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CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative densityCourse
Harbors & Coast and
Dredging year 2012
CourseHarbors & Coast
and Dredging year 2012
Soil mechanical aspects of dredging
Soil parameters relevant for dredging processes
Reinder Meinsma
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
• Objective Lectures
– Introduction into
• The relationship between soil properties and
dredging (earth moving)
• The interaction between soil and water
(hydraulics)
• Objective Lectures
– Introduction into
• The relationship between soil properties and
dredging (earth moving)
• The interaction between soil and water
(hydraulics)
2
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
• Assumption for these lectures
– Basic knowledge about
• Fluid mechanics
• Hydraulic engineering
• Geotechnics
• Assumption for these lectures
– Basic knowledge about
• Fluid mechanics
• Hydraulic engineering
• Geotechnics
Book:
DredgingTechnology (Lecture notes). G.L.M. van der Schrieck
CT5300 Delft University, jan 2010
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relationship between soil properties and dredging processes
Relationship between soil properties and dredging processes
• Soil properties, great influence on:
• Deployability, production of the dredger
• Design and execution of the dredging works
– Stability
– Settlement
– Dynamic behavior of the soil
– Interaction soil and water
• Soil properties, great influence on:
• Deployability, production of the dredger
• Design and execution of the dredging works
– Stability
– Settlement
– Dynamic behavior of the soil
– Interaction soil and water
3
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relationship between soil properties and dredging processes
Relationship between soil properties and dredging processes
• Example Harbor deepening• Example Harbor deepening
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Processes in dredgingProcesses in dredging
• Processes in dredging
• 4 phases:
– excavation
– lifting
– transportation
– disposal
• Processes in dredging
• 4 phases:
– excavation
– lifting
– transportation
– disposal
Backhoe
Bucket dredger
Cutter suction
dredger
Plain suction
dredger
Trailer suction
hopper dredger
Loading pontoon or own loading device
Hopper or barge
Pipe line
Barge unloading device Sand fill
4
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Processes in dredgingProcesses in dredgingProcesses in dredging
• excavating
– Hydraulically
– Cutting
• Mixture /drawing up
• Transportation
– (Barge) ship, Dumper
– Pipeline
– Conveyor belt
• Dispose – under water
– above water
– dump, rain bowing
Processes in dredging
• excavating
– Hydraulically
– Cutting
• Mixture /drawing up
• Transportation
– (Barge) ship, Dumper
– Pipeline
– Conveyor belt
• Dispose – under water
– above water
– dump, rain bowing
Soil mechanical aspects
• Loss & compacte sands
• Cutting of sand
– contractant (decrease of volume)
– dilatant (increase of volume)
• Cutting of clay
– Schearstrength (undrained)
• Cutting of rock
– point load
– fragmentatie
• hydraulically
• mechanically
• plasticity
• density
• strength
• density (relative density)
• accessibility (stability)
• settling
Soil mechanical aspects
• Loss & compacte sands
• Cutting of sand
– contractant (decrease of volume)
– dilatant (increase of volume)
• Cutting of clay
– Schearstrength (undrained)
• Cutting of rock
– point load
– fragmentatie
• hydraulically
• mechanically
• plasticity
• density
• strength
• density (relative density)
• accessibility (stability)
• settling
Specific energy Espec, energy needed to
cut one m3 soil. Expressed kJ/m3. The power in kW needed to cut one m3 of soil
per sec (kW= kJ/sec)
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Processes in dredging exampleProcesses in dredging example
• Case IJburg• Case IJburg
5
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Physical soil characteristicsPhysical soil characteristics
• Book chapter 7 soil mechanical aspects • Book chapter 7 soil mechanical aspects
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Physical soil characteristicsPhysical soil characteristics
• Handout
• Some Definitions
– wet density → ρn, ρw, ρb (kg/m3) of уsat (kN/m3)
– dry density → ρd, ρdry, (kg/m3) of у (kN/m3)
