 Want dat is waarom je hier voor bent om te zien equaties of niet. Dit is een roktrenger die we gebruiken in de hoogte. Je weet, als je van Holland bent, ben je gebruikt om dat als we bijvoorbeeld willen om alle elektriciteerkabels onder de grond of de zuursysteem. We zagen in zand, in klei, we noemen dat soft soil. Maar als je in de buitenkant bent, waar je de buitenkant is, is het een rokkie. Het is een heel harde materiaal. En dan, als je een trench wilt zagen, om alle kabels in te zetten. Je kan niet gewoon dat doen met normaal equipment, je moet zo'n roktrenger. Dus dit is de type van equipment om trenchen in een heel harde materiaal te maken. En in fact in rok, de bedrijf, de kuttingen en de hele proces is al bijna similar, boven water en onder water. Als de water niet te duur is, wat we later zien. Dus dit is een typische roktrenger. Je zag in de disaster in New York, dat storm-sandy, ik denk dat het gehoord was. Je zag dat ze veel problemen hadden met de elektriciteit, want in de U.S. de meeste elektriciteerkabels zijn nog steeds boven de grond. Je ziet die polsen met de kabels in between. En als je zo'n storm hebt, heb je ook een probleem met de elektriciteit. Dus een paar miljoen mensen hebben geen elektriciteit meer. In Europa, we zullen het gewoon onder de grond hebben en het is gewoon een bedrijf van geld. Als je het onder de grond zult worden, is het meer opgeven in het begin, maar je hebt minder maintenance later. In de oildrilling, we hebben ook raken gekregen, en in fact in de oildrilling hebben we de harde raken gekregen, want als je voor de olie bezoekt, moet je door elke materiaal je ontkijken. Het is niet moeilijk hoe hard het is. Dit is een serieus van drilbiten die je gebruikt voor olie en gas. En je kan hier zien zwarte ronde plaatsen. De zwarte ronde plaatsen, we kopen het PVC-bits of Stratopax-bits, en zijn gemaakt van artificieel diamant, want diamant is de harde materiaal. En als je de harde ronde plaatsen wil kopen, dan moet je het materiaal harder. En het enige wat dat harder is, is diamant. Dus we gebruiken diamant-bits om de ronde plaatsen te kopen. Hier heb ik een aantal van die bitsen. Je kunt de stil zien op de onderkant en de zwarte op de bovenkant. Je hebt de artificieel diamant. En ja, dus ze kunnen kopen door elk materiaal. Een groot verschil, wat we ook later zien, is tussen oliebrillen en dredging, is dat in oliebrillen zo'n beetje een diamant is van 10 mm. En je kut een laad van 0,2 mm. Dus de laad die je kut, is heel thin. In feite, je schrijft de materiaal af. En voor oliebrillen is het niet zo'n groot productie, zoals in dredging, welike cubic meters per seconde. Nou, in oliebrillen is het gewoon een beetje, zolang ik door de ronde, en eindelijk ga ik de olie. Deel waar. Dus elke dag en dan moet je de hele drilstring volgen. En je moet ze verplaatsen. Maar het begint natuurlijk op de type van rok en de dept. Hoe vaak moet je dat doen? Maar dat is een van de redenen. Als je deze foto ziet, dan kun je zien dat zo'n drilbit van de bovenkant, die een beetje groter is dan de cilinder achter het. Dus hier, dit is de achterkant van de drilbit en dit deel, je connecteert met de pipe. Nou, dus de drilbit heeft een groter diamant dan de cilinder achter het, de hele drilstring. En dat is omdat door deze pipe, je hebt de vloed heel vaak de drilbit draaien. Dus je kunt, je kunt chooseen tussen rotatie de hele drilstring van, van de platform. Maar je kunt imaginen, als het heel lang gaat, je krijgt veel torgen en wat is de garantie dat uiteindelijk je drilbit wordt rotatie op constant gegeven. Ja, dat is moeilijk, als je een paar kilometer van de pipe hebt. Dus een andere manier om dit te doen is achter de drilbit, je hebt een turbine. Je pumpt een vloed, een gewone vloed door de cilinder en dat gewone vloed drijft de turbine, drijft de drilbit en daarom kun je de revolutions veel beter controleren. En deze vloed komt uit de drilbit en het gaat terug door de annulus rond de pipe. En daarom removeden je alle partijen die je hebt gekregen. Want als je die partijen niet removeden, ja, ze accumuleren achter de drilbit en als je de drilbit terugpullen, het werkt niet meer. Dus je moet removeden alle partijen die je hebt gekregen om het te houden. Normaal gebruiken ze, voor deze vloed, een mix van water en bentonite. Bentonite is een artificieel vloed en bentonite mixed met water. Als je een heel hoge concentratie hebt, dan krijg je vloed. Maar als je een hoge concentratie hebt, dan gebeurt het zoals een zo called Bingham vloed. En een Bingham vloed is een vloed met wat strengte. Normaal vloed, zoals water, we proberen Newtonian vloed en Newtonian vloed niet te hebben strengte. Dus als ik water op de tafel ga, dan zal het vloen uit. Toothpaste is zoals een Bingham vloed. Als ik toothpaste op de tafel ga, dan zal het vluchten voor een while en het kan alleen vluchten als het heeft some internal strength, some shear strength. Toothpaste heeft some shear strength, so it behaves like a Bingham vloed. Bentonite also behaves like a Bingham vloed, so it has some strength of its own. The big advantage of this is that particles that are floating in the Bingham vloed will not really settle because the fluid has strength. So it's easier for the fluid to take all the particles out of the drill hole and keep it clean. But if you would have very big particles they could still settle because if the gravity on a particle is larger than the strength of the fluid it will still settle. But if you have small particles that's not the case, so they will stay floating. Ja, so that's about those drill bits. So if you look at the cutting theories that we will discuss later one of the applications could be drilling for oil. So those were the bits. This is an example of dry mining and you can see this is, well in fact in mining you could distinguish between two types of mining. Mining, well first of all you have wet and dry mining so buffed water and under water but you also have mining in soft soil and you have mining in very hard soil. So if you are mining in a mountain you use this kind of equipment. Usually they have a lot of power and it's all about rock cutting. Rock, whatever. This is another example of a machine they use in tunnel boring but this is tunnel boring in mountains, in rock. So the tunnels in Switzerland and Austria are made partly with machines like this. This is another tunnel boring machine. TBM is an international term for tunnel boring machine and this is the type of machine we can also use in soft soil. The problem in soft soil if you want to make a tunnel in Holland the problem is that you are constantly under the water level and that means if you are digging and you have no protection the water will flow into the machine and everything will be damaged. If you make a tunnel in Switzerland in the mountain you don't have to deal with that groundwater problem. So this is a tunnel boring machine. In fact those machines have the diameter of the tunnel so it makes the tunnel at once. Here you can see two pictures of what it looks like. Usually they are what we call integrated tunnel boring machines which means at the front here en hier they are removing the soil. Then the soil goes into the machine and it depends on whether it's dry soil or