Freezing method for rock cross-cut coal uncovering I: Mechanical properties of a frozen coal seam for preventing outburst

Yue, Jiwei; Yue, Gaowei; Wang, Zhaofeng; Li, Minmin; Wang, Binbin; An, Fenghua

doi:10.1038/s41598-019-52879-y

Cited by 17 publications

(16 citation statements)

References 32 publications

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“…Jia et al [8] concluded that the tensile strength of saturated coal and rock increased below 0°C. Yue et al [9] concluded that as the temperature of coal decreases, the compressive strength and tensile strength increase linearly. Li et al [10] revealed that the strength of ice crystals, the strength of the particle mixture, the friction strength between blocks, and the occlusal strength are the main factors affecting the uniaxial compressive strength of the frozen soil rock mixture and the ice crystals improve the bearing capacity and ductility.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

Liu¹,

Yang²,

Dong³

et al. 2021

Advances in Civil Engineering

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The lateral unloading strength and deformation of surrounding frozen rock are the key parameters for safety evaluation of frozen shaft construction. A low-temperature and high-pressure rock triaxial test system was used to simulate freezing construction, and a constant axial pressure unloading confining pressure test was carried out on frozen sandstone. The effects of freezing temperature, initial confining pressure, and unloading rate on the strength, deformation, and failure modes of frozen sandstone are studied. The main results of the study are as follows: (1) under the initial confining pressure of 20 MPa, the temperature of the sandstone decreases from 20°C to –5°C, and the peak stress and elastic modulus of triaxial compression increase by approximately 3 times. Under lateral unloading conditions, the peak stress of frozen sandstone is about 2∼3 times that of 20°C sandstone, and the peak strain of 20°C sandstone is smaller than that of frozen sandstone. The temperature of frozen sandstone decreases and the rate of increase in the peak stress of triaxial compression is slightly less than the rate of increase in the peak stress of lateral unloading. (2) The initial confining pressure of frozen sandstone increases, the growth rate of axial and radial strain increases, the radial strain dominates the failure process, and the lateral unloading strength decreases significantly. (3) The lateral unloading rate of frozen sandstone increases, the peak strength increases, and the axial and radial strain decrease. At a low unloading rate, partial creep deformation occurs. (4) The frozen rock sample undergoes tensile splitting failure under lateral unloading. According to the stress-strain curve of the frozen rock sample, the relationship between changes in the deformation modulus and changes in the confining pressure unloading amount during the unloading process of the rock sample is obtained.

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Section: Introductionmentioning

confidence: 99%

Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

Liu¹,

Yang²,

Dong³

et al. 2021

Advances in Civil Engineering

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“…e strength of frozen coal body is indeed greatly improved, especially as coal body contains a certain amount of water [22,23]. Yue et al [24] tested the compressive strength, tensile strength, and shear strength of frozen coal specimens and obtained the mechanical parameters of the specimen.…”

Section: Introductionmentioning

confidence: 99%

Freezing Method for Rock Cross‐Cut Coal Uncovering: Aging Characteristic of Effective Freezing Distance on Injecting Liquid Nitrogen into Coal Seam

Zhu

Zhao

et al. 2021

Advances in Civil Engineering

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Based on artificial freezing engineering practice, the comprehensive technology is suggested to realize safe and fast rock cross-cut coal uncovering, which mainly includes four steps of drilling, water injection wetting coal, gas drainage, and injection liquid nitrogen into coal seam. Freezing test of liquid nitrogen injection into coal is carried out to obtain the cooling curves, and comparing the test results, the numerical inverse method is applied to determine the thermal conductivity of coal seam. Then, the model of injecting liquid nitrogen into coal seam is established to simulate and analyze the aging characteristic of effective freezing radius. The results show that the thermal conductivity of wetting coal increases linearly with temperature decreasing. The periodic method with 8h intervals can be adopted to inject liquid nitrogen into coal seam, and the freezing wall is formed around the injection hole. With the increase of freezing time, the effective freezing radius (below 273.15 K) increases by power exponent, and the freezing speed in coal seam decreases gradually. This result will provide a theoretical basis for layout optimization of injection holes in rock cross-cut coal uncovering.

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“…It will not only cause a serious malignant accident of mass casualties, but also result in huge property losses (Pan et al, 2020;Wang et al, 2019). Especially, for rock crosscut coal uncovering (RCCU), although the times of coal-gas outbursts is less, the outburst intensity is larger, and more than 80% of the super large coal-gas outbursts occur in the process of RCCU (Yang et al, 2021;Yue et al, 2019aYue et al, , 2019b. Moreover, with the increase of coal-mining depth, the in-situ stress, temperature and gas pressure gradually increase, which increases the risk of RCCU and seriously threatens safe and efficient mining (Wang et al, 2013;Yu et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Strength characteristics of frozen coal–rock interface for rock crosscut coal uncovering

Zhu

Zhao

et al. 2021

Energy Exploration & Exploitation

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During a freezing method for rock crosscut coal uncovering (RCCU), the mechanical properties of the frozen coal–rock interface have a significant impact on coal-body stability. To investigate characteristic and development mechanism of freezing strength of frozen coal–rock interface, a series of direct shear tests were conducted on frozen coal–rock interface under various testing temperatures, moisture contents in coal and normal stresses. The test results showed that the strength of the frozen coal–rock interface was affected by the moisture content in coal. The larger the moisture content was, the greater strength of the interface was. When the testing temperature was −10°C, the freezing strength increased from 75.46 to 267.42 kPa with the moisture content increasing from 3% to 9%. The ice cementing strength at the interface also increased with testing temperature decreasing. It increased from 6.44 to 73.34 kPa with the testing temperature decreasing from −2°C to −10°C when the moisture content was 5% and the normal stress was 200 kPa. With the increase of normal stress, the residual strength of the frozen coal–rock interface increased. When the moisture content in coal was 9% and the testing temperature was −10°C, the residual strength of the interface increased from 40.68 to 132.28 kPa with the normal stress increasing from 100 to 400 kPa. The testing temperature had no obvious influence on the friction coefficient and the cohesion of residual strength. When the moisture content in coal was 5%, the cohesion of residual strength increased from 23.39 to 98.7 kPa and the friction coefficient of residual strength fluctuated between 0.49 and 0.63 with the testing temperature decreasing from −2°C to −10°C. The relationship between the shear strength and the normal stress followed the Mohr–Coulomb law.

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Freezing method for rock cross-cut coal uncovering I: Mechanical properties of a frozen coal seam for preventing outburst

Cited by 17 publications

References 32 publications

Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

Freezing Method for Rock Cross‐Cut Coal Uncovering: Aging Characteristic of Effective Freezing Distance on Injecting Liquid Nitrogen into Coal Seam

Strength characteristics of frozen coal–rock interface for rock crosscut coal uncovering

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