This thesis presents and analyse laboratory investigations of the shear strength of freeze-bonds created between two saline ice-blocks. One hundred and eighty one experiments were conducted during spring 2012 in the ice laboratory at NTNU and at Hamburg Ship Model Basin (HSVA). The applied experimental setup is similar to the set-up used by Repetto-Llamazares et al. (2011a) and Repetto-Llamazares and Høyland (2011a). The reproducibility of the measurements from these articles and how the freeze-bond strength varies with the physical properties of the ice used to form freeze-bonds were investigated. Investigating the physical properties of the ice involved temperature, salinity and density measurements, thin section analysis and characterisation of the visual appearance of the ice. We consider our results to be important knowledge for future work to perform more accurate small-scale experiments on freeze-bonds. The measured freeze-bond strengths had a range of 1.9 to 94.9 kPa.The following factors were varied during the experiments: a) Two sample dimensions were used: small ice-blocks with dimensions of 60 · 40 · 22 [mm] and 90 · 40 · 22 [mm], with a nominal contact area between the ice-blocks of 60 · 40 [mm], and large ice-blocks with dimensions of 140 · 140 · 27 [mm] and 180 · 140 · 27 [mm], and a nominal contact area between the ice blocks of 140 · 140 [mm]; b) Three contact surfaces were used: artificially produced and the natural top or bottom of the ice-sheet. Groves made during sawing of the artificially prepared surfaces were either normal to or parallel with the longitudinal ice-block direction; c) Two ice-blocks directions were made by having the longitudinal ice-block direction normal to or parallel with the ice-growth direction; d) Assembling the freeze-bond was made by placing the ice-blocks in contact with each other in water or in air; e) The water temperature in the submersion basin was either on, or slightly above the freezing point; f) Changing the time - temperature historie of the ice-blocks were done by either storing the ice at −7 C at all time or for a defined period of time cooling the ice-blocks down to −20 C. The initial ice-block temperature of −7 C, submersion time of 10 min, confinement pressure during submersion of 1.9 kPa and a velocity of the force applying piston of 2 mm/s were kept constant, and are equal to Repetto-Llamazares and Høyland (2011a).Physical properties of the freeze-bonding ice-blocks influenced the freeze-bond strength. Weak freeze-bonds were obtained for ice-blocks with a low initial salinity (S < 1 ppt), and strong freeze-bonds were obtained if the ice-blocks had a high initial salinity (S > 2 ppt). The low salinity ice-blocks were in addition seen to have a transparent look and few brine channels and voids. High salinity ice-blocks had an opaque look and contained many brine channels and voids. Keeping the longitudinal ice-block direction normal to the ice-growth direction, and assembling the samples in water gave stronger freeze-bonds. Freeze-bonds created between two natural bottom surfaces gave the strongest freeze-bonds, while the weakest freeze-bonds were obtained for the artificially prepared surfaces. Surfaces with an initially high surface roughness gave weaker freeze-bonds. The grove direction of the artificially prepared surfaces, the water temperature in the submersion basin, the sample size and the time - temperature history of the ice-blocks did not affect the freeze-bond strength.We did not manage to reproduce the results of Repetto-Llamazares et al. (2011a) and of Repetto-Llamazares and Høyland (2011a). Different submersion time (5 vs. 10 min) and confinement pressure (0.66 vs. 1.9 kPa) in the experiments of Repetto-Llamazares et al. (2011a) and us are probably the main reasons for the observed differences. We believe that comparable freeze-bond strengths would be obtained if identical test parameters had been applied. We do from this consider the experiments of Repetto-Llamazares et al. (2011a) to be reproducible.Repetto-Llamazares and Høyland (2011a) reports a very low average freeze-bond strength, 3.6 kPa, for the submersion time, confinement pressure, initial ice-block temperature and piston velocity applied in our thesis. We have not been able to obtain such low average freeze-bond strengths. We believe that the low freeze-bond strengths obtained by Repetto-Llamazares and Høyland (2011a) is an effect of the physical properties of the ice-blocks applied in their experiments, i.e. transparent ice-blocks with a low salinity.

