Deep geological sequestration is widely recognized as a reliable method for nuclear waste management, with expanded applications in thermal energy storage and adiabatic compressed air energy storage systems. This study evaluated the suitability of granite, basalt, and marble as reservoir rocks capable of withstanding extreme high-temperature and high-pressure conditions. Using a custom-designed triaxial testing apparatus for thermal-hydro-mechanical (THM) coupling, we subjected rock samples to temperatures ranging from 20 degrees C to 800 degrees C, triaxial stresses up to 25 MPa, and seepage pressures of 0.6 MPa. After THM treatment, the specimens were analyzed using a Real-Time Load-Synchronized Micro-Computed Tomography (MCT) Scanner under a triaxial stress of 25 MPa, allowing for high-resolution insights into pore and fissure responses. Our findings revealed distinct thermal stability profiles and microscopic parameter changes across three phases-slow growth, slow decline, and rapid growth-with critical temperature thresholds observed at 500 degrees C for granite, 600 degrees C for basalt, and 300 degrees C for marble. Basalt showed minimal porosity changes, increasing gradually from 3.83% at 20 degrees C to 12.45% at 800 degrees C, indicating high structural integrity and resilience under extreme THM conditions. Granite shows significant increases in porosity due to thermally induced microcracking, while marble rapidly deteriorated beyond 300 degrees C due to carbonate decomposition. Consequently, basalt, with its minimal porosity variability, high thermal stability, and robust mechanical properties, emerges as an optimal candidate for nuclear waste repositories and other high-temperature geological engineering applications, offering enhanced reliability, structural stability, and long-term safety in such settings. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Microbial-induced carbonate precipitation (MICP) is a novel geotechnical reinforcement method that can be used for slope protection, erosion mitigation and seepage control without compromising the soil structure. Based on computed tomography (CT) 3D reconstruction, pore parameters such as the connected porosity, pore equivalent diameter and coordination number are extracted to quantitatively evaluate the effect of the calcium carbonate content on the microstructure of biocemented sand. Then, simulations are conducted to analyze the seepage characteristics of single-phase water flow in the pore space, and 3D visualization of porous seepage in biocemented sand is achieved. The results indicate that as the calcium carbonate content increases, there is a noticeable decrease in total porosity, which is accompanied by an increase in the number of isolated pores and a decrease in the number of connected pores. Concurrently, the average pore equivalent diameter increases, while the pore coordination number decreases. Seepage simulation shows that the permeability of biocemented sand has strong anisotropy, and the pore structure has a strong control effect on the seepage. With increasing calcium carbonate content, the biocemented sand streamlines gradually develop from a network to a branching shape until several main stems remain.

Micropile groups (MPGs) are typical landslide resistant structures. To investigate the effects of these two factors on the micropile-soil interaction mechanism, seven sets of transparent soil model experiments were conducted on miniature cluster piles. The soil was scanned and photographed, and the particle image velocimetry (PIV) technique was used to obtain the deformation characteristics of the pile and soil during lateral loading. The spatial distribution information of the soil behind the pile was obtained by a 3D reconstruction program. The results showed that a sufficient roughness of the pile surface was a necessary condition for the formation of a soil arch. If the surface of the pile was smooth, stable arch foundation formation was difficult. When the roughness of the pile surface increases, the soil arch range behind the pile and the load-sharing ratio of the pile and soil will increase. After the roughness reaches a certain level, the above indicators hardly change. Pile spacing within the range of 5-7 d (pile diameters) was suitable. The support effect was poor when the pile spacing was too large. No stable soil arch can be formed, and the soil slips out from between the piles.

A close relationship exists between the pore network structure of microbial solidified soil and its macroscopic mechanical properties. The microbial solidified engineering residue and sand were scanned by computed tomography (CT), and a three-dimensional model of the sample was established by digital image processing. A spatial pore network ball-stick model of the representative elementary volume (REV) was established, and the REV parameters of the sample were calculated. The pore radius, throat radius, pore coordination number, and throat length were normally distributed. The soil particle size was larger after solidification. The calcium carbonate content of the microbial solidified engineering residue's consolidated layer decreased with the soil depth, the porosity increased, the pore and throat network developed, and the ultimate structure was relatively stable. The calcium carbonate content of the microbial solidified sand's consolidated layer decreased and increased with the soil depth. The content reached the maximum, the hardness of the consolidated layer was the highest, and the development of the pore and throat network was optimum at a depth of 10-15 mm.