Understanding the mechanical properties of continental submarine slopes is critical for the assessment of geo-marine slope stability hazards. This paper presents the first detailed geomechanical study on sediment profiles associated with a geologically recent sliding event at the Goliath submarine complex offshore southern Israel. Sediment samples were extracted from similar to 5-m-long piston cores collected from three representative sites: on the recent slide headscar (PHS3), the adjacent undisturbed slope seafloor (PSL4), and at the dextral tail-depositional lobe (PTL3). The investigation included Gamma-ray and CT scanning, sediment phase measurement, laboratory T-bar penetration, and vane shear testing. The evaluated properties for the three sites are the undrained shear strength, over-consolidation ratio, soil sensitivity, water content, and density. The experimental results show a strong correlation between the findings of the various investigation tools regarding the original soil condition before sliding, the slide scar location, the degradation in properties of the disturbed soil, and the post-slide deposited soil properties. Despite the variation in properties among the different sites, the paper presents a prediction model for the soil strength in the Goliath slide area. Beyond the geomechanical characterization, the analysis of the test results highlights two unique findings: (1) evidence of a long-term strength softening phenomenon in the post-slide period, and (2) insights into the transition of geomechanical properties with depth within the slide scar.

The artificial ground freezing (AGF) method is a frequently-used reinforcement method for underground engineering that has a good effect on supporting and water-sealing. When employing the AGF method, the mesoscopic damage reduces the strength of the frozen sandy gravel and consequently affects the bearing capacity of the frozen curtain. However, a few studies have been conducted on the mesoscopic damage of artificial frozen sandy gravel, which differs from fine-grained soil due to its larger gravel size. Therefore, based on triaxial compression tests and CT scanning tests, this paper investigates both the mesoscopic damage mechanism and variations in artificial frozen sandy gravels. The findings indicate that there are contact pressures between gravel tips within the frozen sandy gravel, with damage primarily concentrated around these gravels during incompatible deformation within a four-phase medium consisting of ice, water, soil, and gravel. Furthermore, numerical simulation validates that failure typically initiates at delicate contact surfaces between gravel and soil particles. For instance, when the axial strain reaches 8%, the plastic strain at the location of gravel contact reaches 4.6, which significantly surpasses most of the surrounding plastic strain zones measuring around 1.3. Additionally, the maximum local stress within the soil sample is as high as 48 MPa. This failure event is distinct from viscoplastic failure observed in frozen fine-grained soil or brittle failure seen in frozen rock. The findings also indicate that the mesoscopic damage is about 0.3 when the axial strain is 10%. The study's findings can serve as a valuable guide for developing finite element models to assess damage caused by freezing in sandy gravel using AGF method.

Cracking of compacted clays during cyclic wetting-drying poses significant challenges to the stability of channel slopes. This study performed a series of unidirectional wet-dry tests to evaluate the cracking behavior of expansive soils collected from a channel slope in northern Xinjiang, China. Using computed tomography scanning and three-dimensional (3D) reconstruction, the internal crack characteristics of expansive soils were quantitatively described. The results indicate that the penetration depth of the cracks was stabilized after five cycles, reaching 31.4% of the initial specimen height. The morphologies of internal cracks revealed a transition in the cracking mode, form shallow and scattered cracks in the initial stage to deeper and more clustered cracks in the final stage. Centralized cracks were prominent in the first three wet-dry cycles, followed by a shift to crack deflection from the vertical plane in subsequent cycles. Four indices (i.e., slice crack ratio, crack length, branching number, and dead-end point) provided a satisfactory quantitative depiction of the evolution of the spatial distribution and connectivity of the cracks over the number of cycles. Additionally, the crack volume fraction and fractal dimension effectively evaluated the 3D cracking behavior of soil crack networks.

Due to natural and anthropogenic disturbances, natural gas hydrates with morphologies of nodules and chunks dissociate and release massive free gas, creating large cavities within fine-grained marine sediments. However, it is still a challenge to quantify the impact of gas cavities on mechanical properties of cavitied fine-grained marine sediments as there is a lack of efforts focusing on the inner structure visualization. In this study, an oedometer test and X-ray computed tomography scans are jointly conducted on marine clayey silt with gas cavities, and the confined compressibility as well as the inner structure change under an undrained condition are explored, followed by development of a theoretical model depicting the void ratio change. The results show that vertical loading induces a void ratio reduction, and the reduced void ratio can fully recover after being unloaded. Although being fully recovered, unrecovered changes of the inner structure still remain after being unloaded. Examples include closed cracks in the lower matrix, new occurring cracks in the upper matrix, and the fragmented gas cavity. In addition, the void ratio linearly increases with the increasing inverse of normalized pore gas pressure, while the coefficient of the effective stress linearly decreases with the increasing inverse of normalized vertical loading stress. The proposed theoretical model captures the essential physics behind undrained confined deformation of fine-grained marine sediments with gas cavities when subjected to loading and unloading.

