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Objective With the rapid increase in construction projects in the western regions in recent years, the impact of seasonal freeze-thaw cycles in the high-altitude areas of western China has become more pronounced. Conducting research on the microscopic characteristics and strength degradation properties of rocks under freeze-thaw cycles is crucial for guiding engineering construction in these cold, high-altitude regions. Methods To study the influence of freeze-thaw cycles on rock structure and mechanical properties, we collected diorite samples from a tunnel in the Kangding area and examined the effects of freeze-thaw cycles on their microstructure and mechanical characteristics. Firstly, thin rock sections were observed under a polarizing microscope to obtain mineral compositions and microstructures. Then, CT scanning technology was used to scan the granite samples after freeze-thaw cycles, and the scanned layers were binarized using threshold segmentation. The scanning images of different layers were binarized using threshold segmentation, and high-resolution 3D data and images of the internal and external structures of the samples were obtained by stacking the binary image layers. Fractal theory was applied to calculate the box-counting dimension of the images and quantitatively assess their complexity. This analysis allowed us to examine the evolution and distribution characteristics of the internal structure of granite under freeze-thaw cycles. Results Under a polarizing microscope, the rock exhibits a block-like structure with a patchy, coarse-grained, and unequal-grained granite texture, with locally visible metasomatic worm structures. The main phenocryst minerals are alkaline feldspar. Other minerals range in size from 0.25 to 4.0 mm and primarily include quartz, plagioclase, and alkaline feldspar. Secondary minerals include biotite and epidote, while accessory minerals comprise apatite, zircon, and pyrite. Microscopically, the rock is identified as porphyritic, coarse-grained, and unequal-grained biotite diorite granite. Freeze-thaw cycles were applied to the granite samples in the laboratory to study the strength evolution and explore the relationship between structural evolution and strength. The results indicate that the freeze-thaw cycle effect leads to an overall increase in the internal porosity of the granite's microstructure, though the rock's permeability changes minimally, with an increase of only 0.003×10−3 μm2. The internal pore development is uneven, primarily due to the emergence of new micropores, causing changes in the overall structure of the sample. After freeze-thaw cycles, the complexity of the internal structure of the rock decreases, but the overall integrity remains good, with the fractal dimension staying at a high level. Fractal analysis shows that 20 freeze-thaw cycles do not cause significant changes in the structural complexity of granite. However, the overall mechanical properties of the sample decline, viscosity increases, and long-term strength shows significant attenuation, raising the strain threshold for entering the creep test stage. Conclusion When evaluating the safety of rocks with dense primary structures, considering only their structure may lead to deviations from the actual situation. It is essential to combine necessary strength indicators for a comprehensive evaluation. After undergoing freeze-thaw cycles, rocks tend to exhibit more significant deformation while maintaining lower strength. Therefore, appropriate treatments are required for construction in high-altitude areas. [ Significance ] This study provides a reference for applying fractal theory to the evolution of rock microstructure and the relationship between rock microstructure and strength evolution. It also offers valuable guidance for engineering construction in high-altitude and cold regions.

The failure of rock mass is mainly due to the failure of the structural plane, which is an important factor to reduce the mechanical properties and stability of rock mass. The shear strength of rock mass is one of the parameters for the stability calculation of large-scale rock mass engineering. The shear strength of a rock structural plane is strongly influenced by surface morphology. Considerable research has been conducted regarding the correlation between two-dimensional structural plane morphology and shear strength. However, quantitative research on three-dimensional (3D) morphology is relatively limited. In this study, 3D printing technology was used to create molds. Using cement and sand as the main materials, additives such as early strength and water-reducing agents were added, and test samples of irregular surface topography were created. The 3D roughness was quantified by formula calculation. Using a ZScanner® 800 hand-held 3D laser scanner to perform scanning on the structural surface, the parameter curve was analysed by generating 3D coordinate information and a 3D image of the fracture surface, and the quantitative parameter Mp3D{M}_{\text{p}}^{3\text{D}} describing the 3D morphology of the structural surface was constructed. The change rule of Rp3D{R}_{\text{p}}^{3\text{D}} and joint roughness coefficient (JRC) were analysed under different scanning resolutions, Δ(r), the scanning precision was suggested, and the functional relationship between JRC and Mp3D{M}_{\text{p}}^{3\text{D}} was established. Finally, a formula for shear strength parameters considering the 3D characteristics of a structural plane surface was established. The model validation results show that the experimental data were within the 95% confidence band of the model curve, the average error of the shear strength was 10.4%, the errors of friction angle and cohesion, C, were 3.4 and 9.4%, and the reliability was fine.

