Underground Mine Tunnels Research Articles

Dynamic Compressive Characteristics of Sandstone under Confining Pressure and Radial Gradient Stress with the SHPB Test

Research on the dynamic compressive characteristics of sandstone under radial gradient stress and confining pressure is conducive to understanding the characteristics of the surrounding rock, especially in an excavation operation for an underground mine roadway and tunnel. The present work aimed at studying the effects of radial gradient stress and confining pressure on the impact of compression of sandstone using a large-diameter split Hopkinson pressure bar. The results showed that the dynamic strength of sandstone under radial gradient stress increased with strain rate following a power function, and the dynamic strength of the sandstone under radial gradient stress was lower and more sensitive to strain rate. The increase in strain at peak stress (peak strain) was linearly correlated with the strain rate under different confining pressures. The sensitivity of the peak strain to confining pressure was lower for the sandstone with a hole, while the values of the elastic modulus were decreased. However, further increasing the stain rate would lead to an increase in the elastic modulus. Also, the ductility of the sandstone with a hole tested in this study was found to improve more significantly. Finally, with an increase in the incident energy, the absorbed energy per unit volume would increase, but would not be affected obviously by the radial gradient stress.

Studies on Propagation Characteristics of Radio Waves for Wireless Networks in Underground Coal Mines

Communication systems relying on wireless technology can significantly improve the safety and production in underground mines; however, their unreliable operation in such high-stress environments is a significant obstacle to achieving this. Underground mine tunnels offers several distinctive features that are quite different from regular rail/road tunnels. While several studies have been performed on electromagnetic (EM) wave propagation in tunnel environments, there is limited understanding of the inter-working of tunnel dimension with long range tilt variations (a typically feature of coal mines) on the propagation characteristics of wireless radio waves. In this paper, we study and describe a new hybrid multimode model for wireless communication applications in underground coal mines; and analyze it with respect to significant parameters such as operating frequency, mine tunnel size, transmitter–receiver position, electrical parameters and antenna gain. The characterization results suggest that the mine tunnel size and transmitter–receiver position affects the signal behavior significantly. However, the electrical parameters have almost negligible effects on the propagation.

A Review of Rock Bolt Monitoring Using Smart Sensors.

Rock bolts have been widely used as rock reinforcing members in underground coal mine roadways and tunnels. Failures of rock bolts occur as a result of overloading, corrosion, seismic burst and bad grouting, leading to catastrophic economic and personnel losses. Monitoring the health condition of the rock bolts plays an important role in ensuring the safe operation of underground mines. This work presents a brief introduction on the types of rock bolts followed by a comprehensive review of rock bolt monitoring using smart sensors. Smart sensors that are used to assess rock bolt integrity are reviewed to provide a firm perception of the application of smart sensors for enhanced performance and reliability of rock bolts. The most widely used smart sensors for rock bolt monitoring are the piezoelectric sensors and the fiber optic sensors. The methodologies and principles of these smart sensors are reviewed from the point of view of rock bolt integrity monitoring. The applications of smart sensors in monitoring the critical status of rock bolts, such as the axial force, corrosion occurrence, grout quality and resin delamination, are highlighted. In addition, several prototypes or commercially available smart rock bolt devices are also introduced.

Effect of Antenna Configuration on MIMO-Based Access Points in a Short Tunnel With Infrastructure

Performance of MIMO technology is highly dependent on the surrounding propagation environment and antenna configuration. In order to benefit from MIMO technology inside underground mines with low angular spread, careful antenna design and deployment strategies are required. In this regard, we studied the effect of uniform-linear-array (ULA) configuration on the MIMO channel capacity inside a short underground service tunnel. With its extensive infrastructure, this tunnel represents a typical midsize underground-mine tunnel. We simulated and measured channel frequency response at 2.49 GHz for grids of transmitters and receivers in different parts of the tunnel while taking into account practical considerations for access point (AP) deployments. All the ULA configurations were deployed either close to the sidewalls or under the ceiling. Among them, two configurations, which show the best performance for AP communications, were identified. For these configurations, we found that interelement separation requires to be four times longer than in conventional indoor environment with rich multipath (i.e., $2\lambda$ ) to provide decorrelation among MIMO subchannels. We also found that infrastructure which has been neglected in previous studies, significantly degrades MIMO performance. Insightful results and guidelines for employing MIMO technology in underground mines can significantly benefit mining industry.

