The proportion of granular ice in sea ice layers has markedly increased due to global warming. To investigate the uniaxial compressive behavior of granular sea ice, we conducted a series of experiments using natural piled and level ice samples collected from the Bohai Sea. A total of 311 specimens were tested under controlled temperature conditions ranging from −15 °C to −2 °C and strain rates varying from 10⁻⁵ to 10⁻² s⁻¹. The effects of porosity, strain rate, and failure modes were studied. The results show that both the uniaxial compressive strength and uniaxial compressive elastic modulus were dependent on strain rate and porosity. Granular sea ice exhibited a non-monotonic strength dependence on strain rate, with the strength increasing in the ductile regime and decreasing in the brittle regime. In contrast, the elastic modulus increased monotonically with the strain rate. Both the strength and elastic modulus decreased with increasing porosity. Level ice consistently demonstrated higher strength and an elastic modulus than piled ice at equivalent porosities. Unified parametric models were developed to describe both properties across a wide range of strain rates encompassing the ductile-to-brittle (DBT) regime. The experimental results show that, as porosity decreased, the transition strain rate of granular sea ice shifted from 2.34 × 10⁻³ s⁻¹ at high porosity (45%) to 1.42 × 10⁻⁴ s⁻¹ at low porosity (10%) for level ice and 1.87 × 10⁻³ s⁻¹ to 1.19 × 10⁻³ s⁻¹ for piled ice. These results were compared with classical columnar ice models. These findings are useful for informing the design of vessel and coastal structures intended for use in ice-covered waters.

Global warming reduces the thickness and duration of seasonal lake ice, increasing the risk of ice cover failure. To investigate the bending behavior of ice cover, six groups of full-scale cantilever beam tests were conducted on a brackish water lake during the winter of 2023–2024, covering the following three ice periods: growth, stable, and melt. A total of 16 upward-loaded beams and 24 downward-loaded beams were tested. The results showed that the flexural strength of brackish ice was 374.21 ± 99.93 kPa, and the effective elastic modulus was 2.77 ± 0.93 GPa. The square root of bulk porosity, fitted with an exponential function, is the optimal predictor of flexural performance. Both flexural strength and effective elastic modulus systematically decreased with increasing porosity, and empirical regression formulas were established. On average, downward-loaded flexural strength was approximately 17.3% to 38.8% higher than upward-loaded strength, whereas elastic modulus showed no significant difference between the two loading directions. Flexural mechanical properties during the melt period reduced significantly, with a strength and modulus about 33.0% to 61.1% lower than those in the growth and stable periods. Comparisons with existing datasets demonstrate that the mechanical properties of brackish ice are lower than those of freshwater ice but higher than those of sea ice. This study provides new in situ data on the full-scale flexural mechanical properties of brackish ice and offers an important basis for assessing ice loads in lakes and estuarine environments under climate change.