On December 18, 2023, an Ms 6.2earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province, causing a large number of geological disasters and threatening people's lives and the safety of infrastructure. After the earthquake, Gansu and Qinghai provincial governments quickly deployed hundreds of geology professionals to carried out the investigation and verification geological disasters in the earthquake area. Based on the results of the earthquake geohazard investigation and verification, this paper analyses the characteristics, control factors and development trend of the earthquake-induced geohazards, and puts forward suggestions on disaster prevention and risk mitigation measures. Till December 23, a total of 2044 geohazards have been checked, including 78 new geohazards, 88 existing geohazards with intensified deformation due to earthquake, and 1 878 existing geohazards without obvious different from before. Most of new and intensified deforming geohazards are collapse, accounting for 67.5%, followed by landslide, accounting for 31.9%. Most of new and intensified deforming geohazards are small in scale, accounting for 84.9%, followed by medium, accounting for 10.8%. Disaster mode of new and intensified deforming geohazards are mostly small collapse threatening houses and roads. The co-seismic geohazards are densely distributed along the seismic fault, and the spatial density increases with the enhancement of earthquake intensity. Data from 206 groups of accelerate-meters within 50 km from the epicenter of the National Geological Safety Monitoring Network showed that the peak acceleration of the earthquake area was 30.4-1969.7 mg. and decayed logarithm with the increase of the distance from the epicenter. In addition, the surface deformation monitoring equipment also recorded the co-seismic displacement curve of a typical landslide. Analysis shows, earthquake put a deteriorate effect to rock and soil, which decreased their integration and strength. There is a magnificent geohazard after-effect of earthquake; collapse, landslide and debris flow will be much often than before. So the authors suggest: (1) update earthquake geohazard database as soon as possible, (2) work out targeted prevention and control measures for the geohazards with large potential danger, (3) conduct comprehensive remote sensing monitoring and research of earthquake-induced geohazard mechanism, (4) improve the meteorological early warning model and threshold. By all this efforts the risk of geohazards after earthquake will be reduced and controlled. [ABSTRACT FROM AUTHOR]

[Objective] With the rapid increase in construction projects in the western regions in recent years, the impact of seasonal freeze-thaw cycles in the high-altitude areas of western China has become more pronounced. Conducting research on the microscopic characteristics and strength degradation properties of rocks under freeze-thaw cycles is crucial for guiding engineering construction in these cold, high-altitude regions. [Methods] To study the influence of freeze-thaw cycles on rock structure and mechanical properties, we collected diorite samples from a tunnel in the Kangding area and examined the effects of freeze-thaw cycles on their microstructure and mechanical characteristics. Firstly, thin rock sections were observed under a polarizing microscope to obtain mineral compositions and microstructures. Then, CT scanning technology was used to scan the granite samples after freeze-thaw cycles, and the scanned layers were binarized using threshold segmentation. The scanning images of different layers were binarized using threshold segmentation, and highresolution 3D data and images of the internal and external structures of the samples were obtained by stacking the binary image layers. Fractal theory was applied to calculate the box-counting dimension of the images and quantitatively assess their complexity. This analysis allowed us to examine the evolution and distribution characteristics of the internal structure of granite under freeze-thaw cycles. [Results] Under a polarizing microscope' the rock exhibits a block-like structure with a patchy, coarse-grained, and unequal-grained granite texture, with locally visible metasomatic worm structures. The main phenocryst minerals are alkaline feldspar. Other minerals range in size from 0.25 to 4.0 mm and primarily include quartz, plagioclase, and alkaline feldspar. Secondary minerals include biotite and epidote, while accessory minerals comprise apatite, zircon, and pyrite. Microscopically, the rock is identified as porphyritic, coarse-grained, and unequal-grained biotite diorite granite. Freeze-thaw cycles were applied to the granite samples in the laboratory to study the strength evolution and explore the relationship between structural evolution and strength. The results indicate that the freeze-thaw cycle effect leads to an overall increase in the internal porosity of the granite's microstructure, though the rock's permeability changes minimally, with an increase of only 0.003x10-3 µm² The internal pore development is uneven, primarily due to the emergence of new micropores, causing changes in the overall structure of the sample. After freeze-thaw cycles, the complexity of the internal structure of the rock decreases, but the overall integrity remains good, with the fractal dimension staying at a high level. Fractal analysis shows that 20 freeze-thaw cycles do not cause significant changes in the structural complexity of granite. However, the overall mechanical properties of the sample decline, viscosity increases, and long-term strength shows significant attenuation, raising the strain threshold for entering the creep test stage. [Conclusion] When evaluating the safety of rocks with dense primary structures, considering only their structure may lead to deviations from the actual situation. It is essential to combine necessary strength indicators for a comprehensive evaluation. After undergoing freeze-thaw cycles, rocks tend to exhibit more significant deformation while maintaining lower strength. Therefore, appropriate treatments are required for construction in high-altitude areas. [Significance] This study provides a reference for applying fractal theory to the evolution of rock microstructure and the relationship between rock microstructure and strength evolution. It also offers valuable guidance for engineering construction in high-altitude and cold regions. [ABSTRACT FROM AUTHOR]

Geohazard is a serious problem in Lanzhou and Minxian County of Gansu Province, northwest China. Three landslides in Lanzhou and Minxian County were selected for universal monitoring construction. According to "Technical guide for geohazardmomtoring and early warning based on the combination of professional and mass monitoring (trial use)", crack-meter, GNSS monitoring, soil moisture monitoring, realtime rain-gauge and alarm apparatus were used in the landslide monitoring network. Power supply of landslide monitoring instruments is from Li-ion battery and solar panels, providing sufficient power to 24 h-per-day working. Data transmission of real-time data is based on LoRa and 2/3/4 G mobilecommumcations, with increasing reliability and cost reduction. Monitoring data were transmitted to national platform and provincial platform simultaneously, providing real-time data for both platforms. The monitoring data were analyzed automatically, using multi-module for landslide prediction and warning. When abnormal data were discriminated, SMS messages were delivered automatically to designated personnels for further processing. Through four months' trial operation, the creep deformation of millimeter-level of landslide was captured. The data is reliable and meets the needs of monitoring and early warning. Through the implementation of three landslide universal monitoring projects, on the one hand, real-time monitoring of landslide deformation and environmental factors is realized, and a reference solution is provided for regions with similar problems. [ABSTRACT FROM AUTHOR]