Analytical and numerical modeling for the effects of thermal insulation in underground tunnels

The heat flow generated from the infinite rock mass surrounding the underground tunnels is a major cause for the increasing cooling demands in deep mine tunnels. Insulation layers with lower thermal conductivities on tunnel walls and roof ceilings are believed to supply a thermo-barrier for heat abatement. However, it is found that no systematic theoretical investigations were made to predict and confirm the effectiveness of underground thermal insulation. Specifically, investigations on the underground insulation problems involving heat flows through the semi-infinite hot rock mass and insulation layer were not sufficient. Thus, in this paper, the thermal characteristics, accompanied with heat flow through the semi-infinite rock mass and the insulation layer, were modeled by both analytical and numerical methods with focus on underground mine tunnels. The close agreements between models have indicated that the thermal insulation applied on tunnel surfaces is able to provide promising heat abatement effects.

Low-Power and Reliable Communications for UWB-Based Wireless Monitoring Sensor Networks in Underground Mine Tunnels

This paper investigates the bit-error-rate (BER) and maximum allowable data throughput (MADTh) performance of a novel low-power mismatched Rake receiver structure for ultra wideband (UWB) wireless monitoring sensor networks in underground mine tunnels. This receive node structure provides a promising solution for low-power and reliable communications in underground mine tunnels with more than 90% reduction in power consumption. The BER and MADTh of the proposed receive nodes are investigated via Monte-Carlo simulations in UWB line-of-sight (LOS) and non-line-of-sight (NLOS) underground mine tunnels. The proposed mismatched receive nodes achieve a MADTh and BER performance approaching the corresponding optimal nodes with ≈1 dB and 1.5 dB BER performance degradation in LOS and NLOS scenarios, respectively. The mismatched PRake (M-PRake) receiver model with [Formula: see text] represents the best choice for low-power and reliable communications in sensor networks in underground mine tunnels with BER performance degradation of 1 dB and 3 dB in LOS and NLOS scenarios, respectively, as compared to the optimum detector. This minimal degradation in performance is traded for more than 90% reduction in power consumption.

Near–optimal rake receivers for green UWB radio communications in NLOS underground mine tunnels

This paper proposes a novel green radio (GR)-mismatched Rake receiver structure for ultra-wideband (UWB) communications in non-line-of-sight (NLOS) underground mine tunnels. The proposed architecture provides a promising solution for wireless GR communications in underground mine tunnels with greater than 90% reduction in power consumption. The bit error rate (BER) and maximum allowable data throughput (MADTh) of the proposed receiver structure are investigated via theoretical analysis as well as Monte-Carlo simulations in UWB NLOS underground mine tunnels and are compared to the corresponding optimal structures. The proposed mismatched receivers achieve an approaching MADTh and BER performance to the corresponding optimal structures with 1.5 dB BER performance degradation.

A node division location detection scheme for chain‐type wireless sensor networks

AbstractAs a special type of wireless sensor network, the chain‐type wireless sensor networks can be used to monitor narrow and long regions, such as roads, underground mine tunnels, rivers, and bridges. In this study, a perpendicular bisector division (PB) method was first presented, in which the location may be divided into more location sub‐areas by a perpendicular bisector of each of two location nodes. Compared with the triangulation division method in Approximate Point‐in‐Triangulation Test (APIT), the computable complexity of PB is lower, and the number of division areas is larger. Furthermore, in order to locate targets under rare location nodes, a virtual location node‐perpendicular bisector division (VPB) was presented by a virtual location node based on the geographic shape of the monitored area. Virtual location nodes increase the density of location nodes, which can improve the accuracy of the location in the location algorithm. Second, two range‐free location algorithms were proposed: the location algorithm based on PB (LAPB) and the location algorithm based on VPB (LAVPB). In the end, the location errors performance of APIT, LAPB, and LAVPB for locating miners in an underground mine tunnel was tested. The results show that LAPB and LAVPB have higher location accuracy and are more robust than APIT. LAVPB is more suitable for locating targets in harsh environments. Copyright © 2014 John Wiley & Sons, Ltd.

