4TU link to Python notebooks : https://doi.org/10.4121/f44790eb-f97d-4f7c-964e-3ed2fb3d3062

S. Alveolata is a tube-dwelling polychaete which can be found all the way from the coast of Norway all the way down to Dakhla in the Western Sahara. It is able to build large reefs structures from sand filtered from the water column. It is known to have importance for biodiversity from animals feeding on the animal to its reefs providing a safe haven for fish. At the same time, a move is happening to using habitat protection and recreation for coastal protection. Several soft habitats such as mangroves, saltmarshes and seagrasses have been studied for their wave damping potential and S. Alveolata holds promise in this aspect. Given these functions, the S. Alveolata biogenic reefs need to be protected from outside influences, but little is known about their (mechanical) behaviour. As such, this study investigates the reef structure, erodibility, compressive and shear strengths of these reef materials and compares these to the commonly encountered loads from walking humans and wave loading. The static load from a person can reach up to 150 kPa while loading from 1.8 m waves can exert 36 kPa.  In agreement with Fournier-Sowinski (2013) and Vovelle (1965) but in contrast to Sanfilippo et al. (2019), the structure of the reefs to consist of three-layered tubes, with an organic sheath which partly contains a layer of flat grains placed next to each other on the inside and a scale-like layer of generally flat grains. These grains are glued together with proteinaceous glue spots showing a particular, bubbly structure. New is the description of bubbles radiating from the center of the glue spots. The grain size distribution shows a bi- or trimodal distribution, which has not been described before. S. Alveolata favours flat grains (in contrast to (Gruet & Bodeur, 1994; Lisco et al., 2020)) of about 1.0 mm size to build their reefs, which is a larger grain size than previously found (Gruet & Bodeur, 1994; Lisco et al., 2020; Naylor & Viles, 2000). As previously observed (Gruet, 1972), the reefs are made up of many tubes curving upward from a solid substrate. However, the first 3D mCT-scans of a whole reef block show enough voids so that small tubes wind their way through the reefs, probably made by juvenile worms. The grain size and mCT data suggest that tubes are reconstructed during the year.  The mechanical properties of these reefs show a very high compressibility with total strains between 10-20% under loads of 604 kPa. The reefs show a yield stress varying from 80-185 kPa. This is about the same stress as a person exerts while standing, the dynamic loads of walking are much higher but the limited time these loads are applied means little damage is done. Even though these yield stresses are far exceeded during testing, the samples hold some amount of cohesion due to interlocking and some unbroken bonds. Loose tubes weather from all sides at the same rate during slake durability tests. Shear box testing was conducted in a stepped manner with four loading steps from 48-380 kPa normal pressure, such that the first two steps are below yield stress at 48 and 96 kPa normal load. These show that the reefs have a cohesion of at least 23 kPa and a friction angle of 21.3°, explaining their resistance to waves. During testing, the reef samples compress strongly with their void ratios decreasing from 1.01 to 0.85. As a result of shearing, the internal tube structure of the sample was strongly deformed and shear bands or planes were formed during shearing. Some voids are also opened up in this process. After shearing samples show an apparent cohesion due deformed tube parts in which some bonds remain intact interlocking with each other. Compared to other cemented sands the S. Alveolata reefs exhibit many of the same features as these sands, such as the applicability of the Mohr-Coulomb criteria and high compressibility. However, unlike other cemented sands their open, tubular structure showed lower friction angles due to the alignment of sand particles in the linings. Also, the S. Alveolata lack the filling of void spaces often found on cemented sands leading to compressive behaviour.  Compared to the pressures to which the reefs are subjected in nature, the reef materials probably hold up well. The results provide a basis for more detailed investigation and testing and highlight key behavioural aspects of the material. It shows the response of the material to mechanical stresses and provides a starting point for using these reefs or solutions inspired upon them in different ways.

