Geohazards such as slope failures and retaining wall collapses have been observed during thawing season, typically in early spring. These geohazards are often attributed to changes in the engineering properties of soil through changes in soil phase with moisture condition. This study investigates the impact of freezing and thawing on soil stiffness by addressing shear wave velocity (Vs) and compressional wave velocity (Vp). An experimental testing program with a temperature control system for freezing and thawing was prepared, and a series of bender and piezo disk element tests were conducted. The changes in Vs and Vp were evaluated across different phases: unfrozen to frozen; frozen to thawed; and unfrozen to thawed. Results indicated different patterns of changes in Vs and Vp during these transitions. Vs showed an 8% to 19% decrease for fully saturated soil after thawing, suggesting higher vulnerability to shear failure-related geohazards in thawing condition. Vp showed no notable change after thawing compared to initial unfrozen condition. Based on the test results in this study, correlation models for Vs and Vp with changes in soil phase of unfrozen, frozen, and thawed conditions were established. From computed tomography (CT) image analysis, it was shown that the decrease in Vs was attributed to changes in bulk volume and microscopic soil structure.

In cold regions, rock structures will be weakened by freeze-thaw cycles under various water immersion conditions. Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock. In this paper, freeze-thaw cycles (temperature range of-20 degrees C-20 degrees C) were performed on the sandstones in different water immersion conditions (fully, partially and non-immersed in water). Then, computed tomography (CT) tests were conducted on the sandstones when the freeze-thaw number reached 0, 5, 10, 15, 20 and 30. Next, the effects of water immersion conditions on the microstructure deterioration of sandstone under freeze- thaw cycles were evaluated using CT spatial imaging, porosity and damage factor. Finally, focusing on the partially immersed condition, the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree. The results show that with increasing freeze-thaw number, the porosities and damage factors under fully and partially immersed conditions increase continuously, while those under non-immersed condition first increase and then remain approximately constant. The most severe freeze-thaw damage occurs in fully immersed condition, followed by partially immersed condition and finally non-immersed condition. Interestingly, the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone. For the same freeze-thaw number, the damage factor increases approximately linearly with increasing immersion volume rate, and the increasing immersion degree exacerbates the microstructure deterioration of sandstone. Moreover, the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates. (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 license (http://creativecommons.org/licenses/by/4.0/).

Insight into the growth of internal microstructure and surface morphology is critical for understanding the robustness of red sandstone artifacts in frigid environments. Since freeze-thaw (F-T) cycles can exacerbate the surface deterioration of water-bearing sandstone, a series of investigation on fresh and weathered water-bearing sandstone samples with different F-T cycle numbers (i.e. 0-100) is performed in this study, including three-dimensional (3D) laser scanning, scanning electron microscope (SEM) and computed tomography (CT) scanning tests, thermal property tests, Brazilian tests, and multi-field numerical simulations. Our results demonstrate that with increasing F-T cycles, the surface fractal dimension and specific surface area of red sandstone samples increase, and the pore size distribution inside rocks shifts from ultrananopores (10-100 nm) to micro-pores (0.1-100 mm) and ultramicropores (100 mm & thorn;). Spatially, the pores generated by the F-T cycles are more prominent near the surfaces of rock samples. Numerical simulation indicates that the uneven pore distribution leads to surface degradation. After 100 F-T cycles, the intergranular (IG) cement of the samples cracks, and the IG fractures are widened; eventually, due to the structural integrity weakening, the tensile strength is drastically reduced by over half. The thermal properties of the water-saturated sandstone can be improved during the F-T cycles, and a strong coefficient of determination of 0.98 exists between the fractal dimensions of sandstone surface and the tensile strength. When assessing the mechanical properties of stone artifacts under F-T cycles, the morphological damage of red sandstone should first be investigated when in situ sampling is inappropriate. (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/).

Coral soil in large quantities of islands has been used for the construction of islands with the development of global marine construction projects. At present, the research on the macro and micromechanical behavior of coral soil during loading is insufficient, which is related to the development of marine engineering. Using the self-developed high-pressure geotechnical CT-triaxial apparatus, the consolidated drained triaxial tests were conducted on coral gravel under confining pressures ranging from 200 to 800 kPa, all the while employing realtime CT scanning to monitor the sample's deformation. The deformation, particle breakage, and porosity of coral gravel could be directly observed by CT images and its post-processing. The results show that the stress-strain relationship of the samples is strain hardening. Notably, particle breakage during consolidation predominantly manifests as corner breakoff, whereas shearing processes primarily induce splitting. The relative breakage Br is not only approximately linear with the average coordination number C-N of particles, but also with the logarithm of average particle size d, porosity n, and local strain s. Observing the evolution of the sample during loading, the increase of confining pressures leads to the decrease of the sample porosity, resulting in a diminishment in pore dimensions, a densification of particle packing, and the increase of contacts between particles. Consequently, this induces particle breakage and continuous volumetric contraction, thus the stress-strain relationship is hardening. The reciprocal influence between macroscopic and microscopic mechanics manifests in coral gravel. The experimental findings could provide valuable insights for marine engineering construction.