Design of an Amphibian Exploring Robot

To design and develop an amphibian exploring robot capable of operation in constrained mine environment puts a tremendous challenge to the system developers from both scientific and engineering perspective. Very few attempts have been made to fulfil these criteria of versatility in design, communication and control. The CSIR-CMERI developed amphibian subterranean robotic explorer (SR) is capable of moving over fairly rough terrain. It can swim as well as crawl over basin floor effortlessly. It is capable of operating at a maximum depth of 10m and can swim at 1 knot. A number of field trials have been carried out for performance testing of the system to ascertain its capability in underground flooded mine tunnels. This paper presents the insight on the design of an amphibian exploring robot for mine safety and disaster mitigation with special features of low power consumption vis-a-vis high mission time.

Development of the Tunnel Wet Dust Precipitator and Testing

The tunnel wet dust precipitator (TWDP) is designed and applied to the underground mine tunnel dust control. The TWDP is a modular design with the disc which the radiant fine stainless-steel filament and nozzle. Discs are used in serial in axial direction in the TWDP to lift the collection efficiency, and discs are parallel in a section to enlarge the volumetric flow rate. The TWDP, which is connected with the local fan, is mounted at the discharging mine platform, and the experiment is conducted for its performance testing. Results show that the collection efficiency for respirable dust is above 80%.

Enhancement Contrast and Denoising of Low Illumination Image of Underground Mine Tunnel

For enhancing low lumination image of underground mine tunnel, a hybrid local histogram equalization with partial differential equation is proposed to combine a local histogram equalization and total variation method with edge-stopping function via partial differential equation. The local histogram equalization is to enhance contrast of image with keeping shape and edge, while total variation method with edge-stopping function is to smooth image by gradient diffusion for lowing noise. In the presented hybrid method, a parallel trade-off scheme is utilized for simultaneous denoising and contrast enhancement. Experiments are carried out to validate the hybrid method using a standard image and a real image of underground mine tunnel. The results prove that it is an alternative processing method for low luminous image of underground mine tunnel.

Sustainable heat extraction from abandoned mine tunnels: A numerical model

Abandoned mines are often associated with enduring liabilities, which involve significant costs for decades after the decommissioning of the mine. Using a decommissioned mine as a geothermal resource can offset the environmental costs by supplying green heat to the communities living in and around the mine area. In this paper, a numerical assessment of geothermal heat extraction from underground mine workings using an open loop geothermal system is carried out. In this study, our focus is on fully flooded mines where the heat flow from the rock mass to the mine cavities is dominantly controlled by conduction in the rock mass. The sustainable heat flux into the mine workings is assessed using a transient two-dimensional axisymmetric heat transfer model. Finite volume method is applied to solve the model and simulate the transient temperature fields in the rock mass and within the water (flowing through cavities). The model is capable of controlling the rate of heat extraction through continuous adjustment of the rate of water flow through the mine. Sustainable rate of heat extraction is calculated for seasonally varied heat loads and for different project life cycles. It is shown that, with proper resource management, each kilometre of a typical deep underground mine tunnel, can produce about 150 kW of usable heat in a sustainable manner. The model is validated by comparing its results with other published models and realistic data available from Springhill mine, Nova Scotia, Canada. It is found that the sustainable heat extraction is controlled dominantly by virgin rock temperature, thermal conductivity of the rock mass, and seasonal heat load variations.

