Underground Tunnelling Research Articles

Fuzzy Cognitive Map for Evaluating Critical Factors Causing Rockbursts in Underground Construction: A Fundamental Study

The rockburst phenomenon in excavation endeavours reveals a multitude of complexities and obstacles that significantly impact both the technical and financial dimensions of project execution. Investigating critical rockburst factors in underground excavations is of considerable importance for addressing pivotal safety issues and operational complexities within the field of underground excavation projects. This research proposes an innovative approach based on an expert-based fuzzy cognitive map (FCM) framework, aiming to identify and prioritize the key critical rockburst factors prevalent in underground excavations and tunnelling. A tailored cognitive map of the parameters of problem was constructed, integrating 56 critical and critical factors meticulously curated by a team of seasoned managers, engineers, deputy managers, trainee engineers and assistant managers. The structured cognitive map was meticulously developed, considering the relative weights of the identified critical factors and their intricate interrelationships—all informed by the invaluable insights and expertise of seasoned engineers in the field. Subsequently, the cognitive map underwent a systematic solution process, whereby the causal relationships and influences amongst the identified critical factors were analysed and factored in. The outcomes of the comprehensive analysis unveiled several critical factors: lack of rockburst risk assessments, high in situ stress, presence of rock seams and weak layers, rock quality variations, and geological heterogeneity as the most paramount concerns demanding immediate attention and strategic intervention. By adopting the proposed FCM approach and leveraging the collective expertise of industry professionals, this research offers a robust and systematic framework for comprehensively assessing and addressing the key challenges associated with rockburst events in underground excavations and tunnelling projects, thereby fostering enhanced project performance and efficacy within the field.

Intelligent prediction method for underbreak extent in underground tunnelling

Underground tunnel excavation using the drill-and-blast method often results in underbreak occurrences due to improper blasting parameters and complex geological environment. This underbreak phenomenon has a profound impact on tunnel safety, stability and construction costs. Traditional approaches for predicting underbreak extent (UE) through field measurements and theoretical models exhibit limitations in terms of accuracy and efficiency. Consequently, it is urgent to develop a novel approach for UE prediction in tunnelling operations. In this paper, extreme gradient boosting (XGBoost) is first applied as the foundational algorithm, and slime mould algorithm (SMA) is implemented for tuning hyper-parameters of XGBoost. Meanwhile, six chaotic maps are integrated with SMA to initialize the population and improve the optimization performance. Subsequently, a dataset of 250 samples is collected from three underground mines in China, involving ten influential factors (RMR, uniaxial compressive strength (UCS), vertical principal stress (σv), lateral pressure coefficient (λ), excavation area (EA), powder factor (PF), specific charge (SC), advance length (AL), periphery hole burden (HB)and periphery hole spacing (HS)). Additionally, four indices, i.e., coefficient of determination (R2), variance accounted for (VAF), mean absolute error (MAE) and root mean square error (RMSE), are used to evaluate the comprehensive performance of these proposed COSMA-XGBoost models and four common machine learning models. Finally, a parametric sensitivity analysis is performed, and the optimal intelligent model is applied in practical tunnelling projects. The results indicate that chaotic optimized SMA models have better convergence ability and higher accuracy compared with the original SMA model. Notably, the PSMA-XGBoost model outperforms other models as the R2, VAF, MAE and RMSE values for the testing set are 0.979, 95.79%, 4.176 and 4.884, respectively, whereas 0.968, 94.25%, 4.274 and 5.012, respectively for training set. EA, RMR and UCS exhibit significant effects on UE. In practical tunneling projects, the engineering application of the PSMA-XGBoost model demonstrates its feasibility and efficiency in predicting UE within underground tunnels.

Development and evaluation of an immersive VR-CFD-Based tool for dust exposure mitigation in underground tunnelling operations

Long-term exposure to respirable coal and silica dust during underground tunnelling operations has gained increasing attention in recent years. The solution to effective mitigation of dust exposure depends not only on higher-order engineering controls, but also on administrative controls for frontline workers. However, there is a disconnect between knowledge gathered in the field of dust exposure monitoring and the frontline worker, resulting in important learnings being overlooked in underground tunnelling operations. To remedy this discrepancy, an immersive educational tool was developed to visualise computational fluid dynamics (CFD) modelling datasets of ventilation and respirable dust flow characteristics in the tunnel face in a virtual reality (VR) environment. An algorithm was developed for processing the large and complex CFD datasets into a form that can be processed and visualised using standalone VR headsets with limited processing power. The VR-CFD system was assessed by an industry expert and via many industry showcases, where regular feedback was received for making significant improvements in this education tool. This tool has been developed as a training platform to allow frontline workers to better understand the results of decisions made during tunnelling operations and the best practices for dust controls. A number of key technological achievements were made that can be used in the future to quickly translate real-world particulate readings collected from underground space into a VR visualiser. This VR-CFD digital technology can readily be extended to mining, construction and other tunnelling operations in the underground space, thus improving health and safety.

