Vdel (e.g. via Digital Terrain Modelling of an upland confined disposal facility) over that same working period, one gets a better approximation of the ƒs factor.
This is, of course, only valid for (almost) instanteneous compacting/consolidating sediments like sands and gravels. Granular sediments/soils bulk more during hydraulic transport, but get back rapidly to their (more or less) original (in-situ) compaction degree. (FYI: the ƒs is quite different from 1 for granular sediments).
Cohesive and/or fine-grained sediments/soils will bulk less, will need time to consolidate to a constant value and will generally keep a residual bulking (within a project-period of months or years). Unless, accelerated consolidation by dewatering is done. (FYI: the ƒs is generally close to 1 for cohesive sediments)
Qdel = ƒs . Qm = ƒs. vm.A. Ca
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 99
Application of concentration-equation: Compaction and Consolidationof Dredged & Delivered Materials
, .. , .. , • , - .. s
, , lO
,
h .. A' 18
lO ., ;1 .. I lO • o • .. ! ; .
" / .... • .... .... .... .... , .... , .... , .... , .... , ..
nm. l ' I I t tinco To(JrMI
-
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 100
Application of concentration-equation: Production-Control and Cyclus-Management
Loadlng Dlagram of a Tralling Suction Hopper Dredger
60000
50000
I~) Drtd , ia; : 1(6) Dumpi., I r ,0,,,",.',, I ~~) Soi!i., foU '0
I ,1 '1 Id .... un
, (J) D~,u.,: I , . opptr loodi., l ' <--> ,
40000
" ~ 30000 3 t ~
, , ~ I I I I
/ I
I
I I
(l ) Ho~pt'r I I ,
.mp~ ... ;
"" I
20000
10000
(1 ) s om. ,.o I Y I I drtd , . '0.'
I I * I
I
o o 20 40 60 80 100 120 140
Cycle-time (minUles)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 101
Double Transformed Loadlng Dlagram of a TSHD
60000 Il'rodu ri.-. timt,
• ,'Í-~ 50000 ~ • ~ ~ , 'O 40000 •
"1 e o "-~ , ~ 30000 "" / 1 ~ • .. ~ e 20000 --1 • l ," ' >
• e S
t - 10000 , ----e , - ,-• , E
,
• u • .. O -" O 40 60 80 100 120 140
-10000
Cycle time (minutes)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 102
Application of concentration-equation: optimization of productivity byincrease of mixture-density
• " ~ I ~
.~
.~ •• " o ~
~
2
1.9
1.8
1.7
1.6
1.5
1.'
1.3
1.1
1 1000
Enect o, Increase in Mixture Volume-Mass on Cyclus-Productlvity (tdsfcyclus)
1050 1100 1150 1200
Increólse in Mixture's _- '!" volume-mass
1250 1300
Original Mixture Volume-Mass (kglm3)
1350 1400 1450
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 103
Hydraulic Transport: Examples of sequence of Volume-Masses and volumes in a dredging & reclamation project
Saturated (water) Dry
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 104
Hydraulic Transport: Hydraulic Process description
The hydraulic transport of sand-water mixtures is (for the time being) too complex and too poorly understood to be describedanalytically. Therefore, engineers have to rely on empiricalrelationships and formulae
The most relevant empirical formulae are based on closed-looplaboratory tests:
- PhD’s theses uit ’50-ies en ’60-ies- R. Durand & E. Condolios (1952) – R. Gibert (1960)- Alfred Führböter (1961)- Jufin-Lopatin (1966)- Wilson (1972-1996)
But the lab-tests had drawbacks:� .too small diameters of pipes (excepted Durand and Wilson)� too limited concentration ranges� selected (near ideal) dredged materials (excepted Durand)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 105
Hydraulic Transport: Two-layered Model cfr Wilson
Wilson (1992-1996)
A = Wet Surface
C = Concentration
V = Volume
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 106
Hydraulic Transport: Two-layered Model further elaborated
Václav Matousek – TU Delft (1997)
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 107
Hydraulic Transport: Real-scale tests on Two-Layered ModelVia verification on real-scale reclamation works, the Two-Layered
model was transformed into a practical engineering tool –Pusan Port Development (South-Korea, anno 2002) 0,300 mm sand
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 108
Hydraulic Transport: Practical engineering State of the Art
Concluding:- Only empirical formulae are used- Parameters are calibrated with site-specific measurements or
experience-data- Corrections to be applied for different pipe-diameters, cutter dredgers
or hopper dredgers,…Careful:- Input-data are generally not precise (too little soil and soil-variability
data)- median grain-size is not easy to determine- effect of coarse materials (boulders,…) is huge : stones> 5 cm diameter are removed from lab-tests- effect of fines on dynamic viscosity- effect of variations in grain-size distribution
- Type of dredging is importantTSHD: Segregation of material in hopper: coarser under
discharge pipeCSD: undercutting vs overcutting
- Variations in process-parameters are not smoothed out over long discharge-pipes
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 109
Hydraulic Transport: Hydraulic characteristic of sand-water mixture
- Relationship is of the following type:
- Minimum of curve: critical velocity/discharge
cQ
baQH ++= ²
vcrit
settling suspension
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 110
Hydraulic Transport: Influence of variable concentrations and grain-sizes (Führböter)
Effect of increasing concentration Effect of increasing median-grain-size
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 111
Hydraulic Transport in Pipelines: Affinities with Grain-Size
water
Counter-Pressures (bar)
Mixture Velocity[m/s]
0 1 2 3 4 5 6 7 8 9 10 11 12
5
10
15
Mediumsand
Coarse Sand
gravel
Fine sand
Water
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 112
Hydraulic Transport in Pipelines: Affinities to Volume-Mass
Counter Pressure[bar]
Mixture Velocity [m/s]V crit
Water
Fine Sand, 1.200t/m³
Fine Sand, 1.500t/m³
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 113
Hydraulic Transport in Pipelines: Affinities with Pipeline-Length
Counter Pressure[bar]
Mixture Velocity [m/s]V crit
Water
Fine Sand, 1.200t/m³, 1000m
Fine Sand, 1.200t/m³, 1500m
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 114
Hydraulic Transport:
END of PART 1
Bernard Malherbe - Dredging Technology: horizontal transport of mixtures 115
Hydraulic Transport: Exercise about Concentration
Input: Dredged Material : Silty SandIn-Situ Volume-Mass :ρ sat = 1.500 kg/m3Measured Volume-Mass in Pressure Tube: ρm = 1.300 kg/m3Measured velocity in Pressure Tube : v = 5 m/sec
ρs=2.65 t/m³ρw=1.025 t/m³
Calculate : • What is the bulking factor due to hydraulic dredging ?• What is the apparent Concentration ?• What is the Delivered Solids Discharge (estimated)?