This thesis is a study of the slamming forces from plunging breaking waves on truss support structures in shallow water. The main parts have been model testing and analysis on an existing 1:50 scale model of a truss support structure for wind turbines at NTNU.An expanding building of offshore structures has led to increased focus on wave forces. Large slamming forces from breaking waves can occur in shallow water. These forces will impact the structure in a much bigger way than non-breaking wave forces. Several researches have been investigating wave slamming forces on single vertical and inclined piles for the last 50 years, but there are still uncertainties at this area. This causes uncertainties in the dimension of structures exposed to these kinds of forces, and are therefore still under investigation.A large number of measurements have been executed. The tests have been run with both regular and irregular waves, with different frequencies and wave lengths. This give waves with different wave heights and breaking points, so that maximum forces can be determined. A “new” analyzing method described by Määtänen (1979) is applied to obtain the wave slamming force for response force time series. This is a simplified analysis based on an assumption of a single degree of freedom system subjected to a total force.The probability of occurrence of plunging breakers on the foreshore is investigated by Reedijk, et al. (2009). The method is used to find the probability of occurrence of plunging breakers on the truss structure for irregular waves. Maximum force response is given by waves that broke some distance away from the structure and not when the wave broke directly at the structure. The wave broke ahead and surged against the structure, which imposed forces with a slamming character in both the top and bottom force transducers.It is significant air entrained in the water during the breaking process, which may influence the results differently in small-scale model testing and in reality. The reason for this may be scale-effects that may impact interpretation of the results. The measured crest height is smaller due to air entrance in the waves as well.

The largest part of an ice ridge consists of unconsolidated ice rubble, whose material properties decide the load from ridges on ships and structures. Material resistance is attributed to the initial freeze-bonds and the friction and interlocking between blocks. The objective of the thesis was to investigate rubble behaviour by two tests: shear box test at NTNU and pile test at HSVA. The shear box test was aimed at investigating freeze-bond mechanisms in rubble. The pile test was aimed at suggesting values for rubble properties for a model scale experiment.The shear box had dimensions 600 mm x 400 mm x 40 mm, and was filled with ice blocks of 60 mm x 22 mm x 40 mm simulating rubble. Confinement was added, the box was submerged for 10 minutes, and tested in a rig by forcing the rubble to fail in shear. Force vs. displacement was measured. Different types of saline ice and submerging water temperatures were used. Pile testing consisted of making an elongated pyramid-shaped pile, baseline 600 mm, of rubble collected from the ice tank at HSVA. The pile was tilted and geometry was measured before and after failure happened in the pile.Main results from the shear box tests were the observation of a first phase deformation of rubble, that displayed a near linear force-displacement relation and a first peak shear stress. Magnitude of first peaks was measured in the range 8.9 kPa to 59.7 kPa, and depended on submersion water temperature, salinity of ice, how blocks were cut in respect to crystal structure in the ice sheet and confining pressure. Pile tests had repose angles ranging from 36.0° to 47.3°, and cohesion for an assumed angle of friction of 30° was in the range of 172 Pa to 342 Pa. First phase shear stress was compared to shear strength of single freeze-bond tests of the same ice, and direct relations were found. The magnitude of first peak shear stress in tests varied most with ice salinity and crystal structure. The measured repose angles for pile tests give an upper limit for internal angles of friction, and values seemed reasonable. The ice was warm, and this may the reason for the low cohesions.

The increasing interest in the Arctic region due to exploitation of natural resources requires methods for estimating design loads on offshore structures. The borehole jack (BHJ) is an ISO approved tool for assessing the in-situ confined compressive strength of ice. On request from the Norwegian University of Science and Technology (NTNU), a BHJ was made by M-Tech and delivered to the University Centre in Svalbard (UNIS) in 2010. This work presents a technical description of the UNIS-BHJ as well as calibration instructions and experimental setup. A classification system of stress – time curves has been developed with focus on post-peak stress behavior. Three field campaigns have been conducted, two in Van Mijenfjorden (first-year level ice) and one in the Barents Sea (young and rafted ice) in March and April 2012. The new classification system proved convenient when used for classifying the results of these experiments. An advantage is that the system is applicable for all BHJs, hence allowing comparisons of different works to be made regardless of the BHJ used. Investigations of the spatial variation of borehole (BH) strength were also done. Sampling areas of sizes 100 by 100 m and 10 by 10 meters were established in Van Mijenfjorden, where both concluded mean BH strength of 16.8 MPa with STD of the larger area 1.9 MPa and the smaller 0.3 MPa. Another three sampling areas of sizes 20 by 20, 4 by 4 and 4 by 4 m were established in the Barents Sea, with BH strengths 13.0, 11.1 and 14.0 MPa and STDs 3.2, 2.0 and 2.4 MPa.