In order to enable the use of Enzyme Induced Carbonate Precipitation (EICP) as a ground im-
provement technique in fine grained soils, the use of guanidinium hydrochloride (GndHCl) as a clay swelling inhibitor has been explored recently by Wennubst-Pedrini (2022). Guanidinium aggregates the clay by binding to the double layer of clay minerals. In that way, the particles become chemically and physically stable. However, it has been suggested that GndHCl as an additive has an effect on the calcium carbonate crystal sizes and polymorphs produced during EICP. However, the exact effect of guanidinium on calcium carbonate precipitation remains unclear. This study sets out to elucidate these effects. This study shows that the addition of GndHCl into the system strongly alters its starting pH from 8 to 4, leading to some samples not precipitating any calcium carbonate as the carbonate equilibrium was towards bicarbonate (HCO 3 ). However, the samples that did produce crystalline calcium carbonate, produced a comparable amount of about 0.65g per sample of the same polymorph (calcite), although crystal size was smaller. The morphology of the produced crystals suggested that guanidine altered the calcite production pathways. This study could not reproduce the promising results found by Wennubst-Pedrini (2022) and as such more research into the role of guanidinium in the EICP process is recommended. The promise that guanidine may hold in order to make EICP a market-ready technique in finer grained soils is worth further exploration.

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.

In 1990, the 44/21a-6 well was drilled in the Southern North Sea. Core material was taken from the Westphalian A/B part of the core. Some of this core material was recently obtained by the TU Delft via the North Sea Core Initiative. Since the Westphalian A/B in the Pennine Basin is fluvio-deltaic in origin, it is highly variable both vertically and laterally. In this thesis we set out to develop a method to extrapolate facies found in the core material to recognize if these are
present in other locations in the well. This means that core material is correlated to the well log. This correlation is then extended over the rest of the well. Two investigation targets were chosen, the first facies is channel base facies, consisting of very coarse sandstone, the second a swamp facies. This firstly requires a detailed core log, and a short study of the well log data. The core log is interpreted in order to try to establish some form of elektrofacies. The well data is then formatted and different principal component analyses (PCA’s) are performed in order to differentiate the facies from their surroundings. For both analyses more than 90% of the variance was explained by the first two component axes, making them reliable. Both target facies require different data sets in order to distinguish them from their surroundings. The swamp facies
becomes easily visible from the third principal component axis, while the channel base sand is harder to differentiate, being recognizable from a point cloud in a principal component plot. In total 40 coals were found to be present over the researched well interval, starting underneath the Zechstein formation, from 12800 to 13800 ft. No other similar channel base coarse sands
were found over the interval apart from the one in the cored material. Overall, it seems that the basics for this method of detection and extrapolation is quite reliable and better than using the original log data, although it does need some further development and improvement.