Assessing the tunnel stability in brittle rocks based on strain bursting assessment

Strain bursting is a phenomenon associated with deep underground excavations and tunnelling in brittle hard rocks that result in a sudden and violent failure, posing high risks and damage. This work aims to assess the strain bursting and the energy response characteristics and develop a guideline that can be utilized in the preliminary investigation stage. The obtained results are intended to enable predicting different brittle behaviours in deep geological environments. Elastic stress analysis using the DISL approach based on boundary element method is established (EX3-software) for the assessment of two tunnel geometries (circular, horseshoe) in granitic rock mass. Two different stress states are modelled to simulate the potential stress regime. The analysis’ results demonstrate that different geometries affect the energy storage capacity and result in different behaviour regarding the bursting potential of the rock mass.

Coupled thermo-mechanical constitutive damage model for sandstone

Underground rock dynamic disasters are becoming more severe due to the increasing depth of human operations underground. Underground temperature and pressure conditions contribute significantly to these disasters. Therefore, it is important to understand the coupled thermo-mechanical (TM) behaviour of rocks for the long-term safety and maintenance of underground tunnelling and mining. Moreover, investigation of the damage, strength and failure characteristics of rocks under triaxial stress conditions is important to avoid underground rock disasters. In this study, based on Weibull distribution and Lemaitre’s strain equivalent principle, a statistical coupled TM constitutive model for sandstone was established under high temperature and pressure conditions. The triaxial test results of sandstone under different temperature and pressure conditions were used to validate the model. The proposed model was in good agreement with the experimental results up to 600 °C. The total TM damage was decreased with increasing temperature, while it was increased with increasing confining pressure. The model’s parameters can be calculated using conventional laboratory test results.

Characteristics and failure analysis of a railway tunnel collapse influenced by cavity in phyllite strata

Tunnelling in phyllite strata with cavity is prone to collapse even with reasonable construction design. Based on a railway tunnel collapse influenced by cavity in phyllite strata, characteristics and failure mechanisms were analyzed by field investigation, in-situ monitoring and numerical simulation, and further explore the failure factors and treatments. The results show that tunnel excavation caused groundwater seepage towards the cavity, and the water invading induced phyllite dissolution and mechanical properties weakening of surrounding rock were mainly attributed to be the causes of the collapse. Based on the results, the treatments of surrounding rock grouting and steel arch replacing were adopted to ensure the stiffness and stability of tunnel structure. Finally, the treatment effectiveness is investigated combined with the monitoring data. The result facilitates prevention and treatment of collapse induced by underground tunnelling near ground fissures. The result contributes to prevention and treatment of tunnel collapse failure in phyllite strata.

Failure analysis and treatments of a loess tunnel being constructed in ground fissure area

Tunnelling in ground fissure areas is prone to collapse even with reasonable reinforcement. Based on the collapse of a tunnel in Xi'an Metro Line 3 near a ground fissure, potential causes and corresponding mechanisms were analysed. Preliminary in-situ investigation indicates that the hydraulic erosion induced loose pressure and crack-rich soil below the unclosed initial support were mainly attributed to be the triggering force of the collapse. Compared with the two common failure modes in tunnels, this collapse is of unique characteristics, showing that special attention to the arch feet is required in similar strata. The collapse mechanisms were subsequently analysed in aspects of geology, soil meso-features and construction. In addition, The failure process was simulated based on discrete element method in MatDEM and stress chains have been observed, showing results consistent with the above analysis. To prevent a secondary disaster, necessary appropriate remedies with considerable resources were implemented at three sites: the tunnel, portal and surface. Combined with the monitoring data during the treatment, their effects and shortcomings were discussed. The result facilitates prevention and treatment of collapse induced by underground tunnelling near ground fissures.

