Underground Mine Tunnels Research Articles

Gas-Solid Flow Characteristics of Airflow and Dust Particles in Blasting Excavation of Underground Metal Mine Tunnels.

Effective dust removal has long been a challenge in the blasting mining of underground metal mine tunnels, and uncontrolled dust diffusion seriously endangers workers' respiratory systems and the underground space safety environment. However, the vast majority of existing numerical studies on dust diffusion are focused on coal mine fully mechanized mining, which is different from metal mine blasting excavation in terms of stope structure and dust properties. Furthermore, the mechanism by which the forced and exhaust ventilation modes affect the diffusion characteristics of inhalable particles is unclear. In this work, gas-solid flow characteristics for dust diffusion in a typical metal mine blasting tunnel were numerically investigated based on the Euler-Lagrange method, where the blasting face instantly released 6.37 × 107 particles with 100 different sizes, ranging from 0.8 to 200 μm. The interphase forces between airflow and dust particles are comprehensively modeled, and the particle diffusion effect caused by fluid turbulence is described by a discrete random walk model. Detailed information for airflow turbulence and particle migration was revealed, and dust removal efficiencies for inhalable particulate matter (PM10) by forced, exhaust, and hybrid ventilation were analyzed. Numerical results predict a complex airflow pattern in the working roadway, including the jet-flow region, return airflow core region, airflow disorder region, and secondary flow region. Dust diffusion temporal characteristics can be divided into three stages, namely, the initial stage of dust generation, the efficient ventilation and dust removal stage, and the later stage of dust diffusion. Dust diffusion spatial characteristics indicate that under the Coanda wall attachment effect, the dust concentration exhibits nonuniform distribution in both vertical and horizontal directions of the return air roadway. The dust removal efficiency of hybrid ventilation on inhalable particles above respiratory height is better than that of forced ventilation, especially in the return air roadway. The additional exhaust air duct based on forced ventilation can discharge more inhalable particles from the tunnel.

A Coal Mine Tunnel Deformation Detection Method Using Point Cloud Data.

In recent years, the deformation detection technology for underground tunnels has played a crucial role in coal mine safety management. Currently, traditional methods such as the cross method and those employing the roof abscission layer monitoring instrument are primarily used for tunnel deformation detection in coal mines. With the advancement of photogrammetric methods, three-dimensional laser scanners have gradually become the primary method for deformation detection of coal mine tunnels. However, due to the high-risk confined spaces and distant distribution of coal mine tunnels, stationary three-dimensional laser scanning technology requires a significant amount of labor and time, posing certain operational risks. Currently, mobile laser scanning has become a popular method for coal mine tunnel deformation detection. This paper proposes a method for detecting point cloud deformation of underground coal mine tunnels based on a handheld three-dimensional laser scanner. This method utilizes SLAM laser radar to obtain complete point cloud information of the entire tunnel, while projecting the three-dimensional point cloud onto different planes to obtain the coordinates of the tunnel centerline. By using the calculated tunnel centerline, the three-dimensional point cloud data collected at different times are matched to the same coordinate system, and then the tunnel deformation parameters are analyzed separately from the global and cross-sectional perspectives. Through on-site collection of tunnel data, this paper verifies the feasibility of the algorithm and compares it with other centerline fitting and point cloud registration algorithms, demonstrating higher accuracy and meeting practical needs.

Coupled thermodynamic and thermomechanical modelling for compressed air energy storage in underground mine tunnels

Compressed air energy storage (CAES) in underground mine tunnels using the technique of lined rock cavern (LRC) provides a promising solution to large-scale energy storage. A coupled thermodynamic and thermomechanical modelling for CAES in mine tunnels was implemented. Thermodynamic analysis of air during CAES operation was carried out. Difference in temperature and pressure evolution when considering real air thermophysical properties and varying heat transfer properties, as opposed to a simplified thermodynamic model, was revealed. Elastic plane strain (EPS) analysis was implemented to evaluate the influences of initial stress of the lining structure, quality grades of surrounding rock, thermal effect and the cyclic nature of loadings on mechanical behaviour. 3D elastoplastic damage (3DEPD) analysis considering steel reinforced concrete (SRC) lining was implemented to evaluate the damaged mechanical behaviour. Divergences between EPS analysis and 3DEPD analysis were unveiled. It is suggested that, when it comes to tunnel stability, simplifying the thermodynamic model is of least concern, instead, the initial stress of the lining structure is of critical importance and 3DEPD analysis considering SRC lining shall replace EPS analysis. The insights of this study will provide important guidance for the designing and feasibility study of LRC in mine tunnels for application of CAES.

