Applying the Doppler principle to emergency geotechnical monitoring management
AUTHORS
Vitor Almeida Santos, GroundProbe, Belo Horizonte, MG, Brasil
Eduardo César Jardim, Vale, Itabira, MG, Brasil
Albert Paulo Sabará, Vale, Mariana, MG, Brasil
Thomaz Franco de Melo Cotta, GroundProbe, Belo Horizonte, MG, Brasil
Bruno Penido Vecchia, GroundProbe, Belo Horizonte, MG, Brasil
ABSTRACT
Geotechnical scenarios encompassing stockpiles, open-cut mines, slopes, and dams face significant risks. Monitoring these structures with reliable tools, including advanced technological solutions, is essential for safety and stability. Reactive monitoring technologies, serving as a crucial control measure, can mitigate impacts when risk scenarios materialize. The primary objective of emergency management sensors is to detect critical conditions on monitored slopes, triggering alarm systems and predefined workflows. These workflows include activating alert mechanisms to warn communities and operational areas downstream and possibly implementing local traffic restrictions (Vale, 2023).
To deploy reactive sensors effectively, it is imperative to establish a robust monitoring process with well-defined alarm thresholds that trigger emergency management procedures. The definition of alarm thresholds must account for various factors, including geotechnical parameters, failure mechanisms, potential impact areas, and maintenance or construction activities. Additionally, it should consider transit possibilities in the monitored paths.
This paper elaborates on the Doppler principle and its application in geotechnical monitoring. It outlines best practices for defining, adjusting, testing, and validating an activation model based on Doppler sensors. The methodology’s application across different geotechnical structures constructed by various methods is demonstrated. The applied alarms filter movement direction, potential displacements in critical areas, target size, and velocity.
Integrating geotechnical monitoring solutions with emergency management procedures offers a proactive approach to handling collapses. Implementing these solutions enables prompt emergency responses, minimizes potential damages, and mitigates human error by activating emergency protocols effectively (Stacey & Read, 2009).
INTRODUCTION
Mining activities have been integral to human history, tracing the earliest civilizations. In Brazil, mining has been crucial for territorial expansion, initially driven by the quest for gold, silver, copper, diamonds, and emeralds. As technology advanced, mining processes evolved to enhance productivity, safety, and resource optimization. Hustrulid et al. (2001) noted that market and macroeconomic factors spurred a shift in the mining industry’s perspective, leading to steeper slope inclinations for greater material extraction, advancements in machinery technologies, and optimization of the waste/ore ratio. These changes introduced new geotechnical challenges, prompting the development of innovative geotechnical solutions.
One area of geotechnical engineering that has experienced significant growth is monitoring. Conventional solutions include water level indicators, extensometers, surface markers, interferometric radars, GNSS, inclinometers, tiltmeters, and Doppler radars. The implementation of these technologies has necessitated more robust control of performance indicators (KPIs) and the development of communication flows and responsibility allocation during the Trigger Action Response Plan (TARP), as highlighted by Morrison (2022).
The current landscape of geotechnical monitoring focuses on managing geotechnical risks, classifying them as critical or non-critical to safety and emergency management. A widely adopted technology for emergency management in open-pit mining and dam facilities is reactive radar utilising the Doppler principle to detect moving objects within its scanning area. Doppler radars can detect a collapse of the monitored structure, ensuring the shortest response time within the TARP framework.
This paper presents monitoring projects developed for dam facilities incorporating alarm systems based on the Doppler principle. It details parameter configurations such as direction, velocity, signal return intensity, movement sequencing, and statistical analysis using histograms and boxplot tools. The paper also discusses best practices for implementing these technologies to enhance geotechnical monitoring and emergency management.
CHALLENGES
Geotechnical scenarios encompassing stockpiles, open-cut mines, slopes, and dams face significant risks. These structures are vulnerable to various failure mechanisms, and monitoring their stability is crucial. However, several challenges arise:
Complex Geotechnical Environments
Geotechnical environments’ diverse and dynamic nature necessitates adaptable and precise monitoring solutions.
Alarm Threshold Definition
Establishing robust monitoring processes with well-defined alarm thresholds is essential but challenging. These thresholds must account for various geotechnical parameters, failure mechanisms, and potential impact areas.
Emergency Response
Ensuring prompt and effective emergency response requires integrating monitoring solutions with emergency management procedures. This involves defining, adjusting, testing, and validating activation models for reactive sensors.
Data Management
Efficiently managing and analysing vast amounts of data collected from monitoring systems is crucial for timely decision-making and action.
SOLUTION
Applying the Doppler principle in geotechnical monitoring to address these challenges offers a reliable and advanced solution. This approach involves:
The Doppler Principle and Its Application
The Doppler effect, first described by Austrian physicist Christian Andreas Doppler, involves the apparent shift in the frequency of a wave emitted by a source as perceived by an observer. This shift varies with the relative motion between the source and the observer. In geotechnical monitoring, pulsed electromagnetic waves are emitted towards an object of interest. The Doppler principle explains the variation in the wave’s frequency upon reflection caused by the object’s movement within the line of sight. Using this principle, objects can be detected, their intensity levels assessed, velocities measured, and movement directions determined.
The general equation for the Doppler effect is expressed as: 𝑓′=𝑓×(𝑉𝑠±𝑉𝑜)(𝑉𝑠±𝑉𝑡)
Equation 1. Doppler’s effect general equation. Uma proposta para o ensino qualitativo e quantitativo do efeito doppler usando smartphones. do Instituto Federal de Educação, Ciência e Tecnologia do Ceará – CE. 2021.