hard soil. If it's dry or wet soil. If it's dry soil very often they have a conveyor belt system in the machine to remove all the soil. If it's under the water line and in the groundwater usually the soil they remove is mixed with water and they have a pipe system and they will pump the material away. It completely depends on where you are. Behind the boring part here you can see they place the segments of the tunnel immediately to say how can such a tunnel boring machine move forward. They place the segments of the tunnel so the cylindrical segments and then you have cylinders which you can see in this picture those cylinders push the front forward so they push over the distance of one segment remove the soil The cylinders pull back the back part of the tunnel boring machine and they can place one more segment of the tunnel. This is the type of machine for example they used for the Throene Hart in Holland where they made the tunnel and I also thought for the Oster Schelde they are busy with the tunnel so somewhere the machine goes underground and then 10 km further it will come up again and at the end you have a full tunnel. How? Oh, you should think of meters per day. It's not very fast so between the moment it goes underground and the moment it comes up again it could be a year. It's very slow because it's not just removing the soil but it's also placing the segments and this is a very accurate business because if you do something wrong the tunnel will start leaking and you have a lot of problems so it's a rather complicated process. In fact for the channel tunnel from France to England they also use such a kind of machine in fact they use two because you have two tunnels so usually for tunnels for normal traffic for each direction you have one machine so they use two machines and one machine could do two lanes something like that. Then I have a picture of the biggest machine in the world and nowadays not many people hear about this but when I was a student we often had excursions you had? Ok, ok. Those are machines for the German brown coal mines and those mines are close to Maastricht just across the border and I think they would have like 20 of those machines in a row they are really huge if you stand beside the tracks you have to look up and it's like a huge building and I think they have 7 of those tracks under each machine well what those machines do you have an area with brown coal and in fact brown coal is the first stage of the formation of you could say black coal or oil oil, gas, coal are created by organic matter which is under pressure and if you wait long enough and you have enough sediment on top of it so you get high pressures at the end you may have oil or gas it depends on the organic matter one of the first stages we also had that in Holland but in Holland we call it fein fein is also that organic matter which compacts a little bit you can burn it and that's why they used it for power plants and so on and in Holland we used that fein for heating houses long time ago well in Germany they had areas and just imagine you have an area of 10 by 10 kilometers and you know there is a layer of brown coal of let's say 20 meters high but on top of that layer of brown coal first you have a layer of 10 meters of normal soil so you have to remove 10 meters of soil 10 by 10 kilometers with those machines before you hit the brown coal so probably they are busy one year or two years to remove the top soil and then they can start producing brown coal I thought one of those machines in those days you talk about 300 or 400 million euros something like that so if you have 20 of those machines you can calculate the investment then you have to work for a year to remove the top soil and start digging the brown coal this is a big what we call dredging wheels so this is cutting the material here you have a conveyor belt then the material is dumped in the central unit to another conveyor belt over here and then on land you have a fixed conveyor belt where they put the material on and then it goes to some railway station they dump everything on a train to be transported to wherever they need it they still use them but of course brown coal is not the cleanest way of getting energy it's one of the reasons why in the past we had this acid rain it came from the brown coal because yeah it's not compact enough and it doesn't burn too clean but nowadays like with coal in huge power plants they can burn things much cleaner and they have many installations to clean the gases that come out of the burning process so now they can do it clean but only in the huge installations then I want to say something about deep sea mining because in dredging if you want to do the masters thesis in dredging one of the topics that is very hot right now is deep sea mining and what is deep sea mining well first of all some impressions deep sea mining means that we like to get metals, minerals in fact whatever is valuable it could also be phosphates we like to get them from the sea floor and why well one of the main reasons is that a number of rare materials and metals are mainly found in China China of course wants to protect their own industry so in the rapid development of China but also the whole world we want to use the things we find in China first for our own industry which makes sense to me but that means since a number of those metals are mainly found in China the rest of the world has a problem so the rest of the world starts searching where can we find those metals and in fact a number of those metals are used iPhones, iPads, have for those screens and so nowadays there is a lot of demand for those metals so they searched in the world and they didn't really find those materials on land but they found it in the sea only on locations where the sea could be 3 kilometers depth 2, 3 kilometers ok, we know it's there but how to get it I must say right now there are not yet real projects to get the material from the sea floor but especially in Holland many companies are busy doing research and making big investments to investigate how can we develop equipment to get those materials from the sea floor and this just gives some impressions so here you have a ship at the surface but in the areas where they have those minerals often the weather is not so nice that you have a smooth surface so there could be a storm or whatever then on the sea floor you have machines digging the material because it's not just sediment laying there it could be rock it could be rock containing 1% gold or something like that and then it's worth to get it but you have to dig it with very tough machines the machines that we use for tunnel boring those kind of machines so that's what you see here and then you also have to get the material to the surface so most people think of a pipeline with a pump somewhere down below pumping the material up but now there are also ideas to start with a sort of lift and use a sort of lift on cables to pull the material up and in fact together with one of the PhD's we are going to write a paper to compare economically but also for the energy we will compare the difference between pumping it to the surface and doing it with a sort of lift this could be 3 kilometers so the picture shows