Real-time semantic segmentation for underground mine tunnel

Semantic segmentation is the underlying technology for many intelligent applications in underground mines. Unlike the ordinary scenario, the lighting of underground mines varies drastically, and there is heavy dust and mist, which results in poor image quality and greatly hinders the application of image semantic segmentation in underground mines. Because there is currently no datasets for underground mine tunnels available, a dataset named Underground Mine Tunnel Semantic Segmentation Dataset (UMTSSD) have to be constructed to support our research. UMTSSD consists of 3461 meticulously annotated images and 17 annotated categories. A real-time semantic segmentation algorithm named Fast Adaptive Deep Dual-resolution Network (FA-DDRNet) which uses Deep Dual-resolution Network (DDRNet) as the backbone is proposed for underground mines. To enhance the semantic segmentation accuracy in underground environment, FA-DDRNet introduces two modules: Fast Adaptive Input Normalization Module (FAINM) and Scale-wise Residual Cascade Module (SRCM). FAINM can autonomously and quickly adjust normal lighting images, weak lighting images, and overexposed images to improve the robustness of semantic segmentation algorithms. SRCM is integrated into the backbone to swiftly fuse multi-scale features in a cascade fashion, resulting in enhanced detection of objects with diverse shapes in underground environment. Finally, our method achieves exceptional performance with a superior inference speed compared to other semantic segmentation algorithms in UMTSSD. The method can realize running in real-time on low computational power embedded devices, which is well adapted to underground environment.

UTD-Based Ray-Tracing MIMO Channel Modeling for the Next-Generation Communications Within Underground Tunnels

Limited work has previously been conducted into deterministic modeling of the 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> Generation (5G) millimeter (mm)-wave wireless communications within geometrically non-uniform tunnels. This study predicts and analyzes broadband Multiple–Input Multiple–Output (MIMO) propagation in underground mine tunnels for 5G communications and beyond. At extremely short wavelength, each rugged and uneven surface of the tunnel is modelled as a group of diffracting rectangular prism wedges. A deterministic Ray-Tracing (RT) MIMO model is developed based on the Uniform Theory of Diffraction (UTD). All predicted MIMO sub-channels have been successfully fitted with the experimental measurements. MIMO multipath fading of underground tunnels are found to be lognormally distributed and strongly depends on the tunnel’s size and shape.

Real-Time Scan-to-Map Matching Localization System Based on Lightweight Pre-Built Occupancy High-Definition Map

High-precision and robust localization in GNSS-denied areas is crucial for autonomous vehicles and robots. Most state-of-the-art localization methods are based on simultaneous localization and mapping (SLAM) with a camera or light detection and ranging (LiDAR). However, SLAM will suffer from drift during long-term running without loop closure or prior constraints. Lightweight, high-precision environmental maps have gradually become an indispensable part of future autonomous driving. In order to solve the problem of real-time global localization for autonomous vehicles and robots, we propose a precise and robust LiDAR localization system based on a pre-built, occupied high-definition (HD) map called the Extended QuadTree (EQT) map. It makes use of a planar quadtree for block division and a Z-sequence index structure within the block cells. Then, a four-level occupancy probability cell value model is adopted. It will save about eight times the storage space compared with Google Cartographer, and the EQT map can be extended to store other information. For efficient scan-to-map matching with our specialized EQT map, the Bursa linearized model is used in the Gauss–Newton iteration of our algorithm, which makes the calculation of partial derivatives fast. All the above improvements lead to optimal storage and efficient querying for real-time scan-to-map matching localization. Field tests in an industrial park and road environment prove that positioning accuracy of about 6–13 cm and attitude accuracy of about 0.15° were achieved using a VLP-16 LiDAR. They also show that the method proposed in this paper is significantly better than the NDT method. For the long and narrow environment of an underground mine tunnel, high-resolution maps are also helpful for accurate and robust localization.

A Coupled Visual and Inertial Measurement Units Method for Locating and Mapping in Coal Mine Tunnel.

