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The pore structure of rock changes significantly during the heat treatment process, which affects the internal emission rate of radon. This study introduces the results of radon emission rate of rock after high temperature and analyzes the effect of the pore structure in rock mass on radon emission. The results show that there is a good positive correlation between temperature and radon emission in rock mass within a certain temperature range, and the higher the temperature, the higher the radon concentration emission. Two igneous rocks have the rate which is highest after the treatment in 400 °C. The absorption and sealing of radon in the microcapillary are the main occurrences of radon in rock mass. This is reflected in the increase in microcapillary porosity and the decrease in D P , which changes the microstructure of the rock and increases the connectivity of the internal pore channels of the rock, thereby increasing the volume and length of the migration channels for radon. These results are helpful to understand the influencing mechanism of radon emission process in rocks.

In cold regions, the anisotropy of sedimentary rocks is modified by repeated frost action, potentially increasing the risks of rock engineering. Hence, a deep understanding of the development of rock anisotropy due to frost action is essential. In this work, two sets of sandstone samples were cored and used in experiments, which contained bedding planes either perpendicular or parallel to the height direction. The P-wave velocity, uniaxial compressive strength, tensile strength, and shear strength of samples were tested after different numbers of freeze–thaw cycles. Several anisotropic indexes were defined by the above parameters and their variations with freeze–thaw cycles were analysed. The results demonstrate that (1) the P-wave velocity, uniaxial compressive strength, tensile strength, and shear strength of both sets of sandstone samples decayed with increasing freeze–thaw cycles; however, (2) the initial values and decay rates of these parameters differed significantly between the two sets. (3) Sandstone bears strong inherent anisotropy and (4) it is enhanced by repeated frost action. Based on direct observations of bedding structures by magnetic resonance imaging, we suggest that the enhancement of anisotropy in sandstone results from a combination of its inherent anisotropy and anisotropic frost damage accumulation. Both originate from sandstone’s structure of interbedded coarse- and fine-grained layers.

Limestone is a widely used natural building material, and its physical and mechanical properties can change greatly when exposed to high-temperature heat sources. In this paper, limestone samples from Linyi City, Shandong Province, were selected and some of them were heated to 650 °C at different heating rates (4, 6, and 8 °C min−1), while the rest of the samples were heated cyclically (200, 300, 400, 500, 600, and 650 °C) at a heating rate of 8 °C min−1, and the acoustic emission (AE) signals were recorded throughout. The results show that the AE signal rate increases with increases in temperature, and the AE signal increases rapidly at 300 °C and 500 °C because of the thermal decomposition of dolomite and calcite. There is a negative correlation between the heating rate and the AE signal rate. The high-frequency data and high-amplitude data generated by AE are negatively correlated with the heating rate. With the increase in the heating rate, AE counts and cumulative AE counts decrease significantly.

High-temperature baked sandstone is widely distributed in the north of Shaanxi, China. The lithology of these rocks has a significant impact on the mining of underground resources such as coal. To understand changes in its physical properties after heat treatment, yellow sandstone was heated for two hour at a constant temperature of 25, 800, 1000, 1100 or 1250 °C. Data on the glossiness, hardness and colour brightness, and surface micrographs, were obtained to study the relationship between surface characteristics and temperature. The relationship between internal structural characteristics and temperature was studied using electrical properties and nuclear magnetic resonance (NMR) spectroscopy. The results showed that below 1100 °C, glossiness and porosity increased and conductivity, hardness and colour brightness decreased, mainly due to melting of the binder. Above 1100 °C, there was melting of clay minerals, quartz and feldspar particles, resulting in a sharp increase in the brightness and hardness of yellow sandstone, a sharp decrease in porosity, and glossiness and conductivity increase rarely. Combining these results with the surface micrographs, the whole thermal change mechanism could be summarised as follows: dehydration condensation of water-bearing minerals → melting of cement → melting of quartz and feldspar particles → pyro-metamorphism.

The detection of concealed water-conducting structures is essential for preventing water inrush disasters. Aiming to mitigate the limitations inherent in using any single technique, a comprehensive approach that combines integrated mining geophysical exploration, hydrogeological drilling, and hydrochemical exploration (GDH) is proposed for the exploration of concealed water-conducting structures. By conducting a thorough analysis of the background geological data obtained through surface exploration, potentially concealed water-conducting structures can be predicted. Then, a combination of the seismic reflection method (SRM) and mine transient electromagnetic method (MTEM) can be used to detect the location and water-bearing properties of the target structures. Afterwards, the target drilling areas are defined by the anomalies detected by the integrated mine geophysical technique, and the drilling method can directly acquire the hydrogeological information of water-conducting structures and verify the results of the geophysical methods. By means of hydrochemical analysis, inrush water sources and their runoff conditions can be identified, and the spatial relationship betweenof the source aquifers and mining space can be determined; hence, the properties, scale, and configuration of the water-conducting structures can finally be evaluated. Employing a water-conducting fault in a mine as a case study, we verified that the integrated method overcomes the limitations and possible biases of each method, providing a multiple-method solution that can accurately detect concealed water-conducting structures to help prevent water inrush disasters.