that it's just 20-30 meters but in reality it could be 3 kilometers deep in the idea of IHC we call it a riser had the pipeline going up it's called a riser and they use 5 pumps and then you also have the problem of how to get the power there so this is just an artist impression well this is another artist impression with a sailing ship and the other ship was more a floating ship this is more a sailing ship and here you see this is from IHC because I recognize this device it's a design of IHC well where can you find those things in fact I think most of you know that our planet is not made of rock but in fact our planet inside is fluid it's magma it's the stuff that comes out of volcanoes and on top of that magma we have tectonic plates so the surface of the planet is not one shell like an egg no it's plates and those plates float on the magma and those plates have a certain velocity not very high but there is a velocity and here you can see different plates so those lines give the borders of those plates and wherever the plates touch each other there is basically three things that can happen the plates hit each other well in such a case if two plates hit each other they get mountains so the Himalaya is typically at the border of two big plates it's also possible that they are removing so the distance is increasing because if somewhere two plates are hitting each other then at the other end two plates have to create more distance well if they create more distance it means you get very deep water so for example near Japan where is it? here somewhere near Japan the Marianetrog in Dutch it's 11-12 km deep over there and that's because they are moving apart and then the third way you can have an interaction is shearing they move like this and basically that's what's happening here at the west coast of the USA if you ever have the opportunity to fly to LA or San Diego take a flight from Amsterdam by KLM they will fly over the North Pole normally everybody would say this is the shortest distance but it's not because the earth is a sphere you fly over the North Pole and then you arrive like this vertically and then from the plane you can actually see this shearing you can see roads that used to be one road and now one road is here and the other part is here because it's sheared like this you can actually see that but you can only see it from a plane if you walk there you don't see a thing but that's the reason why you often have earthquakes in the west coast of the USA and you also have like Mount St. Helens in the north of the USA which had a huge explosion 20-30 years ago and the whole top of the mountain was removed by the volcanic eruption and well that's because you have this shearing because of the shearing sometimes the pressure of the magma is so big it can come to the surface and then you have a volcano that's the way it works luckily those processes are very slow so on the time scale of a human life we don't really have too much trouble of this but if you look on a different time scale there's a lot of activity so here you can see all the places where those plates hit each other here or whatever well in many of those locations because of the volcanic activity there will be certain metals minerals at the sea floor and one of the ways it works and this is what we are looking at specifically at that 3 kilometer water depth you have the heat at the bottom you have heat coming from the magma from the center of the earth on the other hand there is water moving into the pores of the rock of the stone because also rock has a certain permeability so water can flow in rock but usually not as much as in sand the permeability is much lower but it doesn't mean there is no water flowing it's the same as if you look at an electricity wire everybody say the plastic around it is completely isolating for electricity that's not true if you have a sensitive measurement device you can still measure the current coming out of the wire but the current is so small that it's not dangerous for people and we say ok, so it's safe but it doesn't mean there is no flow of electricity out of the wire it's still there there's also a magnetic field around the wire so it doesn't isolate 100% it just isolates enough well in the same way rock, stone has a very low permeability but it doesn't mean there is no water flowing so water is still flowing into the sea floor gets heated by the heat from the magma below and it actually starts cooking the temperature of that water could go up well I know over here the temperature could go up to 400 degrees but because you are under such a high pressure it doesn't yet start cooking but it's already 400 but then you can imagine in the stone maybe it's 1000 it could be very hot well what happens so the water gets heated the water absorbs metals, minerals, whatever it goes into the water and then the water has to find a way out because first of all the volume of water is increasing with temperature the lowest volume you have at about 4 degrees but at 1000 the volume is much bigger so there is a lot of pressure so the water has to get out of the stone and that's what's happening here and then the water mixed with those metals comes out of a sort of mini-volcano it's not a real volcano it's just because of the water and because of all the metals and so on in the water it looks black so that's why we call it a black smoker then it cools and all the particles in the water will settle and that's how this volcano is formed so the longer you wait, the bigger the volcano well all the material that settles on the sea floor and around the black smoker usually contains a lot of metals and minerals they have found cases there where the soil contains 30% copper which is really a lot and if you make an economic calculation well, you can calculate that if you get like 100 cubic meters a day to the surface it could already be profitable because of the price of the copper and you can imagine if you would have 1% gold well, in 1 cubic meter, that means 1 liter of gold which I think is 14 kilos or so well, 1 kilo on the free market is 44.000 euros so that could be profitable so maybe the amount you need is not that much because of the price but how to get it here you can see some pictures of what it really looks like and you should keep those pictures in mind because you can see the sea floor is not a nice flat sea floor by the way those chimneys could be up to 20 meters high we don't know how high this one is but this could be 20 meters so it's not just something on the sea floor it's really big and that also means you can't just put some vehicle on tracks on the sea floor and start digging because the sea floor is not flat it's a lot of mountains and hills and rocks and whatever this is another picture of such a black smoker is what it actually looks like here you can see a picture of what the sea floor looks like and then you can see it's not flat so if you want to use vehicles on tracks first you have to make it flat yourself and then from there you could start getting all the materials from the sea floor this is some idea of what a platform could look like and in fact it's a copy of what we use in the oil and gas business it's a semi submersible you can see the riser here