## 3 Results
### Systematic Content Review Results for Sensors Monitoring Mine Tailings Storage Facilities
#### 3.3.1 Content-Based Data Perspective Analysis
These systems' advantages are (i) they allow the automatic control of variables, (ii) they allow real-time diagnosis, (iii) they offer perpetual operation without maintenance, (iv) they allow control during post-operation, (v) they can transmit data over long distances, and (vi) they can transmit large amounts of data (high transfer rate compared to other wired systems). * Satellite communication or radio communication. These systems allow communication at any time, anywhere, and on any device. Their advantages include (i) simultaneous communication to several receivers and (ii) the capacity to transmit early community warnings. The areas within a mine TSF where sensors are used to monitor structural health and safety management are shown in Figure 19.  
As Figure 19 shows, the dam area is the main sensor location with 14 mentions, followed by the reservoir level area with 12 mentions; the least mentioned areas are the drainage system and cut-off trench, with only one mention each. Nine documents did not specify sensor location areas in the TSF. The selected documents were also analyzed for the implementation of technologies related to Industry 4.0 with monitoring sensors. Figure 20 shows the percentage of mentions of different technologies in the selected papers. Artificial intelligence (AI) is the most  
Figure 17: Types of data transmission implemented for sensor connectivity to monitor TSFs. Figure 18: The use of cables or wireless systems for sensors monitoring TSFs. common technology, with 30% of the total mentions, followed by the IoT with 23% of the total mentions, and cloud computing (CC) with 18% of the total mentions. 3.3.2 Main Applications of Sensor Use to Monitor the Structural Health and Safety Management of TSFs  
Figure 21 shows some examples of the use of sensors to monitor structural health and safety management in TSFs under an Industry 4.0 paradigm. This monitoring permits the study of key variables affecting sustainability, productivity, and safety performance. Currently, the addition of wireless monitoring systems is trending upward via remote monitoring and the use of Industry 4.0-related technologies. As Figure 21 depicts, different sensors for structural health and safety management monitoring in mine TSFs can be used. The following sensors are displayed in Figure 14:0 (i) piezometer (Casagrande and vibrating wire), (ii) temperature sensor, (iii) inclinometer, (iv) pressure cell, (v) settlement cell, (vi) borehole extensometer, (vii) water quality well, (viii) V-notch weir, (ix) crack gauge, (x) vented piezometer, (xi) strain gauge load cell, (xii) rain/wind/moisture content/evaporation gauge, (xiii) central data acquisition, (xiv) drone, (xv) satellite, InSAR and radar (remote sensing), and (xvi) bathymetry with unmanned survey vessel. Figure 22 shows some examples of typical sensors and devices used for these purposes. Figure 14:1 Areas within a TSF where sensors are used to monitor structural health and safety management. Figure 14:2 Technologies related to Industry 4.0 that have been applied in sensors monitoring TSFs. The wireless configuration of the data acquisition system eliminates the need for expensive cabling and manual monitoring in mine TSFs. Laying cables in a mine tailings dam requires trenches and cable protection against issues such as embankment settlements. New sensors must be added as the site grows, again requiring expensive cable installation. A wireless system provides data from sensors in near-real time, versus manually collected readings with a more sporadic periodicity and vulnerability to human error. Figure 14:3 Examples of the use of different sensors for structural health and safety management monitoring in mine TSFs. Adapted from [59].