sink hole presentation

8/3/2019 Sink Hole Presentation

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Sinkhole rehabilitation at RustenburgChrome Mine: Lanxess Mining Pty Ltd

David Nyungu


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Content

Location of Rustenburg Chrome Mine and sinkhole

Background on the sinkhole occurrence and definition of

problem

Challenges faced before and during sinkhole rehabilitation

Rehabilitation of alternative ingress and egress declines

Sinkhole rehabilitation

Outlook of the rehabilitation project so far


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Location of Rustenburg Chrome Mine


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Schematic representation of the sinkholelocation at Rustenburg Chrome Mines 7 East# Declines


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Aerial view of the 7 East # collars and surfaceinfrastructure


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Sinkhole occurrence depicted in 2005 withprojected outlines of old pit highwalls


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Surface sag captured in 2005 30m from theworkshops


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Sinkhole subsequently filled with compactedwaste material temporarily solving the problem


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A shot through the resultant holing into theDecline roadway taken from surface


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Brake test ramp slump noticed in 2010


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Surface tension cracks at the Brake Test Ramp(2010)


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A shot taken from the 7 East # Decline roadwayduring the peak of the 2010 rain season


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Replacement of old rotten timber leggings andcross beams with steel sets and void fill


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Decline hanging and side walls covered withvoid fill. Void fill sagging from water pressure


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Brake test ramp excavated out showing theestimated sink hole position (2011)


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Sloughing of waste rock dump adjacent to thesink hole position on surface (2011)


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Free dig waste rock material previously filledinto the sinkhole being excavated (2011)


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Challenges faced during rehabilitation process

Uncertainty of the exact position of the sink hole and its extend

below surface.

Uncertainty over the rock mass strength hosting the sinkhole.

Excavating blind to expose the sinkhole.

Void fill previously applied in the Declines covered the existing

pillars from assessment for strength and failure. Since the 7 East Declines is the main conveyance Decline there

was need to have a secondary transport Decline.

Onset of the rainy season produced a danger of inundation of

the exposed sink hole. Unavailability of dedicated equipment and machinery delayed

progress


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Extrapolated sinkhole position in relation tothe position of the Belt Decline


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Tent required to cover the sinkhole fromingress of rain water


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The Overstep Decline used as alternativeaccess required support rehabilitation


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Alternative access ways into the mineduring the sinkhole rehabilitation

processThe Overstep Decline and the 7 West Decline


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Decline collared in weathered Norite withportal cut in topsoil


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Weathered Norite hosting the Declines


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Soft weathered Norite walls hosting theDeclines


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Very friable hanging rock mass in the OverstepDecline


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Outlook in the Overstep Decline after a coat ofThin Sprayed Liner (TSL)


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Outlook in the Overstep Decline after supportrehabilitation. RSJ sets with timber cribbingand void fill were installed


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Outlook in the Overstep Decline after supportrehabilitation


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Sinkhole rehabilitation process Remove and re-build the test ramp to a new location

Excavate all fill material from the sinkhole down to the opening in the

Decline roadway Construct a strong base using RSJ steel sets for the concrete plug at the

bottom

Strap and re-enforce all pillars in the Declines

Construct a 45 MPa strength concrete plug at the sinkhole opening in the

Decline

Fill sinkhole with cemented waste aggregate mixed with a binding

accelerator and compacted

Construct a concrete slab and drainage around the sinkhole

Fence off and barricade sinkhole area from traversing by machinery andtrucks


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Excavation of waste fill material and timberpacks previously filled into the sinkhole

k d i b k i l f d


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Waste rock and timber pack material free dugleaving fairly competent weathered Noritewalls

P h b k b h t d t t


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Push back benches were excavated to createaccess ramps for the excavators reach andstable walls

P h b k ll d th i kh l


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Push back walls around the sinkhole

H li t d th D li d


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Holing towards the Decline roadway

Push back area around the sinkhole


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Push back area around the sinkhole


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Outcome

Sinkhole rehabilitation work is still underway

Sinkhole excavation was carried out successfully without injuries or damage

to equipment

Expert advice and people with previous experience with the sinkhole

occurrence were consulted

Sinkhole limits were exposed after excavation of waste fill material allowingfor better planning and design of rehabilitation and filling

The extrapolated position and orientation of the sinkhole were confirmed

The cemented waste fill material will be set on a competent base and all

water sources diverted

Once set the concrete plug should prevent water ingress into the declines

Surface run water drainage and bunkers should divert water from entering

the sinkhole area.

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