Towards Long-Term Monitoring of the Structural Health of Deep Rock Tunnels with Remote Sensing Techniques

Due to the substantial need to continuously ensure safe excavations and sustainable operation of deep engineering structures, structural health monitoring based on remote sensing techniques has become a prominent research topic in this field. Indeed, throughout their lifetime, deep tunnels are usually exposed to many complex situations which inevitably affect their structural health. Therefore, appropriate and effective monitoring systems are required to provide real-time information that can be used as a true basis for efficient and timely decision-making. Since sensors are at the heart of any monitoring system, their selection and conception for deep rock tunnels necessitates special attention. This work identifies and describes relevant structural health problems of deep rock tunnels and the applicability of sensors employed in monitoring systems, based on in-depth searches performed on pertinent research. The outcomes and challenges of monitoring are discussed as well. Results show that over time, deep rock tunnels suffer several typical structural diseases namely degradation of the excavation damaged areas, corrosion of rock bolts and cable bolts, cracks, fractures and strains in secondary lining, groundwater leaks in secondary lining, convergence deformation and damage provoked by the triggering of fires. Various types of remote sensors are deployed to monitor such diseases. For deep rock tunnels, it is suggested to adopt comprehensive monitoring systems with adaptive and robust sensors for their reliable and long-lasting performance

Development and application of a borehole stress meter in rocks surrounding the roadway, based on optical-fiber sensing technology

Stress in rock masses is an important parameter in the design and construction of underground engineering, such as the design and maintenance of mine roadways and the design of mining working faces. It is also a fundamental force causing the deformation and failure of geotechnical engineering excavation. At present, the abutment-pressure monitoring technology of the surrounding rocks of the coal mine roadway in China is not intelligent and systematic and lacks some high-precision sensing instruments and multi-functional monitoring systems. The mechanical model of the rocks surrounding the borehole was constructed by theoretical analysis of problems in the stress monitoring technology for underground rock masses in coal mines. Additionally, the interaction between the surrounding rocks and the borehole stress meter was analyzed. The borehole stress meters for tubular-structure fiber Bragg grating (TS-FBG) and cystic-structure fiber Bragg grating (CS-FBG) were designed by combining the sensing principle and sensing characteristics of fiber Bragg grating, and the performance of the two kinds of fiber Bragg grating borehole stress meters was compared by laboratory test. The track roadway of the 14,301 tested working faces in the Shaqu Coal Mine was taken as an example, and the stress of the rocks surrounding the 14,301-track roadway was monitored in real time by CS-FBG borehole stress meter during the mining of the working face. The following conclusions are drawn from the field application. The rig-site utilization results revealed obvious stress growth and stress peak zones in the mining-stress change curves of each measuring point on the two sides of the 14,301-track roadway in the process of mining the tested working face. Additionally, there were four stages: rapid rise, uniform growth, rapid rise to the peak, and rapid decline. Maximum stress monitored by the second station was 18.5 MPa, and the influence range of stress was over 140 m. Maximum stress monitored by the first measuring station was 19 MPa, the influence range of stress was about 80 m, and the peak stress position was about 20 m in front of the coal wall. Rig-site utilization proved the design of the CS-FBG borehole stress meter to be reasonable. Performance was stable and reliable, and the successful operation of field monitoring achieved the expected effect

Monitoring of strain and temperature in an open pit using brillouin distributed optical fiber sensors

Marble quarries are quite dangerous environments in which rock falls may occur. As many workers operate in these sites, it is necessary to deal with the matter of safety at work, checking and monitoring the stability conditions of the rock mass. In this paper, some results of an innovative analysis method are shown. It is based on the combination of Distributed Optical Fiber Sensors (DOFS), digital photogrammetry through Unmanned Aerial Vehicle (UAV), topographic, and geotechnical monitoring systems. Although DOFS are currently widely used for studying infrastructures, buildings and landslides, their use in rock marble quarries represents an element of peculiarity. The complex morphologies and the intense temperature range that characterize this environment make this application original. The selected test site is the Lorano open pit which is located in the Apuan Alps (Italy); here, a monitoring system consisting of extensometers, crackmeters, clinometers and a Robotic Total Station has been operating since 2012. From DOFS measurements, strain and temperature values were obtained and validated with displacement data from topographic and geotechnical instruments. These results may provide useful fundamental indications about the rock mass stability for the safety at work and the long-term planning of mining activities