This research evaluates two methods for determining the optimal dimensions of a fictive room and pillar (R&P) mine at the Marche Les Dames (MLD) quarry in Belgium. The empirical method, including the Q-system and the R&P design guidelines from NIOSH (2011), is used to calculate roof spans and pillar dimensions. These calculated pillar dimensions are then modelled using the Distinct Element Method (DEM) software, 3DEC, and the results will be compared with those of the empirical method. The pillar is modelled using a Bounded Block Model (BBM) approach and integrating a Discrete Fracture Network (DFN) to account for the fractured rock mass. The empirical method offered straightforward results and is well-suited for preliminary mine design. However, it is unable to incorporate the heterogeneity of the rock mass, providing only a limited understanding of its behaviour. In contrast, the numerical method can incorporate this heterogeneity, offering a more detailed analysis. However, collecting all necessary parameters is challenging, and calibration and validation are required—something that was not fully achieved in this research.

The study found that the numerical model produced unrealistic results when modelling stresscontrolled failure in the pillars at MLD. The pillar strength was much higher than expected. This was attributed to the calibration of the intact rock strength using a UCS sample, which did not account for weaknesses in the intact rock. In contrast, when the failure was structurally controlled and the model did not require the BBM approach, the results were much more realistic, with significantly lower computational time. Still, it is recommended to use the numerical model primarily to investigate the impact of specific features such as karst voids and dissolution joints, which the empirical method cannot incorporate, rather than to determine overall mining dimensions.

The Dutch Ministry of Defence is interested in developing a tool or workflow that can be used to remotely predict Unified Soil Classification System (USCS) classes of any area to aid mobility-related decisions. Therefore, this study was initiated by Cohere Consultants in collaboration with NEO, a Dutch remote sensing company and Utrecht University to create such tool or workflow. This MSc thesis provides a study in how the total geological history (TGH) approach as proposed by \cite{TGHA} can be used for predicting soil USCS classes. This is done by implementing the core concept of the TGH into a decision tree model that makes use of many modules, sub-modules and supporting modules to characterise the tectonic, geologic and geomorphological setting of a soil unit. The modules are divided depending if the unit dealt with is a soil, rock or part of a mountain, whereby the soil module incorporates 7 sub-modules that characterize alluvial, lacustrine, coastal, marsh, aeolian, evaporitic and glacial/periglacial environments. The rock and mountain modules, on the other hand, attempt to determine the presence and characteristics of residual soils using a weathering grade system and a table with the weathering products of 23 common rock types. The performance of the decision tree model was tested using two pilot studies in Konna, Mali and Zamora, Spain and one validation study in 's Hertogenbosch. For each study, a map with the predicted USCS soil classes was generated for the study area. The pilot studies explored the possibility of combining the predicted USCS soil maps with topographic wetness index (TWI) and slope angle maps to make a qualitative prediction on the trafficability of the area. The pilot studies showed that the TGH-based decision tree model has potential for being expanded into a tool for aiding military mobility predictions. Next, the validation study compared the predicted USCS map for 's Hertogenbosch to 5 ground truth data points collected by the Dutch Ministry of Defence. The validation study concluded that the decision tree was in general able to distinguish between coarse grained soils and fine grained soils, however struggled with correctly predicting if a soil has high or low plasticity. Finally, the Mali pilot study was able to compare USCS soil predictions made using the decision tree model to those made by a classification of hyperspectral data (made by \cite{flipsen_2022}). Based on the comparison, there seems to be promise for future works to integrate the two methods to benefit from the detail achievable by the hyperspectral method and the qualitative soil descriptions using the TGH-based decision tree. Future recommendations include fine-tuning the decision tree model so that is is able to incorporate more detailed geologic or soil maps (currently has been trained with maps of about 1:500,000), incorporating remote sensing data to create soil units, quantifying uncertainty and possibly automatising the workflow.

