On a global scale, the present-day demand of coastal protections, port expansions and construction of artificial islands, rises. To be able to accommodate for all these environmental changes, complex dredging operations have to be performed. Depending on the type of soil and in-situ conditions, a suitable excavation and transportation method has to be chosen. From an economic point of view it is desired to make this process as efficient as possible. The only way in doing this, is to understand the physics of the rock cutting process and be able to predict the behavior of the rock formation during cutting. This research focusses on the physics that come paired with the excavation of rock deposits under atmospheric conditions. The removal of rock results from the interaction between the cutting tool and intact rock, destructing the internal structure of the rock formation. A rock may either fail in a brittle tensile, brittle shear or ductile manner. Over the past decades various calculation models have been developed to predict the cutting forces in rock cutting. Most known prediction models assume one failure mechanism to be dominant, using a specific cutting tool geometry. For the sake of this research a sharp pickpoint is used. The elaborated, existing calculation models within this research using a sharp pickpoint as a cutting tool, all consider the rock cutting process to be a two-dimensional problem. To investigate if this hypothesis about the rock cutting process is correct, experimental research is conducted. A distinction is made between two different rock types, both varying in strength (e.g. sandstone and artificial rock). Experimental research revealed that the measured forces greatly underestimate the results of the existing prediction models. The author states that this inaccuracy partially arises from the fact that, in practice, the excavation of rock is actually a three-dimensional problem, since visual observations clearly showed that chips broke out sideways. Based on the experimental measurements, two new calculation models were set up, incorporating this three-dimensional effect. The first model implemented fracture mechanics theory, focussing on the required local crack tip stresses to initiate a tensile crack. Due to several unknown empirical parameters, the tensile-dominated fracture model gave unsatisfactory results, underestimating the measured cutting forces. The second model was set up by focussing on the actual physics that were observed during cutting. Based on visual observations and individual chip investigation, three different failure mechanisms can be substantiated that occur during cutting: crushing, major shear failure and tensile failure. By elaborating on the developed prediction model, it appears that the forces due to crushing dominate the total force spectrum. For a crushed zone to develop, penetration into the material is required. The author discovered that rock's resistance to obtain a certain penetration, needs to be accounted for when calculating the stresses within the crushed zone. By achieving the desired penetration, a large vertical force arises, indicating that frictional effects also need to be considered. This means that forces due to crushing are dependent on the hardness of the rock and frictional resistance between the cutting tool and rock's top interface. Based on production measurements and cutting groove analysis, the crushed zone dimensions were able to be determined, whereupon an expression for the pickpoint's indentation area was found. A surprising discovery was made during the analyzing phase of the force data. Regardless of the pre-set cutting configuration, a basic force level was observed during cutting, which is quite well-approximated by the crush force component, including frictional effects. Despite the formation of a crushed zone, chips failed in a cataclysmic manner. Individual chip investigation revealed that a certain fraction of shear and tensile failure is present along the failure plane. It appeared that the contribution due to tensile failure becomes more significant as the penetration depth of the pickpoint increases. This can be explained by the fact that a tensile crack has the ability to grow and propagate to the rock's top interface. The results of this research show that predictability of the forces increased significantly, compared to the existing two-dimensional calculation models.

