Development and Field Testing of a Seismic System for Locating Trapped Miners - Progress Report. Yi Luo, Keith A. Heasley and Syd S.

Transcription

1 Development and Field Testing of a Seismic System for Locating Trapped Miners - Progress Report Yi Luo, Keith A. Heasley and Syd S. Peng Department of Mining Engineering West Virginia University Acknowledgements This This research project is sponsored by West Virginia Coal Energy Research Bureau West Virginia Office of Miners' Health Safety and Training WVCMI/WVCA Joint Meeting 2 1

2 Presentation Outline Introduction Seismic Methods Proposed WV Seismic Location Systems Field Tests Summary Future Research Works WVCMI/WVCA Joint Meeting 3 Introduction An underground coal mine accident left miners trapped All communications systems compromised - no way to determine the locations of the survivors As instructed, the trapped to signal on the half-hour hour by pounding How to determine the their locations? A special seismic location system seems to be an answer. Issues to study Hardware capabilities and limitations Specialized software Special conditions WVCMI/WVCA Joint Meeting 4 2

3 Seismic Methods Major components of a seismic system Vibration inducer to generate unique and powerful seismic signals to travel the desired distances in the ground Signal receivers (geophones) motion detectors to detect the arrival time and intensity of the ground motion Interpretation software Filtering useful signal from noises Determining locations of the desired features WVCMI/WVCA Joint Meeting 5 Seismic Methods Seismic signals propagate in rock in 2 main forms: P waves primary, compression waves S Waves secondary, shear waves Typical P wave velocities Sedimentary rocks, 600 6,700 m/s Water, 1450 m/s Air, 330 m/s Signal attenuation rate (frequency dependent)? P Wave Propagation S Wave Propagation WVCMI/WVCA Joint Meeting 6 3

4 Geophones Ground motion > > Housing motion Differential movement between coil and magnet Electrical current inducted Output electric voltage depends acceleration Seismic Methods Tri-axial, high precision geophone Deserve most considerations for our system Sensitivity for weak signals Directional (unidirectional vs tri-axial geophones)? WVCMI/WVCA Joint Meeting 7 Reflective Seismic Methods Source and geophones located on surface Signals reflected from subsurface interface were received Common applications: oil or geological explorations, etc. WVCMI/WVCA Joint Meeting 8 4

5 Penetrative Seismic Methods Seismic source located on the other side of the features to be investigated Applications: Downhole seismic geological explorations, etc. Principle similar to the seismic system for locating trapped miners WVCMI/WVCA Joint Meeting 9 MSHA Seismic Location System Equipment Truck Display Unit Developed in the 70 s Older electronic technology There have been some modifications over the years, but it is generally agreed that it is in need of replacement Three large vehicles WVCMI/WVCA Joint Meeting 10 Generator Truck Equipment Trailer 5

6 Proposed WV Seismic Location Systems WV State Mandate Portable seismic locating systems at each of the four regional office for use in locating trapped miners A trained staff at each regional office capable of delivering the portable system to the mine site and to deploy the system immediately and without delay Feasible because of Advancement in Electronic, Computer and Information Technologies Small sized and feature rich geophones Digital transmission and storage of seismic signals Enormous computing power packed in a notebook PC Digital filtering and triggering for enhanced resolution. Data processing and interpretation WVCMI/WVCA Joint Meeting 11 WV Seismic Location Systems Research Objectives Determine and Acquire the best available seismic location system. Conduct field tests to determine the capabilities and limitations of the system Depths, Distances Geology Multiple seams, gob areas, etc. Develop mathematical algorithm and user-friendly computer program for Picking the event signals from noisy background Pin-pointing the locations of the signal sources Long Term: Help develop the hardware and software for a practical location system for trapped miners. WVCMI/WVCA Joint Meeting 12 6

7 WV Seismic Location Systems Technology Requirements Portable Small enough to carry in regular vehicles Require no power beyond portable batteries Easily Deployed Can be deployed in 60 minutes Can be moved quickly Can interconnect with additional units Rugged enough to survive repeated use. WVCMI/WVCA Joint Meeting 13 WV Seismic Location Systems Technology Requirements Simple to Operate Software should be automated enough for on-site technician Produce accurate results in real-time Ability to produce maps Ability to save and transmit seismic data to consulting seismic experts to assist in interpretation Successful Location Within one or two coal pillars for searching and rescuing operations Sub 10-ft accuracy for drilling lifeline holes from surface WVCMI/WVCA Joint Meeting 14 7

8 Field Tests Two Field Tests Performed Test Site No. 1 4 West Mine, Dana Mining Co., Southwest PA Room and Pillar coal mine Depth: ~ 420 ft Participants: Weir Jones, Hilti Mining Success: Yes Test Site No. 2 Federal No. 2 Mine, Peabody Energy, North WV Longwall coal mine Depth: 800 1,000 ft Participants: Weir Jones and ESG Success: Unsure WVCMI/WVCA Joint Meeting 15 Test Site No. 1 Field Tests WVCMI/WVCA Joint Meeting 16 8

9 Test Setup at Site No. 1 Four underground signaling sites spaced 70 ft apart Four surface geophone locations, two buried in drilled holes (1 and 2) and two just simply buried in the soil (3 and 4) WVCMI/WVCA Joint Meeting 17 Field Tests Seismic Equipment Geospace 32CT geophones Terrasciences 24 channel, 24 bit digitizer sampling at 2 khz Notebook PC & car battery WVCMI/WVCA Joint Meeting 18 9