coming from the sea floor and then regularly all the material maybe it's already pre-processed on the semi sub it has to be transported to a shuttle tanker which is this one to bring it to shore this is an impression of IHC Dutch shipyard they are very busy with this they already started a special department for deep sea mining and they have many ideas on how you could deal with it this is a close up of that picture so this in fact is a drum cutter to remove the material but we still have to do a lot of research because the design of such a vehicle depends on what do we actually find here you can see a machine also on tracks here you see the drum cutter and here you can see the connection to the riser so inside the vehicle the material that you are cutting is mixed with water and then it has to go into the pumping system and probably there is already a first pump in the vehicle but that pump will never be strong enough to pump it all the way to the surface another impression here they have two vertical rotating cutters and why do they do that if you make the two cutters counter rotating you don't get a side force on your vehicle if you only have one cutter well not with a drum cutter like this you also don't have a side force but if you would have a cutter like this you always get a side force and is the connection between the tracks and the sea floor strong enough to keep it in the right direction but if you do two counter acting ones you remove the side force 100% because the cutting force on both cutters will never be exactly the same but you can remove most of the side force this is a device they already use in reality but not for those water depth according to me one of the designers of IHC read too many comic books right exactly it's an artist impression this is a clamshell I already showed before because one of the ideas is you can use cutters to cut the material and that means you already create very small particles at the sea floor and then pump it but if with a clamshell you could get big chunks of material en transport it to the surface as a big chunk of material maybe that's cheaper maybe that's more profitable and one of the problems we will see later is that under 300 bars those 300 bars create very high cutting forces if I would crush the same material under atmospheric pressure probably the energy required to crush it is much less so it could be profitable to do that at the surface but we still don't know so that's part of the research we are busy with ok it's 5 minutes before but let's do a break now and then I start the next presentation after the break any more questions? explosives who is going to put them there? one of the things everybody thinks 3 kilometers there is no life there but they are already investigating the whole environment the biology at those water depths and it appears there is a lot of life so nowadays well everybody can see that in the newspapers if you want to do something you have to take care of the environment and then using explosives will be a big problem but also using those machines cutting I know from the Japanese they already do a lot of research into the environment at those water depths and that means the United Nations will probably create new regulations and you have to follow those regulations so using dynamite we do it in dredging but first of all, divers cannot go to those water depths submarines, normal submarines have a maximum water depth of about 300 meters so with a normal submarine you can't go to 3 kilometers who is going to put it there because you have to drill it only works if you drill holes and put the dynamite in the hole it's not a matter of just placing it at the surface and the production will not be high enough and then I think another problem is that part of the working principle of dynamite of explosives is the pressure it creates en especially the pressure difference with atmospheric pressure but there you already have 300 bars so you should ask the question will dynamite work at all under 300 bars I have no idea ok, we have a break ok a little bit about soil mechanics if you really want to know a lot about soil mechanics you should follow a soil mechanics course but I just want to rehearse some of the basics for those who don't know about it first soil creation if we look at soil rock, sand, clay basically in dredging and offshore we distinguish between sand, clay and rock but there are also many mixed grounds well often soil is created in the mountains and the mountains are created by those tectonics movements and what you get in the mountains is you have rock in the rocks you have cracks and because it's always very cold in the mountains there will be water in those cracks the water will freeze, ice is expanding and when the ice is expanding the cracks will grow and at a certain moment pieces of rock will fall down the mountain and usually those are not only the big pieces of rock but also smaller pieces and it will arrive at the bottom of the mountain high in the mountains you have glaciers so if the pieces of rock fall in the glaciers they are transported through the glacier usually because of friction they will already disintegrate a little bit and at the bottom of those glaciers you always see a lot of pieces of rock sand, whatever at the end of the glacier the ice is also melting so you get first a small river we become bigger and bigger and those rivers transport the material all the way to the sea so you can imagine if you start at the glacier you have very angular material because it's just broken from a piece of rock or the mountain so it's very angular it's not a nice round particle it's angular then during the transportation through the river all those particles are transported especially if you have high flow velocities but they also hit each other so there will be some more disintegration particles get smaller and the closer you get to the sea the more round are the particles and also the more fine material you have so at the end of the river usually in an estuary like in Holland Holland is one big estuary the fines will start to settle because the flow velocity is decreasing the river gets wider flow velocity is lower particles start to settle so you have a lot of fines in the bottom of the river and the rest of the material will flow to the sea usually if you look on Google Earth and you look at the end of a river usually in the sea you can see there is a lot of sand which settled over there so the further you are in this transportation process the more round the particles then what can happen through millions of years you have those tectonic movements so it could move up, it could move down there will be more material on top there could be calcium involved and if you have calcium in the sand or in the particles you may get calcium bridges and then you get something we call sandstone so it becomes a sort of stone like material sedimentary rock possibly many things could happen well for sand, clay and silt and one thing and I will show in another picture after this in our way of talking you have sand which is made of quartz and if it becomes very fine we call it silt but in many classification systems they say if I am below a certain particle diameter we call it clay