Physical Simulation Of Sea Ice Action Against Cylindrical-Piles And Inclined Structures And Their Ice Protection Structures

Sea ice generates great threaten to the growing human productivities in ice covered seas. The actions of sea ice on offshore structures have received extensive attention throughout the world. This thesis focused on the ice forces on vertical individual cylinder pile and pile groups. Ice pile-up and ride-up against inclined structures were also studied in laboratory. The effect of the ice protection structure on vertical and inclined structures in shallow waters was studied.The key factor of sea ice in the global climate-change was firstly illustrated. Ice damages in the world for the recent years were shown. The ice damage incidents from the last forty winters in Bohai Sea were listed. The methods and progresses of the research on the actions of sea ice against offshore structures were illustrated, and the main work for this thesis was also illustrated.Then the basis of the model tests on sea ice and structures interactions, including modeling laws, were illustrated. The development of ice tanks and model ice at home and abroad were introduced. The physical and mechanical properties and their testing methods of DUT-1model ice were emphatically expounded. The equipments and testing machines for the model tests in this thesis were also illustrated.The formulas for calculating crushing ice forces on an individual vertical structure were discussed and classified. Taking use of DUT-1model ice, the crushing forces of sea ice against cylinder piles with different diameters were conducted. The scope of application of the aspect ratio for Afanasev Formula was, therefore, enlarged from D/H<6to D/H<50. Meanwhile, the Afanasev Formula was improved and simplified. For the crushing ice loads on the complicated vertical pile-group structures (including large obliquity inclined piles), decomposing method was used to separate the whole structures into several elements. The load on each element was measured and compared with that on an individual vertical pile with the same size. Therefore, the distribution of the total force on the pile-group structures and the sheltering effect among the elements were determined.The design of vertical structures in icy waters is usually based on ice crushing forces. So it is of conservative and uneconomical if the same crushing-force criterion is used for the design ice load on the vertical structures under the conditions. Taking the case of high-pile wharf, we conducted a series of tests of ice loads on cylindrical piles subjected to the impacts of drifting ice to determine the impact ice load for them. Upper border of envelope was applied to determine the relationship between the upper limit of the ice load for an individual pile and the compressive strength of the ice floe and its kinetic energy. With the same method, the upper bound limit load for the pile groups was determined. Considering the corner pile from upstream, always firstly resisted the floating ice, special tests of impact against the corner pile were carried out. The result shows the load on the corner pile was larger than that on an individual pile so that its strength should be strengthened.In order to reduce large crushing ice force on vertical offshore structures from large-size of ice floes, the test of a new kind of icebreaking structure to protect these structures was conducted in laboratory. A vertical cylinder pile was taken as an example; the ice-load reduction effect of the ice breaking structure to it was determined by comparing the crushing ice force on the pile and the ice pieces broken by the ice breaking structure against it. A ratio of ice-load reduction was applied to quantify the ice-load reduction effect. The influence of relative water level and relative distance on the ratio for load reduction was analyzed. The ice-load reduction was obvious while the water level was lower than the summit of it. The level ice load on the structure was measured, and the test of sliding and overturning itself was carried out to determine the stability of the icebreaking structure. The results showed that the stability of the structure was good.Large-area ice floes pile up and ride up under the driving force from tidal currents and winds occur easily, and thus threatening the safety of inclined structures. By laying the ice-breaking structure in the ice movement direction, laboratory model tests were conducted to simulate sea ice pile-up and ride up on it to study its ice protection effect for inclined structures. The climbing angle, the sliding angle, the break length of ice sheet s and the maximum height of climbing slope, and the correlation between the breaking length and the elastic modulus were discussed. The future application of the icebreaking structure in shallow waters was also discussed. The results indicate that as the water level lower than the top of the ice-breaking structure, five different thickness of ice sheets were broken in flexural failure mode. The protection effect of the ice breaking structure to the inclined structure behind it was obvious by initiating the ice ride up and pile up in front of the inclined structure. When the pile height approached to an appropriate value, the height cannot rise any more with the moving ice. Instead, a new ice pile on the sloping slope of the previous one appeared which will be helpful for the safety of inclined structures.