Mobile robots moving fast or in scenes with poor lighting conditions often cause the loss of visual feature tracking. In coal mine tunnels, the ground is often bumpy and the lighting is uneven. During the movement of the mobile robot in this scene, there will be violent bumps. The localization technology through visual features is greatly affected by the illumination and the speed of the camera movement. To solve the localization and mapping problem in an environment similar to underground coal mine tunnels, we improve a localization and mapping algorithm based on a monocular camera and an Inertial Measurement Unit (IMU). A feature-matching method that combines point and line features is designed to improve the robustness of the algorithm in the presence of degraded scene structure and insufficient illumination. The tightly coupled method is used to establish visual feature constraints and IMU pre-integration constraints. A keyframe nonlinear optimization algorithm based on sliding windows is used to accomplish state estimation. Extensive simulations and practical environment verification show that the improved simultaneous localization and mapping (SLAM) system with a monocular camera and IMU fusion can achieve accurate autonomous localization and map construction in scenes with insufficient light such as coal mine tunnels.

Wi-Fi Direct based WSN Node Deployment in Underground Mine Tunnels

Wi-Fi Direct based WSN Node Deployment in Underground Mine Tunnels

Underground Mine Tunnel Modelling Using Laser Scan Data in Relation to Manual Geometry Measurements

Underground mine tunnels, drifts, and mine headings are susceptible to the impact of convergence. The convergence has a big influence on further measurements such as airflow and the volume concentration of methane and other gases. In most cases, deformation of arch supports lead to getting a smaller cross-section area. A comparison is made between five methods of measuring the cross-sectional area of a mine tunnel. The reference size of the six cross-section mine drift areas were obtained by Terrestrial Laser Scanning, which were then compared with the cross-section areas obtained by four other methods. The following methods were considered: area calculation using CAD software, an empirical method, approximation by a semi-ellipse and approximation by a semi-ellipse with attached straight sections. This article presents the quantitative and qualitative differences of the obtained results. Differences in the calculated cross-sectional areas of the mine drift are discussed, and reasons for the differences are determined. In addition, the advantages and disadvantages of each method are indicated.

Stress corrosion cracking of cable bolts in tunnels: An in-situ testing approach

Premature failure of cable bolts in underground tunnels is a major concern for the mining and civil industries. The unexpected failure of cable bolts in tunnels can threaten the safety of excavation operations and cause subnational economic losses. In this study, an in-situ testing method was developed to identify the cause of failure in the environment where the cable bolts are installed. The testing was conducted in two underground mine tunnels in Australia. The coupon made from non-galvanised and galvanised cable bolt wires with multiple stressed sections were installed in the tunnel roof, allowing direct exposure of coupons to different rock strata environments. The coupons were retrieved from the tunnels after almost ten months and analysed for corrosion. Results from both tunnels showed the occurrence of stress corrosion cracking (SCC) in both non-galvanised and galvanised coupons. The cracking predominantly occurred in the sections exposed to claystone layers. The framework developed in this study can be applied to different regions of any underground spaces to assess the propensity of the environment to cause premature reinforcement failure.

Autonomous Driving Robot That Drives and Returns along a Planned Route in Underground Mines by Recognizing Road Signs

In this study, an autonomous driving robot that drives and returns along a planned route in an underground mine tunnel was developed using a machine-vision-based road sign recognition algorithm. The robot was designed to recognize road signs at the intersection of a tunnel using a geometric matching algorithm of machine vision, and the autonomous driving mode was switched according to the shape of the road sign to drive the robot according to the planned route. The autonomous driving mode recognized the shape of the tunnel using the distance data from the LiDAR sensor; it was designed to drive while maintaining a fixed distance from the centerline or one wall of the tunnel. A machine-vision-based road sign recognition system and an autonomous driving robot for underground mines were used in a field experiment. The results reveal that all road signs were accurately recognized, and the average matching score was 979.14 out of 1000, confirming stable driving along the planned route.

Contribution to the Understanding of Specific Signatures in the Interaction of Surface Waves with Underground Voids

Shallow cavities, such as karstic caves in carbonate bedrock and near-surface underground mine workings or tunnels, constitute serious hazards for people and existing constructions due to the risk of collapse and subsidence. This phenomenon is growing fast with climate change causing damage to buildings and increased urban development costs. Karstic features, voids, surficial dissolution, fissuring, alteration and unconsolidated material are thus major challenges for geophysical methods that could play a major role in detection. Recent investigations have reported good results for cavity imaging using surface wave seismic methods. However, despite successful case histories, business as usual void detection is still challenging due to the complexity of near surface materials and probably a lack of understanding regarding the interaction of surface waves with voids. Recent data acquired in the context of a search for underground unpaved cavities provide new insights into the use of surface waves for the detection of these objects. Considering the findings, it appears that surface waves penetrating above and below the void may still propagate horizontally without clear features of altered propagation characteristics with respect to different actions, variations in dispersion, or both, which encourages rethinking of the systematic nature of diffraction research in operational applications.

