Great achievements have been made regarding the stress field in the two-dimensional state, however the study of three-dimensional stress field visualization has still not been comprehensively examined. The model with internal cracks was prepared by the laser-medium interaction (3D-ILC), and with the aid of the photoelastic test technology, it visually showed the distribution characteristics of the stress field inside the rock with defects under the three-point bending test method. Primarily, based on the two-dimensional and three-dimensional stress optics law, the isometric fringes were converted into phase differences or optical path differences to visualize the stress field. Moreover, transparent glass, which had better transparency and brittleness closer to real rock was selected as the specimen material. Internal cracks changed the stress fringe distribution of the specimen, and the combination of 3D-ILC technology and photoelasticity provided a new way to visualize the three-dimensional stress field of brittle materials with internal cracks. Through the secondary development and utilization of ABAQUS finite element analysis software, the internal stress fields of brittle solid materials with horizontal internal cracks were visualized. Accurate characterization of the three-dimensional stress field of brittle solid materials has been a long-term goal pursued by researchers in the field of fracture, and it is also the basis and key to solving many practical engineering problems such as design, safety analysis and evaluation.

To investigate the tensile failure phenomenon of rock masses with filled natural defects, the mechanical behavior of 3D printed rock-like materials containing filled kinked fissures under uniaxial tension was identified. Different inclination angles of branch fissure were considered, and cement and gypsum slurry were selected as the infilling materials. It was found that filling materials enhanced the strength of the specimen, which presented to be cement filling > gypsum filling > no filling. The change of inclination angle of branch fissure had significant influence on the strength and failure mode of the specimen and the strength order was −135° > −45° > 90° and +45° > 90° > +135°. Two types of failure pattern, namely tip failure and non-tip failure, were observed in the experiment. Three types of newborn cracks were identified using a high-speed camera. The result achieved by using the digital image correlation technology indicated that different filling conditions led to the position change of high-strain zone. The displacement field of the filled specimen developed from being continuous to being discontinuous. Furthermore, the extended finite element method was adopted to simulate the filled and unfilled specimens, consistent with the experimental results. This study can provide a reliable reference for studying the tensile stress zones in rock exploration.

This study concerns the influence of chemical corrosion and geometric parameters on the macroscopic damage characteristics of brittle limestone containing a kinked fissure under uniaxial compression. The specimens are prepared in chemical solutions with different NaCl concentrations and pH values. The acoustic emission (AE) technique is adopted to detect the inner distortion of the failure behaviour. The physical process of the crack coalescence of kinked fissures is synchronously captured by a high-speed camera. Seven failure patterns are identified based on the final failure mode and the failure process. Furthermore, the stress intensity factor of kinked cracks under chemical corrosion is obtained by a theoretical analysis. Chemical erosion with an acidic solution has a relatively strong effect on the compressive strength of the tested specimen, while the initial crack angle is not affected by short-term chemical corrosion.

In this work, the recently proposed cracking elements method (CEM) is used to simulate the damage processes of structures with initial imperfections. The CEM is built within the framework of the conventional finite element method (FEM) and is formally similar to a special type of finite element. Disconnected piecewise cracks are used to represent the crack paths. With the advantage of the CEM for which both the initiation and propagation of cracks can be captured naturally, we numerically study uniaxial compression tests on specimens with multiple joints and fissures, where the cracks may propagate from the tips or from other unexpected positions. Although uniaxial compression tests are considered, tensile damage criteria are mainly used in the numerical model. On the one hand, the results demonstrate the robustness and effectiveness of the CEM, while, on the other hand, some drawbacks of the present model are demonstrated, indicating directions for future work.

The large-scale accumulation of coal gangue has created increasing environmental pressure, while its use as aggregate in cementitious materials remains limited by its high water absorption, porous structure and unstable mechanical performance. This study develops a machine learning-assisted multi-objective optimization framework for lightweight shotcrete incorporating surface-pretreated coal gangue aggregates and polyvinyl alcohol fibres. Two pretreatment methods—namely, silica-fume slurry coating (CGACM) and dry adsorption activation (CGACD)—were applied to improve the aggregate surface characteristics. Experimental data on compressive strength, splitting strength and density were used to train backpropagation neural networks and support vector machine and random forest models, with hyperparameters optimized by the Beetle Antennae Search algorithm. The trained models were then coupled with a multi-objective optimization procedure to balance mechanical performance, density, material cost and CO₂ emissions. The results show that surface pretreatment can improve the performance of coal gangue lightweight shotcrete, while the proposed optimization framework can identify mixture designs with balanced strength, reduced density and improved economic and environmental performance. Compared with untreated or non-optimized mixtures, the optimized surface-pretreated mixtures achieved a more favorable trade-off among mechanical, cost and carbon-emission objectives. This study provides a data-driven approach for the sustainable design and practical utilization of coal gangue in lightweight shotcrete.