While detailed equations for each displacement scenario of the targets are beyond the scope of this article, they can be referenced in the study conducted by Almeida et al. (2021) at the Federal Institute of Education, Science, and Technology of Ceará – Brazil. Figure 1 illustrates a simplified schematic of the Doppler effect’s application in geotechnical monitoring, where the Doppler device remains static, and the wavelength (λn) reflected by the object of interest exhibits varying values as the object undergoes displacement.
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Figure 1. Simplified Doppler Effect Diagram. Uma proposta para o ensino qualitativo e quantitativo do efeito doppler usando smartphones. do Instituto Federal de Educação, Ciência e Tecnologia do Ceará – CE. 2021.
The change in wave frequency can be used to determine the target’s position and velocity based on the time the wave travels through the atmosphere. This allows for the detection of objects, assessment of their intensity levels, measurement of velocity, and determination of movement directions.
The Reactive Geohazard Radar (RGR) Velox, marketed by GroundProbe, was employed for data collection in this study. The RGR-Velox is a Doppler radar system specifically designed for geotechnical monitoring. The following data, collected using the RADAR Doppler principles, are summarised in Table 1:
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Table 1. Output from targets detection by RGR-Velox. Source: GroundProbe.
Methodology for Alarm Detection and Parameterization
The RGR-Velox, marketed by GroundProbe, was employed for data collection. The RGR-Velox is a 2D reactive radar system designed for emergency management to detect moving targets within its line of sight. It features built-in GPS and North-finding capabilities and an automatic target tracker to configure alarms based on the specific characteristics of each geotechnical structure under surveillance. Alarms in the RGR-Velox can be configured with up to four confirmation triggers: velocity, signal return intensity, movement sequencing (zone), and displacement direction. Accurate definition of these triggers is essential for optimizing the tool’s effectiveness (GroundProbe, 2023).
Integration with Emergency Management Procedures
In Brazil, national regulations mandate the installation of automated siren activation systems and other appropriate mechanisms to alert downstream populations about anomalies in mining dams with medium or high associated potential damage (DPA) (Brasil, 2022). The alarm activation in the RGR-Velox system can trigger the automatic activation of sirens, either exclusively or in conjunction with other technologies. Defining a detection model for alarms associated with automatic siren activation can reduce the response time of the geotechnical monitoring center to emergencies, alert the operator to occurrences outside their immediate knowledge, and enhance safety and control levels in the risk area.
RESULTS
Two case studies were conducted to demonstrate the application of the calibration methodology in defining parameters for triggering automatic alarms using the RGR-Velox.
Case Study 1 – Demonstration of Drone Detection
A specific drone was employed as a dynamic target within the tailing storage facility (TSF) area to calibrate the positioning of targets detected by the RGR-Velox. The drone’s movement simulated a real collapse over the TSF and its slopes, traversing six intrusion zones. The implemented flight plan lasted approximately 50 seconds, with the drone’s speed indicated in 94% of detections, ranging between 13.5 and 16.5 m/s. The configured alarms activated as expected based on the target detection in their respective zones.
Case Study 2 – Calibration of Speed and Geopositioning Using a Motor Vehicle and GPS
A motor vehicle with a GPS device and a metallic object calibrated the RGR-Velox system. The vehicle was driven along the berms of the tailing storage facility, covering approximately 300 meters at speeds ranging from 0 to 20 km/h in two separate attempts. The signal return intensity data from RGR-Velox during both attempts were compared for analysis. The case study yielded satisfactory results, with consistent signal return intensity data observed during both attempts along the conducted path and detected speeds ranging between 5 and 9 m/s by both measurement tools.
CONCLUSION
This paper has demonstrated the application of reactive monitoring technologies, specifically the Doppler principle, for emergency management in critical geotechnical scenarios. Establishing a mature monitoring process and defining appropriate alarm thresholds are vital to the effectiveness of these solutions. By incorporating detailed information about the monitored structures, geotechnical parameters, failure mechanisms, and potentially affected areas and integrating with emergency management procedures, reactive geotechnical monitoring solutions become an initiative-taking approach to addressing imminent collapse situations.
The ability to detect, alert, and activate emergency procedures based on sensor information using the Doppler principle enables a rapid response to emergencies. This minimizes potential damage and reduces the risk of human error in triggering emergency flows. The effective integration of these technologies provides an additional layer of security in critical areas, including mining and other industries, particularly in open-pit mines and dams.
As monitoring practices and associated risk and emergency management strategies improve, the environment is better prepared to address potential geotechnical challenges, thereby protecting lives, properties, and communities. This proactive approach ensures higher preparedness and safety, reinforcing the importance of advanced monitoring technologies in managing geotechnical risks.
REFERENCES
Almeida, S. B. B., Pimentel, P. A., & Neves, W. Q. (2021). Uma proposta para o ensino qualitativo e quantitativo do efeito Doppler usando smartphones. Instituto Federal de Educação, Ciência e Tecnologia do Ceará.
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Hustrulid, W. A., McCarter, M. K., & Van Zyl, D. J. A. (2001). Slope stability in surface mining.
Magalhães, G. G. de. (2023). 8 lições na construção do monitoramento geotécnico orientado a dados. Acessado em 23 de outubro de 2023.
Morrison, K. F. (2022). Tailings management handbook: A life-cycle approach.
Peixoto, G. G. (2006). Assinaturas de sinais de radar de alvos simples e de modelos de alvos complexos: Um estudo na banda X em câmara anecóica (Tese de mestrado). Instituto Tecnológico de Aeronáutica, São José dos Campos.
Stacey, P., & Read, J. (2009). Guidelines for open pit slope design. CRC Press.
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Vale. (2023). Plano de ação de emergência para barragens de mineração (PAEBM).
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