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Fracture Mechanical Properties of Frozen Sandstone at Different Initial Saturation Degrees
https://orcid.org/0000-0001-8253-234X
Abstract The fracture mechanics of frozen rock are important to engineering in cold regions, yet the basic properties and influences remain unclear. The fracture toughness of semi-circular bend (SCB) samples with different initial saturation degrees (ISDs) was tested at − 20 ℃. Acoustic emission (AE) and digital image correlation (DIC) systems were used to capture AE signals and surface deformation under load testing. In addition, the phase composition in rock pores was measured by low-field nuclear magnetic resonance (LF-NMR). It was found that: (1) Fracturing of frozen sandstone generally consists of three stages: pore or microcrack closing, elastic deformation and microcrack propagation which is evidenced by the variation of AE counts and the maximum horizontal strain within the fracture process zone (FPZ) under loading. (2) The ISD has a great influence on fracture toughness and the microcrack propagation process. With increases in ISD, both the fracture toughness and fracture energy of frozen sandstone varies in a mode of slow increase (ISD < 40%), rapid increase (ISD 40–90%) and slight decrease (ISD 90–100%). (3) The phase composition in pores of frozen rock with low ISD (< 40%) is significantly different from that with high ISD (40–100%). At ISDs of < 40%, the ice in rock pores mainly originates from adsorbed water; however, at ISDs of 40–100%, the ice increasingly comes from free and capillary water. Based on the test results, the difference in fracture mechanical properties of frozen sandstone introduced by different ISDs can be attributed to the changes in pore phase composition, which determines the interaction between pore ice/unfrozen water and rock skeleton involving three processes: strengthening due to the filling effect of pore ice, strengthening due to the adhesion force and tensile strength of pore ice, and weakening due to frost damage.
Highlights Freezing strengthens water-bearing sandstone significantly, and the fracture toughness of frozen sandstone increases with its initial saturation degree.Initial saturation degree differs the fracturing process of frozen sandstone in terms of energy release and range of fracture process zone.Pore phase composition primarily determines the fracturing behaviour of frozen sandstone involving ice–pore interactions.The ice–pore cementation and tensile strength of ice are the main contributors to the increase of fracture toughness of frozen rock.
Fracture Mechanical Properties of Frozen Sandstone at Different Initial Saturation Degrees
https://orcid.org/0000-0001-8253-234X
Abstract The fracture mechanics of frozen rock are important to engineering in cold regions, yet the basic properties and influences remain unclear. The fracture toughness of semi-circular bend (SCB) samples with different initial saturation degrees (ISDs) was tested at − 20 ℃. Acoustic emission (AE) and digital image correlation (DIC) systems were used to capture AE signals and surface deformation under load testing. In addition, the phase composition in rock pores was measured by low-field nuclear magnetic resonance (LF-NMR). It was found that: (1) Fracturing of frozen sandstone generally consists of three stages: pore or microcrack closing, elastic deformation and microcrack propagation which is evidenced by the variation of AE counts and the maximum horizontal strain within the fracture process zone (FPZ) under loading. (2) The ISD has a great influence on fracture toughness and the microcrack propagation process. With increases in ISD, both the fracture toughness and fracture energy of frozen sandstone varies in a mode of slow increase (ISD < 40%), rapid increase (ISD 40–90%) and slight decrease (ISD 90–100%). (3) The phase composition in pores of frozen rock with low ISD (< 40%) is significantly different from that with high ISD (40–100%). At ISDs of < 40%, the ice in rock pores mainly originates from adsorbed water; however, at ISDs of 40–100%, the ice increasingly comes from free and capillary water. Based on the test results, the difference in fracture mechanical properties of frozen sandstone introduced by different ISDs can be attributed to the changes in pore phase composition, which determines the interaction between pore ice/unfrozen water and rock skeleton involving three processes: strengthening due to the filling effect of pore ice, strengthening due to the adhesion force and tensile strength of pore ice, and weakening due to frost damage.
Highlights Freezing strengthens water-bearing sandstone significantly, and the fracture toughness of frozen sandstone increases with its initial saturation degree.Initial saturation degree differs the fracturing process of frozen sandstone in terms of energy release and range of fracture process zone.Pore phase composition primarily determines the fracturing behaviour of frozen sandstone involving ice–pore interactions.The ice–pore cementation and tensile strength of ice are the main contributors to the increase of fracture toughness of frozen rock.
Fracture Mechanical Properties of Frozen Sandstone at Different Initial Saturation Degrees
https://orcid.org/0000-0001-8253-234X
Abstract The fracture mechanics of frozen rock are important to engineering in cold regions, yet the basic properties and influences remain unclear. The fracture toughness of semi-circular bend (SCB) samples with different initial saturation degrees (ISDs) was tested at − 20 ℃. Acoustic emission (AE) and digital image correlation (DIC) systems were used to capture AE signals and surface deformation under load testing. In addition, the phase composition in rock pores was measured by low-field nuclear magnetic resonance (LF-NMR). It was found that: (1) Fracturing of frozen sandstone generally consists of three stages: pore or microcrack closing, elastic deformation and microcrack propagation which is evidenced by the variation of AE counts and the maximum horizontal strain within the fracture process zone (FPZ) under loading. (2) The ISD has a great influence on fracture toughness and the microcrack propagation process. With increases in ISD, both the fracture toughness and fracture energy of frozen sandstone varies in a mode of slow increase (ISD < 40%), rapid increase (ISD 40–90%) and slight decrease (ISD 90–100%). (3) The phase composition in pores of frozen rock with low ISD (< 40%) is significantly different from that with high ISD (40–100%). At ISDs of < 40%, the ice in rock pores mainly originates from adsorbed water; however, at ISDs of 40–100%, the ice increasingly comes from free and capillary water. Based on the test results, the difference in fracture mechanical properties of frozen sandstone introduced by different ISDs can be attributed to the changes in pore phase composition, which determines the interaction between pore ice/unfrozen water and rock skeleton involving three processes: strengthening due to the filling effect of pore ice, strengthening due to the adhesion force and tensile strength of pore ice, and weakening due to frost damage.
Highlights Freezing strengthens water-bearing sandstone significantly, and the fracture toughness of frozen sandstone increases with its initial saturation degree.Initial saturation degree differs the fracturing process of frozen sandstone in terms of energy release and range of fracture process zone.Pore phase composition primarily determines the fracturing behaviour of frozen sandstone involving ice–pore interactions.The ice–pore cementation and tensile strength of ice are the main contributors to the increase of fracture toughness of frozen rock.
Fracture Mechanical Properties of Frozen Sandstone at Different Initial Saturation Degrees
Wang, Ting (author) / Sun, Qiang (author) / Jia, Hailiang (author) / Shen, Yanjun (author) / Li, Guoyu (author)
2022
Article (Journal)
Electronic Resource
English
BKL:
38.58
Geomechanik
/
56.20
Ingenieurgeologie, Bodenmechanik
/
38.58$jGeomechanik
/
56.20$jIngenieurgeologie$jBodenmechanik
RVK:
ELIB41
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