To study the seepage and deformation characteristics of coal at high temperatures, coal samples from six different regions were selected and subjected to computed tomography (CT) scanning studies. In conjunction with ANSYS software, 3D reconstruction of CT images was used for the establishment of fluid-solid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal. In addition, the structure of coal was studied in 2D and 3D perspectives, followed by the analysis of seepage and deformation characteristics of coal at high temperatures. The results of this study indicated that porosity positively correlated with the fractal dimension, and the connectivity and seepage performances were roughly identical from 2D and 3D perspectives. As the porosity increased, the fractal dimension of coal samples became larger and the pore-fracture structures became more complex. As a result, the permeability of coal samples decreased. In the meantime, fluid was fully heated, generating high-temperature water at outlet. However, when the porosity was low, the outlet temperature was very high. The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension. The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.

Study on seepage and deformation characteristics of coal microstructure by 3D reconstruction of CT images at high temperatures

To study the creep property of salt rock, uniaxial compression creep tests on salt rock specimens were carried out. The test results indicate that there is no steady creep of the salt rock used in ...

Creep properties and damage constitutive model of salt rock under uniaxial compression

Rock burst is one of the main coal and rock dynamic disasters in steeply inclined and extremely thick coal seams (SIETCS). Timely identification of potential precursor information enables effective and specifically targeted measures to mitigate hazards. To provide a reference for the determination of precursor information in SIETCS with similar conditions, an in situ investigation that lasted for more than 1 year was conducted on the + 450 horizontal no. B3 + 6 fully mechanized top-coal caving face of the Wudong coal mine. This mine has an average dip angle of 87° and experienced a total of three rock bursts. The investigation focused on the consequences of rock burst (including the source location, energy, damage range, and modes of ensuing damage), the temporal and spatial evolution laws of the monitoring parameters of microseismic (MS) and acoustic emissions (AE), and the relationship between precursory information of both the AE and MS monitoring systems. Furthermore, a comparison of the evolution laws of the precursory characteristics between steeply and gently inclined coal seams was conducted. The obtained results indicate that rock burst failure mainly shows a directionality from south to north of the roadway, and the main factor causing the rock burst was the suspended rock pillar. Prior to the rock burst, sources of MS events gradually clustered and congregated around the rock pillar or coalface, and high-energy events (energy > 103 J) noticeably increased. Similar variations of sharp rise–sharp drop were found for both daily total energy and event counts. Prior to rock burst or large energy mine tremors, the AE energy deviation continued to rise, a peak was observed in the total number of high-value daily AE deviations, and the precursory information of AE was ahead of the precursory information of the MS monitoring system. The evolution laws of MS precursor information prior to rock burst differed between SIETCS and gently inclined coal seams. These evolution laws can be used as precursory warning for rock burst in SIETCS. Integrated monitoring of the AE and MS monitoring systems realizes the real-time monitoring and early warning from the germination stage to the occurrence of rock burst, and can determine the danger area in space. This can improve the early warning efficiency and provides a solid foundation for safe mining in SIETCS.

Precursor of Spatio-temporal Evolution Law of MS and AE Activities for Rock Burst Warning in Steeply Inclined and Extremely Thick Coal Seams Under Caving Mining Conditions

Flaws widely exist in rock mass, which significantly influences the strength and failure behavior of rock. The study of the flaw effect on the mechanical and cracking behavior is important to predi...

Mechanical and cracking behavior of granite containing two coplanar flaws under conventional triaxial compression

With the gradual depletion of mineral resources in the shallow part of the earth, resource exploitation continues to move deeper into the earth, it becomes a hot topic to simulate the whole process of rock strain softening, deformation and failure in deep environment, especially under high temperature and high pressure. On the basis of Lemaitre’s strain-equivalent principle, combined with statistics and damage theory, a statistical constitutive model of rock thermal damage under triaxial compression condition is established. At the same time, taking into account the existing damage model is difficult to reflect residual strength after rock failure, the residual strength is considered in this paper by introducing correction factor of damage variable, the model rationality is also verified by experiments. Analysis of results indicates that the damage evolution curve reflects the whole process of rock micro-cracks enclosure, initiation, expansion, penetration, and the formation of macro-cracks under coupled effect of temperature and confining pressure. Rock thermal damage shows logistic growth function with the increase of temperature. Under the same strain condition, rock total damage decreases with the rise of confining pressure. By studying the electron microscope images (SEM) of rock fracture, it is inferred that 35.40 MPa is the critical confining pressure of brittle to plastic transition for this granite. The model parameter F reflects the average strength of rock, and M reflects the morphological characteristics of rock stress–strain curves. The physical meanings of model parameters are clear and the model is suitable for complex stress states, which provides valuable references for the study of rock deformation and stability in deep engineering.

Thermal damage constitutive model for rock considering damage threshold and residual strength

Studying the thermal damage constitutive model of rock using statistical theory can better reflect the damage evolution process and the stress–strain relationship of rock under temperature and load...

Thermo-mechanical coupling damage constitutive model of rock based on the Hoek–Brown strength criterion:

A three-parameter permeability model for the cracking process of fractured rocks under temperature change and external loading

Rock burst is a severe disaster in mining and underground engineering, and it is important to predict the rock burst risk for minimizing the loss during the constructing process. The rock burst proneness was connected with the acoustic emission (AE) parameter in this work, which contributes to predicting the rock burst risk using AE technique. Primarily, a rock burst proneness index is proposed, and it just depends on the heterogeneous degree of rock material. Then, the quantificational formula between the value of rock burst proneness index and the accumulative AE counts in rock sample under uniaxial compression with axial strain increases is developed. Finally, three kinds of rock samples, i.e., granite, limestone and sandstone are tested about variation of the accumulative AE counts under uniaxial compression, and the test data are fitted well with the theoretic formula.

Zhi-zhen Zhang

Papers

Thermo-mechanical coupling damage constitutive model of rock based on the Hoek–Brown strength criterion:

Thermal damage constitutive model for rock considering damage threshold and residual strength

A three-parameter permeability model for the cracking process of fractured rocks under temperature change and external loading

Rock burst proneness prediction by acoustic emission test during rock deformation