Underground Space最新文献

Rockburst has always been a challenge for the safe construction of deep underground engineering. This study investigated the rockburst characteristics in highly-stressed D-shape tunnels under impact loads from rock blasting and other mining-related dynamics disturbances. The biaxial Hopkinson pressure bar was utilized to apply varying biaxial prestress and the same impact loads to cube specimens with D-shape hole. High-speed camera and digital image correlation (DIC) were used to capture the failure process and strain field of specimen. The test results demonstrate that the D-shape hole specimen experience rockburst under coupled static stress and impact load. Under this circumstance, the rockburst mechanism of the D-shaped hole specimens involves spalling in sidewall induced by impact load, indicating dynamic tensile failure. The high static prestress provides the initial stress field, while the impact load disrupts the stress equilibrium, result in the stress or strain concentration in the sidewall of the D-shape hole, inducing rockburst. Moreover, the rockburst process can be divided into (1) calm stage, (2) crack initiation, propagation, and coalesce stage, (3) spalling stage and (4) rock fragments ejection stage. Impact load triggers rockburst occurrence, while vertical stress further determines the rockburst characteristics. The influence range and magnitude of strain concentration zone and displacement deformation of the tunnel surrounding rock increases with increasing vertical stress, thus inducing more severe rockburst.

Rockburst is a frequently encountered hazard during the production of deep gold mines. Accurate prediction of rockburst is an important measure to prevent rockburst in gold mines. This study considers seven indicators to evaluate rockburst at four deep gold mines. Field research and rock tests were performed at two gold mines in China to collect these seven indicators and rockburst cases. The collected database was oversampled by the synthetic minority oversampling technique (SMOTE) to balance the categories of rockburst datasets. Stacking models combining tree-based models and logistic regression (LR) were established by the balanced database. Rockburst datasets from another two deep gold mines were implemented to verify the applicability of the predictive models. The stacking model combining extremely randomized trees and LR based on SMOTE (SMOTE-ERT-LR) was the best model, and it obtained a training accuracy of 100% and an evaluation accuracy of 100%. Moreover, model evaluation suggested that SMOTE can enhance the prediction performance for weak rockburst, thereby improving the overall performance. Finally, sensitivity analysis was performed for SMOTE-ERT-LR. The results indicated that the SMOTE-ERT-LR model can achieve satisfactory performance when only depth, maximum tangential stress index, and linear elastic energy index were available.

Rockburst is a major challenge to hard rock engineering at great depth. Accurate and timely assessment of rockburst risk can avoid unnecessary casualties and property losses. Despite the existence of various methods for rockburst assessment, there remains an urgent need for a comprehensive and reliable criterion that is easy to both apply and interpret. Developing a new rockburst criterion based on simple parameters can potentially fill this gap. With its advantages, this criterion can facilitate a more effective and efficient prediction of rockburst potential, thereby contributing significantly to enhancing safety measures. In this paper, combined with the internal and external factors of rockburst, four control variables (i.e., integrity index, stress index, brittleness index, and elastic energy index) were selected to be incorporated into a comprehensive rockburstability index (RBSI). Based on 116 sets of rockburst cases, the rockburst potential was accurately quantified and predicted using the categorical boosting (CatBoost) model and the nature-inspired metaheuristic African vultures optimization algorithm (AVOA). In its performance validation, the criterion achieved the highest accuracy of 90.48%, verifying the reliability and effectiveness of the proposed RBSI criterion. Additionally, an interpretive method was applied to analyze the variable influence on the criterion, facilitating the explanation of predictions and the analysis of the formula’s robustness under different conditions. In general, compared with existing criterion methods involving relevant indicators, the newly proposed RBSI criterion enhances the accuracy of rockburst potential prediction, and it can effectively and swiftly evaluate the preliminary risk of rockburst. Lastly, a graphical user interface was developed to provide a clear visualization of the assessment of rockburst potential.