In this thesis I conducted ground penetrating radar (GPR) and ground conductivity meter (GCM) surveys to detect the presence of simulated clandestine burials at the Amsterdam Research Initiative for Subsurface Taphonomy and Anthropology (ARISTA) test facility, and determine their characteristic response in this environment; providing valuable insights and recommendations for forensic investigations. I performed four days of GPR and GCM surveys over three simulated clandestine burials at ARISTA. I collected common-offset GPR data to investigate changes to burial detectability due to different central antenna frequencies (250 MHz and 500 MHz), different GPR instruments (NOGGIN or pulseEKKO), changes to survey grid orientation relative to burials, and increased soil moisture content in the survey area. Additionally, I acquired common-source GPR data to examine the efficacy of electromagnetic interferometry (EI) and adaptive subtraction (AS) methods in improving burial detectability. I conducted GCM surveys with two coil configurations, (horizontal co-planar (HCP) and vertical co-planar (VCP)), three intercoil spacings (0.32 m, 0.71 m, 1.18 m), two different line spacings (0.5 m, 0.25 m) and in the presence of variable soil moisture content. I also performed low induction number (LIN) correction and elevation correction procedures on GCM data to determine the extent to which these influence the detectability of clandestine burials in this environment.
In common-offset radargrams characteristic burial anomalies take on many forms, appearing as disruptions to existing features (direct-wave arrivals and soil horizons) and as isolated reflection events (hyperbolic events and burial length horizontal anomalies). In timeslices, burials are characterized by high or low amplitude rectangular anomalies. When used in conjunction, radargrams and timeslices produced characteristic responses regardless of survey grid orientation, consistent with the locations of the burials. Increased soil moisture at the site improved the detectability of burials and the 250 MHz antenna was found to be superior to the 500 MHz antenna in obtaining a characteristic burial response, though both were successful to a large extent. EI and AS processing techniques were successful in removing direct-wave contributions in radargrams, though detectability was not significantly improved when compared to raw data. Overall, the three burials were detected using GPR to various extents, and in future work thorough historical data in addition to zero-measurements should be obtained for all burials in order to investigate the source of these differences. GCM surveys conducted in this work were largely unsuccessful in detecting simulated clandestine burials due to significant conductive noise sources (metal fence, sensors, etc.) and the limited conductivity contrast in the soil. Low conductivity zones were detected over some burials using HCP at an intercoil spacing of 1.18 m, however, confidence in the validity of these responses is low due to the dominating noise sources.

Terps are artificial dwelling mounds mostly found in the northern regions of the Netherlands, built to provide safe ground against water in such areas affected by flooding, storm surges, and high tides, before the development of dikes. In this thesis, the stability of these terps was evaluated via FEM models and analyses performed on PLAXIS. Results highlight considerable stability risks when the terp slopes are subjected to considerable external loading, such as those exerted by heavy agricultural vehicles being operated in proximity of these.

The lack of insight regarding the stability of many dolmen in the Netherlands is problematic. In 2019, a capstone fell down dolmen D14, greatly damaging this cultural heritage. In order to decide on whether it would be wise to reconstruct this dolmen, it is useful to understand the stability of potential reconstruction scenarios without having to perform invasive tests that could damage the structure. To this end, this research has focused on the application of non-destructive, digital methods to analyze the stability of dolmen D14. Laser scanners were used to obtain point cloud data from the zone around the dislocated capstone, with which 3D meshes were created. Furthermore, tests were conducted to estimate the relevant parameters to quantify the shear strength of the rock contact areas. This was done in the field using the Equotip and Barton’s comb and by performing tilt tests and Golder shear box tests in the laboratory. For the rock parameters, a basic friction angle of 33° was found with tilt tests and a residual friction angle of 31.2° and 30.5° was found for the Golder shear box on a flat sample. The meshes and rock parameters were used as input to conduct stability analyses in 3DEC. Two different models were analyzed, one based on the rock configuration as it was in 2019 (Model 1) and the second model with a rock configuration as it was in 1925 (Model 2). In the stability analysis, it was found that Model 1 is much more unstable compared to Model 2. The minimum pushing force for instability of the structure was 2 kN for Model 1 and 94 kN for Model 2, for the conditions under research. Furthermore, it was found that the number of cycles used in the analysis, mesh coarseness and rock joint friction angle all have a significant impact on the model results. All in all, this research has demonstrated the potential for using digital and non-destructive methods to analyze the stability of megalithic structures.