Efficient and realistic 3-D boundary element simulations of underground construction using isogeometric analysis

The paper outlines some recent developments of the boundary element method (BEM) that makes it more user friendly and suitable for a realistic simulation in geomechanics, especially for underground excavations and tunnelling. The innovations refer to the introduction of isogeometric concepts, elasto-plastic analysis and the simulation of ground support. The introduction of isogeometric concepts for the description of the excavation boundaries results in less user and analysis effort, since complex geometries can be modelled with few parameters and degrees of freedom. No mesh generation is necessary. Heterogeneous and inelastic ground conditions are considered via general inclusions and rock bolts via linear inclusions. A comparison of results of test examples with other numerical methods and analytical solutions confirms the efficiency and accuracy of the proposed implementation. A practical example with a complex geometry is presented.

Artificial neural network for prediction of rock properties using acoustic frequencies recorded during rock drilling operations

Determining properties of rocks in rock mechanics/engineering applications such as underground tunnelling, slope stability, foundations, dam design and rock blasting is often difficult due to the requirements of high quality of core rock samples and accurate test apparatus. Prediction of the geomechanical properties of rock material has been an area of interest for rock mechanics for several years now. Nowadays, soft computing methods are used as a powerful tool to estimate the rock properties, cost and duration of the project. This has led to a lack of necessity to develop a model to predict rock properties in the field of rock mechanics. ANN (artificial neural network) models were developed to predict geomechanical properties of the sedimentary rock types using dominant frequencies of an acoustic signal during rock drilling operations. A set of experimental drilling operations test conditions around 875 were used as input parameters including drill bit spindle speeds (rpm), drill bit penetration rates (mm/min), drill bit diameters (mm) and dominant frequencies of the acoustic signal (Hz). The response (output) was uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), density ( $$\rho $$ ) and abrasivity (%). The developed models were checked using various performance indices. The results from the analysis show that the suggested ANN model approach is efficient, fits the data and accurately reflects the experimental results. The ANN models predicted physico-mechanical rock properties through the dominant frequency of acoustic signals during rock drilling operations.

Multisensor information-based adaptive control method for cutting head speed of roadheader

An adaptive control method to improve the cutting head speed of roadheaders using multisensor information is proposed, so as to solve the problems of low cutting efficiency and low intelligence of roadheaders during underground tunnelling. The operation of a roadheader is analysed, and a control strategy for its cutting head speed is proposed. In addition, the cutting head speed is categorised into five gears according to the multisensor information of different cutting states. The controller for speed estimation is designed using a back propagation neural network optimised using an improved particle swarm optimisation algorithm. A control system is established in MATLAB to analyse the effectiveness of the method. The simulation results show that an IPSO-BP controller has the best control effect and can attain the target speed. The response time was lower than those of fuzzy logic controllers and traditional PI controllers by 46% and 68%, respectively, and the overshoot decreased by 4.69% and 12.19%, respectively. Furthermore, experimental research verified the effectiveness of this method. This method can adaptively adjust the cutting head speed of a roadheader using multisensor information and is important (both theoretical and practically) for extending the service life of roadheaders and improving tunnelling efficiency.

Machines for Mechanical Mining of Hardly Workable and Abrasive Rocks

Abstract Mechanical mining is a widely used method for separating material from mined rock in the mining branch, tunnelling, road and construction industries. Depending on the mechanical properties of rocks, most often defined by uniaxial compressive strength, various machines and tools are applied. Apart from rock strength, the efficiency of the mining process is determined by abrasiveness, which affects the rate of tool abrasive wear. Currently, disc mining by static pressure or rear undercutting are the most developed methods. Undercutting can be supported by high pressure water jet or disk oscillation. Mining with drills also utilizes static pressure. In addition to discs, conical picks are applied; they are mounted on cutterheads. In underground mining and tunnelling, there is an increasing need to cut abrasive rocks with a strength of more than 120 MPa in places where explosive materials cannot be used. In the article, the recently applied and developed methods of cutting abrasive rocks characterized by high strength, such as copper, gold, tungsten or platinum ores and diamond deposits, have been presented. Next, the latest machines and machine systems used for their mining are reviewed. Leaders in the mining machinery industry, such as Joy (Komatsu), Epiroc (Atlas Copco), Sandvik and Aker Wirth are developing proprietary designs of cutting machines based on both well-known and completely new ideas.