and basically you should not do that because clay is a completely different mineral chemically than sand so if you have quartz powder you may call it silt but once you talk about a different mineral like bentonite that is clay and clay has a completely different behavior than sand but people mix it up because if you have silt of let's say 2-3 microns very fine particles you get the so called van der Waals forces that take care of some attraction between the particles and it may look in the behavior a little bit like clay but it's not clay has chemical behavior silt has no chemical behavior because basically quartz is chemically inert for us they make some classification diagrams this is just an example so you don't have to learn this by heart but it's just an example where you say we have clay silt and sand and then depending on the composition in percentage they call it sandy loam or clay sand or whatever usually in what we are doing in dredging we are either working with sand or we work with clay or we work with rock and we don't have to deal too much with those mixing soils it could be that you have some clay in your sand but usually we talk about sand or clay this is an example of how people classify materials and you can see for the very fine particles they say we call it clay and then here you get the silt and then from fine sand to very coarse sand and if you go further down you would call it gravel and boulders and so on and so on but that's what I wanted to say clay is chemically different from sand so in fact it shouldn't be in such a list but in most books you will find such a classification for rock I put this in the lecture notes on blackboard you also don't have to learn but this just gives an overview of the many types of rock that could exist one of the big problems of rock for us is that many people think rock is very homogeneous it's massive but in reality in rock you already have a lot of fractures and the amount of fractures determine how easy it is to cut the rock so if you have really very homogeneous rock it's very hard to cut if it already has a lot of fractures it's much easier to cut but how do you know it so you need testing to determine how strong is the rock really I will show you some tests later then particle size distribution in any type of soil you do not have a material where all the particles have the same diameter so you have a certain distribution and this is a typical graph of a particle size distribution in Holland we start here with the smallest diameter this is in millimeters and here you see the biggest one but in American magazines or journals I often see it reversed they start here with the biggest diameter and they end with the smallest diameter but it's easy to see because you always have such an S curve and if the S curve is opposite it means you have the opposite scaling how does it work well this is a so called cumulative grain distribution curve that means for example if I go here to 50% and I look at the diameter in this case it would be something like 0.15 millimeter that means that by weight 50% of the particles is smaller than 0.15 millimeter if I take 10% here and for example the red curve well I'm at something like 0.022 millimeter which means 10% of the particles is smaller than that diameter that's the way this works in practice we usually work with what we call the D50 so the D50 is the diameter matching the 50% so here it would be the 0.15 here it's much smaller but only the D50 doesn't tell you everything because the steepness of this curve is also important if you only know the D50 you don't know nothing about the steepness of the curve so for example if I have a very steep curve an almost vertical curve that would mean all the particles have about the same size well if all the particles have the same size just do an experiment for yourself with marbles, knickers so they are spheres if I put spheres in a box I get quite a high porosity because there are no particles in the pores between those marbles so I get quite a high porosity but if I have a very low steepness of my curve it means I have very small particles and I have very big particles so there will always be smaller particles fitting in the pores between the bigger particles that means I can have a much higher density because all those pores can be filled up with smaller particles it also means I will probably have a much lower permeability permeability is how easy the water will flow through the material and if I have big pores water will flow easy so if you take gravel water hardly has any resistance flowing through the gravel it has resistance but relatively small if I would have sand with very low steepness and very small particles then probably the permeability will be very low it's very hard for the water to flow so the steepness of the curve determines on one hand the density so if it's steeper it's less dense a descent as a whole not the density of quartz but the density of descent per cubic meter so with a less steep curve the density will increase the permeability will decrease another parameter which we will see later is the angle of internal friction so how much friction do we have if I have particles in the pores between the bigger particles I will probably also have a higher angle of internal friction so some people use the D15 and the D85 for this others use the D10 and the D90 so if I know here the D10 this point and I know the D90 in fact I can put a straight line between them and I have a measure for my steepness whether I do it with the D10 and the D90 or the D15 and the D85 that's a matter of choice ja both because the particle density for quartz is 2.65 so 2650 kg per cubic meter for normal sand we always use 2000 2.0 in tons per cubic meter but in fact sand that's if you have 40% porosity but sand could have a porosity let's say between 30 and 50% so you can calculate what the range of the density is so densities could start at something like 1800, 1900 go up to 2100 for situ sand but it completely depends on whether it's already compacted then it will be a little bit more than 2000 if you just let it settle freely probably you are at 1900 or something ja and when it's solid depends on the grain distribution because in dredging now we dredge in the pipeline up to 1800 but 1700 is already rather common we could go up to 1800 but of course only if it's still fluid otherwise you can't pump it so I could make a sand with the density of 1800 which is a solid sand but I can also make one which is a fluid sand and if you say which one is the most important well if we talk about cutting processes and so on we deal with the density of the sand in situ so that's the 2000 if we talk about hydraulic transport and sedimentation in hoppers you have to deal with the settling velocity of particles and then it's the density of the quartz that's important ja so it depends on which application you know the problem of dredging is that we are constant at the interface of solid mechanics and fluid mechanics we start with sand and clay as a solid but as soon as we cut it and it goes into the pipeline system it's a fluid and the problem is the people of fluid mechanics sometimes they do what we call two phase flow water and solids or water