Due to the existence of ice in rock fissures and the complex ice–rock interactions, the exact role of fissure ice in altering the mechanical behaviour of frozen rock mass remains unclear. In this study a series of uniaxial compression experiments were conducted on frozen sandstone samples that bearing precut fissures of different angles at both freezing and room temperatures. The failure process of samples was recorded using a high-speed camera. Besides, a particle flow code-based simulation, addressing the role of fissure ice, was performed. The results indicate that: (1) Freezing does not alter the trend of strength variation concerning the fissure angle, but it does strengthen the samples significantly. (2) At both room and subzero temperatures, the crack initiation mode of the specimens showed a changing trend of \"tensile cracking → shear cracking → tensile cracking\" as the fissure angle increased. (3) The change in fissure angle leads to a change in the stress state at the fracture end, while the fissure ice, through ice–rock interaction, further alters the fracture's stress state, thereby affecting the initiation and expansion mode of the fracture. Based on the simulation results, three strengthening mechanisms of fissure ice are proposed: (I) under compression, the ice acts as a filling support; (II) the fissure ice shortens the fracture length, resulting in a reduction of the stress intensity factor at the fracture ends; (III) under tensile or shear states, the ice acts as a binder. The above strengthening effects of fissure ice act simultaneously or alternatively at different fissure angles. Article highlights Freezing does not alter the variation trend of strength with the fissure angle, but it strengthens the samples significantly. The mechanical properties of frozen fissured sandstone are controlled by both the freezing effect and the fissure angle. Fissure ice could provide resistance to compressive, tensile and shearing load, and thus strengthens frozen rock mass.

Frost damage of concrete has significant effects on the safety and durability of concrete structures in cold regions, and the concrete structures after repair and reinforcement are still threatened by cyclic freezing and thawing. In this study, the new-to-old concrete interface was reinforced by steel bar. The shear strength of the new-to-old concrete interface was tested after the new-to-old combination was subjected to cyclic freeze–thaw. The effects of the diameter of the steel bar, the compressive strength of new concrete, the number of freeze–thaw cycles and the freezing temperatures on the shear properties of new-to-old concrete interface were studied. The results showed that, in a certain range, the shear strength of the interface was proportional to the diameter of the steel bar and the strength of the new concrete. Meanwhile, the shear strength of the reinforced interface decreased with the decreasing of the freezing temperature and the increasing of the number of freeze–thaw cycles.

Anisotropy in rock could significantly affect the stability and safety of rock engineering by differing physical and mechanical properties of rock in different directions. Another major factor for physical and mechanical properties of rock is moisture state, however, whether anisotropy can be altered by it remains unclear. This study investigated variation in anisotropy (by conduct-ing ultrasonic tests) with moisture state (measured by nuclear magnetic resonance) in layered sandstones, and interpreted the phenomenon from the perspective of linking dehydration with pore structure of rock. The results show that (1) sandstone with more obvious bedding bears stronger anisotropy, the P-wave velocity in the perpendicular direction is much lower than that in the parallel direction. (2) The anisotropy index fluctuates around 1 with dehydration of sandstone without obvious bedding, while the anisotropy in sandstone with obvious bedding was significantly enhanced be dehydration. (3) During dehydration bulk water escaped firstly then capillary water and bound water. (4) Dehydration is controlled by the bedding structure. The different dehydration rates of pore water in different directions inevitably lead to heterogeneity in moisture state that change the anisotropy of the rock, which is reflected by the non-synchronous changes in P-wave velocities in different directions.

The block-stone embankment is a special type of embankment widely used to protect the stability of the underlying warm and ice-rich permafrost. Under the influence of multiple factors, certain damages will still occur in the block-stone embankment after a period of operation, which may weaken or destroy its cooling function, introducing more serious damages to the Qinghai–Tibet Highway (QTH). Ground-penetrating radar (GPR), a nondestructive testing technique, was adopted to investigate the damage properties of the damaged block-stone embankment. GPR imagery, together with the other data and methods (structural characteristics, field survey data, GPR parameters, etc.), indicated four categories of damage: (i) loosening of the upper sand-gravel layer; (ii) loosening of the block-stone layer; (iii) settlement of the block-stone layer; and (iv) dense filling of the block-stones layer. The first two conditions were widely distributed, whereas the settlement and dense filling of the block-stone layer were less so, and the other combined damages also occurred frequently. The close correlation between the different damages indicated a causal relationship. A preliminary discussion of these observations about the influences on the formation of the damage of the block-stone embankment is included. The findings provide some points of reference for the future construction and maintenance of block-stone embankments in permafrost regions.