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By Alex Milev, Steve Spottiswoode and Thabang Kgarume
Coseismic and Aseismic Deformations of the Rock Mass Around Deep Level Mining By Alex Milev, Steve Spottiswoode and Thabang Kgarume
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Coseismic and Aseismic Deformations of the Rock Mass Around Deep Level Mining
Definition of quasi-static and dynamic deformations Integrated monitoring systems Underground sites Data analysis Case study of M 2.1 seismic event at Mponeng mine Coseismic and aseismic deformations related to mining Conclusions
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South Rand VAAL RIVER WEST WITS Moab Khotsong Mponeng Tau Lekoa /
Johannesburg VAAL RIVER WEST WITS Moab Khotsong Mponeng Tau Lekoa / Goedgenoeg Tona Ko panang Great N oligwa Weltevreden Kloof Ergo Tau Tona
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Tilt – monitoring system and data analysis
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Cubby Borehole Geophones (G GY & GZ) Side Wall (SW) Geophone
Tilt meters (T1 &T2) Cubby Borehole Geophones (G GY & GZ) Data recorder Side Wall (SW) Geophone Footwall Wall (FW) Pier 0.7 m into the Footwall SW Tilt meter
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Mponeng Mine Level 113 Cross-cut 45
Borehole Geophones GX, GY & GZ T2 +TX2 +TY2 T1 +TX1 +TY1 SW FW
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Mponeng Mine Level 116 Cross-cut 45
JP/DE G3 TUNNEL y CUBBY T 2 x x 1.0 m x T 1 JP/DE y BB y G1 G2 G1, G2 and G3 – CSIR geophones T1 and T2 – CSIR Tiltmeters BB – USGS Broadband JP/DE – Japan/Germany Instrumentation
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Acquisition system Dynamic section Quasi-static section
Store readings from both geophones and tilt meters in a trigger mode Store readings from the tilt meters every minute
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Coseismic and aseismic tilt
Coseismic tilt Aseismic tilt Time Aseismic tilt is measured as a change in the tilt between two consecutive events
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Coseismic and aseismic tilt
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Tilt during the “fast” seismic event
-10 10 20 30 40 50 60 70 80 -20 -15 -5 5 15 Time (min) Tilt (microradians) Tilt X Tilt Y Tilt before 'fast' seismic event 08/02/ :45:51 Tilt after 'fast' seismic event Before tilt After tilt
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Example of “slow” seismic event
Tilt before and after a "slow" seismic event (2006/07/06 07:36) -60 -50 -40 -30 -20 -10 10 20 30 40 50 100 150 200 250 Time (minutes) Tilt difference (microradians) x (T1) y (T1) x (T2) y (T2) Tilt before and after a "slow" seismic event (2006/10/16 16:02) -200 -150 -100
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Tilt associated with M=2
Tilt associated with M=2.1 seismic event on 12/27/2007 located close to the Site 116 Mponeng mine
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Tilt associated with M=2
Tilt associated with M=2.1 event on 12/27/2007 located close to the Site 116, Mponeng mine
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Tilt changes associated with M=2
Tilt changes associated with M=2.1 event on 12/27/2007 located close to the Site 116, Mponeng mine
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Closure – monitoring system and data analysis
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Instrumentation Closure Meter PVD Triaxial geophone meter Closure
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Underground site at Klerksdorp area
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Strong ground motion and closure
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Coseismic and aseismic deformations relative to mining
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Conclusions The coseismic tilt and closure suddenly increase during the seismic event and blasting Much of quasi-static deformations were found to occur independently of seismic events and were described as ‘slow’ or aseismic events The tilt before and after a seismic event shows lack of after-tilt in most of the cases studied The after-tilt associated with M=2.1 seismic event is a result of the aftershock sequence following the event Coseismic deformations are associated with stress regime outside the fracture envelope while the aseismic deformations are associated with mobilization of fractures and stress relaxation within the fracture envelope
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Thank you
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