Experimental Study On Uniaxial Compressive Strength Of Ice And Influence Factors

In cold region, ice load is regarded as a control load in the design of hydraulic and offshore structures, and the compressive strength is a key parameter of ice load calculation. As a natural composite material, the properties of ice are very complicated by the influence of hydrological and meteorological conditions and environmental factor, so physical and mechanical properties of ice are also different. At the same time, due to regional differences of the tested objects and different testing methods, different research results, have acquired by scientists Therefore, artificial freezing method is an effective experimental means to simulate natural ice; it is essential that experiment studies of the uniaxial compressive strength and the effect of many factors on uniaxial compressive strength were conduced to enrich result and theory study; it is very significant to further study the relationship of compressive strength and influence factors for different type ice.In the low temperature laboratory, freshwater ice was prepared through the freezing method of decreasing temperature step by step in a dynamic water tank of ice growth and decay. A series of tests was conducted on artificial freshwater ice, reservoir ice and sea ice under uniaxial compression by an electronic universal machine equipped with a low temperature cabinet with high precision. Reservoir ice and sea ice were collected from the Hongqipao reservoir in the Heilongjiang Province and the Liaodong Bay respectively. The crystal structures for the artificial freshwater ice, reservoir ice and sea ice were analyzed through horizontal and vertical crystal thin sections of the ice. The corresponding average grain size was calculated by the method of the equivalent circle diameter; the bubble distribution in ice and bubble content curves with depth change were given; salinity of sea ice with different depth presented nearly "C" type change tendency.The stress-strain curves of the artificial freezing ice, reservoir ice and sea ice were respectively described through analysis of test data, and the different curves showed that the ice samples had the different deformation pattern. The corresponding damage stress and damage time relationship curve was presented, and the ice samples had mainly bulge failure, shear failure and split failure through the test observation. The corresponding failure phenomenon of the ice samples was different.Choosing different temperatures and wide range of strain rates as test conditions, and the effect of some factors such as temperature, strain rate, loading direction and average grain size of ice on the uniaxial compressive strength were analyzed. The test results show that:the artificial ice, reservoir ice and sea ice have significant strain rate sensitivity; there are ductile region, ductile to the brittle transition region and brittle region. Ice uniaxial compression strength and temperature have close relations, the uniaxial compression strength value of the ice decreases with increasing temperature under the same strain rate, and ductile to brittle transition region change with decreasing temperature. The relationship between the method peak compression strength and temperature was fitted using the nonlinear method, which meets more physical fact that ice strength is almost zero when the temperature of ice closes to freezing. The effect of average grain size on the uniaxial compressive strength is discussed under the same sample size condition, and ratio of average grain size and sample size (D/A) is introduced, the uniaxial compressive strength of ice increases with the decrease of (D/A) when D/A is less than1.5. For the reservoir ice, the uniaxial compressive of the upper layer ice is not influenced by the loading direction, which shows the isotropy property of granular ice; the effect of loading direction on the uniaxial compressive strength of the lower layer ice is not obvious due to existing simultaneously of granular ice and columnar ice. For freshwater ice, the statistical relationship between the uniaxial compressive, strain rate and temperature is established by fitted test data; for sea ice, the curved-surface relationship between the uniaxial compressive strength and porosity within a wide range of strain rate is described quantitatively.The application of the compressive strength of ice in engineering design is discussed, and the peak compressive strength of reservoir ice and sea ice and historical research results in the same areas is being within the same limit respectively. Therefore, the peak compressive strength is regarded as the design strength in engineering design. In ice management, uniaxial compressive strength of ice is introduced on the basis of acquired ice parameters including atmospheric temperature, water temperature, ice depth, ice speed and so on through established meteorological forecast, numerical study modes on sea ice depth and drift in Bohai Sea. Forecasting process of ice load for sea ice is established through the quantitative relationship among the uniaxial compressive strength, strain rate in wide range and porosity, and the alarming index of ice load is set to reflect the structure state under the action of ice load and to provide the alert for worked feeling, normal operation and safe operation of structures, and scientific guidance is provided for alariming system for safety operation of structures in ice region.