Publications

Tree-Based Solution Frameworks for Predicting Tunnel Boring Machine Performance Using Rock Mass and Material Properties

Numerical investigation on the stress evolution and failure behavior for deep roadway under blasting disturbance

Stability Analysis and Support Control for a Jointed Soft Rock Roadway Considering Different Lateral Stresses

3D Morphology Analysis and Shear Strength Prediction Model for a Backfill–Rock Interface

Effects of fluid salinity and composition on subcritical crack growth in marble

Characteristics of Mining-Induced Stress Rotation Due to Unloading in Deep Roadway Excavation and Surrounding Rock Control Countermeasures

As metal mines advance into deep mining, the increase in tectonic stress and horizontal stress leads to a higher degree of joint and fissure development in roadway surrounding rocks, along with a significant rise in both the fragmentation degree of the rock mass and the support cost. This paper adopts field monitoring and numerical simulation methods to analyze the characteristics of mining-induced stress rotation after unloading due to deep roadway excavation in the Jinchuan mining area, and proposes corresponding surrounding rock control countermeasures and optimized schemes for the original support. The research results show that after the unloading caused by the excavation of deep roadway surrounding rock, the magnitudes and directions of the maximum, intermediate, and minimum principal stresses all exhibit a trend of slow change, followed by drastic change, and finally gradual stabilization. When the roadway advances to 4 m in front of the monitor section, the adjustment of the magnitude of principal stress of the surrounding rock is the most drastic. Moreover, as the working face moves away from the monitor section, the principal stress gradually stabilizes and becomes lower than the initial stress value. When the roadway advances to 6 m in front of the monitor section, the adjustment of the direction of the principal stress of the surrounding rock is the most drastic. The rotation angle of the maximum principal stress shows a trend of first increasing and then decreasing with the increase in the excavation step, while the rotation angles of the intermediate and minimum principal stresses show a trend of first decreasing and then increasing as the excavation step increases. Based on the spatial distribution characteristics of joints and fissures in the roadway surrounding rock, the sensitive area for the rotation of mining-induced stress direction is defined. By changing the advancing direction of the roadway, the rotation trajectory of the principal stress can be deviated from the sensitive area, thereby improving the self-stabilization ability of the roadway surrounding rock. It is proposed that asymmetric coupling support be adopted to reinforce the positions where the principal stress rotation of the rock mass around the anchorage is severe, which can effectively reduce the range of the plastic zone in the roadway surrounding rock. The research results provide new ideas for the surrounding rock control of deep roadways, as well as a theoretical basis for the design and optimization of roadway support parameters in similar mines.

Experimental Studies on Rock Thin-Section Image Classification by Deep Learning-Based Approaches

Experimental studies were carried out to analyze the impact of optimizers and learning rate on the performance of deep learning-based algorithms for rock thin-section image classification. A total of 2634 rock thin-section images including three rock types—metamorphic, sedimentary, and volcanic rocks—were acquired from an online open-source science data bank. Four CNNs using three different optimizer algorithms (Adam, SGD, RMSprop) under two learning-rate decay schedules (lambda and cosine decay modes) were trained and validated. Then, a systematic comparison was conducted based on the performance of the trained model. Precision, f1-scores, and confusion matrix were adopted as the evaluation indicators. Trials revealed that deep learning-based approaches for rock thin-section image classification were highly effective and stable. Meanwhile, the experimental results showed that the cosine learning-rate decay mode was the better option for learning-rate adjustment during the training process. In addition, the performance of the four neural networks was confirmed and ranked as VGG16, GoogLeNet, MobileNetV2, and ShuffleNetV2. In the last step, the influence of optimization algorithms was evaluated based on VGG16 and GoogLeNet, and the results demonstrated that the capabilities of the model using Adam and RMSprop optimizers were more robust than that of SGD. The experimental study in this paper provides important practical value for training a high-precision rock thin-section image classification model, which can also be transferred to other similar image classification tasks.

An experimental study of fracture mechanism and morphology of granite specimens under various dynamic loading rates

Case studies of groundwater flow into tunnels and an innovative water-gathering system for water drainage

Floor heave mechanism and stiff control technology by I-beam for deep mine roadway

Anisotropic rock permeability evolution model based on wing crack propagation after dynamic load testing

Abstract The permeability evolution of rock is essential in geotechnical engineering, which is related to seepage. A permeability evolution model, which is based on the wing crack propagation model and Darcy’s law, is created for rock after dynamic load testing with confining pressures. It is assumed that permeability has two types: isotropic initial permeability and anisotropic microcrack-induced permeability. In this model, the wing crack length is associated with the absorption energy per unit volume of the rock specimen under dynamic loads, in accordance with the surface energy theory. Assuming that the initial crack families are evenly distributed, the contribution of each crack family to permeability in different directions is investigated. In this study, an expression of permeability, which is related to axial stress, confining pressure, and absorbed energy per unit volume, is obtained. Two groups of dynamic load testing with confining pressures of sandstone are conducted using a modified split Hopkinson pressure bar technique. In group A, the incident energy is a variable, whereas in group B, the confining pressure is a variable. After the dynamic load testing, the permeability of the sandstone specimens is measured using the pulse decay method on MTS 815. Owing to the limitations on the test equipment, only the permeability in the direction of the dynamic load is measured. The permeability obtained from the dynamic load testing is in good agreement with the permeability calculated by the model. In this model, the anisotropy of rock permeability is theoretically studied. The minimum microcrack-induced permeability in all directions is about 0.65 of the maximum permeability value. In summary, the model discussed here enables the prediction of the permeability of the rocks under dynamic impact and establishes the relationship between macro-mechanical parameters and micro-mechanical parameters. In addition, it provides a new idea for the research on the anisotropy of rock permeability.