The clay adhesion phenomenon has been problematic in multiple engineering projects involving soft cohesive soils. In this dissertation, the adhesive characteristics of offshore high plasticity clay will be analyzed in support to deep sea mining applications. Adhesion of clays are particularly relevant in 2:1 swelling clays, where the magnitude of the force is highly dependant on the clay properties itself, working conditions and the soil engaging component surface material. The most prevalent force in offshore saturated conditions arises from the suction forces between micro-channels in the clay and the soil engaging component. Methods to reduce this adhesive force were assessed, ranging from solutions such as vibrations and electro-osmosis, to modifying the soil engaging surface to break continuous contacts between the clay and component. The natural adhesion of two typical offshore clays were experimentally determined by interface shear tests for the shear adhesion and pull-out tests for tensile adhesion. Interfacial shear strength was measured for typical materials found in the offshore industry, that being steel, aluminium, rubber and a polymer coating. Results from the tests showed that materials do have an impact on adhesive stresses. Similarly, pull-out tests showed this variation pattern. The influence of pull-out rates and contact time on adhesive tensile strength were also assessed and showed to increase with faster rates and longer contact times, respectively. In application to a typical rotational cutterwheel in deep sea mining, a scaled test-setup of a rack of cutter-teeth was dragged through the test clay to acquire horizontal cutting forces with the utilization of the experimentally found natural adhesion in the interface tests. The found adhesion value for the test clays were utilized to validate the cutting clay model from "The Delft Sand, Clay & Rock Cutting Model" (Miedema, 2019). Practical results from the scaled experiment seemed to coincide relatively well with the theoretical model. It is therefore recommended to further investigate the use of experimental means to determine adhesion of clays to develop an even more accurate empirical model.

The aim of this study is to look into the effect of water content in clays on the electrical conductivity as obtained from measurements of an frequency domain electromagnetic induction survey and a laboratory resistivity test. The laboratory test results are compared to theoretical conductivity models. The focus is hereby on determining the relationship between decreasing water content in clay and the electrical conductivity. The research has been performed in collaboration with the land geophysics department at Fugro. I would like to thank Veerle Steenhuisen for giving me the opportunity to carry out this research at Fugro and Serkan Elgun for supervising my thesis on behalf of Fugro. I also want to thank Evert Slob and Dominique Ngan-Tillard for the help on academic level and supervising my thesis.

A pilot research was set up to determine the possibilities for using gamma-ray spectrometry to and possible value in mine waste piles. These waste piles consist of different waste rocks without any value and ore that was processed incorrectly. This method, if proven eective, will be used on mine waste from different commodities all over the world. However, there will be started with the waste pile Halde Haniel in the Ruhr area in Germany. The Ruhr area has been selected because of the manageable travelling time from Delft, the long history of coal mining activities in the area and the open-access of the waste pile. The thriving days of coal mining have left us with large amounts of waste piles (170 waste piles in the Ruhr area). Therefore, it will be essential to know if these waste piles have an impact on the environment by emitting gamma radiation. In Europe, this problem has not been addressed. However, in other countries, these waste piles are the cause of increased health risks. The Halde Haniel waste pile is a human-made object and consist mainly of shale, sandstone and bits of coal. Gamma-ray spectrometry is often used to determine lithology of a rock formation. To determine the lithology measurements are done on outcrops present in nature. In most literature gamma-ray spectrometry is used to determine the lithology of rock formations. However, in this research, the measuring location is a human-made object, which has destroyed the natural sequencing of the rocks. Therefore, the measurements taken on the Halde Haniel makes the research more challenging. Therefore, the accuracy of the measurements done on a site consisting of multiple rocks, such as the Halde Haniel, are essential to know in order to apply this method in future research. Field measurements were taken for two dierent reasons. First, a control study was executed in the Green Village in Delft. The main goal of these measurements was to select a correct measuring time for the measurements at the Halde Haniel waste pile. The rest of the measurements were done at the Halde Haniel waste pile. At the Halde Haniel waste pile, four dierent measuring locations were selected. From the results can be concluded that the amount of gamma radiation emitted from the Halde Haniel waste pile is higher than at a location without mining activities. However, this increase is still not high enough to result in health risks. The measuring error could not be determined to a satisfactory standard, because of the lack of soil moisture samples and the signicant impact of soil moisture on the error of measurements. Gamma-ray spectrometry should be supported with information about the lithology and the chemical composition of the rocks, because otherwise nding value in waste piles will be hard.

