Meso-scale mechanical properties of mudstone investigated by nanoindentation

Sun, Changlun; Li, Guichen; Gomah, Mohamed Elgharib; Xu, Jiahui; Rong, Haoyu

doi:10.1016/j.engfracmech.2020.107245

Cited by 32 publications

(11 citation statements)

References 47 publications

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“…The total volume of pore (V p ), the total crosssectional area of pore (S p ), and the number of cracks will decrease permanently compared with shallow coal before excavation. In the process of mining, with the gradual weakening and dissolution of confining pressure, cracks with a certain volume and scale will be formed in coal [40], as shown in Table 1. When we select the specimens of mechanical experiments, the specimens with obvious macroscopic cracks are often excluded.…”

Section: Water Absorption and Structural Characteristics Of Deep Coal...mentioning

confidence: 99%

Study on Energy Density Distribution and Mass Fractal of Deep Saturated Coal Samples under Uniaxial Stepwise High Stressed Loading and Unloading Path

et al. 2022

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The geostress in deep coal roadway is high and affected by mining frequently; under the influence of water-rock interaction, the bearing capacity of coal continues to deteriorate. Based on the characteristics of short water absorption process and low moisture content of deep coal samples in this experiment, the threshold range of quantitative division of water absorption stage of coal samples is given, and the structural characteristics of deep coal samples that are more susceptible to cracks are analyzed. The actual loading process is simulated through uniaxial stepwise high stressed loading and unloading experiments, the gradual development of cracks was the root cause of instability of coal, and saturated water mainly aggravates the instability process through these cracks; the stepwise high stressed loading and unloading path makes cracks more likely to occur in the sample. After each level of loading and unloading, the average stiffness is approximately linear trend degradation. By calculating the energy density of deep coal samples in each stage before the peak, the change of energy density indexes between saturated and dried samples is different from relative shallow samples, and the energy density indexes do not decrease but increases instead. However, the proportion of each energy is generally positive and inverted "U"-type distribution. The change trend of plastic energy in proportion to dissipation energy can be used as the judgment feature of coal sample instability. The instability of deep coal samples is mainly caused by the gradual dissipation of plastic energy to generate cracks and divided into fragments with large and long edge, resulting in low mass fractal dimension. In engineering practice, the loading times should be reduced and the suitable pressure grouting should be conducted timely to delay the deterioration process of crack development in deep water-bearing coal under high stress disturbance.

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Section: Water Absorption and Structural Characteristics Of Deep Coal...mentioning

confidence: 99%

Study on Energy Density Distribution and Mass Fractal of Deep Saturated Coal Samples under Uniaxial Stepwise High Stressed Loading and Unloading Path

et al. 2022

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“…where P max is the maximum value of the load, A is the contact area, and β is the geometric constant of the Berkovich indenter (β = 1:034). If the effects of nonrigidity on the measurements of elastic modulus are neglected, the microelastic modulus (E mi ) of indents can be represented by the reduced elastic modulus [36]. Otherwise, it should be calculated by [47]…”

Section: Nanoindentation Testmentioning

confidence: 99%

“…Fracture toughness, reflecting the resistance for crack initiation and propagation [27,28], is another crucial parameter for rock fragmentation and hydrofracturing [29][30][31][32]. At the microscopic level, the fracture toughness of indents can be determined by the crack length method [33] or energy method [26,[34][35][36] based on nanoindentation results. It is documented that the microfracture toughness of indents holds a linear relation with its microelastic modulus.…”

Section: Introductionmentioning

confidence: 99%

Estimating Macrofracture Toughness of Sandstone Based on Nanoindentation

et al. 2021

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An upscaling method for estimating macrofracture toughness by nanoindentation results was proposed in this study. Grid nanoindentation tests were conducted on sandstone samples to obtain micromechanical properties of indents, including elastic modulus, hardness, and stiffness. Multifactor cluster analysis was then carried out to categorize the sandstone into five mechanical phases. Finally, the macrofracture toughness was predicted by using the macroelastic modulus of the sample and the critical energy release rate of the weakest phase. To verify this method, the upscaling result was compared with the macrofracture toughness measured by the notched semicircular bending (NSCB) test. The discrepancy in the macrofracture toughness from our method and the NSCB test was 8.8%, which was acceptable. Also, it is proved that our method can provide more accurate upscaling results compared to other methods.

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“…The shallow-buried mudstone has a higher compressive strength, which is mainly manifested as a brittle failure, while the buried mudstone at 1,000 m has a lower compressive strength, which is mainly characterized by ductile failure, but has relatively good permeability [31][32][33]. The hardness and elastic modulus of clay matrix and silt inclusion in mudstone were obtained through the nanoindentation test, and it was found that the elastic modulus of key mineral components was greater than that of mudstone itself [34].…”

Section: Introductionmentioning

confidence: 99%

Effect of Moisture on the Macro Failure Characteristics of Weakly Consolidated Mudstone: Mesomechanism

Rong

et al. 2022

Geofluids

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Mudstone, whose significant characteristic is water-weakening, widely exists in all kinds of geotechnical engineering, which brings great security risks to engineering safety. In this paper, through a series of macro and meso test methods, the macro and meso action mechanism of water on the weakly consolidated plane of mudstone was studied. In the uniaxial compressive strength test, the mudstone cementation plane was the main part of the fracture derived. Under the moist state, the strength of mudstone would decrease significantly, which was inversely correlated with relative moisture content. In the case of flooding, mudstone cracking occurred only along the cementation plane. Through ESEM+mapping test, results showed the humidification curing caused obvious damage to the cemented plane, where sodium and calcium were lost without a certain cause. The cemented plane was rich in kinds of clay minerals in mesoscale and presented an inhomogeneous state. The surface hardness data obtained from nanoindentation were discrete and difficult to quantitatively evaluate the mesomechanical properties. However, compared with the dry state, the data set of the moist state had a significant decline, showing a weakening effect. The mudstone is prone to fail along these weakly consolidated planes. Moisture intrudes into the bedding plane further deteriorating their consolidation.

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Meso-scale mechanical properties of mudstone investigated by nanoindentation

Cited by 32 publications

References 47 publications

Study on Energy Density Distribution and Mass Fractal of Deep Saturated Coal Samples under Uniaxial Stepwise High Stressed Loading and Unloading Path

Study on Energy Density Distribution and Mass Fractal of Deep Saturated Coal Samples under Uniaxial Stepwise High Stressed Loading and Unloading Path

Estimating Macrofracture Toughness of Sandstone Based on Nanoindentation

Effect of Moisture on the Macro Failure Characteristics of Weakly Consolidated Mudstone: Mesomechanism

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