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Large Scale Backfilling of Shallow High-Extraction
Room and Pillar Coal Mines for Residential Development
Large Scale Backfilling of Shallow High-Extraction
Room and Pillar Coal Mines for Residential Development
Presented by Ray Predika, P.Eng.
Stewart Creek Phase 1Stewart Creek Phase 1
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Site LocationSite Location
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Located in Canmore, Alberta CanadaLocated in Canmore, Alberta Canada
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Stewart Creek DevelopmentStewart Creek Development
Medium density Residential – 3 story Apartments and Townhouses
2.5 acres required Backfilling
“Paste” was selected as the backfill material over low-strength concrete
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What is Paste?What is Paste?
A non-segregating mixture of solids and water that possesses a yield stress, exhibits minimal water bleed when left idle and has no critical flow velocity.
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Paste Feed MaterialsPaste Feed Materials
Inorganic soils
Mine/Quarry waste
Mine/Quarry plant tailings
Mine/Quarry pre-stripping
Screened to use the portion less than ¾”
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Post-Screening GrainsizePost-Screening Grainsize
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Screening PlantScreening Plant
Concrete vs PasteConcrete vs Paste
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ConcreteConcrete
Cost -- $ 65 cy
Strength – 5MPa (700psi) minimum for a pumpable mixture
8 to 10 wt% cementing materials
Max radius in rubble 2.5m (8ft)
Max pumpable distance in tunnels 10m (30ft)
Uses commercially available ingredients
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Paste BackfillPaste Backfill
Cost – $43 cy
Strength – 500kPa (70psi) to 2MPa (280 psi)
4 wt% cementing materials
Slump variable between 1” and 10” with very little change in water content (or strength)
Max pumpable radius in rubble 10m (30ft)
Max pumpable distance in tunnels 100m (300ft) or more
Uses locally derived materials
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So where are the real cost savings?So where are the real cost savings?
Drilling costs are reduced by about 75%
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Stewart Creek Phase 1 LayoutStewart Creek Phase 1 Layout
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No. 4 Mine, No. 4 SeamNo. 4 Mine, No. 4 Seam
High-Extraction Room and Pillar
15 degree dip
2.8m (9 ft) extraction height
Currently largely collapsed
8m (25 ft) high rubble pile
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No. 4 Mine, No. 4 SeamNo. 4 Mine, No. 4 Seam
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Up-dip end of No.1 Morris Seam HeadingUp-dip end of No.1 Morris Seam Heading
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Rubble in BoreholeRubble in Borehole
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Rubble in BoreholeRubble in Borehole
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Primary injectionPrimary injection
15m (50 ft) grid – 78 holes
Max Volume cut-off (30% X rubble thickness X area of 50 ft diameter circle)
Max pressure cut-off (twice overburden)
Primary Volume injected: 7596 m3 (9935 cy)
Total duration: 60 days
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Secondary InjectionSecondary Injection
One hole for every 4 primary holes – 42 holes
Max Volume cut-off (rubble thickness X area of 50 ft diameter circle)
Max pressure cut-off (twice overburden)
Secondary Volume injected: 72 m3 (94 cy) (0.9% of primary)
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ReichDrill 650 ReichDrill 650
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Injection Plant SetupInjection Plant Setup
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Wellhead SetupWellhead Setup
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Mixer truckMixer truck
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Three stages of pressurizationThree stages of pressurization
Flat-line, near zero well head pressure
nominal pressure maintained at well head
Refusal
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GA05-022GA05-022
Injection time – 2 hr 40min
Volume injected – 98 m3 (128 cy)
Max pressure – 170 psi
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Injection Pressure LogInjection Pressure Log
-200
-150
-100
-50
0
50
100
150
200
250
300
350
7:40:48 8:09:36 8:38:24 9:07:12 9:36:00 10:04:48 10:33:36 11:02:24
Time
Inje
ctio
n Pr
essu
re (p
si)
raw
filtered
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Paste flowing out of BHPaste flowing out of BH
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Paste flowing into BoreholePaste flowing into Borehole
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Other Undermining workOther Undermining work
Myra Falls Crown Pillar Stabilization
Ground deformation estimation
AMD/ARD solutions
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Who’s Golder Associates?Who’s Golder Associates?
Global group of consulting companies specializing in ground engineering and environmental services
Has more than 4,500 people operating in local companies and 100 offices across Africa, Asia, Australia, Europe, North America and South America
Golder Associates Inc. (U.S.) works out of 31 offices across the country from Anchorage, Alaska to Boca Raton, Florida
Projects range from decontaminating and decommissioning a submarine cable manufacturing facility to investigating groundwater supplies, ensuring slope stability or conducting an Environmental Site Assessment for potential brownfieldsites
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Thanks to…Thanks to…
Three Sisters Mountain Village Ltd. (www.tsmv.ca)
LPR Contracting
Beck Drilling and Environmental
Golder Paste Technology Ltd.
TRB Subcommittee
ITGAUM
QUESTIONS?
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