The Netherlands has for long been witnessing problems due to subsidence. While urban infrastructure is mostly safeguarded from differential settlement by deep pile foundations, the same cannot be said about greenhouses. The greenhouses of the Netherlands has enabled the country to become the largest exporter of vegetables, second only to the United States of America. It is imperative that these greenhouses which form the backbone of the agriculture infrastructure of the country, are monitored continuously to minimize unprecedented damage.

This thesis aims to study the feasibility of using time series Interferometric Synthetic Aperture Radar (InSAR) as a means to monitor differential settlement in greenhouse structures. The analysis was primarily done using RADARSAT-2 data. In case of translucent surfaces of greenhouses, it was important to firstly identify the physical targets that are associated to scattering centres. This was done by analysing the statistics of the heights of the scatterers which helps in ascertaining where the radar signal is getting back-scattered from. It was inferred that the persistent and distributed scatterers are primarily identified from objects on the roof and outer walls of the greenhouses.

Moreover, the magnitude of deformation estimated from the scatterers have been corroborated with geotechnical data. It was seen that higher magnitudes of deformation was seen in locations with compressible soil types such as clay and peat close to the ground surface. It was also seen that greenhouse structures are prone to differential settlement when the depths of the piles are insufficient in areas with varying soil types. The effect of thermal contributions has also been studied and it was found that the estimation of thermal expansion does not significantly affect the estimated deformations.

From the study, it is evident that time series InSAR offers an effective means to monitor differential settlements in greenhouses. In order to check for differential settlement in individual greenhouses, it is proposed that a persistent scatter interferometric analysis be done initially and if it is seen that the density of these scatterers is insufficient, the analysis can be followed up with time series interferometry of distributed scatterers. Incorporating multiple track directions of radar data increases the number of greenhouses that can be monitored. Moreover, it was also seen that persistent scatterers were identified from additional greenhouses when Sentinel-1 data was used, despite its poorer spatial resolution. For further study, it is recommended that corner reflectors are used to validate the positions of the targets that are identified as persistent and distributed scatterers.