Freeze-thaw cycling is a critical issue in cold-climate engineering because these cycles impact the mechanical properties of soils due to the translocation of water and ice at temperatures near 0 degrees C. Reinforcement methods have been developed to decrease these adverse effects, including the use of polypropylene (PP) fibers. However, few macrostructural investigations have been able to demonstrate the underlying physical basis for their effectiveness. This study used computed tomography (CT) images of clay samples reinforced with 2% PP fibers and subjected to unconfined compression and Brazilian tests before and after up to 10 closed-system freeze-thaw cycles (FTCs). Significant effects of the FTCs on soil structure include a reduction in macropores and an increase in mesopores. The addition of PP fibers reduces this change in the number of macropores from 28% to 18% following 10 FTCs. Unreinforced samples also show more localized propagation of shear/tensile cracks during tests than reinforced samples as a result of having a higher failure strength and ductility. The bridging effect of fibers, deviation of the failure path, and formation of microcracks around fibers are clearly illustrated in the CT images. This study provides significant insights relevant to engineering design in cold regions.

The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility. The geomechanical part of the research included studying the dependence of rock permeability on the stress-strain state in the vicinity of the wells, and physical modeling of the implementation of the method of increasing the permeability of the wellbore zone- the method of directional unloading of the reservoir. The digital part of the research included computed tomography (CT)-based computer analysis of the internal structure, pore space characteristics, and filtration properties before and after the tests. According to the results of physical modeling of deformation and filtration processes, it is found that the permeability of rocks before fracture depends on the stress-strain state insignificantly, and this influence is reversible. However, when downhole pressure reaches 7-8 MPa, macrocracks in the rock begin to grow, accompanied by irreversible permeability increase. Porosity, geodesic tortuosity and permeability values were obtained based on digital studies and numerical modeling. A weak degree of transversal anisotropy of the filtration properties of rocks was detected. Based on the analysis of pore size distribution, pressure field and flow velocities, high homogeneity and connectivity of the rock pore space is shown. The absence of pronounced changes in pore space characteristics and pore permeability after non-uniform triaxial loading rocks was shown. On the basis of geometrical analysis of pore space, the reasons for weak permeability anisotropy were identified. The filtration-capacitance properties obtained from the digital analysis showed very good agreement with the results of field and laboratory measurements. The physical modeling has confirmed the efficiency of application of the directional unloading method for the reservoir under study. The necessary parameters of its application were calculated: bottomhole geometry, stage of operation, stresses and pressure drawdown value. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone (CRL), making it difficult to study mechanical behaviors. With X-ray computed tomography (CT), 112 CRL samples were utilized for training the support vector machine (SVM)-, random forest (RF)-, and back propagation neural network (BPNN)-based models, respectively. Simultaneously, the machine learning model was embedded into genetic algorithm (GA) for parameter optimization to effectively predict uniaxial compressive strength (UCS) of CRL. Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL. The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data. Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density, pore structure, and porosity of CRL are strongly correlated to UCS. However, the P-wave velocity is almost uncorrelated to the UCS, which is significantly distinct from the law for homogenous geomaterials. In addition, the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone (CFL) and coral boulder limestone (CBL), realizing the quantitative characterization of the heterogeneity and anisotropy of pore. The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting 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/).

The deep cement mixing (DCM) is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns. The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression. In this study, a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours. It is found that the drainage condition affects significantly the stiffness, peak and residual strengths of the DCM samples, which is mainly due to the state of excess pore water pressure at different strain levels, i.e. being positive before the peak deviatoric stress and negative after the peak deviatoric stress, in the undrained tests. The slope of the failure envelope changes obviously with the confining pressures, being steeper at lower stress levels and flatter at higher stress levels. The strength parameters, effective cohesion and friction angle obtained from lower stress levels (c(0)' and phi(0)') are 400 kPa and 58 degrees, respectively, which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 kPa. Additionally, the computed tomography (CT) scanning system was adopted to visualize the internal structures of DCM samples. It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour, which is one of the main reasons for the high variability of the DCM samples. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting 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/).

Cracking behavior can reduce soil hydraulic and mechanical properties and is a preferential pathway for water flow and pollutant transportation, resulting in polluted environment, such as application to landfill liners and capping. Recently, researchers have advocated the use of waste materials for clay mixtures using various measurement and analysis methods. Therefore, this study aims to conduct a bibliometric analysis of the scientific literature published between 2002 and 2021 obtained from Scopus to quantitatively identify research trends, key research areas, and future research paths in this field on desiccation and crack behavior using waste materials as landfill liners. The VOS viewer software was used to analyze 41 articles in which the paper selection process was filtered. The results showed that the fly ash mixture's application as a landfill liner could reduce cracking significantly. Furthermore, fractal analysis and X-ray computed tomography measurements have proven to be good candidates for measuring cracks because they are the most accurate for calculating the crack value. Waste materials such as fly ash can be applied as landfill liners with other materials, such as bentonite and coconut coir fibers. This study is beneficial for improving the design and selecting the appropriate materials for landfill liners.