Abstract
The geological condition is essential for mining design and disaster control in underground coal mines. The present research focuses on the real‐time assessment method on rock mass condition during drilling boreholes. In situ comprehensive experiments were carried out using three methods, which are measurement while drilling (MWD) system, vibration measurement while drilling (VMWD) system, and borehole camera detecting system. In the MWD system, the operating parameters of the drilling machine were recorded, and a dimensionless index Id based on the collected parameters was adopted to assess the geological condition along the borehole. The results show that the state of rock mass can be well classified using the MWD system for both the cross‐layer and in‐seam boreholes. In the VMWD system, the vibration of the drilling bit was monitored, and the signal was analyzed in both time domain and frequency domain. The results indicate that the rock mass condition can be quantitatively evaluated using the mean square value of the signal and qualitatively estimated using the energy of the spectrum. In the borehole camera system, the photos of the rock mass along the borehole could be well captured, and the identified rock mass condition was used to verify the results of the MWD and VMWD systems. Comprehensive compassion between the results from the three systems shows that all the methods can give valuable information for the geological condition, and the outcomes of the different methods are generally comparable. For practical purposes, the advantages of the involved three detecting systems are discussed.
Highlights
Limited by the resolution of the photos, it is difficult to classify the state of rock mass into four categories, as in the measurement while drilling (MWD) and vibration measurement while drilling (VMWD) systems
Taking the cross-layer borehole No 12 and in-seam borehole No 22 for an example, we give the curves of the index Id from the MWD system and the root mean square (RMS) from the VMWD system in Figure 20 for the cross-layer and in-seam boreholes. e classification criterions are shown in the figure
To determine the geological condition in the underground coal mines, comprehensive real-time methods are tested in the present study, which are MWD system, VMWD system, and borehole camera system. e drilling process of crosslayer and in-seam boreholes is monitored. e main conclusions are as follows: (1) In the MWD system, the operating parameters of the drilling machine are recorded
Summary
Erefore, it is not suitable to determine the geological condition only based on the values of pressure parameters or drilling rate, when the drilling machines are different. Where k is a constant and for the hydraulic motor used here is 60, when the unit of M0 is N·m and P1 is MPa. en, the resistance torque Mr may be determined by the import pressure of the hydraulic motor P0, which is monitored when the bit rotates but without cutting the rock. For the in-seam borehole No 22 (Figure 11(c)), the monitored pressure is lower than those in the cross-layer boreholes and the Id values are all over 3. Compared to those of the cross-layer boreholes, the variation of index Id is less. An algorithm with a threshold can be used to eliminate the time intervals
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