and gas but very low concentrations they never work with the concentrations we work with we can work up like I said 1.8 when you have 50% volumetric solids concentration usually they don't work with that also if you go to hydraulic engineering here in this building and you talk about erosion processes in rivers usually the concentrations are much lower it could be 5%, 10% but maybe in the Yellow River in China the concentration is a bit higher they really have a high concentration of solids but not like what we do so and I will also explain the difference well maybe I already did but the main difference with soil mechanics and what we do in soil mechanics in general they want to construct something from soil that stays there for a very long time building a dyke, building a road, building a railroad and what we do we want to destroy it in a fraction of a second because we want to cut it and transport it and after this I will show you active and passive soil failure and then you can see the difference between the two but anyway this was the particle size distribution if you take the derivative of this you could model it as a normal distribution not 100% but it could get close to a normal distribution and what I do myself is I take the bottom part below the 50% and use that as one normal distribution and the top part as another normal distribution both having 50% of the probability and then if you combine two normal distributions and then integrate them you can get a good curve for almost any type of soil some parameters, Atterberg limits I must say I don't know too much about them because we don't really use it but in soil mechanics they often use it what are they, well you have the maybe there are more limits but the plastic limit and the liquid limit basically with the liquid limit what you do is you take some clay those are parameters for clay you take some clay you add water until it starts closing because it gets so fluid it starts closing and then you determine the water content and that's your liquid limit the plastic limit is often that you take a piece of clay you start rolling until you see cracks in the clay and that's what you call the plastic limit well they have equipment for that but we cannot really relate those limits to parameters like tensile strength, shear strength and for the cutting process we need the compressive strength the shear strength, the tensile strength maybe there are empirical equations relating the two but if I can measure the compressive strength directly and there is a good device for that why would I start correlating with those things so I just mention them because in soil mechanics they use them but we don't really use them mass-volume relations those are important for example you have density well density is very simple density is the mass divided by the volume and then you get the density but soil consists of solids water and maybe air if you are above the water level probably you also have air in the soil so you should also know what is the porosity so porosity is the percentage of pores void ratio is the percentage of pores divided by the percentage of solids so it's a different number but the meaning is the same but we always use the porosity well density as such specific gravity is the density of a material divided by for example the water density in fact in general we say the fluid density because it doesn't always have to be water but if you divide it by the water density for normal applications so the specific gravity of sand is 2.65 sand is 2650 water is about 1.0 so you get 2.65 if you want to be very accurate it depends on is it sweet water salt water and sweet water is a little bit more than 1.0 and salt water is usually 1.03 ok then I should divide the 2650 by 1030 and I'm a little bit more accurate but for normal calculations we just say 2.65 relative density is where are you if you consider a sand can have a minimum porosity and a maximum porosity at the minimum porosity we say the relative density is 100% because then it's the most heavy at the maximum porosity we say the relative density is 0% so you get a scale from 0 to 100% but because the 0%, the porosity of 0% and the porosity of 100% depends on the type of sand so it gives you some relative feeling where am I but you can't say 0% is always a porosity of 50% it depends on the type of sand but they did research on that so here you see the scale of 0 to 100% for the relative density vertically the so called SPT value which I will explain later in detail but it basically is you take a cylinder you hit it with a certain weight and you count the number of hits to get one feet into the ground that's the SPT value and then you can see well if my relative density is 0% so that means the highest porosity so I have very loose sand so the SPT value is almost 0% and at 100% it's pretty high then permeability permeability is how easy can the water flow through the material and in normal sense by the way here it's in centimeters per second and here you can see different types of material well in normal sense we have a permeability of about 10-4 let's say between 10-3 and 10-5 that would be a normal permeability for sand but as we will see later the cutting forces are in certain cases are proportional with the permeability so if I have a range of 10-3 to 10-5 that's a factor 100 if I don't know the correct permeability I could make a mistake of maximum a factor 100 in my cutting forces and if I'm designing a dredge and I calculate the design loads with a factor 100 in the wrong direction I have a problem later not if it's 100 times too much it will always work but it will be too expensive so that's permeability if you look at clay the permeability in clay it depends on the type of clay but it could be like 10-10 10-11 so compare it with sand there is a factor of about 10-6 lower which means it's 1 million times less permeable than sand and in rock it really depends on the type of rock if it's rather homogeneous rock the permeability may even be smaller than in clay but if you have rock with a lot of fractures so you can't say you can't give a general answer although in those tables we have some numbers for different types of rock angle of internal friction and that's a very important one the angle of internal friction mechanical engineers are used to think of friction coefficients civil engineers are usually used to think in terms of an angle of friction what is the difference if you take the tangent of the angle of internal friction you have the friction coefficient so basically it's the same it's just another way of putting it this angle of internal friction you will find in all equations whether we are talking about clay, sand, rock you have to deal with the angle of internal friction now a very important thing I always notice at exams that people mix it up friction depends on normal stress or normal force so the friction force is the normal force times the friction coefficient if I don't have any normal force I don't have any friction force later we will also talk about cohesion and adhesion cohesion is shear strength well adhesion is the sticky effect of a material and adhesion does not need normal force so if I take adhesive tape and I put it on the table