In this study, a functional relationship for frozen soil at different temperatures, confining pressures, and triaxial compressive strengths is established through macroscopic and mesoscopic comparative tests. Additionally, a three-dimensional pore network model at the mesoscopic scale is constructed. Morphological characterization parameters are introduced to quantify the pore structure, and the evolution of the pore structure in frozen soil during the stress process is analyzed, as well as the influence of temperature and confining pressure on the pore characteristics and failure morphologies. The results reveal that at the macroscale, frozen soil exhibits a power function relationship with temperature, confining pressure, and triaxial compressive strength. During mechanical loading, frozen soil undergoes compaction, pore development, and pore expansion stages, leading to changes in pore size and connectivity. Additionally, temperature and confining pressure significantly impact the pore characteristics and failure morphologies of frozen soil. At lower temperatures, frozen soil experiences severe bulging and brittle failure, accompanied by increased pore size, enhanced connectivity, and complex morphology. Increasing the confining pressure reduces the degree of bulging and damage, decreases the porosity and connectivity, enhances the complexity of the pore morphology, and results in a denser and more stable internal structure in frozen soil. Through this study, a better understanding of the damage behavior of frozen soil under different temperatures and confining pressures is achieved. Furthermore, this research provides a theoretical basis and reference for addressing related engineering problems.

While the fabric of soil can significantly influence its behaviour, the effect of varying fabric parameters on the subgrade shear response is still not well understood. This study creates soil specimens with different fabrics which are then captured through X-ray microscopic-computed tomography scanning and quantified by image processing techniques. A comprehensive laboratory investigation is conducted to understand how the soil fabric affects its monotonic and cyclic shear behaviour. The results indicate that the consolidation method creates a more homogeneous fabric with mainly small-to-medium interconnected pores, whereas the compaction technique creates significantly large and mostly inter-aggregate pores with lower connectivity. In this regard, the consolidated specimens exhibit an elastic-perfectly plastic behaviour, while the compacted specimens show strain-hardening transformation during isotropic monotonic shearing. Under anisotropic conditions, the compacted specimens exhibit a greater strain softening response and excess pore pressure than the consolidated specimens because they have a weaker fabric. Furthermore, the compacted specimens show a smaller threshold strain at a lower critical number of cycles due to the collapse of large pores. These current findings prove the decisive role that soil fabric plays in determining the shear response and failure of subgrade soils.

Artificial frozen sandy gravel exhibits the characteristics of wide distribution of particle size and complex composition, which are quite distinct from frozen fine-grained soils such as clay and silt. It may be more accurate to use both macroscopic and microscopic scales to evaluate the damage of artificial frozen sandy gravel. Therefore, this paper proposes an investigation on the macro-plastic damage and micro-crack damage of artificial frozen sandy gravel through triaxial compression and X-ray CT scanning tests. The two types of damage are obtained from completely different macro-plastic and micro-crack damage theoretical calculation methods. It can be concluded that the evolution law of the two damages is similar, but the value is different. Moreover, the defined cross-scale modified damage which is fitted through the calculated macro-plastic damage and micro-crack damage is proposed. The fitting functions reveal the evolution law of frozen sandy gravel damage more accurate, which is beneficial to the safety of the artificial ground freezing project and provides a valuable reference for subsequent numerical simulations of the frozen sandy gravel constitutive relationship.

The damage to microbial solidified engineering residue by freeze-thaw cycles increases the amount of material prone to wind erosion. Microbial solidification of engineering residue was carried out, and freeze-thaw cycle and indoor wind tunnel tests were conducted on the microbial solidified samples to reveal the interaction mechanism between different numbers of freeze-thaw cycles and the wind erosion degree. The test results showed that the larger the number of freeze-thaw cycles, the greater the mass loss of the microbial solidified engineering residue sample due to wind erosion and the lower the surface strength and surface thickness of the sample. However, the surface strength and surface thickness were relatively stable after more than 7 freeze-thaw cycles. The mass loss of the sample was 13 g after 9 freeze-thaw cycles at the maximum wind speed (15 m/s), higher than that of the sample exposed to no freeze-thaw cycles (6 g) but far lower than that of the undisturbed sample (3647 g). The results indicated that the microbial solidified engineering residue had high freeze-thaw resistance. The microbial solidified engineering residue was analyzed by computed tomography (CT) before and after the freeze-thaw cycles, and three-dimensional reconstruction was performed using digital image processing. The microstructure analysis showed that the freeze-thaw cycles did not change the content and spatial distribution of the microbial solidified products but reduced the ability to cement the microbial solidified products and the soil particles. The calcium carbonate inside the hard shell became more fragmented, the equivalent radius of the crystals and the stability of the hard shell decreased, and the porosity increased. However, the microbial solidified engineering residue exhibited high resistance to wind erosion and freeze-thaw cycles.

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.

The cultural heritage sector has increasingly explored the use of micro-CT (mu CT) across numerous projects seeking to better understand past cultures and the materials they have left behind. As such, the role of micro-CT (mu CT) is still being developed and projects continue to show novel ways that the technology can be adapted to. The Gjellestad ship, located in Halden (ostfold in Viken), Norway, is dated to the Viking Age and was found in a poor state of preservation. Both organic and metallic materials were deteriorated to the degree that standard excavation methods would have resulted in further damage to, or even the destruction of, these elements. A new approach was needed, and this presented an opportunity to explore the use for mu CT as a documentative tool for field archaeology and conservation. As the remaining rivets were too fragile to handle directly, they were removed together with the surrounding matrix as soil blocks. To retain important stratigraphic and position information, a georeferencing system was developed that would be visible to mu CT and included within each soil block. This enabled the spatial (re)positioning of the soil blocks by use of 3D GIS and in alongside with other spatial documentation gathered at the time of excavation. The quantity of soil blocks will give us a large dataset to work with and, although we continue to document the soil blocks with mu CT, we now can discuss our preliminary results pertaining to the positive impact that mu CT has for the documentation, conservation, and reconstruction of cultural heritage.(c) 2023 The Author(s). Published by Elsevier Masson SAS on behalf of Consiglio Nazionale delle Ricerche (CNR).