10 Test Protocol Signaling devices Hilti mining tools: DX76, Hilti DX460, Hilti DX462 8 lb sledge hammer Crib block Signaling Locations Roof bolt Roof rock Pillar rib 5 5 impacts, wait 30 seconds, next device Underground events precisely timed and recorded WVCMI/WVCA Joint Meeting 19 Received Event Signal Received signal for vibration generated by crib block Expanded View Event at frequency Hz WVCMI/WVCA Joint Meeting 20 10

11 Effects of Offset Distance 0 ft offset, D = 420 ft 70 ft offset, D = 426 ft, 9.5 o Geophone No detectable signal when offset is 210 ft, D = 470 ft, 26.6 o WVCMI/WVCA Joint Meeting ft offset, D = 443 ft, 18.3 o Directional Components Z X/Y Z component Need tri-axial geophones? X component WVCMI/WVCA Joint Meeting 22 11

12 Effects of Geophone Installations Buried in drilled hole about 2 ft deep About 4 times stronger signal in drilled hole Simply buried WVCMI/WVCA Joint Meeting 23 Peak Particle Velocities Crib Block on Roof Rock Hammer on Roof Rock Crib Block on Roof Bolt Crib Block on Roof Rock Hammer on Roof Rock Crib Block on Roof Bolt Crib Block on Roof Rock Hammer on Roof Bolt Hammer on Roof Rock Approx. Noise Level Offset = 140 ft Offset = 70 ft Offset = 0 ft Particle Velocity, μm/s For different vibration inducers at field test site No. 1 (420 ft deep) Received crib block signals (lower frequency) are 20-40% stronger than hammer signals better choice! WVCMI/WVCA Joint Meeting 24 12

13 Findings from Field Tests No. 1 Crib Block on the Roof Rock appeared to be the strongest Crib on Roof Bolt Hammer on Roof Rock Hammer on Roof Bolt Hilti tools, though very powerful, were hardly detected? Higher Frequencies? Good detection out to 140 ft (18 degrees) Not at 210 ft (26 degrees) WVCMI/WVCA Joint Meeting 25 Findings from Field Tests No. 1 Mostly Vertical Ground vibration Buried geophones provided about twice the peak particle velocity Better connection? Less soil? Increase in distance not totally responsible for signal attenuation Polarized source? Horizontal bedding? WVCMI/WVCA Joint Meeting 26 13

14 Algorithm to Detect Event Signals Determine standard deviation from incoming data, σ Set an appropriate abnormality number, N Detections Condition If V > N σ If V < N σ Detection Event signal Noise Action Take Record data for further analysis Delete data from the files Amount of data to be stored and analyzed will be greatly reduced Before After MB zip files 4.77 MS Excel file or about 1 MB zip file WVCMI/WVCA Joint Meeting 27 Algorithm to Detect Event Signals Before processing, data from every 30-second period occupies an entire Excel file (about 4.8 MB in size after compressed) After processing, all data fit in one Excel file and can be plotted ted together 8.E-05 6.E-05 GP1-Z GP2-Z 4.E-05 GP3-Z GP4-Z 2.E-05 GP5-Z GP6-Z 0.E+00-2.E-05-4.E-05-6.E-05-8.E-05 8:58:34 9:01:26 9:04:19 9:07:12 9:10:05 9:12:58 9:15:50 9:18:43 9:21:36 9:24:29 9:27:22 9:30:14 9:33:07 9:36:00 9:38:53 9:41:46 9:44:38 9:47:31 9:50:24 9:53:17 9:56:10 9:59:02 10:01:55 10:04:48 10:07:41 Signaling at Signaling at Signaling at 0 ft Offset 70 ft Offset 140 ft Offset WVCMI/WVCA Joint Meeting 28 14

15 Algorithm to Detect Event Signals Expanded view of the detected events when signals were sent from 0 ft offset location Times and magnitudes of detected events clearly shown Signaling Location 8.E-05 6.E-05 4.E-05 2.E-05 GP1-Z GP3-Z GP5-Z GP2-Z GP4-Z GP6-Z 0.E+00-2.E-05-4.E-05-6.E-05-8.E-05 9:04:19 9:04:28 9:04:36 9:04:45 9:04:54 9:05:02 9:05:11 9:05:20 9:05:28 9:05:37 9:05:46 9:05:54 9:06:03 9:06:12 9:06:20 9:06:29 9:06:37 9:06:46 9:06:55 9:07:03 9:07:12 WVCMI/WVCA Joint Meeting 29 Field Test No. 2 A longwall mine Two sets of seismic equipment deployed Two Sites Prepared Site No. 1 At the toe area of a steep hill Beside a large water pond Depth: ft Tests conducted Site No. 2 Top of the hill Depth: ~ 1000 Tests not conducted WVCMI/WVCA Joint Meeting 30 15

16 Unable to detect event signals by both sets of seismic equipment Noisy background? Sites close to mine shaft, refuse disposal area? Depth too large (~ 800 ft)? Efforts continue to find why s Field Test No. 2 WVCMI/WVCA Joint Meeting 31 Summary Crib block and sledge hammer as more appropriate signaling tools to pound on the roof rock An effective and portable seismic system for locating trapped miner may be achievable for most West Virginian coal mines A simple algorithm can be used to automatically detect the event signals and to reduce data volume More research works needed to have better understanding of the capabilities, limitations and ways to improve the system, testing procedure, and data processing and interpretation WVCMI/WVCA Joint Meeting 32 16

17 Future Research Works Purchase our own seismic system To reduce dependence on equipment venders for future testing To conduct tests more frequently and at varying conditions to fully understand its capabilities and limitations as well as ways s to improve Develop the algorithm and computer program for locating the seismic source more accurately for drilling lifeline vertical holes Investigate effects of offset distance/angle Explore possibility of wireless seismic system in our applications WVCMI/WVCA Joint Meeting 33 Future Research Works Wireless Seismic System WVCMI/WVCA Joint Meeting 34 17

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