Layers of possibilities

A Burst-Prone Ground Support Study at Morrison Mine

Sia Taghipoor Dan Laing

Serge Tousignant Dean Switzer

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18-Apr-26 Numerical Investigation of Rockbursts at Morrison Mine 2

Levack Mine: Location

The Levack Mine is located in Levack Township within the City of Greater Sudbury, approximately 45 km northwest of the city.

The property lies immediately east of the Town of Levack, east of KGHM’s McCreedy West Mine and west of Vale’s Coleman Mine operations.

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The Levack Mine is situated on the margin of the 1.85 Ga Sudbury Structure, a remnant of a deformed multi-ring impact crater.

Sudbury Igneous Complex (SIC), its associated offset dykes, and footwall-hosted pseudotachylite, locally known as Sudbury Breccia (SUBX).

Mining operations are currently focused on footwall Cu-Ni-PGE mineralization within the Morrison Deposit.

Introduction

Mining-induced seismicity is directly associated with the interaction of mine excavations and the local rock mass (including geological structures) with regional and local stress fields (Urbancic & Trifu, 1997).

Due to the steep in-site stress gradient, stiff rock mass and significant mining depths, mining-induced micro-seismicity is a common hazard faced at many operations located within the Sudbury Igneous Complex.

Seismic energy is released when the local stress conditions approach and / or exceed the shear strength of the rock mass or pre-existing geological structures respectively. It can adversely affect the safety of mine personnel and mine productivity.

As mining continues to greater depths in the future, the adverse effects of micro-seismic events on mining personnel and productivity is likely to have substantial economic implications.

Manifesting as strain/pillar bursting and stress induced damage, managing the risk associated with micro-seismicity is typically achieved through a combination of approaches.

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Review of Seismicity Since 2013

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A Review of Large Seismic Events at Morrison Mine

Some of the recent large events are believed to be structurally driven, and are mainly related to the H-Fault.

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The number of large events over +1.5 Mw has been increasing.

Controls: Microseismicity Risk Mitigation Techniques

Mine design

Numerical modeling to identify high stress areas or fault/structure behavior

Access location (affects the number of working faces)

Diminishing pillars

Top-Down, no diminishing pillar, shotcrete delay/cost, small opportunity for waste fill

Bottom-up mining, diminishing pillars/seismicity problem, requires special attention in design, great opportunity to reduce cost by dumping waste

Microseismic monitoring system

Re-entry protocols

Destressing methods

Burst prone ground support

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Focus of this presentation

Class A Burst Prone Ground Support

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Why Do We Install Class A?

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Class A Extended Down The Walls?

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Why Do We Install Class Z Ground Support

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Risk of Microseismicity at Morrison Mine

A dynamic reinforcement system was designed to withstand loads associated with a peak particle velocity (PPV) of 1.3 m/s.

This PPV can be induced by a large seismic event of 2 Mw located at 5 meter distance from excavation boundary, or larger events at farther distance.

The burst-prone ground support (the dynamic reinforcement system) is installed in areas that are assessed as being at ‘high’ and ‘severe’ levels of micro-seismic risk.

High Risk: area is identified as burst-prone but no seismic activities has occurred yet,

Severe Risk: area has already experienced large seismic events (Mag>+1.5)

The risk of seismicity is identified through numerical modeling conducted using ITASCA’s FLAC 3D platform.

Super swellex was the main component of Morrison mine’s burst-prone support.

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Burst-Prone Ground Support Study

Low productivity of Super Swellex (Atlas Copco) installation with hand held drilling equipment (jacklegs and stoppers),

Drilling and installing a 12 ft super swellex would take approximately 30 minutes.

A short boom jumbo was designed and assembled for drilling for super swellex in small headings (8 ft boom), which was a great achievement for health and safety of the crews,

However the number of the bolting jumbos was limited compared to the number of working headings.

There was a need for a more efficient (less labor-intensive) burst-prone support,

As a part of an initiative, alternative ground support systems were investigated in 2016.

Versa BoltTM (Mansour Mining) was considered as alternative.

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Short-Embedment Pull Tests

This included an extensive number of short-embedment pull tests conducted on two different types of burst-prone ground support; Versa bolts and Super Swellex Bolts.