– specific density → ρk, ρs, ρp (kg/m3) of уspec (kN/m3
– watercontent → w
– porosity → n (pore content)
– Void ratio → e (pore number)
– Air content → vl
– Degree of saturation → Sr
• Handout
• Some Definitions
– wet density → ρn, ρw, ρb (kg/m3) of уsat (kN/m3)
– dry density → ρd, ρdry, (kg/m3) of у (kN/m3)
– specific density → ρk, ρs, ρp (kg/m3) of уspec (kN/m3
– watercontent → w
– porosity → n (pore content)
– Void ratio → e (pore number)
– Air content → vl
– Degree of saturation → Sr
6
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Physical soil characteristicsPhysical soil characteristics
Fill in the table Home work
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Physical soil characteristicsPhysical soil characteristics
• Pore number e (void ratio)
and Pore content n (porosity)
• Definition
– Porosity n
– Void ratio e
• Pore number e (void ratio)
and Pore content n (porosity)
• Definition
– Porosity n
– Void ratio e
watergrain
wetgrainn
ρρ
ρρ
−
−=( )e
en
+=
1
( )n
ne
−=
1
( )n
ne
−=
1
During shearing it depends on the value of the actual in situ
porosity n1 or n2 relative to the value of the so called ‘Critical
density’ at porosity ncrit
n min n maxn crit
n value range dilitant behavior n value range compactant behavior
n1 n2
( ) wrkn nSn ρρρ ⋅⋅+⋅−= 1
kgrain ρρ = nwet ρρ =
7
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Physical soil characteristics Contractant & Dilatant behavior
Physical soil characteristics Contractant & Dilatant behavior
• Engineering applications:
– Volume change tendency
– Strength
• Engineering applications:
– Volume change tendency
– Strength
Simple cubic (SC), e = 0.91,
Compactant behavior
Cubic-tetrahedral (CT), e = 0.65, Dilate
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Bulking factorBulking factor
• Bulking factor (B)
– Result of dredging (excavating) soil
• Increase of the pore volume (n)
– Definition
• Bulking factor (B)
– Result of dredging (excavating) soil
• Increase of the pore volume (n)
– Definition
volumesituin
volumedredgedB =
8
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Bulking factorBulking factor
• Calculation of the bulking factor B
– Keep in mind the volume changes not the quantity
of solid matter
– Porosity→
– Dry density→
– Wet density→
• Calculation of the bulking factor B
– Keep in mind the volume changes not the quantity
of solid matter
– Porosity→
– Dry density→
– Wet density→
( ) ( )2211 11 nVnV −⋅=−⋅
( ) ( )2211 dd VV ρρ ⋅=⋅
( ) ( ) ( ) wnn VVVV ρρρ ⋅−+⋅=⋅ 212211
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Bulking factorBulking factor
Task: project Sand mining
Dredging and transport cycle
100.000 m3 of in situ sand is dredged
What is the amount of sand (m3) when:
a) transported in the barges?
b) measured in the sand fill?
9
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Bulking factorBulking factor
Task: project Sand mining 100.000 m3 of insitu sand is dredged
What is the amount of sand (m3) when:
a) transported in the barges?
b) measured in the sand fill?
Answer:a) If ρsitu = 2010 kg/m3 means a porosity (nsitu) of 38,8%.For the 100.000 m3 sand in situ only 85% (85.000 m3 insitu sand) is transported by the barges. The transported sand contains (1-nsitu)= 61,2% of grains, so
61,2% *85.000 m3 = 52.020 m3 of dry matter (grains). Measured in the barge with an porosity n of 45% means that 52.020/(1-0,45) = 94.582 m3 is transported by the barges.
b) At the sandfill the porosity is decreased to 40%. The volume of sand is now
52.020/(1-0,6) = 86.700 m3 of which 5% is washed by the dewatering boxes. So at the sandfill only 95% of 86.700 m3 is measured (82.365 m3)
( ) wrkn nSn ρρρ ⋅⋅+⋅−= 1
100.000 m3
95.000 m3 82.000 m3
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Answer:
Water content =23% = (ρn-ρd)/ρd → dry density (ρd) = 1870/1.23 =1520 kg/m3
pore volume (n) = 1-( ρd/ρk) = 1-(1520/2600) = 0.415
so volume water per m3 = (0.23*1520)/1000 = 0.35
A) The required layer height is 0.75m, the minimum layer to be constructed
is around (1700/1520) * 0.75 = 0.84m
B) The pore volume after compaction is n= 1-1700/2600= 0.346
the volume water per m3 was 0.35 and fills now the pores so
W =around 100%
C) Waterpressure measurements
Bulking factorBulking factor
Question 2
A layer of sand is constructed. The height of the sandlayer is to determined at a later stage.
