Real-Time Monitoring of Slope Behaviour Using Integrated TDR Based Wireless Sensor Network

Abstract

Mining is one of the significant industries which drive the overall economic growth of the country. However, the risk involved in the mine occupation is high in comparison to a normal work environment. With increased supply demands of raw materials from different industry such as cement, steel, etc. the opencast mine operation is going deeper. Increasing depth also increases the severity of slope stability problems of the opencast mines. This may result in slope failures, causing human and financial loss to any organization. Accidents due to slope instability are one of the leading causes in surface mining operations, and unexpected movement of the ground has the potential to endanger lives, demolish equipment, or destroy mine infrastructure. Motivated from such a crucial problem of the mining industry, this thesis aims to propose a reliable and efficient solution to the problem statement. As a part of the solution, critical reviews of instrumentation along with laboratory and field investigations were carried out in Manganese Ore India Limited (MOIL). Also, a model/algorithm was developed for reliable monitoring of slope behaviour as a multidisciplinary research problem for design and monitoring of slopes in an opencast mine. Establishment of the magnitude of deformation by Time Domain Reflectometry (TDR) in a slope is the main contribution proposed in this work. Available Geotechnical sensors include vibrating wire piezometers, wireline extensometers, borehole extensometers, Inclinometers; tilt meters, for sensing the changes in slope conditions, besides widely practiced total station monitoring. Technicians in the field monitor these geotechnical sensors, and the available wireless monitoring systems like SSR, LiDAR, Laser monitoring techniques are more expensive. Due to economic reasons, such potentially dangerous and unstable slopes are only monitored sporadically. In order to overcome this, efficient and economically feasible measurement systems for slope monitoring are needed. This research work is focused on the application of electronics and communication to eliminate the manual slope monitoring, and with the help of Wireless Network Infrastructure to replace the need for physical cables. The Radio Frequency (RF) module and interfacing unit were integrated with TDR to acquire the data, and the data transfer algorithm was developed for the establishment of wireless communication and tested in the laboratory. A Graphical User Interface (GUI) was developed using Python code for automatic storing and plotting of real-time data. Based on this received information, mine official could alert the workers who are working near the prone area. The integrated system was installed at the mine site. The real-time monitoring of ground deformation was accomplished using TDR via coaxial cables installed in three boreholes and are connected to a TDR system through a multiplexer that automatically recorded and transferred these measurements to mine office by the RF module. Based on the laboratory experiments for establishment of magnitude of deformation of coaxial cable using TDR, Development of wireless communication modules and Field experiment with TDR-WSN system, the Reflection Coefficient (RC) values for different magnitude of deformation for coaxial cables i.e. RG 213, RG 6, RG 58/U and RG 59 was established by the laboratory model for the deformation in the range of 0-6mm in the coaxial cables. RC values of corresponding coaxial cables are in the range of 0.0027-0.14, 0.0916-0.332, 0.00218-0.137 and 0.0116-0.0964 respectively. The integrated RF modules were programmed to minimize the data loss during the wireless transmission and observed a very less packet loss during laboratory test. The Range test for RF module conducted at different locations in the laboratory showed Received Signal Strength Indicator (RSSI) from -31dBm to -87dBm which comes under normal range. To improve the range of communication, an 8dB antenna was integrated with the XBee-PRO module. A code was developed using python programming for continuous storing and plotting of graph for slope monitoring data in the PC.

The field experimental trial was conducted successfully with an integrated TDR-WSN system in three locations of a typical opencast metal mine for the period of five months during 1st August 2017 to 27th December 2017. The conventional system of slope behavior monitoring during the above period using total station did not show any significant surface movements. Similarly, the TDR time series also indicated no significant change in initial RC values (0.25 to 0.28) during an experimental trial indicating stability of slope and supporting the conventional system of slope behaviour monitoring. However, the change in the RC value exceeding 0.332 (as established through laboratory model) can be considered as deformation of about 6 mm in the cable. TDR is proved effective real-time subsurface monitoring system, and this is a first attempt to understand its performance for Indian mining conditions for future implementation. This type of monitoring was performed for the first time in India. This research work is a part of S&T project, funded by Ministry of Mines (MoM), Government of India(GoI), supported by M/s Dongri Buzurg (DB) Mine, Manganese Ore India Limited, Nagpur, Maharashtra and implemented by Mining engineering department, National Institute of Technology, Rourkela.