and I start pulling I'm not pushing on the tape the tape has adhesive strength itself so cohesion and adhesion are shear strength and they do not require a normal force friction you only have if you also have normal force or normal stress here we talk about the angle of internal friction and for normal sense I would say the angle of internal friction is somewhere between 30 degrees and 45 degrees those are not absolute limits but somebody can always find a scent with 25 degrees or 50 degrees I would say 95% of the scents is between 30 and 45 degrees something like that here you see a small table again they use the SPT value in many some mechanics books you will find that and the reason is that SPT is so easy to determine it's very cheap and you can do it anywhere in the world you don't need an expensive laboratory for that so you can see a classification of scent very loose scent has a very low SPT value and an angle of internal friction of about 30 degrees here they say 29, but it's 29, 30 is about the same then loose 29, 30, medium 30 to 36 dense 36 to 41 and very dense scent bigger than 41 now this angle of internal friction does not only depend on the density of the scent how compact it is it also depends strongly on the angularity of the particles so if I have very round particles it will be lower if I have very angular particles it will be higher so if you do a dredging project up in the mountains probably you will have a much higher angle of internal friction if you do it in the sea near an estuary probably the scent is already quite rounded the friction angles will be a little bit smaller here you also see in fact what you have here here the SPT value and here the angle of internal friction and there is some correlation equation for that so if I know my SPT value I can determine the angle of internal friction but the red lines give the scatter of those measurements so there is a scatter of plus minus 3 degrees which is quite a lot this is a picture I found in a book of petroleum engineering here about mining and it gives the relation between the friction force and the normal force for many types of rock and if you put some lines through it in fact this angle gives you the angle of internal friction and that's the angle between friction and normal force but if you take the lowest points I think you would get at somewhere like 20 degrees or 25 degrees but it's just an example of measurements they did in rock of course it's more difficult to determine the angle of friction than in sand if you just take two pieces of sandpaper you stick one to the table and the other one at the top and you put a certain weight on it and then you start pulling and you take the normal force and the pulling force you already have your angle of friction of that sandpaper and that's how you can do it and if you want to know the external friction angle which is the friction between sand and some other material like steel well just put the sandpaper on a piece of steel and do the same experiment and you measure the friction angle between sand and steel external friction angle so that's the angle between sand or rock or whatever and in our case it's always the cutter head so that's steel in general what people do you see some correlations here and I always do I take two-thirds of the angle of internal friction it doesn't have to be that way it could be a little bit different but first of all the angle of external friction that you can measure can never be bigger than the internal friction angle theoretically it could but suppose I have a blade and sand is moving over the blade and the friction between the sand and the blade is bigger than the angle of internal friction what will happen is the particles will stick to the blade and one layer away from the blade the particles will start sheering over each other with the angle of internal friction so in such a case I will measure the angle of internal friction although I could make a surface of sand particles I glue all the sand particles to that surface and that way I create a higher friction angle but still what I measure will be the internal friction angle because the sand will start sheering internally so that's why I say the maximum external friction angle is the internal friction angle you will never measure more although theoretically it could but in general I take 0.67 or 2-3 and that works very fine but it's just a rule of the thumb and if you want to know exactly you have to do measurements but I noticed we did a lot of cutting tests in our laboratory and what I noticed with giving some sand samples to the soil mechanics laboratory and then you get values for this external friction angle they do not match what we found in the laboratory because during a cutting test you have completely different stress conditions as in a standard test in the laboratory so I prefer to get my data from the real experiments clay cohesion adhesion later we will talk more in detail about it but cohesion is the internal shear strength of a material so in clay we often talk about cohesion but we also talk about shear strength in fact for steel you could also talk about cohesion but nobody does everybody will call it shear strength but cohesion is equivalent to shear strength for me in the way we talk and adhesion is the external shear strength so in both cases you talk about shear strength and they are not depending on any normal stress or normal force here you get a table with some values well we talk about very soft clay well here they talk about the UCS I will explain later it's the unconfined compressive strength which normally is 2 times the cohesion smaller than 24 that would be a clay that you used when you were little in Dutch we say bootsier clay so very soft clay it's also very sticky and often the adhesion of such a clay has about the same value as the cohesion so the external sticky effect is about the same as the internal sticky effect and of course that depends on the other material but and then the harder you get and here you have almost 400 kPa UCS value the harder it gets the smaller the adhesion so if you take a very hard clay it is possible that it hardly has any adhesion anymore and with certain types of rock in fact if you keep compacting the clay it could become a sort of sedimentary rock and if you put your hand on the outside of such a rock you will not notice any sticky effect so the adhesion is almost zero or it is zero so with clay you cannot really say adhesion is like 50% of the cohesion no, for very small cohesions it's almost equal for very high cohesions it's almost zero in offshore they have to deal a lot with clays for example with suction anchors and other types of anchors and if you look at the regulations of the classification bureaus like API and DNV and so on they have a rule that you take the adhesion 50% of the cohesion well this completely depends on is it soft clay or hard clay you cannot say it's 50% but what is the task of those classification bureaus so in Europe we use fairy toss a lot DNV, Lloyds, API is from the American Petroleum Institute what is their task they work for an insurance company so their task is to set rules that they care it will not be damaged it will take care that if you build a ship