The subsoil is rather hard, so no settling is expected.
The layer is compacted quiet short after it has been disposed. The density of the disposed sand is 1870 kg/m3. The
water content is 23% and the specific density of the grains is 2600 kg/m3.
After compaction the dry density of the sand must be at least 1700 kg/m3. The height of the sand layer must be at
least 0.75m.
Asked.
A What is the initial height of the sandlayer before compaction? In other words what is the height of the layer to be
disposed?
B What is the water content after compaction?
C What kind of extra mitigating measurements would you use in order to check if the dry density is required?
Task : Sand fill
10
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relative densityRelative density
• The packing of sand has two extremes
– Loose packed sands nloose= nmax
– Dense packed sands ndence = nmin
• Relative density (parameter for non cohesion soils).
– Is says something about the state of compaction
– The in situ density of sands after disposal is
expressed in relative density.
• Relative means how the density of sand is
related to the extremes. so
Maximum density at a porosity (n) of 0%.
Minimum density at a porosity (n) of 100%.
• The packing of sand has two extremes
– Loose packed sands nloose= nmax
– Dense packed sands ndence = nmin
• Relative density (parameter for non cohesion soils).
– Is says something about the state of compaction
– The in situ density of sands after disposal is
expressed in relative density.
• Relative means how the density of sand is
related to the extremes. so
Maximum density at a porosity (n) of 0%.
Minimum density at a porosity (n) of 100%.
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relative density
Absolute value of soil density not so important – what matters is how dense is the soil relative to its maximum possible value and its minimum possible value
Absolute value of soil density not so important – what matters is how dense is the soil relative to its maximum possible value and its minimum possible value
minmax
max
nn
nnDr situ
−
−=
Densest possible state (emin, or ρρρρdmax)
(obtained by vibration under load)
ID
1 or 100%
Loosest (stable) state (emax, or ρρρρdmin)
(obtained by pouring with funnel)
Density index ID (relative
density) –
where density lies in the range
min. to max. -
or rather where void ratio lies
between loosest (emax) and
densest (emin) state
minmax
max
ee
eeI situ
D−
−=
ID (%) 0 – 15 15 – 35 35 – 65 65 – 85 85 – 100
State Very loose Loose Medium Dense Very dense
11
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relative (compaction) densityRelative (compaction) density
• Rn (Dr) “relative porosity content”
• Re “relative void ratio” or ID density index
• Rn (Dr) “relative porosity content”
• Re “relative void ratio” or ID density index
%100%100max
min
minmax
max ⋅−
−=⋅
−
−=
ndrmidr
drdrr
nn
nnD
ρρ
ρρ
%10011
11
%100
maxmin
min
minmax
max ⋅
−
−
=⋅−
−=
dd
drdD
ee
eeI
ρρ
ρρ
Extreme values :
- maximum density (ρdry max). nmin
- minimum density (ρdry min). nmax
- Critical density (ρdry crit)
Laboratory tests
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relative densityRelative density
Relative density Dr is defined as:Relative density Dr is defined as:
( )%100minmax
max ⋅−
−=
nn
nnDr
( )%100minmax
max ⋅−
−=
ee
eeID
1001
1 min ⋅−
−⋅=
situ
Dn
nDrI
12
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
In the fieldIn the field
• How to estimate Re;insitu• Now exact method yet (we are
working on it)
• Present use CPT tests → and
correlations like Baldi et al.
• How to estimate Re;insitu• Now exact method yet (we are
working on it)
• Present use CPT tests → and
correlations like Baldi et al.
( )
=
1'ln
1
02
C
cr
C
q
CD
σ
σ’= vertical effective strain [MPa]
qc= cone pressure [MPa]
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
In the fieldIn the field
• What to do??
– Adjust design
– Compacting
– Adjusted Dredging methods
• What to do??
– Adjust design
– Compacting
– Adjusted Dredging methods
13
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Relative densityRelative density
• task
– question nr 3
– Study the handout ‘Soil’ related to relative density
– Hand outs presented on the BB
• task
– question nr 3
– Study the handout ‘Soil’ related to relative density
– Hand outs presented on the BB
CT - lecture 1
Introduction
What and why dredging
Content lectures
Processes in dredging
Physical soil characteristics
Bulking factor
Relative density
Questions so far