Monitoring Technology of Surrounding Rock Deformation Based on IWFBG Sensing Principle and Its Application

To address the challenge of achieving precise real-time monitoring of significant deformation in deep roadway surrounding rock, a quasi-distributed strain-sensing cable (SSC), which has a spatial resolution of 1 m, was developed based on the principle of Identical Weak Fiber Bragg Gratings. The performance of SSC has been evaluated through a series of calibration tests, revealing a range of 0%–3%, an accuracy level of 0.5%, a strain sensitivity measuring at 1.23 pm/με, and a temperature sensitivity recorded as 10.78 pm/℃. Furthermore, a real-time deformation monitoring system has been established to monitor rock deformation, consisting of SSC, supporting installation equipment, demodulation equipment, and monitoring software. Moreover, the proposed methodology was applied in the deep roadway of Guqiao coal mine. The results showed that the maximum surface displacement of the roadway is 103.47 mm, while the lateral contrast error stands at 5%. The maximum strain value of the surrounding rock measures 27,095 με. The depth of rock rupture zone is about 3 m, while the boundary of rock damage zone extends up to 6 m. This information serves as the foundation for determining the parameters of the roadway reinforcement support design

Towards Long-Term Monitoring of the Structural Health of Deep Rock Tunnels with Remote Sensing Techniques

Due to the substantial need to continuously ensure safe excavations and sustainable operation of deep engineering structures, structural health monitoring based on remote sensing techniques has become a prominent research topic in this field. Indeed, throughout their lifetime, deep tunnels are usually exposed to many complex situations which inevitably affect their structural health. Therefore, appropriate and effective monitoring systems are required to provide real-time information that can be used as a true basis for efficient and timely decision-making. Since sensors are at the heart of any monitoring system, their selection and conception for deep rock tunnels necessitates special attention. This work identifies and describes relevant structural health problems of deep rock tunnels and the applicability of sensors employed in monitoring systems, based on in-depth searches performed on pertinent research. The outcomes and challenges of monitoring are discussed as well. Results show that over time, deep rock tunnels suffer several typical structural diseases namely degradation of the excavation damaged areas, corrosion of rock bolts and cable bolts, cracks, fractures and strains in secondary lining, groundwater leaks in secondary lining, convergence deformation and damage provoked by the triggering of fires. Various types of remote sensors are deployed to monitor such diseases. For deep rock tunnels, it is suggested to adopt comprehensive monitoring systems with adaptive and robust sensors for their reliable and long-lasting performance

Investigation of fiber-optic displacement sensor

Аннотация: статья посвящена исследованию волоконно-оптических датчиков смещения, для обеспечения безопасности и постоянного мониторинга при работах на карьере. Проведенное исследование позволяет утверждать, что волоконно-оптические датчики и контрольные кабели линии связи, выполненные на основе одномодовых оптических волокон, позволяют с высокой точностью измерять деформации и смещения горного массива на расстояниях 30-50 км. Статья представляет собой образец для изучения всего процесса деформации и смещения горного массива с оптимизацией работы на карьере и предотвращения аварии.Abstract: the article is devoted to the study of fiber-optic displacement sensors to ensure safety and constant monitoring during work at the quarry. The conducted research suggests that fiber-optic sensors and control cables of the communication line, made on the basis of single-mode optical fibers, make it possible to measure deformations and displacements of the mountain range at distances of 30-50 km with high accuracy. The article is a sample for studying the entire process of deformation and displacement of the mountain range with optimization of work at the quarry and accident prevention