During dislocation, a tunnel crossing the active fault will be damaged to varying degrees due to its permanent stratum displacement. Most previous studies did not consider the influence of the tunnel’s deep burial and the high in-situ stress, so the results were not entirely practical. In this paper, the necessity of solving the anti-dislocation problem of deep-buried tunnels is systemically discussed. Through the model test of tunnels across active faults, the differences in failures between deep-buried tunnels and shallow-buried tunnels were compared, and the dislocation test of deep-buried segmental tunnels was carried out to analyze the external stress change, lining strain, and failure mode of tunnels. The results are as follows: (1) The overall deformation of deep-buried and shallow-buried tunnels is both S-shaped. The failure mode of deep-buried tunnels is primarily characterized by shear and tensile failure, resulting in significant compressive deformation and a larger damaged area. In contrast, shallow-buried tunnels mainly experience shear failure, with the tunnel being sheared apart at the fault crossing, leading to more severe damage. (2) After the segmental structure design of the deep-buried tunnel, the “S” deformation pattern is transformed into a “ladder” pattern, and the strain of the tunnel and the peak stress of the external rock mass are reduced; therefore, damages are significantly mitigated. (3) Through the analysis of the distribution of cracks in the tunnel lining, it is found that the tunnel without a segmental structure design has suffered from penetrating failure and that cracks affect the entire lining. The cracks in a flexible segmental tunnel affect about 66.6% of the entire length of the tunnel, and cracks in a tunnel with a short segmental tunnel only affect about 33.3% of the entire length of the tunnel. Therefore, a deep-buried tunnel with a short segmental tunnel can yield a better anti-dislocation effect. (4) By comparing the shallow-buried segmental tunnel in previous studies, it is concluded that the shallow-buried segmental tunnel will also suffer from deformation outside the fault zone, while the damages to the deep-buried segmental tunnel are concentrated in the fault zone, so the anti-dislocation protection measures of the deep-buried tunnel shall be provided mainly in the fault zone. The results of the above study can provide theoretical reference and technical support for the design and reinforcement measures of the tunnel crossing active fault under high in-situ stress conditions.

Micro-disturbance grouting is a recovery technique to reduce the excessive deformation of operational shield tunnels in urban areas. The grout mass behaves as a fluid in the ground before hardening to form a grout–soil mixture, which highlights the necessity of using fluid–solid coupling method in the simulation of grouting process. Within a discrete element modeling environment, this paper proposes a novel fluid-solid coupling method based on the pore density flow calculation. To demonstrate the effectiveness of this method, it is applied to numerical simulation of micro-disturbance grouting process for treatment of large transverse deformation of a shield tunnel in Shanghai Metro, China. The simulation results reveal the mechanism of recovering tunnel convergence by micro-disturbance grouting in terms of compaction and fracture of soil, energy analysis during grouting, and mechanical response of soil-tunnel interaction system. Furthermore, the influence of the three main grouting parameters (i.e., grouting pressure, grouting distance, and grouting height) on tunnel deformation recovery efficiency is evaluated through parametric analysis. In order to efficiently recover large transverse deformation of shield tunnel in Shanghai Metro, it is suggested that the grouting pressure should be about 0.55 MPa, the grouting height should be in the range of 6.2–7.0 m, and the grouting distance should be in the range of 3.0–3.6 m. The results provide a valuable reference for grouting treatment projects of over-deformed shield tunnel in soft soil areas.

The Sichuan-Xizang Railway is a global challenge, surpassing other known railway projects in terms of geological and topographical complexity. This paper presents an approach for rapidly profiling rock mass quality underneath tunnel face for the ongoing construction of the Sichuan-Xizang Railway. It adopts the time-series method and carries out the quantitative analysis of the rock mass quality using the depth-series measurement-while-drilling (MWD) data associated with drilling of blastholes. A tunnel face with 15 blastholes is examined for illustration. The results include identification of the boundary of homogeneous geomaterial by plotting the blasthole depth against the net drilling time, as well as quantification of rock mass quality through the recalculation of the new specific energy. The new specific energy profile is compared and highly consistent with laboratory test, manual logging and tunnel seismic prediction results. This consistency can enhance the blasthole pattern design and facilitate the dynamic determination of charge placement and amount. This paper highlights the importance of digital monitoring during blasthole drilling for rapidly profiling rock mass quality underneath and ahead of tunnel face. It upgrades the MWD technique for rapid profiling rock mass quality in drilling and blasting tunnels.

