Abstract
Fracture toughness and crack behavior of frozen rocks have an important guiding significance for engineering in cold regions, where the freezing temperature is one of the main factors that affect the mechanical properties of frozen rocks. Therefore, both mechanical properties (fracture toughness, compressive strength, and tensile strength) and pore phase composition of water-saturated sandstone at different freezing temperatures (0 °C, −2 °C, −4 °C, −6 °C, −8 °C, −10 °C, −12 °C, −15 °C, −20 °C) were tested in this paper. High-speed photography was used to capture the crack propagation process of the semi-circular bending (SCB) specimen. Also, morphological characteristics of the fracture surface under different freezing temperatures were analyzed. The results show the following: (1) The fracture toughness of saturated sandstone increases exponentially with the decrease of freezing temperature, reaching an increase of 402 % at −20 °C. (2) When the freezing temperature decreases from 0 °C to −8 °C, the crack growth rate increases rapidly. (3) The fracture surface roughness coefficient (Rs) of the SCB specimen shows a two-stage decreasing trend: a rapid decrease (0 °C to −8 °C), and a slow decrease (−8 °C to −20 °C). (4) The change of phase composition with freezing displayed two distinct stages: the unfrozen water content decreases rapidly and the ice content increases rapidly (0 °C to −4 °C) and then the unfrozen water content decreases slowly and the ice content increases slowly (−4 °C to −20 °C). Based on the above test results, we suggest that: (1) With the decrease of the freezing temperature, the pore phase composition changes significantly, resulting in enhanced mechanical properties of the rock. (2) The cementation and filling effect of pore ice reduce the dissipative energy in the process of crack expansion, increasing the brittleness index, so the crack growth rate of the SCB specimens increases rapidly.
Published Version
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