Fig. 1. Location of open-pit mine slopes. (a) Digital elevation model of Sandu Coal Industry Area, Xiyang County (data source: MAPWORLD); (b) location of the open-pit mine area (data source: MAPWORLD); (c) an open-pit mine slope stability monitoring system composed of single-mode strain optical cables, communication optical cables, and Brillouin optical time-domain reflectometer

Fig. 2. Exterior diagram of the data acquisition center located 2 km on the slope of the open-pit mine and equipment diagram for internal monitoring

Fig. 3. Installation site of optical cable sensing systems. (a) Communication cable; (b) armored strain optical cable; (c) excavated trench; (d) anchor bolt; (e) anchor rods fixed to the strain optical cables and backfilled with sandy mudstone soil; (f) patch cords connecting optical cables; (g) junction box placed in the electricity meter box; (h) optical cable laying site

Fig. 4. Working principle of BOTDR sensing technology

Fig. 5. Strain changes of optical cable within 24 h, and the strain data are collected at hourly intervals

Fig. 6. Monitoring data for laying optical cables. (a) Monitoring data of optical cable laying lengths of 10 km; (b) monitoring data corresponding to position A; (c) monitoring data corresponding to position B; (d) monitoring data of the optical cable laying length of 3300 m; (e) monitoring data corresponding to position C; (f) monitoring data corresponding to position D; (g) monitoring data of the optical cable laying length of 3500 m; (h) monitoring data corresponding to position E; (i) monitoring data corresponding to position F