Effect of Microwave Irradiation on Computed Tomography and Acoustic Emission Characteristics of Hard Rock

Microwave-induced fracturing of hard rock can be used to assist mechanical rock breakage and release stress on rock masses in deep underground engineering operations. This is significant to those aiming to improve the construction efficiency and safety of underground tunnelling and ore extraction operations. The research was devoted to exploring the computed tomography (CT) and acoustic emission (AE) characteristics of hard rock subjected to microwave irradiation. For this purpose, microwave irradiation tests at a given power for different irradiation times were conducted on basalt collected from Chifeng, China by utilising a multimode cavity working at a frequency of 2450 MHz. By applying an infrared camera, the temperature distribution on the surface of samples during microwave irradiation was measured. Three-dimensional (3-d) microscopic CT was conducted on samples treated, and not treated, with microwave irradiation to explore the crack propagation regimes in such samples. Based on CT value and P-wave velocities, the damage characteristics of microwave treatment on basalt samples were evaluated. Afterwards, uniaxial compression strength tests were conducted and AE information in the loading process of samples was collected. After conducting microwave irradiation, internal cracks of samples propagated to generate fracture surfaces and surface temperatures of samples were found to have been non-uniformly distributed. The longer the irradiation time, the higher the degree of crack propagation in samples; P-wave velocities both decreased with increasing irradiation duration. With increasing irradiation time, the brittle failure characteristics of basalt shown in the time-dependent change curve of stress on basalt were gradually weakened while ductile failure characteristics were gradually strengthened. The uniaxial compressive strength, corresponding AE energy and cumulative AE energy at peak strength all gradually decreased with increasing irradiation time. The failure stress, the level of stress drop, AE energy, and cumulative AE energy of basalt after different irradiation times reflected consistent fracturing characteristics of basalt, which were interactively validated.

European legal framework related to underground mining and tunnelling concerning commission directive (EU) 2017/164, 31 January establishing a fourth list of indicative occupational exposure limit values

Directive (EU) 2017/164 establishes a fourth list of indicative occupational exposure limit values (IOELVs) to protect workers from risks of exposure to hazardous chemicals. It states that in underground mining and tunnelling, Member States may benefit from a transitional period regarding IOELVs for nitrogen monoxide, nitrogen dioxide, and carbon monoxide, during which the existing established IOELVs may be applied. The European Advisory Committee on Health and Safety at Work questions the technical feasibility of the proposed IOELVs in underground mining (CO, NO and NO2) and tunnelling (NO and NO2). Challenges arise concerning the availability of measurement methodologies for compliance with proposed IOELVs (NO2) in underground mining and tunnelling environments.

Mechanical Properties of Layered Composite Coal–Rock Subjected to True Triaxial Stress

Underground mining or tunnelling activity is always associated with the composite geological formations. The mechanical properties of layered composite coal–rock subjected to true triaxial stress conditions are significantly different from those under conventional triaxial or uniaxial stress conditions. In this work, we conducted a series of true triaxial tests using the self-developed true-triaxial apparatus to investigate the mechanical response (e.g., deformation, strength, and failure characteristics) of the layered composite coal–rock (CCR). The results show that the uniaxial strength of CCR lies between the strength of pure sandstone and coal, and the direction of the bedding affects the overall strength of the samples. The true triaxial strength of both the pure rock and CCR increases first and then decreases with the increase of the intermediate principal stress. Moreover, for a given loading direction, as the thickness of the sandstone layer increased, the strength of the CCR increases. The deformation of the CCR shows more obvious plasticity than that of the pure sandstone due to the coordinated deformation of the coal and sandstone layers. In addition, a new true triaxial strength criterion expressed by the first and third equivalent principal stress invariants was proposed, which can well describe the strength characteristics of different coal rocks. The stress states, weak structural planes, and localized stress have a great influence on the failure modes of CCR. The local stress concentration near the contact surface promotes the development of the secondary failure fractures. These findings are of great significance in stability designing in deep underground engineering.

Hydrogeochemical modelling of corrosive environment contributing to premature failure of anchor bolts in underground coal mines

Anchor bolts are commonly used throughout underground mining and tunnelling operations to improve roof stability. However, premature failures of anchor bolts are significant safety risks in underground excavations around the world due to susceptible bolt materials, a moist and corrosive environment and tensile stress. In this paper, laboratory experiments and hydrogeochemical models were combined to investigate anchor bolt corrosion and failure associated with aqueous environments in underground coal mines. Experimental data and collated mine water chemistry data were used to simulate bolt corrosion reactions with groundwater and rock materials with the PHREEQC code. A series of models quantified reactions involving iron and carbon under aerobic and anaerobic conditions in comparison with ion, pH and pE trends in experimental data. The models showed that corrosion processes are inhibited by some natural environmental factors, because dissolved oxygen would cause more iron from the bolts to oxidize into solution. These interdisciplinary insights into corrosion failure of underground anchor bolts confirm that environmental factors are important contributors to stress corrosion cracking.

