David Bell Mine Underhand Cut and Fill Sill mat Test

9th International Symposium on Mining with Backfill
Jaimie Donovan, Jeff Dawson,


J. Donovan, Senior Engineer, Williams Mining Corporation

J. Dawson, EIT Underhand Cut and Fill Planner

W. F. Bawden, University of Toronto


Underhand cut and fill mining is being planned for selected areas at the David Bell mine
where high ground stresses have resulted in particularly challenging mining conditions.
In order to trial the placement and performance of a variety of underhand cut and fill
paste mats three different mat designs have been installed and instrumented along the
Zone 9C ore sill. Upon developing beneath these mats quantitative and qualitative
measures will be used to determine which design is the most suitable for application in
underhand mining at David Bell.

The 9C ore sill is approximately 87m long, 4.0m high, and 6.0m average width. The sill
was broken into 3 sections each of which will contain one of the sill mat designs outlined
below. The underhand sill will be mined 3.75mW x 3.5mH, allowing for some overbreak
while minimizing the risk of the back span exceeding the design limit of 4.0mW. Each
test sill mat includes pre and post-support and includes 0.5m (18”) broken muck mat
placed along the sill floor.

1.0): DYWIDAG MAT: Pre-support consists of 1.2 x 2.4m (4’ x 8’) 9g weld mesh
screen placed on top of the broken muck mat, from hanging-wall to footwall with 0.2m
overlaps between sheets. 2.4m (8’) long dywidag bolts will then be placed on 1.2.m
centres plated at the top and bottom and held in place by steel wiring. Post-support will
consist of tightening the bottom plate of pre-placed dywidag bolts in the back.

2.0): CHAIN LINK SCREEN MAT: The second fill mat pre-support consists of 9g
chain link screen placed over the broken muck, rolled up the walls of the sill (0.8-1.0m)
and held in place using 2 x 0.914m (3’) mechanical bolts or rebar on each side wall,
placed on a 1.2m spacing. Post-support in the back consists of bolting through pre-
screen with 1.8m (6’) swellex bolts on a 1.2m x 1.2m spacing.

Sidewall support for the first two designs will consist of 9g weld mesh screen, bolted
with either 1.5m (5’) rebar or 1.8m (6’) swellex bolts down to 1.5m from the sill floor on
a 1.2m x 1.2m spacing.

3.0): GEOFABRIC MAT: The third section of the sill mat will be used to determine the
benefits of a geotextile/fabric in preventing paste leakage through broken muck. A
geofabric/textile will be laid over the broken muck from footwall to hanging-wall. Post-
support for the backs and sidewall will consist of 9g weld mesh and 1.8m (6’) swellex
bolts installed on a 1.2m x 1.2m spacing.

The sill will be tight filled using a 6% cement, 6% flyash, binder plus 600ml of #1466
admixture (supplied by Masterbuilders Degussa) to produce pastefill with a strength in
the 2.3 to 2.5MPa range. The three sill mat sections will contain seven MPBX
instruments to measure vertical displacement of the pastefill on undercutting, two total
pressure cells to monitor horizontal fill loading and four contractometers combined with
extensometers in each wall placed evenly along the sill to measure total closure.

The paper will provide a detailed review of the design of and quality control measures
used during placement of the A-Zone 9C ore sill underhand cut and fill trial sill mat test.
Instrumentation results following undermining of the test sill mats will be discussed
including laboratory testing of the pastefill itself and numerical modelling of the test
Keywords: Underhand Cut and Fill, Sill mat, Numerical modelling, Rock mass - fill interaction, Ground support, Instrumentation, Field test
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