The low-temperature environment and initial saturation degrees cause the I-II mixed fracture failure mode of rock to exhibit a complex response, posing significant challenges for rock mass engineering in cold regions. Three-point bending tests were performed on semi-circular bending sandstone specimens with different initial saturation degrees (ISDs) and prefabricated crack dip angles (β) at a low temperature of − 10 °C. Acoustic emission (AE), nuclear magnetic resonance, and numerical simulation techniques were utilized to investigate the influence mechanisms of pore phase composition and β on the mixed-mode I-II fracture mechanics characteristics of frozen sandstone. The results indicate that: (1) The curves of peak force, fracture toughness, and fracture energy as functions of ISD all exhibit a two-stage variation characteristic with distinct transition points, and the transition points for specimens with different β vary. (2) The response of fracture toughness to β in different ISDs intervals exhibits a phased nonlinear characteristic. Specifically, it demonstrates an overall negative correlation in the low ISDs range (0%–20%), an irregular fluctuating downward trend in the medium ISDs range (40%–60%), and a regular, characteristic fluctuation in the high ISDs range (80%–100%). (3) The increase in ISD and β markedly intensifies the activity of AE signals, thereby not only accelerating the compaction rate of internal pores within the specimen but also modifying the initiation and propagation mechanisms of cracks. (4) The pore ice content serves as the primary controlling factor influencing the fracture characteristics of frozen rocks with different ISDs. Changes in β induce a dynamic response in the stress field at the tip of the prefabricated crack during loading. The above research results facilitate a more in-depth understanding of the fracture mechanics properties associated with mixed-mode I-II fractures in frozen sandstone and represent a valuable addition to the field of fracture mechanics for frozen rocks.Highlights<OrderedList> <ListItem> <ItemNumber>(1)</ItemNumber> <ItemContent> With the increase of initial saturation degree, the fracture toughness and fracture energy of frozen sandstone increase first and then decrease. </ItemContent> </ListItem> <ListItem> <ItemNumber>(2)</ItemNumber> <ItemContent> The pore phase composition is the main controlling factor affecting the fracture strength of frozen sandstone with different initial saturation degrees. </ItemContent> </ListItem> <ListItem> <ItemNumber>(3)</ItemNumber> <ItemContent> The crack dip angle changes the stress state at the crack tip, resulting in the fracture toughness of frozen sandstone transforming from mode I to mode II and mixed-mode. </ItemContent> </ListItem> </OrderedList>

Mixed-Mode I-II Fracture Mechanical Behaviors of Frozen Sandstone with Different Initial Saturation Degrees

期刊论文
发表日期：

2026年3月3日

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Zhenxing Pan,
Hailiang Jia,
Gengshe Yang,
Ting Wang,
Peixiong Gao,
Liangfu Xie,
Qingzhi Wang

摘要

The low-temperature environment and initial saturation degrees cause the I-II mixed fracture failure mode of rock to exhibit a complex response, posing significant challenges for rock mass engineering in cold regions. Three-point bending tests were performed on semi-circular bending sandstone specimens with different initial saturation degrees (ISDs) and prefabricated crack dip angles (β) at a low temperature of − 10 °C. Acoustic emission (AE), nuclear magnetic resonance, and numerical simulation techniques were utilized to investigate the influence mechanisms of pore phase composition and β on the mixed-mode I-II fracture mechanics characteristics of frozen sandstone. The results indicate that: (1) The curves of peak force, fracture toughness, and fracture energy as functions of ISD all exhibit a two-stage variation characteristic with distinct transition points, and the transition points for specimens with different β vary. (2) The response of fracture toughness to β in different ISDs intervals exhibits a phased nonlinear characteristic. Specifically, it demonstrates an overall negative correlation in the low ISDs range (0%–20%), an irregular fluctuating downward trend in the medium ISDs range (40%–60%), and a regular, characteristic fluctuation in the high ISDs range (80%–100%). (3) The increase in ISD and β markedly intensifies the activity of AE signals, thereby not only accelerating the compaction rate of internal pores within the specimen but also modifying the initiation and propagation mechanisms of cracks. (4) The pore ice content serves as the primary controlling factor influencing the fracture characteristics of frozen rocks with different ISDs. Changes in β induce a dynamic response in the stress field at the tip of the prefabricated crack during loading. The above research results facilitate a more in-depth understanding of the fracture mechanics properties associated with mixed-mode I-II fractures in frozen sandstone and represent a valuable addition to the field of fracture mechanics for frozen rocks.

Highlights (1)

With the increase of initial saturation degree, the fracture toughness and fracture energy of frozen sandstone increase first and then decrease.

(2)

The pore phase composition is the main controlling factor affecting the fracture strength of frozen sandstone with different initial saturation degrees.

(3)

The crack dip angle changes the stress state at the crack tip, resulting in the fracture toughness of frozen sandstone transforming from mode I to mode II and mixed-mode.