Mechanics of Mine Backfill - research- .Thought the publications listed are not part of the thesis,

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

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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

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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

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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

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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

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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