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Using an innovative free fall sediment profiler for measuring mud and sediment layers to support tests

on a new maintenance concept in the port of Rotterdam

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Port of Rotterdam

• Surface of dredging areas: 3.155 ha (30 km²)

• Maintenance depths: 3,65 – 24,00 m (cd)

• Annually dredged quantity 4 – 7 million m³, done by hopper dredgers

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Port of Rotterdam: Maintenance concept

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Step1: Over depth creation in the central navigation channels

• In the middle of the main navigation channels an over-depth is created of 1 to 1,5 m on a depth of 24m.

• The trench is installed by a hopper dredger.

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Step 2: Liquefaction and mobilisation of the sediment

• Liquefaction of the zones around the trench by WID

• Mobilisation in steps towards the trench

• Creation of an angle of repose

• Creation of density flows by a step by step dredging procedure towards the trench

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Step 3: Consolidation in the over depth and follow up

• In the over depth the liquefied mud can consolidate and the over depth acts as a buffer

• In the over depth a nautical depth criterion can be installed

• The follow up of the consolidation process is done by a free fall penetrometer

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WID dredging towards the trench

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Tests

• Test 1: Evaluate of novel measurement equipment to measure in situ mud rheology by a free fall penetrometer

• Test 2: Erosion and liquefaction of underwater sediment– Zone in the beerchannel at 23m

– Followed up with multibeam echosounder and GraviProbe

• Test 3: Mobilisation of the sediment towards an over depth– Zone near the Amazonehaven on a turning circle at 23 m

– Followed up with multibeam echosounder and GraviProbe

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Free fall penetrometer

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GraviProbe

The rheological conditions of the soil layers are determining the probe’s dynamical behavior. The data acquired from on-board accelerometers, inclinometers and pressure sensors is feeding a dynamical model which determines the rheological and density parameters of the intruded.

Measurement principle

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GraviProbe

As a result the GraviProbe is able to very accurately distinguish the depth of the fluid mud and consolidated mud layers, even in gassy environments.

Measurement principle

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GraviProbe

Every measerement point is registered with a bluetooth gps module, the position of the drop can be processed on a map for visualization purposes.

Measurement principle

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Sediment profiler Mud Map

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Working principle

• Acceleration

• Speed

• Position

• Tip resistance

• Shear stress

Fshear= τshear.A

Fgravity = m.g

Fcone= τcone.V/d

∆z

∆z

∆z

Newtonian equation

F=ma=mg – Ftip - Fshear

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GraviProbe compared to a standard CPT measurement

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Port of Rotterdam: Test zones

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2

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Multibeam and GraviProbe locations

Before WID After WID

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Dynamic cone resistance over time

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Interpolated strength profiles

AcousticsignalLoose

mud

Consolidatedmud

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What sediment volume can be affected by the cutting nozzles?

• Pressure = 1 bar = 100kPa• Flow = 12000 m³/h• Water nozzle speed = 23 m/s• Ship speed = 1,25 knots (2340m/h)• Beam width = 14 m

Fshear= τshear.A

Fgravity = m.g

Fcone= τcone.V/d

• Tip resistance = 1kPa to 2MPa• Falling speed = 7 m/s

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Influence depth

(transport potential)

• Accurate cutting depth of water injection at 100 kPa pressure

Dillution to 1,1 t/m³

(transport quantity)

• Accurate bulk density measurements on low and high density sediments

Performance estimators for WID

DensXGraviProbe

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Transport potential Transport quantity

Practical example

100 kPa

Strength (volume estimator) + Density (quantity estimator) = injection quantity per square meter m³H2O / m²

1.5 m³/m²

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Transport potential Transport quantity

Practical example

100 kPa

12000 (m³H2O/h) / (14 (m) * 2340 (m/h)) = 0.366 m³H2O/m²

1.5 m³/m²

1.5 / 0.366 = 4.1 injections

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Transport potential Transport quantity

Practical example

100 kPa

12000 (m³H2O/h) / (14 (m) * 2340 (m/h)) = 0.366 m³H2O/m²

At least 4 injectionsneeded

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Port of Rotterdam: Test zones

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2

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Multibeam top mud

Before WID After WID

• On the entrance of the Amazonehaven there is a natural collection of sediment.

• A multibeam image was taken of the area of investigation. In yellow green the accumulated sediment area is visible.

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-26

-25,5

-25

-24,5

-24

-23,5

-23

-22,5

-22

-1 9 19 29 39 49

Die

pte

(m)

TCPR (kPa)

TCPR vs t 008D

TCPR t0

TCPR t1

TCPR t2

Top mud measured by multibeam

4kPa level before and after WID

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4kPa level map

Before WID After WID

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Cross section

• A pocket of loose mud is created. In total a volume of 190.000 m3 of loose mud was created by 8 hours of WID dredging.

• The total of loose mud was not fully mobilized due to the shape of the bed of channel. In this case a distance of 600m needs to be bridged between agitated area and the over depth area.

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Conclusions

• Operational• Erosion and liquefaction of sediment with

WID is feasible and efficiency is proven• Mobilisation of sediment needs to be done

under correct repose angels and control over the distance

• Upcoming full scale test by installation of a central trench in the Beerchannel

• Advantages• Predictability of the maintenance• From corrective to preventive

maintenance• Smoothening of the navigation channel• Nautical depth criterion in the over

depth trench • Optimal balance between WID and

hopper dredgers

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Company Introduction