Research on automation and intelligent operation of tunnel boring machine (TBM) is receiving more and more attention, benefiting from the increasing construction data. However, most studies on TBM operations optimization were trained by the labels of human drivers’ decisions, which were subjective and stochastic. As a result, the control parameters suggested by these models could hardly surpass the performance of a human driver, even the possibility of subjective incorrect decisions. Considering that the geomechanical feedback to TBM under drivers’ actions is objective, in this paper, a transformer-based model called the geological response for tunnel boring machine (GRTBM), is proposed to learn the relationship between operation-adjust and TBM monitoring changes. Additionally, with the model-based offline reinforcement learning, this paper provided a novel approach to optimizing the TBM excavation operations. The decision processes, recorded in the Yin-song TBM project for a waterway tunnel in Jilin Province of China, were used for the validation of the model. By adopting an implicit perception of geological conditions in the GRTBM model, the suggested method achieved the desired state within a single action, greatly outperformed the practical adjustments where 500 s were taken, revealing the fact that the proposed model has the potential to surpass the capability of human beings.

Mechanical softening behaviors of shale in CO₂-water–rock interaction are critical for shale gas exploitation and CO₂ sequestration. This work investigated the cross-scale mechanical softening of shale triggered by CO₂-water–rock interaction. Initially, the mechanical softening of shale following 30 d of exposure to CO₂ and water was assessed at the rock-forming mineral scale using nanoindentation. The mechanical alterations of rock-forming minerals, including quartz, muscovite, chlorite, and kaolinite, were analyzed and compared. Subsequently, an accurate grain-based modeling (AGBM) was proposed to upscale the nanoindentation results. Numerical models were generated based on the real microstructure of shale derived from TESCAN integrated minerals analyzer (TIMA) digital images. Mechanical parameters of shale minerals determined by nanoindentation served as input material properties for AGBMs. Finally, numerical simulations of uniaxial compression tests were conducted to investigate the impact of mineral softening on the macroscopic Young’s modulus and uniaxial compressive strength (UCS) of shale. The results present direct evidence of shale mineral softening during CO₂-water–rock interaction and explore its influence on the upscale mechanical properties of shale. This paper offers a microscopic perspective for comprehending CO₂-water-shale interactions and contributes to the development of a cross-scale mechanical model for shale.

In this paper, a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall. The segmented isolation layer consists of a rigid layer and a flexible layer. The rigid layer is installed at the joint section between the structural sidewall and slab, and the flexible layer is installed at the remaining sections. A diaphragm wall-segmented isolation layer-subway station structure system is constructed. Seismic and vibration control performance of the diaphragm wall-segmented isolation layer-subway station structure system is evaluated by the detailed numerical analysis. Firstly, a three-dimensional nonlinear time-history analysis is carried out to study the seismic response of the station structure by considering the effect of different earthquake motions and stiffness of segmented isolation layer. Subsequently, the vibration response of site under training loading is also studied by considering the influence of different train velocities and stiffness of the segmented isolation layer. Numerical results demonstrate that the diaphragm wall-segmented isolation layer-subway station structure system can not only effectively reduce the lateral deformation of station structure, but also reduce the tensile damage of the roof slab. On the other hand, the developed reduction measure can also significantly reduce the vertical peak displacements of site under training loading.

Since the classical element model cannot describe the nonlinear characteristics of rock during the entire compressive creep process, nonlinear elements and creep damage are generally introduced in the model to resolve this issue. However, several previous studies have reckoned that creep damage in rock only occurs in the accelerated creep stage and is only described by the Weibull distribution. Nevertheless, the creep damage mechanism of rocks is still not clearly understood. In this study, a reasonable representation of the damage variables of solid materials is presented. Specifically, based on the Gurson damage model, the damage state functions reflecting the constant creep stage and accelerated creep stage of rock are established. Further, the one-dimensional and three-dimensional creep damage constitutive equations of rock are derived by modifying the Nishihara model. Finally, the creep-acoustic emission tests of phyllite under different confining pressures are conducted to examine the creep damage characteristics of phyllite. And the proposed constitutive model is verified by analyzing the results of creep tests performed on saturated phyllite. Overall, this study reveals the relationship between the creep characteristics of rocks and the corresponding damage evolution pattern, which bridges the gap between the traditional theory and the quantitative analysis of rock creep and its damage pattern.