Several waterway protection structures in the Netherlands dealt with rapid degrading armourstone after construction. This suggests that the current selection procedure of armourstones is not flawless to all degradation mechanisms, especially in dynamic environments. In this work armourstone is meant to include all rock that is used in river, coastal and offshore constructions, including rip rap and rock fill. Armourstones are in the Netherlands selected by their CE marking, which lists the description of the armourstone product and information on regulated characteristics. These characteristics are tested according to the European standard EN 13381-1&2:2002, which specifies the properties of aggregate acquired by processing natural materials for use as armourstone. This research is executed to provide a contribution in the quality control and assessment of armourstone and rock fill to ensure proper handling and installation in coastal and waterway protection structures. The research started with a durability investigation according to the standard EN 133831&2:2002 on sampled sandstones and limestones that will be used in a submarine trench backfill, to check the regulated armourstone characteristics. Next, a petrographic analysis under the microscope was performed on methylene blue (MB) stained thin rock sections to investigate the presence of deleterious constituents and structures. This analysis was followed by extensive index testing to investigate the applicability of simple testing tools in a durability investigation. These tools include the Brazilian tensile strength (BTS) test, an indirect tensile strength test, the Equotip test, a surface hardness tester that records the surface rebound of an impact body, and the MB adsorption and staining test. MB is a dye that colours constituents with an excess in negative electric charges. The tests according to EN 13383-1&2:2002 suggested that the sampled armourstone bulk satisfies the required durability parameters and no evidence was found that indicates rapid degradation during the engineering lifetime. Nevertheless, variability in the armourstone pieces was spotted and some individual rock pieces approached or exceeded minimum durability requirements. The BTS test revealed considerable variation in tensile strength, a key parameter to assess degradation, between armourstone blocks and within a single block when a similar orientation of the bedding was maintained. Moreover, the orientation of the bedding in the sandstone had large influence on the tensile strength, where the values obtained perpendicular on the bedding were twice as high than parallel to the bedding. Single impact method (SIM) Equotip measurements on rough, untreated aggregate surfaces were consistent. The rebounds correlated to visual features like grain size, cracks, surface roughness and degree of weathering within handheld specimens. Equotip measurements on the rock cores and sawn surfaces obtained higher mean rebound values and smaller standard deviations. The mean and standard deviation are considered most suitable to be used in a durability investigation. The repeated impact method (RIM) by the Equotip was not successful to indicate the degree of weathering of single hand specimens. The mean Equotip values on the aggregate correlated well to the water absorption when divided into proper density and size classes. The mean rebounds on the cores distinguished well between weathered and intact cores when saturated, and correlate well to the unconfined compressive strength (UCS) values. Furthermore, the Equotip mean rebound value related to the BTS value when performed on isotropic rock disks. The MB adsorption test and MB staining of the thin sections indicated the presence of localised spots and laminae rich in clay or organic matter. The staining of sawn aggregate surfaces agreed with some of the deleterious structures in the thin sections, yet was not consistent throughout the tested rock pieces and varied between the dark coloured limestone and light coloured sandstone. The Equotip test, BTS test and MB adsorption test are quick, easy and cheap methods to obtain more understanding in variability and rock behaviour which are not necessarily captured by the standard laboratory tests according to EN 13383-1&2:2002. The simple index tests should always be accompanied by the standard laboratory tests to provide a proper reference and understanding. Detailed mechanical durability tests, like the slaking test or wet-dry cyclic tests, should be performed when the durability assessment indicates a high amount of deleterious minerals and structures, to identify the amount of degradation caused by swelling behaviour of these minerals.

This thesis is part of a longer series of research into the use of geophysical methods for inves-tigation for forensic purposes, a collaboration between the Delft University of Technology (TU Delft) and the Netherlands Forensic Institute (NFI). In this investigation, the difference between a grave containing a human body and a refilled empty pit is explored at the Amsterdam Research Initiative for Subsurface Taphonomy and Anthropology (ARISTA) facility, using common-offset GPR data collection. In addition, common-offset data is gathered at a test site at TU Delft, in order to redefine the locations of previously buried targets. Multiple-offset GPR datasets are also col-lected at both sites, one of which is processed using electromagnetic interferometry (EMI) and adaptive subtraction (AS) in an attempt to remove direct waves.
The positions of the targets at the TU Delft site were redefined, but with some questions as to whether the site has been altered in the past year without the knowledge of the author. High lev-els of interference in the ARISTA facility data due to close proximity to various metal and plastic objects makes it difficult to determine the true differences caused by the presence of the cadaver. The author suggests using a 500-MHz antenna for further investigations at the site due to high wave velocity which leads to a low resolution when using a 250-MHz antenna, and due to more homogeneous soil at the ARISTA facility. The optimal procedure for EMI+AS is discussed, and sug-gested to be the use of a bandpass filter to remove very high and low frequencies from the raw data prior to EMI. The method is shown to be reasonably effective, especially when the data is strongly impacted by the presence of direct waves, where simply topmuting the data would re-move too much information. A script was prepared in MATLAB which has been optimised for the application of EMI to GPR data, and further scripts were prepared for use in Seismic Unix for the purpose of AS, in the hopes that others may find these a useful beginning to further applications of this method.