For present-day drilling operations in deep and challenging well sections, a technology called casing while drilling can be used. It involves isolating and ‘casing’ a formation while drilling, where the casing itself is used as the drill pipe, which is cemented in after a certain depth is reached. By doing this, the need for separate casing runs will be eliminated and well stability is improved. The concept has become increasingly popular since the beginning of the 21st century, due to an increase in technical possibilities and use of this technique, which makes it more profitable. To enlarge a wellbore past its original drilled size, to enable lowering of the casing, an underreamer is used. Under reaming can be performed in a reaming while drilling (RWD) configuration. To perform these operations, the bottom-hole assembly (BHA) containing the underreamer is lowered in the casing string to a depth just below the casing shoe. Afterwards, drilling fluids are used to fill the casing and pumps will be engaged to drive a hydraulic piston in the underreamer assembly that opens the cutter blades. Hydraulic pressure is used to fold the blades outward and prohibits closure of the tool. The width of the reamed borehole is not only determined by the outer diameter of the casing couplings that have to fit thru, but there also has to be a clearance for the drilling mud. The annular space between the borehole and casing is relatively small which causes relatively high friction losses during current operation. Because of this, the dynamic pressure loss of the drilling fluid along the outside of the casing becomes too high. To lower the pressure, the borehole needs to be enlarged further than possible with underreamers currently available. There are also limitations on the length of the underreamer. From tests carried out by Huisman, it is found that an increase in length has adverse effects on the steering behaviour of the BHA. Therefore, the length of the reamer should be kept at a minimum. The DRILLSTAR Z600H design that is currently being used does not allow for a diameter enlargement. New concepts must be devised to enable this. A solution to this problem can provide Huisman Well Technology (HWT) with the opportunity to perform the drilling of more and deeper wells. A solution to the problem was found by splitting the piston and spring internally. This enabled the spring to be placed in the top part of the underreamer while the piston remains in the lower part. The blocks are located in the middle and fold out eccentrically to reach a hole diameter of 228.6 mm (9 inch). The angle under which the blocks fold out has been reduced from 60 degrees to 45 degrees to allow the underreamer to be shorter by 66 mm.

For years, ESI Eurosilo have successfully stored several, mostly low-density, non free-flowing bulk materials in their silo’s. Recently, demand has arisen whether bulk materials outside their current range could be stored using the same reclaim screw system. Unfortunately, the theory behind the screw dates from the 1980s and assumes fine powdered bulk material, making it difficult to predict the reclaim screw performance. This paper demonstrates the effects of bulk materials on the scraping process of a reclaim screw by modelling its mechanics using DEM, as scraping is most prone to external influences like consolidation. The reclaim screw has been simplified to a single linearised flat disk, which is still able to exhibit a behaviour similar to the screw. The effects of bulk parameters have been investigated using the DEM model by a comparison to the analytical model to see whether the simulation results agree, a screening process to find the most significant bulk parameters on the scraping process and an optimisation to find the optimal screw design of a low- and high-density bulk material.

Transportation of slurries over a distance has always been one of the main objectives for the dredging industry. To accomplish a transport, centrifugal dredge pumps and mixture pipelines need to be perfectly intertwined. For the centrifugal dredge pump, available information is relatively scattered or confidential. The performance of a centrifugal pump is mainly determined by conducting experiments with actual slurries or estimated on the performance characteristics obtained from water. Besides empirical research in laboratories and field studies, numerical Computational Fluid Dynamics (CFD) simulations have become an interesting asset in creating models for multiphase situations. This mainly due to increasing computational power that is currently available. The goal of this research is to gather and analyse information on particle trajectories near impeller blades and its unsteady head characteristics in a centrifugal dredge pump for visual validation of Cao et al. (2019) CFD model outcomes. In the literature research, information was gathered on empirical models, CFD simulations, an analytical description of particle behaviours along impeller blades, (dimensionless) pump characteristics and impeller/shell designs. On the experimental side, the executed experiments consist out of head and discharge recording by throttling the exit valve for pump characteristics in single phase water conditions and mixture conditions at 564, 846, 1128 and 1410 RPM. The used impeller has a diameter of 155 mm and is a so called "open impeller". At mixture conditions, delivered volumetric concentration (Cvd ) of 5%, 8%, 12%, 15% and 20% are reached with glass bead particles of 1.5mm and 3.0mm with a density of 2500 kg /m3 . High speed image recording are made of the impeller blades at above mentioned situations but with a steady exit valve set to 50% open. The experimental study gives an interesting inside on the behaviour of particles internally. On the particle trajectory side, where PIVlab image analysis are conducted, the result can be used partially on the streamline verification from the CFD model of Cao et al. (2019). This especially applies for the single phase situations and partially less for the mixture situation due to problems with particle distinguishing. Summarised, this means that the conducted experimental study is not able to fully verify the CFD model outcomes of Cao et al. (2019) for the instantaneous streamlines and concentration distribution between the impeller blades. Though, it supplies a steady base for further research. For the unsteady head characteristics that are enhanced during mixture loading at high-concentrations on the other hand, interesting data is collected. The unsteady head characteristics shows an enhancement in noise at the lower side of the spectra with an increase of concentration and engine speed. At low engine speed, the unsteady head amplitude has a wider spread that results in a lot of short quick amplitude changes. For an increase in speed, these quick amplitude changes are reduced and become more stable. The conditions are similar as in single phase water conditions due to a shift towards the lower side of the spectra. This same behaviour is visible in Cao et al. (2019) CFD model outcome.

