CEDA DMC Works On A Guidance Paper For Soil Investigation

CEDA Dredging Management Commission WG on Soil Investigation (Credit: CEDA)
CEDA Dredging Management Commission WG on Soil Investigation (Credit: CEDA)

Did you ever start a project and it turned out that the conditions were different than expected? Welcome to the dredging industry. One of the most underestimated preparations for a dredging project is the soil investigation. As this investigation is of the utmost importance for the dredging community, the DMC is preparing a guidance paper on this topic1, which we discussed last meeting (February 7, 2020, IMDC, Antwerp).

Working for a dredging equipment manufacturer, I am not much involved in the actual soil investigation. However, often our clients base their purchase of a specific type of equipment on the soil investigation and as such we are often presented with the reports on soil investigation. Based on these reports, we calculate the possible production for various types and advise the client for a dredge that will meet their requirements on the maximum production. most of the time we provide a good advise and the client is happy.

Off course there have been occasions where the performance was not as expected. Often because the report on the soil investigation was inadequate. Either the report did not contain all the details, or the investigation itself was lousy. Either way, rubbish in, is rubbish out. Just as an example, let me tell you what can go wrong, when the information is not representing the real circumstances.

One of our products are the so called ‘DOP Dredges’2. They are based around the versatile DOP pump. Basically, it a DOP suspended on an A-frame on a pontoon with a powerpack. The DOP can be lowered into the sediment and create a typical suction dredge pit. The production is more based on the rate that water can enter the bank face and the velocity that the banks recede. Our client provided us a Particle Distribution Diagram of the available sediment3. It was a nice narrow graded sand, but there was a considerable fines tail on the lower end. This was being dealt by the washing and screening installation. According to the client was this the sand characteristic from the whole pit. And what could be better? If you excavate all the material, you really know what is there, right?

Difference between expected soil conditions (left) and real situation (right)
Difference between expected soil conditions (left) and real situation (right)

Well no. As it happened, there were cohesive silt layers between the narrow graded sand layers. When dredging, they sucked at the bottom of the pit. Any silt layers gradually broke of and disintegrated by the eroding density flow. As the pit was created over a long period, the falling chunks of silt just slid down the slope, without causing any harm.

Enter: the new DOP dredge. It started in a new corner of the pit and initially had some trouble penetrating the silt layer. Eventually it managed to get through and started excavating a cavity below the silt layer. These broke of, burying the DOP. Without any possibility to recover the DOP, it turned into a very expensive anchor.

Risk of getting your DOP trapped in a cavity under the cohesive silt layers and the solution
Risk of getting your DOP trapped in a cavity under the cohesive silt layers and the solution

If the presence of these cohesive silt layers would have been known, we would have adapted the suction pipe for a deeper penetration. That prevents the DOP becoming covered and facilitates easier extraction. This story proves two things: 1. A proper soil investigation can prevent costly accidents and budget runovers. 2. A DOP can be modified to most requirements, when the circumstances are known.

Meanwhile, the DMC is preparing its guidance document to assist you in preventing problems like this. Follow CEDA for updates4.

Standard suction tube (left) and long suction tube (right)
Standard suction tube (left) and long suction tube (right)

References

  1. Dredging Management Commission, CEDA
  2. DOP Dredger, Damen
  3. A Sample of Soil Samples, Discover Dredging
  4. News, CEDA

See also

We Choose To Adopt Energy Transition, But How Will We Succeed?

President John F. Kennedy speaking at Rice University on September 12, 1962 (Credit: NASA)
President John F. Kennedy speaking at Rice University on September 12, 1962 (Credit: NASA)

‘We choose to go to the moon.’ Was the famous speech at Rice University of President John F. Kennedy to express his ambition to send his nation to the Moon1. At the time, his call was far from clearly achievable. But it was a very clear roadmap and it quickly gained traction. The success of the Apollo project is well known. Neil Armstrong did land on the Moon within a decade and the American flag is still planted on its surface.

Panel discussion at the CEDA Dredging Days 2019 with Mike van der Vijver
Panel discussion at the CEDA Dredging Days 2019 with Mike van der Vijver

At the CEDA Dredging Days 20192, there was an interesting panel discussion on ‘Energy transition: the views in our dredging community’3. Panel members were: Eric de Deckere, Michael Deruyk, Kaj Portin and Klaas Visser. The discussion was moderated by Mike van der Vijver from MindMeeting. As an introductory teaser to the audience, he posited the claim: ‘Excessive ambition drives breakthroughs’. The question is: ‘Is the dredging industry ambitious enough to convert to a new fossil free energy source?’ The audience was polled for their opinion on a scale from one to ten and the response ranged from three to eight. The three represented the position, that the industry is not doing much. What is visibly done, are only single purpose, company specific solutions that are not adopted by the community. On the other hand, there was also a very positive signal with an eight for ambition. The sense of urgency is very well present in the community. Most companies are developing plans and cooperating in working groups, such as the CEDA Working Group on Energy Efficiency4. Also, the government is pitching in with initiatives on zero emission maintenance dredging, where the dredging community is actively participating in putting forward proposals.

So, why is there still no zero emission dredge? What is the ambition lacking? The hint is the opinion that the effort is not focussed. The strong motivation in Kennedy’s speech was that there was a very clear picture what to do. What do we do: ‘Put a man on the Moon’. When: ‘By the end of the decade’. How: ‘Bring him safely back’. Ambition with a clear plan can indeed achieve great things. Ambition without motivation will only bring daydreaming and lethargy.