Peat is formed by biochemical processes and the accumulation of the soil depends on the aerobic and anaerobic conditions. The soil covers five to eight percent of the land surface of the earth. For this thesis a peat coming from a site called Markermeeer, which is a lake between the provinces Noord-Holland and Flevoland in the Netherlands, is used. The fabric of peat consists of a fine dark peat material and fibres. The peat material is made of water and decomposed plant tissue whereas the fibres consist of fragments of (semi-)degraded wood, stems, branches and grass. Furthermore the cell walls of the fibres consists of a primary and a secondary wall which are mostly made of cellulose and lignin. Knowing the fabric of wet peat is of importance to better understand the role of fibres in the unusual behavior of the soil. Previous studies on imaging wet peat with X-ray micro CT has proven to be difficult due to the indistinguishable linear attenuation coefficient of the peat organic matter and water. This coefficient is a function of the interactions of X-rays with the materials present in peat. Flushing a peat sample with lead(II)nitrate have shown to be the most successful approach to show the stems and branches in a peat sample using X-ray micro CT. However, according to \cite{kettridge2008x} this flushing approach showed that the focus was limited on the larger fibres present in the sample because the different materials in peat have almost the same linear attenuation coefficient and therefore this thesis also focuses on two other techniques to image the fabric of wet peat.
Neutron CT was performed on cylindrical peat samples. This technique uses a thermal neutron beam to image a sample and was available at the Reactor Institute Delft. The resolution of this imaging station is 150 $\mu$m. Since the cell walls and the peat material between the fibres in peat have both a large attenuation coefficient for neutrons, it was not possible to distinguish the fibres from the peat material between the fibres, using this technique. To gain a contrast heavy water was used to replace the water because it has a low attenuation coefficient. Flushing a peat sample with heavy water showed the most effective way to do so. The aim of this procedure was to get a contrast difference between the peat material between the fibres and the fibres itself. A triaxial setup was used to flush the sample with heavy water. Heavy water diffused in the water present in the peat inducing a decrease in attenuation of the peat material between the fibres. The reconstructed tomographic images were filtered using a 3D visualization program Avizo version 9.4. Only the air-filled fibres could be observed on the tomographic images whereas the water-filled fibres could not be observed. Samples of the same peat were scanned in a dry and wet state using a X-ray micro CT scanner present at the geoscience section of TU Delft. On the tomographic images of the wet sample, white halo were observed representing the cell walls of the fibres.
X-ray phase CT present at the Ghent University Centre for X-ray CT was performed on a peat sample coming from the same site. This method results in an image contrast using a large fixed distance for low absorbing materials like peat. The aim of this scan was to reveal more fibres than observed with the X-ray micro CT scan at TU Delft. However, edge enhancement did not occur because of the filtering needed during reconstruction of the raw data to visualize different structures in peat. \\ The white halo could be thresholded and filtered in avizo resulting in a 3D image of the rod-like fibres. These fibres were randomly orientated. On the micro CT scan of the sample in a dry state other fibrous structures than the rod-like fibres were observed. These fibres were not shown as white halo on the tomographic images of the wet samples.

According to themselves, Argentinians are living with their backs towards the sea. In order to turn this around, a feasability study has been done to find out how a network of marinas along the coast of the province would look like, based on a MCDA including all urban areas along the coast and a fleet analysis. A final network has been proposed and a conceptual design of such a marina has been made.

