Measuring pillar width in trona mines using a body wave based in-seam seismic technique

A body wave based in-seam seismic technique was developed for measuring the width of barrier pillars in trona mines for the purpose of assessing the dissolution rate of barrier pillars when in contact with water, a critical problem faced by the trona industry. The main difference between this technique and the conventional in-seam seismic technique is that this technique makes use of high frequency P- and S-wave signals. The technique was tested at two trona mines in Wyoming. Three mine sites were utilized for the study, where the pillar widths varied from 82 to 107 m. The velocity survey showed that the trona seam under study was very stable for the wave propagation with a mean standard deviation of only 1.5% for both P- and S-wave velocities. High frequency signals, in the range of 2500–5000 Hz, were utilized for high resolution surveys. Three types of reflected signals were observed, which are P-waves, S-waves and S-waves due to the mode conversion at the seam-void interface. The elliptical mapping method was used to accommodate highly irregular survey lines encountered in underground mines. The method also allowed all reflected signals to be used simultaneously and, as a result, significantly increased the physical data available for the pillar width calculation. The average mapping error was estimated within ±4.6 m, or about 5% of the pillar width. This body wave based in-seam seismic technique may also be utilized for other mines, such as limestone mines, where the seam impedance is similar to or higher than the impedance of surrounding rocks.

► Developed for assessing pillar dissolution rate, a main problem faced by trona mines ► High frequency signals, up to 5,000 Hz, were utilized for high resolution surveys. ► Tested extensively at two trona mines with pillar widths varied from 82 to 107 m. ► Officially demonstrated to US Mine Safety and Health Adm. and trona industry. ► Applicable for other mines with high seam impedances, such as limestone mines.