Development of a wireless system to measure the strain/deformation of rock bolts

In this study a smart set-up integrated with rock bolts was proposed to automatically monitor, record and analyse rock mass deformation. The proposed system which includes sensors and a wireless data acquisition system, rapidly and readily generates data sets along with customisable graphs, calculations and analysis in a cloud system and can be used in modern mining. To evaluate the developed technique, rock bolts were instrumented lengthwise using resistive strain gauges and then connected to the wireless data logger system. Elastic tensile tests as well as pull-out tests were conducted and the strain values along the rock bolts were successfully and accurately measured, recorded and uploaded to the cloud system

Comparing methods of controlling unauthorized access to fiber-optic transmission lines

In present day telecommunication systems the topical problem is protection of the subscribers' personal data against possible thefts and hacking fiber-optic information transmission guide lines, as this causes a number of dangerous situations and problems. The attackers, in spite of the legislative framework for the information protection, are still trying to read information from a fiber-optic transmission line (FOTL). This possibility arises due to incorrect installation and configuration of error protection, unauthorized access to information is possible. This article discusses two methods of detecting unauthorized admission (unauthorized access). The results of the study using an optical laser radiation source and power meter, as well as a YOKOGAWA optical reflectometer are presented. As a result, it was concluded that the method of preventing unauthorized access at the wavelength of 1625 nm can be used, since continuous FOTL monitoring will not interfere with the traffic

Converged data and sensing over optical fiber networks

Internet connectivity, data and sensors have become increasingly important across all spheres of business and industry, especially in the mining sector. Recent years have seen deeper mining explorations as a result of the depletion of natural resources in shallow strata. Due to complex and unexpected geological conditions as well as significant ground stresses, deep stratum mining operations encounter a number of difficulties. It is essential that the mining industry be more innovative with their equipment and monitoring systems given the rise in expenses caused by energy consumption, concessions to surface integrity, worldwide freshwater shortage, as well as health and safety of miners. Any attempt to eliminate these mining consequences must start with early discovery. An effective plan to anticipate, prevent, or manage geohazards events must be in place because to these complex and unpredictably occurring geological circumstances. Due to their capacity to combine gigabits of data from remote locations within the mine to a centralized control centre, optical fiber offers a variety of distinctive advantages within the mining industry. In order to attain maximum productivity, modern and effective mining operations use enhanced control techniques and increasing mechanization. Additionally, optical fibers can be utilized in a mine to safely monitor seismic activity, methane, roof collapses, rock bursts, explosions, and dangerous underground mine settings. Multimode or multi-core fibers represent a particularly intriguing alternative for transmissions over small distances, especially for broad band local area networks like LANs, as they enable the use of affordable components. Due to the current state of these issues, there is a drive to create fiber optic communication links that can also function as distributed optical fiber sensors, where each point along the fiber can function as a continuous array of sensors. In this thesis, we suggested and experimentally demonstrated a converged solution for precise vibration sensing and high-speed data in mining applications. With wireless access for people and equipment inside cavities, the solution uses multimode fiber to link nearby mining cavities. To track vibrations and earth tremors causing rock falls, polarization-based vibration sensors over multimode fiber is used. With a modal dispersion penalty of just 1.6 dB, photonic data transmission across 100 m of multimode fiber is successfully accomplished. Successful 1.7 GHz wireless transmission across a distance of 1 m is demonstrated, and vibrations between 50 Hz and 1 kHz may be reliably detected to within 0.02 percent of the true value.Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 202

Integration of Instrumentation and Computer Modelling to Understand and therefore Better Design and Represent the Rock bolt Support Behaviour

A safe and efficient ground control system is one of the most vital components of an underground mine’s operations. Current rockbolt ground reinforcement design methods do not consider the actual in-situ behaviour of the rockbolt. Instrumented rock bolts can be used to understand the actual rockbolt response under different loading conditions. Work done in this thesis aims to integrate the actual in-situ response of rockbolt with improved numerical modelling procedures for designing better ground support