Backward erosion piping is a dike failure mechanism. It is the internal erosion process by which sand is eroded away from underneath a dike or levee by seepage flow. This erosion process progresses in the direction opposite to the direction of seepage flow and forms a small pipe directly beneath the dike. As erosion continues, this process can lead to dike failure. During this erosion process, the groundwater flow pattern is subject to continuous change, due to the growth of the pipe. Self-potential (SP) monitoring is sensitive to changes in the groundwater flow pattern, because of the electrokinetic coupling between fluid flow and the streaming potential. The SP field due to flow underneath a test dike was modeled with a FreeCAD -> Gmsh -> pyGIMLi workflow. This workflow can also be used to effectively resolve a wide range of standard and customizable geophysical modeling and inversion tasks. After modeling, field experiments were conducted, on the same test dike, to further assess the possibilities and limitations of SP monitoring to track the progress of backward erosion piping. Given that it is essential to have an accurate resistivity model in order to find the location of the SP source, an integrated electrical resistivity tomography (ERT) and SP monitoring system was designed. The electrodes used in this monitoring system were polarizable stainless steel stakes. The reliability of polarizable electrodes was greatly overestimated, as they turned out to give unstable SP measurements. The reason for the inferior reliability of polarizable compared to non-polarizable electrodes, was found through extensive literature research. The reason being that the largest potential in any electrode originates from the contact between the metal and the electrolytes in solution. The metal of polarizable electrodes is in direct contact with the electrolytes in the soil, which have variable concentrations. Therefore, the potential measured fluctuates together with the concentration of soil electrolytes in contact with the metal. The metal of non-polarizable electrodes, on the other hand, is in contact with a solution of its own salt, which has a constant concentration. Finally, piping is not expected to be measurable with SP monitoring, before a large sand boil is visible in the field. Once a positive SP anomaly develops at the sand boil, changes in the SP field due to the growth of the pipe are expected to be too small relative to the SP anomaly associated with water flow through the sand boil. Even though an integrated ERT and SP monitoring system is known to provide useful information about the hydrology of a dike, such a system is not sensitive enough to be able to monitor the development of a backward erosion pipe.

Chalk putty is a soil-like material that is formed when intact chalk is disturbed. Recently, it has become of special interest due to the development of offshore wind farms in the North and Baltic Seas, where in a number of sites piles are driven into chalk strata. Several pile tests reported in the literature show increased shaft capacity up to 4 months after driving. Although it is a widespread remark in the scientific publications that chalk properties improve over time, laboratory replications of this phenomenon are scarce and the results are inconclusive. The aim of this thesis is to develop a specimen preparation technique yielding representative specimens as well as feasible for commercial purposes. Thereafter, the evolution of the characteristics of chalk putty over time is assessed through laboratory tests. Triaxial with Bender Elements, Direct Simple Shear, Constant Rate of Strain and Thixotropy have been conducted on specimens aged up to 3 months. Finding that the behavior of chalk putty cannot be classified among the classic types of soils. On one hand, Constant Rate of Strain tests have shown that the response is comparable to silty soil, with a gradual transition between re-loading and virgin compression lines, leading to difficulty in the determination of the yield point. On the other hand, in shear, the critical state friction angle is in the range of dense sand. Regarding the volumetric response, there is an initial compressive response, succeeded by a constant volume phase during destructuration and eventual dilation or contraction at larger strains. Furthermore, it was determined that the material possesses thixotropic properties when mixed with de-ionized water. Finally, no increase in the shear strength or was recorded while the initial shear stiffness decreases with aging time -due to unconfined preservation of the samples. However, the ultimate dilatancy of the specimens increases over time, this may be a result of dissolved calcium carbonate during crushing and saturation which re-precipitates or re-cements around the grains.

In total 326 terpen in the Netherlands are classified as national monuments. A large portion of the terpen are located in the province Groningen. Groningen is often in the news, because of the earthquakes that took place, which were caused by the gas-extraction activities. The earthquakes caused damage to infrastructure and they can also be a threat to the stability of the terpen. Since the earthquakes can lead to soil liquefaction. The goal of this report is to investigate the risk of liquefaction to the terpen due to induced earthquakes. Furthermore, fine sands was the most liquefiable soil type. The Naaldwijk and Eem formations have the highest liquefaction potential based on their soil compositions, densities and age. The Naaldwijk formation is the most prone to liquefaction since it is located more shallow in the underground. Afterwards, cone penetration test data was used to evaluate the soil classes, soil unit weights and soil behaviour indexes. The soil behaviour index values were used to asses the liquefaction potential. In the end, none of the three chosen terpen were liquefiable. Moreover, 2D and 3D visualizations were made in order to better understand the heights and slopes of the terpen.