This study introduces a novel, interdisciplinary method that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided Digital Volume Correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay-sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray Computed Tomography (mu CT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles, and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the Iterative Closest Point (ICP) method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through subvoxel registration via a three-dimensional inverse compositional Gauss-Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.

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.

Determining the evolution characteristics of cracks and shear bands is important for understanding the damage mechanisms of geotechnical materials. However, there are few experimental studies on the mesoscopic evolution characteristics of cracks in shear bands. In this study, micro -chromatography (micro -CT) is used to evaluate the triaxial test processes of granite residual soil samples under confining pressures of 50 kPa, 100 kPa, 200 kPa and 300 kPa. Then, advanced digital volume correlation (DVC) is used to obtain three-dimensional strain fields and shear bands at different test loading stages, the evolution characteristics of cracks inside and outside the shear band are further measured basis on this. The results indicate that, if the maximum gradient region of the crack distribution in the initial state of the sample can form a trend surface similar to the interface , then the shear band may be generated in this region. After the formation of the shear band, the penetration degrees of the shear bands are similar to an S curve with the increasing axial strain. The crack volume densities of the shear bands are obviously smaller than those of whole specimens. The crack volume densities on the shear bands first decrease rapidly and then increase gradually with increasing axial strain, and the increasing rate decreases with increasing confining pressure. Among the various crack types on the shear bands, the volume contents of brand-new cracks increase the fastest and exceed half, indirectly reflecting the severe deformation characteristics on the shear bands.