Impacts of different environmental factors on tunnelling behaviour of the subterranean termite Odontotermes formosanus (Shiraki)

The subterranean termite Odontotermes formosanus (Shiraki) is one of the most serious pests of dikes and dams in China, and can build large subterranean cavities inside earthen dikes and dams through workers’ tunnelling behaviour. For a better understanding of underground tunnelling strategies of O. formosanus, we used the tunnelling device to investigate the effect of substrate type, moisture content and ambient temperature on tunnelling behaviour. We found that the workers displayed significantly higher-tunnelling efficiency and bigger maximum tunnelling distance in sandy soil when compared to soil and sand. Meanwhile, the workers expressed significantly higher-tunnelling efficiency and bigger maximum tunnelling distance under 20% moisture content than those under 10% and 15% moisture contents. Additionally, the workers exhibited significantly higher tunnelling efficiency and bigger maximum tunnelling distance at 28 °C as compared to 22 and 25 °C. These findings suggest that the above three environmental factors had the significant impacts on tunnelling behaviour of the subterranean termite O. formosanus.

“Wireline + Wireless” Networking Remote Monitoring Technology for Analysing the Unloading Deformation Characteristics of the Fractured Surrounding Rock Mass Induced by Underground Excavation

Collapse or large deformation of fractured surrounding rock mass occurs frequently in underground tunnelling and results in many casualties and extensive property damage. This paper proposed a new type of remote telemetry system for monitoring the mechanical responses of underground tunnels during unloading. This system adopted both wired and wireless networking schemes, including a signal collection and transmission subsystem, a management analysis subsystem, and a remote receiving subsystem, in the tunnels. The application of this new approach in a subway tunnel indicated that the complete unloading performance of a surrounding rock mass can be captured in real time and high frequency using this method, recording the deformation of the surrounding rock, the stress in the bolts, and the stress in the shotcrete between the surrounding rock and steel arch. The in situ experimental study also found that deformation of the fractured surrounding rock mass in the Dashizi Tunnel showed a step‐like fluctuating growth pattern. Additionally, the mechanical response of the surrounding rock mass during unloading tended to stabilize when the opening face was approximately 35 m away from the monitoring section, providing new ways to optimize the excavation process and support measure.

An equivalent anchoring method for anisotropic rock masses in underground tunnelling

Rock bolting has been widely utilized for reinforcing underground openings, such as tunnels and mining. To ease the complexity of numerically simulating of the bolted rock mass, a novel method for equivalent anchoring simulates the reinforcement effect of the bolts by considering the anisotropic characteristics of the layered rock mass. The jointed material model in ABAQUS is improved by incorporating the anisotropy through the programming language FORTRAN. Based on the improved jointed material model, the equivalent anchoring parameters of the bolted layered rock masses are studied through a series of numerical tests. The numerical outcomes reveal that the improved jointed material model can be used to simulate the anisotropic features of the layered rock mass by comparing the classic and analytic solutions. The degree to which the supporting parameters affect the equivalent reinforcement performance are different in anisotropic rock masses, and the sensitivity of their influence is bolt length > bolt spacing > bolt diameter. Furthermore, an equivalent anchoring model for bolted rock masses (the formula of the improved parameter between the ratio of bolt length to tunnel diameter and the ratio of bolt diameter to bolt spacing) is proposed through numerical results analysis by the multiple linear regression method. An application case shows the field monitoring agreed well with the predicted vertical displacement of the tunnel demonstrating the feasibility of the proposed simulation method for the bolted rock mass. The results show the proposed method in this study can be conveniently utilized for efficient simulation of the mechanical behavior of bolted rock masses.

A unified critical state model for geomaterials with an application to tunnelling

This paper is prepared in honour of Professor E.T. Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author's research career in geomechanics and geotechnical engineering. As a result, we have picked a topic that reflects two key research areas in which Professor E.T. Brown has made seminal contributions over a long and distinguished career. These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials. Partially due to Professor Brown's influence, the first author has also been conducting research in these two areas over many years. In particular, this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils.

English

English