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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

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-50

0

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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?