Graduation Omar Karam: Rock Cutting The Egyptian Way

Graduation presentation of Omar Karam
Graduation presentation of Omar Karam

Egypt is a great nation when it comes to ancient engineering. No other country has such a concentration of impressive monuments and such an interesting history as over there. If you are not convinced that modern Egyptians are not capable of great engineering feats you are wrong. Last Monday, Omar Karam graduated at our R&D department of Damen Dredging Equipment1 on his thesis about ‘CSD Rock Cutting.’

Cutting processes have been extensively described by Sape Miedema in ‘The Delft Sand, Clay & Rock Cutting Model’2. Omar has been using the frame work of Miedema to make some useful tools for the estimation of the production of our dredging equipment in rock. In due time, you will find the results of his thesis in the online dredge selection tool ‘Sandy’. Omar’s curiosity and ingenuity does not end here. He will continue studying at a university, but I do hope to meet him again, as he would be a valuable asset for our dredging community. Keep an eye out for him.

Program structure diagram of cutting force calculations
Program structure diagram of cutting force calculations

His graduation brings me back to my first lessons in dredging technology at the Delft University of Technology by the illustrious professor de Koning. In a sense he was an old school engineer, who hammered it in to us that thinking is done by doing it with your hands3. Back than the Polytechnic School was just rebranded to University and he was mocking that as a university, we had to set the topics in a broader perspective. So, he started his introduction on cutting technology with some slides of the unfinished obelisk at Aswan4 as every aspect of the cutting process could be illustrated.

Phases of chip forming in rock cutting
Phases of chip forming in rock cutting

The story according to de Koning is: ‘Around the quarry of the obelisk, they have found diorites5. These are some sort of volcanic balls of rock. In combination with the marks and scratches all around the obelisk, archaeologists believe these stones have been used to pound the granite. The impact compresses the bedrock and the resulting stresses fracture the contact surface(1). For every hit a whiff of dust is created. Eventually the dust is collected and scooped away for the next layer. Next, trees would be planted in the trench on one side of the obelisk. The growing root system displaces volume and create shear stress underneath the obelisk that would sever the obelisk from the bed rock(2). At last the trees are removed and dry wooden dowels would have been inserted in the shear cracks. Saturating the wooden dowels will make them grow. The last strands of rock will now be broken due to tensile stresses(3). Repeated insertion of new dry dowels and saturating them will lift the whole obelisk enough to pull some ropes under and carry the obelisk away to the building site.’

Although the diorites and the scratch marks are a smoking gun, current archaeologists argue about the feasibility of this process as experiments yield a very low production and it is doubted that the obelisk could be finished in the lifetime of the client6. Even if disputed, de Koning told a story that conveys the message; I vividly remember it and makes me understand the rock cutting process.

These mysterious monolithic ornamental spires have been an inspiration for many legends and stories. When we have solved the riddle of the rock cutting with diorite balls, it may inspire the development of new rock cutting technology for the dredging community and we can put the story of the obelisks to an end.7

End of the story on the cutting of obelisks (Credit: Uderzo)
End of the story on the cutting of obelisks (Credit: Uderzo)

References

  1. Innovation, Damen
  2. The Delft Sand, Clay & Rock Cutting Model, TU Delft
  3. De Koning (1978), Denken met de handen’, TU Delft
  4. Unfinished obelisk, Wikipedia
  5. Diorite, Wikipedia
  6. The Unfinished Obelisk, NOVA
  7. Asterix and Cleopatra, Goscinny-Uderzo

See also

Modern Uses And Legendary Excuses For Manual Depth Sounding

Depth sounding lead and rope
Depth sounding lead and rope

Never waste a moment to tell a good story. Usually, you’ll find informative or educational stories on this platform. This time, I literally found an opportunity to tell you a fun story. All it took, was this nifty little classic navigational instrument. The crew on the dredge used to calibrate their modern survey system1 or checked the delivered depth with this ancient tool. Ever seen one like this? It is a depth sounding lead2. Well, I doubt this one was made from lead, based on the estimated weight and appearance, but it does have all the other characteristics of a normal depth sounding lead.

Evolving from a stone on a rope, the depth sounding lead was used to sound the depth. The plummet was made from lead. The rope was marked at regular intervals according to the shoe size of the current king. Cast overboard, the lead sank and keeping the rope tight, the depth at that location could be read from the markings on the vertical rope. It involved some nimble dexterity to stand at the lee side of a fast moving vessel in a choppy sea to handle the lead, a bundle of coiling rope and accurately reading the depth at the right moment. Hands down to all those seafarers that explored the world in old times and managed to navigate the globe on this instrument.

Sounding the depth manually with rope and lead (Credit: Wikipedia)
Sounding the depth manually with rope and lead (Credit: Wikipedia)

The depth was not the only information gained from this action. When you look closely, there is a hole at the bottom of the lead. On the picture above it is empty, but it ought to be filled with grease or wax. When the lead touched the bottom, some of the dirt was caught in the grease. When the lead was retrieved, the cling-ons were inspected. These could be either: sand, mud, gravel, peat, silt or even shells and other biological detritus. The material was reported on the charts also. This made navigation in charted waters easy: compare the sample with the indicated bottom condition. And that brings me to my fun story.

Before the Dutch reclaimed their land, there was a large water body in the Netherlands, called the ‘Zuiderzee’3. Or, South Sea as opposed to the North Sea, which most of you might know. This Zuiderzee, was extensively used for fishing. The skippers did not have charts, but they relied on oral tradition handed down through the ages of where what kind of soil would be available. Near Urk, you might find rocks. Near Pampus, there will be a lot of mud and around Stavoren, there is the famous ‘Vrouwenzand’ (Sand Bank of the Lady of Stavoren4). So, when the fishermen cast their depth sounding leads out, they knew the location of their vessel and the depth beneath it.

Map of the ‘Zuiderzee’ (Credit: Wikipedia)
Map of the ‘Zuiderzee’ (Credit: Wikipedia)

One of those skippers boasted he did not even have to see and feel the sample, but just by tasting it, he could pinpoint his location within a hundred yards. Hard to believe, right? The cabin boy on board thought likewise. So, he devised a cunning plan. After lunch, the skipper went down to the cabin for a short nap and instructed the cabin boy to bring him the lead to taste the sample. But, our clever cabin boy sank the lead in the crate with potato’s. The bottom of the crate was covered with clay from the potato’s. Carefully bringing the sample to the skipper, the cabin boy woke him up and awaited his reaction. The skipper woke up groggily and grappled for the lead with half closed eyes. He stuck his finger in the sample hole and tasted the material inside. Suddenly, his eyes went wide open and he exclaimed: Oh, disaster! The dikes have broken again! The land is flooded and we are sailing over farmer John’s potato patch!

You never know what you dredge from the bottom of a potato crate
You never know what you dredge from the bottom of a potato crate

References

  1. Positioning and survey system, Damen
  2. Depth sounding, Wikipedia
  3. Zuiderzee, Wikipedia
  4. Lady of Stavoren

See also

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