Several calculation models have been developed to predict the cutting forces in the linear rock cutting process. Rock failure can occur in different manners: brittle tensile, brittle shear and ductile. Each failure mechanism has a corresponding calculation model with specific cutting geometries and assumptions to predict the cutting forces as accurate as possible. However, several researches conducted in the past show that the predicted forces can differ considerably from the forces measured in the experiments. In this research the author proposes expansions to the existingmodels to increase the accuracy of the force predictions and thereby contribute to a more (cost) efficient cutting process. The calculation models considered in this research are based on two main assumptions: the cutting process is 3D and the tip of the cutting tool is sharp. In a 2D cutting process the width of the cut is equal to the width of the pick point and stays constant throughout the cut. During experiments the sideways outbreaking of rock pieces is observed which can increase the width of the cut tremendously and therefore increase the actual cutting forces. This sideways outbreaking makes the rock cutting process in fact a 3D problem. The assumption of a sharp cutting tool results in another inaccuracy in the force predictions. A sharp cutting tool will penetrate the rock more easily and create a clean cut. If the sharpness of the cutting tool decreases, for example due to wear and tear during the cutting process, a crushed zone will appear in front of the cutting tool, while a wear flat arise at the tip of the cutting tool. These phenomena result in extra forces that has to be overcome by the cutting force. For large cutting depths these effects might be negligible, but for small cutting depths these forces need to be considered. In some applications in the offshore environment only small cutting depths are encountered, such as the vertical drilling for monopile installation or the scraping techniques used in the oil and gas industry. An expansion to include these phenomena in the force prediction models would therefore be a widely applicable concept. After conducting experiments on sandstone samples the magnitudes of the 2D force prediction models, the forces due to the 3D effects and the indentation forces are established. Afterwards the empirical relations of these terms are composed based on the rock characteristics and cutting geometry. The results of this research show that the proposed expansions increase the accuracy of the cutting force predictions tremendously. It also shows that for cutting at a very small depth the forces predicted by the 2D models are negligible compared to the 3D expansion and the indentation expansion, but the 2D models are necessary to calculate the angle and length of the shear plane. However, if the cutting depth increases the indentation force converges to a constant value and the influence of the 3D expansion decreases as well, while the forces in the 2D models increase. The author therefore suggests to keep the 2D effects into the equation to keep the total formula broadly applicable.

