Two main varieties of ice strength change are considered: the first one - variation at purposeful strengthening methods affecting ice by using certain cooling facilities and the second one - strength variation under natural conditions at the ice contact with engineering structures and soil. In the first case only manufactured ice obtained by a spray cone method is studied; such ice is considered as structural material for different engineering structures. The second case concerns interaction of natural ice cover with structures and of manufactured ice with the soil foundation; here we have the less scope of investigations.
Structure building using manufactured ice requires solutions of specific structural and engineering problems many of which are now in engineering practice. Regardless of the location and purpose of ice structures there are problems and contradictions common for all ca-, ses. The larger the ice structure is the higher the intensity 9_f its building must. b~. BU, t at a high intensity of ice mass formation it is difficult to cool it, and due to low ice strength it is impossible to build up large ice structures. The review of the completed works and examples of the problem are given at the end of this paper. The stressed state of ice structures is connected with the seasonal fluctuation of natural processes. In the case when dikes, wharves and other hydraulic structures are considered, particularly its building in the mouth of the northern rivers and on the shelf of arctic seas, it becomes obvious that these areas are very cold and have little water available in winter, and due to this fact the ice mass strength is maximal whereas loads on it are minimal. In summer the conditions change: loads increase and ice strength characteristics decrease.