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.

Context: The shift to green energy offers a need for offshore wind farms. The transition from a relatively cheap energy production from carbohydrates, to a young offshore wind energy industry needs innovations to lower the cost. Increasing the efficiency of wind turbines and lowering the installation cost of a wind farm, will eventually make wind energy cheaper then energy produced by coal. A part of the installation process is the burial of the submerged power cables. The fragile power cables have to be buried a couple meters below the seabed, to be protected from anchors, fallen objects, and fishing activity. Problem definition: To submerge the power cable into the seabed, a trench have to be made. The soil of the seabed can consist of sand, silt, clay, rock or any combination of them. This research focuses on the trenching though clay. Clay has a very low permeability compared to sand, and clay has cohesive strength. For trenching in clay, a narrow plough is mostly used. These ploughs have a small frontal area and are build to cope with the high ploughing forces. A prediction of ploughing forces and velocities are made by models in preparation of cable burial projects. With accurate predictions, the best equipment can be chosen and a planning of the trenching operation can be made. The prediction models take into account the geometry of the plough and the soil characteristics. A reduction in pulling force results in an increase in ploughing velocity and therefore lowering the time and cost of cable installation. Approach: A large part of the pulling force in clay is caused by the adhesive force on the sides of the plough sliding through the clay. The adhesive force is therefore the main focus of this research. There are two main goals: the first goal is to investigate the adhesion force in relation to the strength of the clay; the second goal is to investigate ways to reduce the force caused by the adhesion. The adhesion factor is a parameter that is included in the prediction models. In literature of construction and agricultural engineering, predictions of adhesion factors and ways to reduce the adhesive force can be found. However, the circumstances during subsea ploughing are vastly different then in the other fields of engineering. Therefore, the approach of this study is to use small scale ploughing experiments with different strengths of clay to investigate the two goals under subsea ploughing conditions. For the experiments, a test setup is used. In this setup, a block of clay of a meter long can be hold into place in a water tank and be submerged. On top of the water tank, an electric motor can pull a cart over rails. A small scale plough can be bolted underneath the cart. During an experiment, the plough is pulled through the clay and the velocity and pulling forces are measured with sensors. Results and conclusions: The adhesion factors of three types of clay are found. The softest clay with a undrained shear strength of 25 kPa has a adhesion factor of 0.43. Literature shows that the adhesion force is about 1.0 at 25 kPa. This low adhesion factor could be the result of the frontal cutting that disrupt the clay. The residual shear strength is lower then the undisturbed clay. For the medium (80 kPa) and hard (131 kPa) clay the adhesion factor is respectively 0.68 and 0.53. These values are on the higher side of what literature reports. This could have to do with the relative high velocity during ploughing. The downward trend of adhesion factor with increasing clay strength does correspond to literature. To research the possibility of reducing the adhesion force, three small scale ploughs with modified adhesion surfaces are tested. The Alpha plough, which uses vertical gaps, reduced the adhesion force by 52 percent in both soft and hard clay. The Bravo plough, which uses convex shapes, reduced the adhesion force 39, 72 and 54 percent in respectively soft, medium and hard clay. The Charlie plough, which uses water nozzles at the adhesion surface, reduced the adhesion force by 70 percent in soft clay and 63 percent in hard clay. This experimental study obtained valuable knowledge of the adhesion factor and possibilities to reduce the adhesion force.