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 1
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 2
Port of Rotterdam: Maintenance concept 3
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. 4
Step 2: Liquefaction and mobilisation of the sediment • • Liquefaction of the zones around Creation of an angle of repose the trench by WID • Creation of density flows by a step by step • Mobilisation in steps towards the dredging procedure towards the trench trench 5
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 6
WID dredging towards the trench 7
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 8
Free fall penetrometer 9
GraviProbe Measurement pri rincip iple le 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. 10
GraviProbe Measurement pri rincip iple le 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. 11
GraviProbe Measurement pri rincip iple le Every measerement point is registered with a bluetooth gps module, the position of the drop can be processed on a map for visualization purposes. 12
Sediment profiler Mud Map 13
Working principle • Acceleration Newtonian equation • Speed • Position F=ma=mg – F tip - F shear F shear = τ shear .A • Tip resistance • Shear stress F cone = τ cone .V/d ∆z ∆z ∆z F gravity = m.g 14
GraviProbe compared to a standard CPT measurement 15
Port of Rotterdam: Test zones 1 2 16
Multibeam and GraviProbe locations After WID Before WID 17
Dynamic cone resistance over time 18
Interpolated strength profiles Consolidated mud Acoustic Loose signal mud 19
What sediment volume can be affected by the cutting nozzles? F shear = τ shear .A • 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 F cone = τ cone .V/d F gravity = m.g • Tip resistance = 1kPa to 2MPa • Falling speed = 7 m/s 20
Performance estimators for WID Dillution to Dill o 1,1 ,1 t/m t/m³ Influ In fluence depth th (transport quanti (tr tity) (transport pot (tr oten enti tial) • • Accurate cutting depth of water Accurate bulk density injection at 100 kPa pressure measurements on low and high density sediments DensX GraviProbe 21
Practical example Strength (volume estimator) + Density (quantity estimator) = injection quantity per square meter m³H 2 O / m² Transport potential Transport quantity 1.5 m³ /m² 100 kPa 22
Practical example 12000 (m³H 2 O/h) / (14 (m) * 2340 (m/h)) = 0.366 m³H 2 O/m² Transport potential Transport quantity 1.5 / 0.366 = 4.1 injections 1.5 m³ /m² 100 kPa 23
Practical example 12000 (m³H 2 O/h) / (14 (m) * 2340 (m/h)) = 0.366 m³H 2 O/m² Transport potential Transport quantity At least 4 injections needed 100 kPa 24
Port of Rotterdam: Test zones 1 2 25
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. 26
TCPR vs t 008D -22 -1 9 19 29 39 49 Top mud measured by multibeam -22,5 4kPa level before and after WID -23 -23,5 Diepte (m) TCPR t0 -24 TCPR t1 TCPR t2 -24,5 -25 -25,5 -26 TCPR (kPa) 27
4kPa level map Before WID After WID 28
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. 29
Conclusions • 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 • 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 30
Company Introduction 31
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