Around the world severe damages were observed due to reliquefaction during repeated earthquakes, whereas precise understanding of its mesoscopic mechanism is not much discovered. Influence of these earthquakes on reliquefaction needs to be investigated to understand its significance in contributing to inherent sand resistance. In the present study, centrifuge model experiments were performed to examine the influence of foreshocks/aftershocks and mainshock sequence on resistance to reliquefaction. Two different shaking sequences comprising six shaking events were experimented with Toyoura sand specimen with 50 % relative density. Acceleration amplitude and shaking duration of a mainshock is twice that of foreshock/aftershock. In-house developed advanced digital image processing (DIP) technology was used to estimate mesoscopic characteristics from the images captured during the experiment. The responses were recorded in the form of acceleration, excess pore pressure (EPP), subsidence, induced sand densification, cyclic stress ratio, void ratio and average coordination number. Presence of foreshocks slightly increased the resistance against EPP before it gets completely liquefied during the mainshock. Similarly, aftershocks also regained the resistance of liquefied soil due to reorientation of particles and limited generation of EPP. However, application of mainshocks triggered liquefaction and reliquefaction and thus eliminated the beneficial effects achieved from the prior foreshocks. Reliquefaction was observed to be more damaging than the first liquefaction, meanwhile the induced sand densification from repeated shakings did not contribute to increased resistance to reliquefaction. The apparent void ratio estimated from the DIP technology was in good agreement with real void ratio values. Average coordination number indicated that the sand particles moved closer to each other which resulted in increased resistance during foreshocks/aftershocks. In contrast, complete liquefaction and reliquefaction have destroyed the dense soil particle interlocking and made specimen more vulnerable to higher EPP generation. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics. (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/).

In recent years, owing to the advancement of highway infrastructure, modified asphalt has been extensively employed in pavement engineering. Asphalt mixture will invade the soil under high-temperature conditions, affecting soil cracking. Cracking characteristics caused by dryness of the mixed samples of modified asphalt and soil accounting for 0%, 2.5%, 5%, and 7.5% of the total weight were investigated in this paper. According to the water loss situation, the degree of cracking was determined. The crack development was quantitatively analyzed by digital image processing technology, so as to analyze the influence of modified asphalt on soil cracking under different contents. The results show that the soil was relatively better than the normal state. Under the same conditions, the moisture content of modified asphalt soil with 2.5%, 5%, and 7.5% increased by 30.17%, 63.49%, and 110.37% compared with that without modified asphalt. At the same time, due to its special bonding properties, it can effectively improve the cracking of soil. The cracking rate of modified asphalt soil with 2.5%, 5%, and 7.5% content is reduced by 11.58%, 20%, and 31.58%, respectively. The soil added with modified asphalt can effectively increase the total porosity of the soil, thus improving the ability of water absorption, and also can well inhibit the rate of soil evaporation and reduce cracking. Modified asphalt can be rationally applied not only to have soil mechanical properties improved but also to have waste asphalt utilized to reduce environmental pollution.

The lack of researches on the intrinsic microstructure evolution of coarse-grained soil fillers during subgrade compaction-operation period (SCOP), resulting in a deficiency of theoretical guidance for the lifecycle health monitoring of high-speed railway subgrade. In this paper, the self-developed intelligent vibratory compaction instrument (IVCI) was used to rapidly simulate the loading action on high-speed railway gravel aggregate (HRGA) during SCOP. Additionally, two physical-mechanical indicators, dry density rho d and dynamic stiffness Krb, were used to characterize the physical-mechanical properties of HRGA fillers. Besides, the microstructure (coarse particles and voids) evolution within the HRGA fillers during SCOP were in-depth explored based on X-Ray computed tomography (X-CT) technology. The results indicate that the rho d exhibits a continuous slow increase trend, but the Krb exhibits distinct deteriorating characteristics, with a consistent gradual decline after compaction periods. The particle rearrangement is crucial in the compaction periods of HRGA fillers, and the optimal compaction level (referred to the locking point) can be determined by the particle rearrangement indicator Hr. Besides, the particle local shape indicators (angularity coefficient and contour coefficient) as well as void local shape indicator (abundances) can used to explain the deterioration characteristics of HRGA fillers during operation periods. It is important to note that under the vibratory loading, insufficient crushing occurs at the particle corners within the internal skeleton, decreasing the stability of skeleton and giving rise to the content of fine particles, which can fill up the large-sized voids and generate a significant number of morphologically flawed middle-sized and small-sized voids. The finding of this research not only provide a refined analysis and insight understanding of the construction and operation of high-speed railway subgrade, but also can contribute to establishing a solid theoretical foundation for the lifecycle health monitoring of subgrades.

The geometry of joints has a significant influence on the mechanical properties of rocks. To simplify the curved joint shapes in rocks, the joint shape is usually treated as straight lines or planes in most laboratory experiments and numerical simulations. In this study, the computerized tomography (CT) scanning and photogrammetry were employed to obtain the internal and surface joint structures of a limestone sample, respectively. To describe the joint geometry, the edge detection algorithms and a three-dimensional (3D) matrix mapping method were applied to reconstruct CT-based and photogrammetry-based jointed rock models. For comparison tests, the numerical uniaxial compression tests were conducted on an intact rock sample and a sample with a joint simplified to a plane using the parallel computing method. The results indicate that the mechanical characteristics and failure process of jointed rocks are significantly affected by the geometry of joints. The presence of joints reduces the uniaxial compressive strength (UCS), elastic modulus, and released acoustic emission (AE) energy of rocks by 37%-67%, 21%-24%, and 52%-90%, respectively. Compared to the simplified joint sample, the proposed photogrammetry-based numerical model makes the most of the limited geometry information of joints. The UCS, accumulative released AE energy, and elastic modulus of the photogrammetry-based sample were found to be very close to those of the CT-based sample. The UCS value of the simplified joint sample (i.e. 38.5 MPa) is much lower than that of the CT-based sample (i.e. 72.3 MPa). Additionally, the accumulative released AE energy observed in the simplified joint sample is 3.899 times lower than that observed in the CT-based sample. CT scanning provides a reliable means to visualize the joints in rocks, which can be used to verify the reliability of photogrammetry techniques. The application of the photogrammetry-based sample enables detailed analysis for estimating the mechanical properties of jointed rocks. (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/).

Soil-rock mixture (S-RM) is widely distributed in some accumulation slopes and commonly used as a backfill material in the field of geotechnical engineering. The mechanical properties of S-RM play a pivotal role in ensuring the stability of geotechnical engineering projects. The discrete element method (DEM), which can construct S-RM's microstructure model, is an effective tool for studying its mechanical properties. Currently, the most realistic and precise approach for constructing a three-dimensional (3D) microstructure model of S-RM is digital image processing (DIP) technology using computed tomography (CT) scanning device or 3D laser scanning device. However, these devices are very expensive. This study aims to develop an economical and accurate DEM for constructing the 3D microstructure of S-RM using DIP technology with a conventional digital camera. Firstly, a digital camera was used to capture three sets of 2D images on real rock blocks around four circles at different angles. DIP technology was then applied to process the 2D images and construct the refined 3D rock block grid models. Subsequently, the geometric parameters of the grid models were compared with those of the corresponding real rock blocks to validate the accuracy and applicability of this method. The microstructure model of S-RM in the large-scale direct shear test was then established and verified for DEM simulations. Finally, the mechanical properties of S-RM were analyzed based on the evolution of the shear band, the rotation of rock blocks, and the change of contact force chain.