ct dredging soil lecture1a 2012

1

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


Content lectures



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)

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CT - lecture 1

Introduction


Content lectures



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


Content lectures



Bulking factor

Relative density

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

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CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative density



• Example Harbor deepening• Example Harbor deepening

CT - lecture 1

Introduction


Content lectures



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

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CT - lecture 1

Introduction


Content lectures



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


• 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


Content lectures



Bulking factor

Relative density

Processes in dredging exampleProcesses in dredging example

• Case IJburg• Case IJburg

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CT - lecture 1

Introduction


Content lectures



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


Content lectures



Bulking factor

Relative density


• 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

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CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative density


Fill in the table Home work

CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative density


• 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 =

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CT - lecture 1

Introduction


Content lectures



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


Content lectures



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 =

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CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative density


• 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


Content lectures



Bulking factor

Relative density


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?

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CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative density


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


Content lectures



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


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

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CT - lecture 1

Introduction


Content lectures



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


Content lectures



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

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CT - lecture 1

Introduction


Content lectures



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


Content lectures



Bulking factor

Relative 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

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Introduction


Content lectures



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


Content lectures



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

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CT - lecture 1

Introduction


Content lectures



Bulking factor

Relative 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


Content lectures



Bulking factor

Relative density

Questions so far

ct dredging soil lecture1a 2012

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