Experimental Study on the Floor Heave and Failure Process of Rock Samples under Biaxial Step Loading

Floor heave is a typical tunnel issue in tunnelling engineering. To gain deep insights into the deformation mechanism and failure processes of floor heave at the bottom of a tunnel in layered rock, biaxial step-loading tests were conducted on rock samples (including schist and sandstone) with and without prefabricated invert arches. The failure processes of the samples were observed by the three-dimensional digital image correlation technique (3D-DIC) during the test. The test results showed that the deformation evolution processes of the floor heave of the sample included the following steps: (1) crack initiation at the interlayer weak planes; (2) separation of the rock matrix into platy structures along the bedding planes and flexures; and (3) fracture and uplift of the platy structures in the middle part. As the stress redistributes on the bottom plate of the sample, and stress concentration zones shift toward locations far away from the arching surface, the deformation evolution shows a similar variation trend with the stress. Continuous buckling fracturing takes place progressively from the vicinity of the arch surface to certain distant regions. Based on the test results, the key location of internal surrounding rock deformation was determined, and the mechanism of floor heave was clarified. The schist sample SC-BI-10 began to experience floor heave at 1064.4 s, and the deformation curve (the relationship between Y and U) showed a convex shape in the range of 0–20 mm in the Y-coordinate. The displacement reached its maximum value at y = 11.7 mm, corresponding to the position where the rock slab was broken. In addition, the influence of the interlayer properties and cover depth of rocks on bottom uplift was also studied. The design of tunnel supports and the monitoring and prevention of floor heave can benefit from this study.

Effects of external dynamic disturbances and structural plane on rock fracturing around deep underground cavern

Abstract The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities. Thus, a combined finite-element method was employed to simulate the failure process of an underground cavern, which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes, disturbance direction, and dip angles of the structural plane. The crack-propagation process, stress-field distribution, displacement, velocity of failed rock, and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures. The simulation results indicate that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state, while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load. The crack distribution around the circular cavern exhibited an asymmetric pattern, possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route. Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances, during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane. Additionally, the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states. These results indicate that the failure behavior should be the integrated response of the excavation unloading effect, geological conditions, and external dynamic disturbances.

Numerical study on shear behavior of backfill-rock rough interface considering 3D morphology of surrounding rock in a mining stope

Experimental study of the mechanical and fracture behavior of flawed sandstone subjected to coupled static-repetitive impact loading

3D spatial fracture behavior of sandstone containing a surface flaw under uniaxial compression

Experimental study on energy and damage evolution of dry and water-saturated dolomite from a deep mine

The deformation and failure of a rock is closely related to the strain energy consumption during the load process of rock. To investigate the effect of water on energy evolution and damage characteristics of dolomite samples from a deep mine, the uniaxial compression tests were carried out on dry and water-saturated dolomite samples at different burial depths (900 m–1200 m). The effects of water on the evolution characteristics of elastic and dissipative energy ratios ( U e / U and U d / U) during rock deformation and failure was analyzed. Based on the variation rate of damage factor ( D f ), a new brittleness index is proposed, which can effectively characterize the brittleness characteristics of water-bearing dolomite. The results show that the uniaxial compressive strength and elastic modulus of the water-saturated dolomite are significantly reduced compared to dry sample. The energy and damage evolution process of dolomite can be divided into four stages: initial damage stage, stable damage stage, pre-peak accelerated damage stage and post-damage stage. The variation rate of damage factor of the rock samples in the stable damage stage and the pre-peak accelerated damage stage appeared to increase significantly after water saturation treatment. Compared with water-saturated samples, more pronounced energy hardening characteristics and brittleness characteristics were observed in dry samples. In addition, the possible impact on the stability of deep rock engineering after the deterioration of rock mechanical properties and energy storage properties caused by water was analyzed. Groundwater can somewhat reduce rock burst proneness. However, it also has the potential to lead to greater rock engineering destabilization and failure hazards.

Characteristic stress and strain precursor information for fine-grained granite during failure process under triaxial loading and unloading conditions

The unloading effect by excavation may cause irreversible and severe damage to the surrounding rock masses in underground engineering. In this paper, both conventional triaxial compression (CTC) tests and triaxial unloading confining pressure (TUCP) tests were conducted on fine-grained granite to study its triaxial compression failure processes due to unloading. Based on the crack volumetric strain (CVS) method, the crack axial strain (CAS) method and crack radial area strain (CRAS) method were proposed to identify the failure precursor information (including stress thresholds and axial strain at the initiation point of crack connectivity stage) during the rock failure processes. The results of the CTC tests show that the stable crack development stress σsd, unstable crack development stress σusd, and crack connectivity stress σct identified by the CAS method are 6%, 74%–84%, and 86%–97% of the peak stress, respectively. For the TUCP cases, as the confining pressure increases, the stress thresholds, axial pressure at failure and axial strain at the start of the crack connectivity stage increase, while the time ratio of the crack connectivity stage to the entire unloading stage decreases. This indicates that fine-grained granite is prone to generate more cracks and leads to fail suddenly under high confining pressure. Furthermore, this new method demonstrates that the point at which the derivative of the radial crack area strain transitions from stable to a sudden increase or decrease is defined as the precursor point of rock failure. The results of axial strain at the starting point of the crack connectivity stage are very close to those predicted by the AE method, with β1 no more than 11%.