Most of these pull tests were focused on the Versa bolt to better understand the required anchorage length and the impact of related parameters such as

Rock type (ore/waste),

Hole size,

Resin cartridge diameter.

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Super Swellex Bolts

18-Apr-26 15 http://www.atlascopco.ca http://www.slideshare.net/

The Swellex bolt and is made from a folded thin-wall steel tube.

Bushings are pressed onto both ends of the bolt, which are sealed by welding.

The lower bushing has a small hole through which water is injected into the bolt at high pressure to expand the steel tube.

During the expansion process, the Swellex bolt compresses the rock surrounding the hole and adapts its shape to fit the irregularities of the borehole

Versa Bolts

The Versa bolt has extremely high elongation properties.

Four deformation paddles are placed at the end anchor to provide well-anchorage.

In the case of a rock burst, the two smooth sections between the anchors (L2 and L3 sections in figure) will stretch.

The high elongation capacity of bolt provides high energy capacity to maintain the dislodge material.

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www.mansourmining.com

Part 1: Versa Bolts Short-Embedment Pull Testing

Test Set-up

Material and Equipment:

20 mm 7 ft Versa bolts

33 mm (new) bits and 30.1 mm (used) bits,

Jackleg application

Holes drilled to a depth of approximately 83 inches.

Resin cartridges are 18”, 24”, and 27” long

Ground Condition

Both ore (mainly Chalcopyrite) and waste rock (mostly Sudbury Breccia and Granodiorite Gneiss)

Tests conducted in walls

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Test Results: Ore vs. Waste Rock, 28 mm Diameter Resin Cartridges

With 27” long 28 mm diameter resin cartridges, the bolts installed in waste rock showed a stiffer bond.

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It can be related to over-size holes in ore as with the same bit, holes drilled in ore are on average 3-4 mm larger than holes in waste rock.

Test Results: Ore vs. Waste Rock, 30 mm Diameter Resin Cartridges

With 24” long 30 mm diameter resin cartridges, bolts installed in ore and waste all behaved very similarly, with the exception of one bolt in ore, which was slightly more deformable.

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It can be related to the volume of resin inserted in the holes. 24” long resin cartridges provide enough rock/resin/bar bond stiffness to hold the anchor in place strongly and let the bar yield.

Test Results: 18” and 24” Long 30 mm Dia Resin in Ore

24” long resin behaved slightly stiffer as it creates longer bond.

Generally both lengths provide enough stiffness to let the bar yield.

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Test 4-5 – 24”- 30 mm, used bit, ore

Test 4-5 – 24”- 30 mm, used bit, ore

Test 4-5 – 24”- 30 mm, used bit, ore

Test M-1 – 18”- 30 mm, used bit, ore

Test M-2 – 18”- 30 mm, used bit, ore

Test M-3 – 18”- 30 mm, used bit, ore

Part 2: Super Swellex Short-Embedment Pull Testing

Test Set-up

Material:

8 ft super swellex

51 mm new bits

Jumbo application

Holes drilled to a depth of approximately 83 inches.

Inflation section was kept 24 inches by installing expansion-restricting sleeves

Ground Condition

Both ore (mainly Chalcopyrite) and waste rock (mostly Sudbury Breccia and Granodiorite Gneiss)

Tests conducted in walls

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Test Results: Ore versus Waste Rock

Inconsistent results were obtained, specially for tests in waste rock,

Generally the tests carried 9 to 17 tones in both ore and waste rock,

All test slip after 10 to 30 mm of displacement.

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Comparison and Discussion

Versa bolts carried more loads with smaller (2ft) anchorage requirement but showed a more rigid behavior,

Super Swellex bolts provide more flexible rock-bond system,

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Summary and Conclusion

The results indicate that Super Swellex bolts necessitate longer anchor while providing a less rigid anchorage.

However, Versa bolts require shorter anchorage length but are more rigid.

A more deformable bond system provides more efficiency to dissipate the energy of a rock burst while a shorter anchorage length provides more cost-efficiency of operation.

Two classes of burst-prone ground support were designed based on each of these bolts depending of the size of excavations;

Versa bolts for small excavations (max 18 ft wide) and Super Swellex bolts for larger spans (over 18 ft wide).

Great achievement toward health and safety of workers and economy of the operation.

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Questions?

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