Capacity and Outage Analysis of MIMO and Cooperative Communication Systems in Underground Tunnels

In underground mine and road tunnels, multipath fading is much more severe than in the terrestrial wireless channels. To overcome the multipath fading in underground tunnels, MIMO (Multiple Input Multiple Output) and Cooperative Communication system can be utilized. Since the underground channel characteristics are significantly different from those in terrestrial environments, the channel capacity and the outage behavior of such systems need to be investigated based on underground tunnel channel models, which had not been addressed by the research community yet. In this paper, the capacity distribution and outage probability of MIMO and cooperative communication systems are investigated in underground tunnel environments. Explicit formulas of the capacity distribution and outage probability are developed as functions of environmental conditions and system configurations. Based on the capacity and outage analysis in underground tunnels, the optimal MIMO antenna geometry design scheme is proposed for MIMO systems; and the cooperative relay assignment protocol is developed for cooperative communication systems. Simulations are conducted to validate the theoretical results.

Energy optimal routing for long chain-type wireless sensor networks in underground mines

Wireless sensor networks are useful complements to existing monitoring systems in underground mines. They play an important role of enhancing and improving coverage and flexibility of safety monitoring systems. Regions prone to danger and environments after disasters in underground mines require saving and balancing energy consumption of nodes to prolong the lifespan of networks. Based on the structure of a tunnel, we present a Long Chain-type Wireless Sensor Network (LC-WSN) to monitor the safety of underground mine tunnels. We define the optimal transmission distance and the range of the key region and present an Energy Optimal Routing (EOR) algorithm for LC-WSN to balance the energy consumption of nodes and maximize the lifespan of networks. EOR constructs routing paths based on an optimal transmission distance and uses an energy balancing strategy in the key region. Simulation results show that the EOR algorithm extends the lifespan of a network, balances the energy consumption of nodes in the key region and effectively limits the length of routing paths, compared with similar algorithms.

Radio Wave Characterization and Modeling in Underground Mine Tunnels

Results are presented on wideband radio propagation measurements and statistical modeling at 2.4 GHz and 5.8 GHz in real underground mine tunnels. This peculiar type of confined environment is characterized by very rough surfaces and a frequent absence of a line-of-sight between transmitting and receiving antennas. The resulting propagation characteristics differ from those frequently encountered in more typical indoor environments such as offices and corridors. Indeed, the rms delay spread shows little or no correlation with respect to transmitter-receiver distance and, in addition, no impulse response path arrival clustering effect is observed. However, the path amplitude distribution does tend to follow a Rice distribution in the line-of-sight case, and a Rayleigh distribution otherwise.

Backdraft in Descensionally Ventilated Mine Fire

The backdraft in an underground mine tunnel fire is investigated by means of experimental simulation. According to the results, such a backdraft phenomenon is different from a general one in a compartment fire. A backdraft of tunnel fire takes place in an open system with flowing gases and no newly formed vents are needed to result in it under such an occasion. The backdraft occurs with the reversal of descensionally ventilated airflow. The results obtained extend the range where a backdraft can occur and promote a better understanding of the backdraft phenomenon.

Mechanization of underground mining: a quick look backward and forward

Mine mechanization, especially the mechanization of underground hard rock mines provides a large potential for reduced costs and improved profitability. This paper examines a number of successful developments mechanizing underground mine excavation, including raises, shafts, tunnels, and stopes. It then examines mechanization developments, which are under way, and others which are not yet being developed. A look back at mine mechanization projects that have failed is included as a perspective when considering projects for the future. Factors influencing the development of mine mechanization are reviewed, as well as some of the factors that will be required for successful mechanization in the future. It appears that the development of mechanization for fundamentally new mining systems will require complex joint ventures involving mining companies, equipment suppliers, governments, and academic partners working together on a long-term commitment. These technical joint ventures will require long-term commitments of capital to produce the technology that will be required for mechanizing the underground mines of the future.

Integrated Communication Perspectives for Mine and Surface Tunnels

The paper presents challenges encountered in establishing communication systems in railway road and underground mine tunnels and the concepts which have helped establishing communication in different types of tunnels. Communication systems established on the basis of work done by the authors in underground mine tunnel is described in detail and the perspectives of development of integrated communication systems for allied problems in India in the future are presented.