Design of Initial Shotcrete Lining for a Mine Shaft Using Two-Dimensional Finite Element Models Considering Excavation Advance Rate

Shotcrete is widely used as a temporary support element in the construction of underground mine excavations, tunnels, and shafts. It is sprayed on the excavation walls to provide safe working conditions for mine personnel and equipment until the permanent support is installed. Therefore, the ability of the shotcrete liner to resists falls of ground is of paramount importance. In this paper, a two-dimensional finite element program is used to simulate a three-dimensional excavation advance and a shotcrete liner that is used as temporary support in a mine shaft. The mechanical properties of the shotcrete are determined based on existing empirical equations by considering the shaft advance rate. The study uses three methods to analyze the stability of the initial shotcrete liner. The first method pertains to the calculation of the load factor of safety based on the convergence confinement method. In the second method, the shotcrete liner is simulated using a structural element with elastic properties, and its stability is analyzed using support capacity diagrams. In the third method, a material model is used to explicitly simulate the shotcrete liner with elastic perfectly-plastic material behavior. This method allows for capturing the progressive yielding of the shotcrete liner during the excavation advance. The results of numerical simulations are then used to calculate a strain factor of safety for the shotcrete liner by dividing the lateral strain capacity of the shotcrete by the radial strain of the liner due to the shaft convergence. The study infers that the strain factor of safety for the 100 mm shotcrete liner is greater than unity although its load factor of safety is less than unity. Therefore, it is concluded that the 100 mm shotcrete liner can be used as temporary support until the installation of the final concrete liner.

Four-point dynamic leveling method for drilling platform application

PurposeIt is essential to level the drilling platform across which a drilling robot travels in a slant underground coal mine tunnel to ensure smooth operation of the drill rod. However, existing leveling methods do not provide dynamic performance under the drilling conditions of the underground coal mine. A four-point dynamic leveling algorithm is presented in this paper based on the platform attitude and support rod displacement (DLAAD). An experimental drilling robot demonstrates its dynamic leveling capability and ability to ensure smooth drill rod operations.Design/methodology/approachThe attitude coordinate of the drilling robot is established according to its structure. A six-axis combined sensor is adopted to detect the platform attitude, thus revealing the three-axis Euler angles. The support rod displacement values are continuously detected by laser displacement sensors to obtain the displacement increment of each support rod as needed. The drilling robot is leveled according to the current support rod displacement and three-dimensional (3 D) attitude detected by the six-axis combined sensor dynamically.FindingsExperimental results indicate that the DLAAD algorithm is correct and effectively levels the drilling platform dynamically. It can thus provide essential support in resolving drill rod sticking problems during actual underground coal mine drilling operations.Practical implicationsThe DLAAD algorithm supports smooth drill rod operations in underground coal mines, which greatly enhances safety, reduces power consumption, and minimizes cost. The approach proposed here thus represents considerable benefits in terms of coal mine production and shows notable potential for application in similar fields.Originality/valueThe novel DLAAD algorithm and leveling control method are the key contributions of this work, they provide dynamical 3 D leveling and help to resolve drill rod sticking problems.

Shooting-Bouncing-Rays Technique to Model Mine Tunnels: Algorithm Acceleration

We present and discuss acceleration of a shooting and bouncing rays (SBR) algorithm for ray-tracing electromagnetic analysis of electrically very large structures such as underground mine tunnels at modern wireless communication frequencies. The acceleration is based on the parallelization of the SBR technique on NVIDIA GPUs using the OptiX application programming interface. The results show dramatic speedups of the parallel SBR algorithm compared with serial implementation.

A system for underground road condition monitoring

Poor road conditions in underground mine tunnels can lead to decreased production efficiency and increased wear on production vehicles. A prototype system for road condition monitoring is presented in this paper to counteract this. The system consists of three components i.e. localization, road monitoring, and scheduling. The localization of vehicles is performed using a Rao-Blackwellized extended particle filter, combining vehicle mounted sensors with signal strengths of WiFi access points. Two methods for road monitoring are described: a Kalman filter used together with a model of the vehicle suspension system, and a relative condition measure based on the power spectral density. Lastly, a method for taking automatic action on an ill-conditioned road segment is proposed in the form of a rescheduling algorithm. The scheduling algorithm is based on the large neighborhood search and is used to integrate road service activities in the short-term production schedule while minimizing introduced production disturbances. The system is demonstrated on experimental data collected in a Swedish underground mine.