or a platform it will stay intact for a long time at least like 30 years because if it doesn't they have to pay so all their rules contain safety factors don't try to explain their rules with scientific equations because you will get confused often it doesn't work in fact for the holding capacity of anchors I found that you have certain graphs from API and you also have certain graphs from a company in Holland named Freihoff anchors who produce anchors the line of API is very conservative so the holding capacity of anchors is relatively low but if you take the book of the anchor company it's much higher for exactly the same anchor so I once gave students an assignment I want to see what do you find based on science and they found a line in the middle and then you can say of course API wants to be conservative otherwise they have to pay if it goes wrong and Freihoff anchors wants to sell anchors so they are more positive that's the way it works but if you look in those books or on internet be careful with what you find there because usually it doesn't have enough scientific base it contains safety factors and when you make a design in your master thesis we want to see the scientific basis and then if you say well this is what I calculated and I like to put a safety factor of 1.5 or 2 on it perfect but then it's clear what is the safety factor so we always want to see everything based on science ok this was some clay quickly we will do some of the testing equipment this is an unconfined compressive stress well in fact you just take a cylinder of material you start compressing it until it fails and you measure the relation between stress and strain so here you have the stress here the strain you will probably find the maximum which we call the compressive strength and usually after it collapses the stress will also collapse because the material already failed and the shape of such a diagram tells you something about the material so that's the UCS value and like I already said the cohesion the shear strength is usually 50% of the UCS value but I will explain that more in detail when we do the more circle unconfined tensile strength you want to have a sample like this you do a tensile you start pulling on it and when it fails that's the tensile strength what we use more for rock is the so called Brazilian split test the Brazilian tensile test you will find the abbreviation BTS in many books which comes from this test what they do they take a cylinder of rock start you put it horizontal start pushing on it and if you push hard enough it will split in two at once so you get a split over this line and then you have a simple equation of calculating the tensile strength of the material so this is an important one because we use it often in dredging and especially when you do deep sea mining people will say what is the BTS value brittle versus ductile brittle you can have brittle in two ways well let's first talk about ductile ductile means that you have a nice continuous failure process with plastic deformations but no cracks it's a nice continuous failure mechanism it's like when you are cutting steel in a turning machine you get a continuous chip hardly any fracture so that's ductile steel is a ductile material but if you cut rock everybody knows if I put a pick point or whatever in battle or in the rock and I start pushing at a certain point the whole chip will be blown out and that's what we call brittle now basically you have two types of brittle you have tensile failure which can cause brittle failure and you have shear failure so suddenly it shears like this that could also be brittle so brittle is not just a tensile fracture it could be a shear fracture and in rock cutting very often both mechanisms occur at the same time during the process of rock cutting well if you are busy with ductile cutting and you do a test you will see the stress increases and at a certain point it's almost constant it can still increase a little bit and that's when you have ductile behavior if you have the brittle behavior like we saw in the UCS test you get a maximum stress and after that it collapses because the material fails maybe it could even go back to zero depends on the test some other tests the SPT I already mentioned it SPT you take a cylinder with a certain diameter and a certain cone angle that's important that the cone angle is standard it's 60 degrees usually you hit with a certain weight in fact the way they start that you drop the weight over a fixed distance and you get a certain impulse on the cylinder and then you count the number of hits they call it the number of blows per feet so it's an American invention and the number of blows per feet that's the SPT value so you can imagine if the ground is harder I need more blows per feet and I have a higher SPT value so this gives an example of that then we also have the CPT the cone penetration test it's also a cylinder with a certain diameter also a cone of 60 degrees but in this case you need much more equipment you push it into the ground with a fixed velocity so it's not with blows it's with a constant velocity and if you look at those devices they put many different transducers in so you can measure the resistance but you could also measure the porosity of the ground by having pressure transducers or whatever you can measure the friction and the adhesion on the cylinder by having special segments for that in fact you could measure whatever you want to measure so those are much more complicated devices and you need this truck with enough weight otherwise you don't have enough force to push it into the ground so this is already a much more expensive way of determining something from the soil but it's more fundamental it is better but it's also more expensive those are some of the cones they have and usually you can see behind the cone there is a section where they measure the friction triaxial test very important I will tell more about it when we do the Mohr circle but here you have a piece of material it could be sand it could be clay just a piece of material in this chamber you could put a certain pressure you could do that you could say I want a hydrostatic pressure of 300 bars like in deep sea mining and then I will do my test you could do that then you start pushing from the top and then when the material fails you get a so called Mohr circle out of that but usually I like more circles at different confined pressures to get the angle of internal friction we will look at that when we do the Mohr circle this is a device this is the real device they use it a lot in soil mechanics this is a simple test to measure shear here you have your soil you push with a certain stress you put a normal stress on it and you can measure your friction or adhesion that's also a way and you can make it as fancy as you want and then we have the vein shear test they often use this in for example silt or weak clay but if the clay is too hard probably it won't work so here you have a vein you start rotating it you measure the resistance and that's a measure for your shear strength of in this case it's the shear strength I think that's it for today and then next week we will continue with Mohr circle, active passive and with sand cutting