Block diagram of influencers for energy transition in the dredging community
Block diagram of influencers for energy transition in the dredging community

To achieve something, we need motivation. And who is responsible for pulling this off? Mike polled the audience again for: 1) Government, 2) Public opinion, 3) Companies, 4) Technology. There was not a clear picture here either. All positions are valid. Another driver is the reward for the effort. The Apollo project effectively created part of our modern society. What would the energy transition yield for the dredging community: ‘Learning by challenge’, ‘Flexibility and resilience in energy generation’, ‘Low maintenance and higher independence’?

At this website I can’t change the world, but addressing most issues mentioned, I can only put forward my idea on the ‘How’ motivation. We know how to apply power. As long as the power arrives electrically, we can use it. Essentially, we have to generate electricity with a flexible power source. The investment lifetime of a dredge often exceeds 30 years, but under the current circumstances, the power plant only lasts ten. The solution would be to have some separate module for power generation. Either locally, near the dredge, or remote at the end of the pipeline. As every project and application will be different, it will be a challenge to design the specific solution. But I am looking forward in developing the solutions below with any interested customer5.

Transition schedule to convert to fossil fuel free dredging equipment
Transition schedule to convert to fossil fuel free dredging equipment

References

  1. We choose to go to the Moon, Wikipedia
  2. CEDA Dredging Days 2019, CEDA
  3. Programme 7 November 2019, Panel Discussion, CEDA
  4. CEDA Working Group on Energy Efficiency, CEDA
  5. Innovation at Damen Dredging Equipment, Damen

See also

Innovations In The New MAD Series To Increase Uptime And Reduce Fuel Consumption

Innovative Marine Aggregate Dredge for gravel dredging
Innovative Marine Aggregate Dredge for gravel dredging

This week, there will be a lot of interesting presentations at the CEDA Dredging Days 2019 in Rotterdam1. I would like to draw your attention to one particular presentation that I was involved with at certain moments in the project, though not in writing the paper. Kudos to my colleagues Frank & Frank to write the interesting manuscript2.

The topic of the presentation will be the change of perspective for the concept of marine aggregate dredging. Historically, the marine aggregate dredging takes place relatively close to shore. With the depletion of the deposits and the increase in demand, other locations further out at sea are coming into focus. As Damen, with a heritage in the design of offshore operating vessels, it was a natural choice to cross breed the offshore supply vessels with the marine aggregate dredges. The resulting offspring: the MAD series of hopper dredges3. Frank de Hoogh will elaborate on the seakeeping abilities of this innovative design.

Other dredging related innovations are the suction tube and ancillary equipment, the screening towers and the process sensors. Of those, I have some personal anecdotes on the screening towers and the density sensor. For all other interesting stories, you’ll have to attend the presentation.

The screening towers are fundamental to the efficiency of the process. If the screening is improved, shorter dredge cycles are possible and a better product can be landed onshore. Also, if the requirement for the product change, the screens have to be adapted to the new specifications. Ideally, this changing has to be done at one unloading phase, otherwise you miss a complete dredge cycle. A lot of effort has been done to optimise the design. But the real test was to actually build, modify and test the complete screening tower, before it was even installed on the vessel. So, we had this construction right here at our doorstep for a thorough evaluation.

Screening towers for fit and fat testing at our yard
Screening towers for fit and fat testing at our yard

One other component, that I was even more involved with, was the non-radioactive density sensor. There are regulations in place to phase out nuclear density sensors4 and a lot of alternatives are available. Back in the !VAMOS! project5, we had the opportunity to test a unit of an electro tomography system. The results indicated a good reliability and a worthy replacement for the traditional nuclear sensor6. Because of the tomography picture, there was an additional benefit: we received an early warning on the slurry behaviour. We could actually see when we were too close to the deposition limit in the pipe line. This enabled us to work with higher densities at lower velocities, resulting in better efficiency and less wear. As the rough process conditions in the mining pit were similar to the marine aggregate dredging industry, we proposed to use this on this MAD also. How we further developed and tested this system is for you to hear and see at the presentation.

Testing the non-radioactive density sensor
Testing the non-radioactive density sensor

Due to the physical processes involved in slurry transport, the mixture does not behave like a normal Newtonian fluid. It is some non-linear viscous substance. At high speeds and low concentrations, it is similar to the carrier water. Slowing down, there is a certain critical speed, where there is a minimum hydraulic gradient. At that flow condition, the specific power consumption of moving a cubic meter of soil is the lowest. So, although working at critical speed is dangerous, it has its advantages: low fuel consumption and less wear. Actually seeing the mixture approaching this critical speed from the deposition is an interesting feature of this new density measuring sensor.

Explanation on slurry flow conditions, critical speed and specific power consumption
Explanation on slurry flow conditions, critical speed and specific power consumption

References

  1. CEDA Dredging Days 2019, CEDA
  2. Next generation marine aggregate dredger as platform for innovation and basis for fleet renewal, CEDA
  3. Damen unveils Marine Aggregate Dredger, Damen
  4. Regeling bekendmaking rechtvaardiging gebruik van ioniserende straling, Staatscourant
  5. Project ¡VAMOS! Let’s Go Real!
  6. Real time production efficiency based on combination of non-nuclear density and magnetic flow instrumentation, WEDA

See also