Optimal Deployment of Antenna for Field Coverage in Coal Mine Tunnels

A deployment strategy for antennas is proposed to enhance the field coverage of wireless devices in underground coal mines, which uses the multimodal approach. Based on the attenuation coefficient of each mode, the propagation loss of the vertically polarized modes with n = 1, 2, and 3 and that of the horizontally polarized modes with m = 1, 2, and 3 are less. For the signal propagation in the near-field region of the source, these modes play significant role. According to the coupling of the antenna to the modes, the significant modes can be effectively excited by mounting horizontally polarized antenna on the ceiling or the vertically polarized antenna on the sidewall. For the signal propagation in the far-field region, the (1, 1) mode is significant, and the horizontally polarized excitation is preferred due to smaller attenuation. By comparing the total coupling efficiency of the antenna-radiated power, stronger excitation power can be obtained by mounting the antenna near the center of the ceiling or that of the sidewall. The field strength in the near-field and far-field region coverage can be maximized by optimizing the antenna polarization and position. For verification, a grid-based test system was designed and a series of measurements inside an underground coal mine tunnel were conducted. The measured results have a good agreement with the theoretical ones. In addition, the EM interference caused by the infrastructure in real mines on the signal received by the antennas at different positions was also measured and compared. Results show that the influences of cables with long-term stable loads, such as power cables and communication cables, can be neglected.

A line-of-sight propagation performance study for underground mining in an arched-shaped tunnel environment

ABSTRACTThis article investigates the effect of antenna polarization, directivity and placement on the line-of-sight wideband radio channel characteristics of an arch-shaped underground mine tunnel over the 2.4 GHz frequency band. Access point-to-access point and access point-to-mobile wireless communication configurations were examined for linearly and circularly polarized antennas mounted in the center, on the wall and ceiling. The circularly polarized directional antennas offer higher coherent bandwidth, whereas the linearly polarized omni-directional antennas offer lower attenuation rate. A higher directive antenna enhances coverage area, coverage reliability and channel coherent bandwidth. For access point-to-mobile communication, a circularly polarized directional antenna with a horizontally polarized omni-directional antenna gives the best performance in terms of attenuation rate and coherent bandwidth.

Comparative analysis of ANFO and emulsion application on overbreak and underbreak at blasting development activity in underground Deep Mill Level Zone (DMLZ) PT Freeport Indonesia

Underground Deep Mill Level Zone (DMLZ) mine PT Freeport Indonesia (PTFI) is still in development stage and currently has no production activities yet. In underground DMLZ mine, a trial of emulsion explosive has conducted since March 15th, 2017 where previously used was Ammonium Nitrate Fuel Oil (ANFO) explosive for tunnel blasting. This study purposes to analyse the results and impact of ANFO and emulsion explosive in order to know the advantages and disadvantages of each explosives. In this study, an overbreak and underbreak comparison evaluation was performed by ANFO explosives and emulsion in underground DMLZ mine tunnel blasting. Furthermore, processing data based on explosives specification data, explosives quantity, heading location and time that detonated, solid design and actual tunnel DMLZ of PT. Freeport Indonesia, also cross section data. After all the data were processed and analysed, it was concluded that the emulsion explosive was more effective for use in tunnel blasting. To optimize the effective blasting results it is necessary to redesign new drilling patterns and blasting geometry by used of radial crack method, so that they can be applied to DMLZ tunnels in the future.

Deterministic Modeling of 5G Millimeter-Wave Communication in an Underground Mine Tunnel

This paper presents broadband simulations and measurements of Millimeter-Waves (mm-wave) propagation in a rugged underground mine environment. Mathematical formulation was carried out in the framework of Uniform Theory of Diffraction (UTD) to develop a deterministic Ray-Tracing (RT) model under Line-Of-Sight (LOS) condition. The developed theoretical model was then validated experimentally in Frequency Domain (FD) and Time Domain (TD). A significant agreement between simulations and measurements is achieved in both domains. The rough surfaces of the mine are modeled deterministically as groups of diffracting wedges having random dimensions (heights, angles) being transversely oriented throughout the gallery. Acute (inferior to 30°) and obtuse (superior to 120°) wedges angles are found to have significant effects on the overall propagation performance. In the mm-wave band, the UTD diffraction phenomenon is evident and must be considered in the design of underground mine channels. In fact, the presented model is found to be capable of predicting the complex multipath of underground mine channels, due to the ray-optical behavior at mm-wave bands.