# Strata Control by Roof Blasting for Bord and Pillar Mining Method in Mechanized Depillaring Panels
## 6 Instrumentation and Monitoring  
Strata behavior during the proposed mechanized depillaring of the panel needs to be studied through field instrumentation and monitoring. The purpose of the field instrumentation is to enhance the safety of the working to protect men and machinery from any risk and also to increase the production and productivity of the mine along with verification of the design of different structures involved. It may provide some quantitative values of strata movement and concentration of induced stresses in and around the workings for a better understanding of the rock mass behavior and further, in optimization of the design. It is important to study roof sagging in galleries, with special attention to the junctions using roof extensometers. It is always good to opt for a simple approach to instrumentation and monitoring. However, attention is to be paid to the selection of durable and robust instruments, suitable for the underground coal mining environment. Attempts are made to monitor the readings of the instruments nearly continuously in time. The density of the instruments at the studied sites is optimized through available experiences of such monitoring. A preliminary instrumentation plan for monitoring the performance of underground structures in panels is shown in 26, respectively. This plan may be modified on the extent of development possible, the geological discontinuities unraveled, strata control experiences during work in the panel at different stages, and the selection of pillars extracted from the panel. It should be noted here that extra caution is needed while correctly installing the different geotechnical instruments before commencement of MD operation. An attempt is to be made to monitor the readings of the instrument installed in the active mining zone (AMZ) frequently. Actions to be taken during depillaring operation on the basis of roof displacement are shown in Table 9. Details of the instruments proposed to be used for strata control monitoring in these panels are mentioned in Figure 26. Considering the panel for CM-based mechanized depillaring at this mine, extra caution has been taken to maintain  
Figure 25: Proposed method of charging of blast holes. safety during pillar extraction by the installation of a series of geotechnical instruments at suitable locations and comprehensive monitoring. Figure 26: Proposed location of different instruments to be used in the panel. \begin{table}
\begin{tabular}{c c c} \hline
**SI. No.** & **Convergence Observation** & **Action to Be Taken** \\ \hline
1 & up to 5 mm & No action required, monitoring should be continued but must inform to \\  & & Strata Control Officer and discussed. \\
2 & 5–10 mm & Inform the Strata Control Officer, Supervisor, and Manager special \\  & & attention at the observed location. \\  & & If sudden increase \\
3 & 10–15 mm & Stop development work, assess conditions, and install additional support \\  & & in the said zone by 1.7 m length resin grouted bolts with a ’W’ strap. \\  & & Flexi bolts of 1.7 m length should be installed \\  & & Immediately inform the Strata Control Officer, Supervisor, and Manager. \\  & & Stop development work and withdraw the machine to the outby side of the \\  & & work place. \\
4 & \textgreater{}15 mm & Additional supports to be installed in the gallery based on the consultation \\  & & of the mine manager with the scientific institute in the said zone. \\  & & All workmen and machines shall be withdrawn to a safe place within the \\  & & gallery, and no work related to production shall be allowed. \\ \hline \end{tabular}
\end{table} 
Table 9: Actions to be taken during depillaring operation. The main roof fall is expected to occur at an average roof span of around 8700 m\({}^{2}\) in the goat. Since the width of the panel is not sufficient during the first five rows (33 DW-29 DW), the, first main roof fall would not occur until working in 29 DW. It is expected that the main roof fall will take place during or after extraction in 28 DW.