To realize sustainable development, offshore wind energy has been a highly valuable solution to meet the demand for renewable energy. Accompanied with the construction of the offshore wind turbines, cable casting and the following cable trenching process in the underwater condition are necessarily required. The research on the underwater sand cutting process so far has been limited to some extent. (Miedema, 2014) has suggested the analytical solution and performed the experiments of underwater sand cutting. But all the work until then was in 2D and the description of the water influence was in the scope of statics. Thus, it is necessary to carry out the numerical simulation to describe the cutting process and the effect of the fluid by means of DEM-CFD coupling. (Chen et al., 2015) suggested a framework of modelling the underwater excavation process. The method is to describe the particle phase by Discrete Element Modeling (DEM) and the flow phase by Finite Volume Method (FVM). Starting from this method, the software package CFDEM coupling, LIGGGHTS for DEM calculation and OpenFOAM for CFD calculation, is applied. In the coupled simulation, DEM transfers the particle information to CFD. CFD solves the governing equations and updates the pressure field and velocity field. Then the fluid-solid interaction forces are calculated in CFD and transferred back to DEM. Sand particle is not spherical in reality. To describe the sand particles more accurately, a constant directional torque is added to each spherical particle to restrict its angular movement. And the sphericity of the particles is adjusted to make the sand sample in the simulation have reasonable permeability. Two sets of the numerical simulations of underwater sand cutting are conducted in this research, the simulations of 2D effect and 3D effect. The results from the simulations of 2D effect are validated with the analytical and experimental results, while the ones of 3D effect are mainly analyzed to investigate the fluid flow field and the fluid-solid interaction force. Many factors are analyzed to find out their effects on the cutting process, such as the blade geometry, the cutting layer thickness, the hydrostatic pressure, the cutting speed and the particle size. Many conclusions are found from the simulation. It turns out that the stress on the blade increases with the blade angle, the cutting layer thickness and the cutting speed. The relation between the stress and cutting layer thickness is approximately linear. And the stress has nothing to do with the hydrostatic pressure and the particle size. The features of the fluid flow field show some differences according to low, medium and high cutting speeds. The dilatation happening in the shear zone can be observed from the distribution of the fluid pressure. With a higher cutting speed, the pressure gradient in the shear zone is larger. For the fluid-solid interaction force, the effect of the cutting speed is very obvious. Besides, the dimensionless cutting forces from the simulation matches good with those from the experiments by (Miedema, 2014). From the simulation with large blade angles, a wedge between the blade and the layer cut is observed both from the velocity distinction of the particles and the stress on the blade. With the good matching in the validation work, this research confirms the reliability of DEM-CFD coupling to describe the underwater sand cutting process. Although the analysis is into depth in many aspects, further research is still needed. Using spherical particles with a constant counter torque to describe sand particles gives reasonable results. Non-spherical particle is another possible solution that is worthy to try. And the analysis about the cavitation is necessary to be performed.

In the last two decades, the global economy and population have been growing steadily. Due to these global trends the demand for dredging, trenching and deep sea mining activities have grown dramatically. In these engineering practices, underwater excavation is one of the major procedures which involves complicated physics. In dredging, operations with clamshell buckets in saturated cohesive soils often leads to a decreased production due to the highly adhesive properties of these soils. And, in offshore wind farm installation operations, the vulnerable power cables transporting the generated energy must be buried a couple of meters under the seabed for their protection, so trenching in saturated cohesive soils becomes indispensable. Miedema has developed "The Delft Sand, Clay and Rock Cutting Model", in which several sets of equations are derived for each type of seabed soil. In the scenario of clay cutting, both the cohesion and adhesion should be known as the input parameters. However, very few information is available to define the relation between cohesion and adhesion. Yet, it is of great importance to get a better understanding of the relationship between cohesive and adhesive forces, because the large surfaces on dredging tools can generate a lot of resistance; limiting production for materials with increasing adhesion. First, literature is reviewed to get a better understanding into the relevant soil mechanical properties and cutting theories. Existing models for the adhesion factor, which is defined as the ratio between the adhesion or stickiness of a cohesive soil and its cohesion or internal shear strength, are analyzed and new models for the adhesion factor are constructed. To validate these new models, a new dedicated test setup is constructed with the help of the National Engineering Research Center for Dredging Technology and Equipment based in Shanghai, China. Tests are performed on two different cohesive soils (clays) to obtain the adhesion and cohesion of the samples. Furthermore, the test data is analyzed and the data is used to validate the models. Finally, the obtained relation between the adhesion and cohesion is implemented in a numerical discrete element model for clay cutting. Two models are constructed to validate the properties of the numerical clay sample, after which the full cutting model is validated using existing experimental data obtained by Chijiiwa and Hatamura . With this validated cutting model, it is now possible to simulate the cutting force on more complicated geometries.