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Mechanics of Mine Backfill
By
Matthew Helinski
This thesis is presented for the
Degree of Doctor of Philosophy
The University of Western Australia
School of Civil and Resource Engineering
December 2007
DECLARATION FOR THESES CONTAINING PUBLISHED WORK AND/OR WORK PREPARED FOR PUBLICATION
The examination of the thesis is an examination of the work of the student. The work must have been substantially conducted by the student during enrolment in the degree. Where the thesis includes work to which others have contributed, the thesis must include a statement that makes the students contribution clear to the examiners. This may be in the form of a description of the precise contribution of the student to the work presented for examination and/or a statement of the percentage of the work that was done by the student. In addition, in the case of co-authored publications included in the thesis, each author must give their signed permission for the work to be included. If signatures from all the authors cannot be obtained, the statement detailing the students contribution to the work must be signed by the coordinating supervisor. Please sign one of the statements below. 1. This thesis does not contain work that I have published, nor work under review for publication. (Note: A number of journal and conference papers have been published on various aspects of the work, as listed Page v at the start of the Thesis. However, these are not part of the thesis per se.)
Signature: Thought the publications listed are not part of the thesis, the work included in them forms a central part of the thesis. The candidate, Mr Helinski, is first author on all of the publications, and can claim a contribution of > 70% to each of them.
Signature: (Martin Fahey, coordinating supervisor) 2. This thesis contains only sole-authored work, some of which has been published and/or prepared for publication under sole authorship. The bibliographical details of the work and where it appears in the thesis are outlined below. Signature......................................................................................................................................................... 3. This thesis contains published work and/or work prepared for publication, some of which has been co-authored. The bibliographical details of the work and where it appears in the thesis are outlined below. The student must attach to this declaration a statement for each publication that clarifies the contribution of the student to the work. This may be in the form of a description of the precise contributions of the student to the published work and/or a statement of percent contribution by the student. This statement must be signed by all authors. If signatures from all the authors cannot be obtained, the statement detailing the students contribution to the published work must be signed by the coordinating supervisor. Signatures......................................................................................................................................................... Signatures.........................................................................................................................................................
Mechanics of Mine Backfill Matthew Helinski The University of Western Australia
i
ABSTRACT
Mine backfilling is the process of filling large underground mining voids (stopes)
with a combination of tailings, water and small amounts of cement, to promote regional
stability. Stopes are often in excess of 20 m 20 m in plan dimensions and 40-50 m tall,
and can be filled within a week. Barricades are constructed in all tunnels (drives) that
access the stope to contain the backfill material. In recent years, a significant number of
failures of mine backfill barricades have occurred, resulting in the inrush of slurry
backfill into the mine workings. In addition, sampling has shown material strengths in
situ to be far greater than equivalent mixes cured in the laboratory (indicating the
potential for reducing the cement content). The purpose of this thesis is to apply soil
mechanics principles to the mine backfill deposition process with the intent of providing
some insight into these issues.
In many cases, filling, consolidation and cement hydration all take place at a similar
timescale, and therefore, to understand the cemented mine backfill deposition process it
was necessary to appropriately couple these activities. Developing appropriate models
for these mechanisms, and coupling them into a finite element code, forms the core of
this thesis.
Firstly, the fundamental processes involved in the cementing mine backfill deposition
process are investigated and represented using theory founded on basic physical
observations.
Using this theory, one- and two-dimensional finite element models (called CeMinTaCo
and Minefill-2D, respectively) are developed to fully couple each of the individual
mechanisms.
A centrifuge experiment was undertaken to investigate the interaction between
consolidation and total stress distribution in a cementing soil. The results of this
experiment were also used to verify the performance of Minefill2D. Due to scale
effects, the centrifuge experiment was unable to fully couple the interaction of the
cement hydration and consolidation timescales. To achieve this, a full scale field
experiment was undertaken. The simulated behaviour achieved using Minefill-2D (with
independently derived material properties) provided a good representation of the
consolidation behaviour.
Mechanics of Mine Backfill Matthew Helinski The University of Western Australia
ii
Finally, a sensitivity study carried out using Minefill-2D is presented. This study
enables some useful suggestions to be provided for managing the risk of excessive
barricade stress, and for preparing laboratory samples to more appropriately represent in
situ curing conditions.
Mechanics of Mine Backfill Matthew Helinski The University of Western Australia
iii
ACKNOWLEDGEMENTS
Firstly I would like to acknowledge the support of my wonderful family throughout the
period of my studies. My wife Libby, who after initially being somewhat apprehensive
about my decision to return to university, has provided me with undivided support
throughout this period. Jessica who was undesirably juggled during my early years of
study always had a wonder smile to greet me with and Lucy, our recent addition, who I
am equally proud of. To my parents, grandparents and sister who have provided me
with the wonderful gift of education and support throughout my life, I am forever
grateful of this.
To my supervisor Professor Martin Fahey, a true professor in the way he can make the
most complicated aspect of soil mechanics appear so clear and simple through the
application of his fundamental knowledge. This is something I aspire to. My supervisor
Professor Andy Fourie, whose guidance and friendship during my research was
essential in developing this project. Andy, I feel very fortunate that you arrived in
Australia and supported me when you did. Also, thanks to Dr Mostafa Ismail who
assisted me in the laboratory component of this work and Professor Jack Barrett who
helped shape this project during the early stages.
Thanks to all of my university colleagues, in particular James Schneider and James
Doherty and Shambu Sharma, I am extremely appreciative of your supervision and
guidance throughout this thesis.
Also my industry colleagues Cameron Tucker, Mat Revell and Tony Grice, I appreciate
all of your support and encouragement with this work.
Thanks to all of the academic and support staff in the Civil Engineering department in
particular Binaya, Clair and Natalia (who sadly passed away during this thesis) for their
ongoing patience with my chaotic style in the laboratory as well as Tuarn, John, Shane,
Phil, Bart, Don and Neil for their assistance with centrifuge testing.
Finally, this work would not have been possible without the wonderful post graduate
scholarship foundation at The University of Western Australia. The late Robert John
Gledden for establishing the Gledden trust that provided the majority of financial
support throughout this work. Merriwa for their wonderful top-up scholarship that
Mechanics of Mine Backfill Matthew Helinski The University of Western Australia
iv
provided both financial and equipment support. Mrs N. Shaw who established the
F.S.Shaw scholarship in memory of her late husband, which provided much needed
funding towards the latter stages of this research. And the UWA travel scholarship
which allowed me to attend the Minefill 07 conference in Canada.
Mechanics of Mine Backfill Matthew Helinski The University of Western Australia
v
DECLARATION
I hereby declare that, except where specific reference is made in the text to work of
others, the contents of this thesis are original and have not been submitted to any other
university.
During the compilation of this thesis some of the work has been published in various
journals and conference proceedings. I acknowledge the contribution of my co-authors
in preparing these publications. Details of these publications are as follows:
Journal publications