load-deformation characteristics of mine fills with particular reference to arching and stress

264 Pages·2008·8.42 MB·English

This file is part of the following reference:

Pirapakaran, Kandiah (2008)

Load-deformation characteristics
of minefills with particular reference
to arching and stress developments.

PhD thesis, James Cook University.

Access to this file is available from:

http://eprints.jcu.edu.au/4789
LOAD-DEFORMATION CHARACTERISTICS OF
MINEFILLS WITH PARTICULAR REFERENCE TO
ARCHING AND STRESS DEVELOPMENTS

A Thesis Submitted by
Kandiah PIRAPAKARAN BEng(Hons)
in February 2008

for the degree of Doctor of Philosophy
in the School of Engineering
James Cook University
STATEMENT OF ACCESS

I, the undersigned author of this work, understand that James Cook University will make this
thesis available for use within the University Library and, via the Australian Digital Theses
network, for use elsewhere.

I understand that, as an unpublished work, a thesis has significant protection under the
Copyright Act and;

I do not wish to place any further restriction on access to this work

_____________________________________ ______________
Signature Date
STATEMENT OF SOURCES

DECLARATION

I declare that this thesis is my own work and has not been submitted in any
form for another degree or diploma at any university or other institution of
tertiary education. Information derived from the published or unpublished work
of others has been acknowledged in the text and a list of references is given.

…………………….. …………………..
Signature Date

DECLARATION-ELECTRONIC COPY

I, the undersigned, the author of this work, declare that to the best of my
knowledge, the electronic copy of this thesis submitted to the library at James
Cook University is an accurate copy of the printed thesis submitted.

……………………. …………………
Signature Date

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ACKNOWLEDGEMENTS

I would like to express my deepest gratitude to my research supervisor
Associate Prof. Nagaratnam Sivakugan for his guidance and constant support
in helping me to conduct and complete this work successfully. Further, I want
to thank my associate supervisors Dr. W. Karunasena and R. Rankine for
supporting me to complete my PhD work as well as their generous advice. I
want to thank my fellow graduate student Shailesh Sign in the Civil and
Environmental Engineering for their help in this research. Many thanks to all the
people I have come to know at the James Cook University. I especially want to
thank Professor. K.G.H.N. Seneviratne, Department of Civil Engineering,
University of Peradeniya, Srilanka, for his inspiration and encouragement for
my higher studies. Finally, I want to extend my profound appreciation to my wife
Birunthagini and beloved parents for their love, affection, and invaluable
support during my life and studies.

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Abstract

Mining is one of the major export industries in Australia. When the ore is removed from
the ground voids are backfilled. There are different types of backfills depending on
their nature and usage. Hydraulic and paste fill are most common backfills in industry.
The strength and drainage properties of hydraulic fills are required for better design
and safety of the mines and miners. Arching is a well known phenomenon identified in
geotechnical and mining applications as reduction in the vertical stresses compared to
overburden pressure at any depth within the fill. Paste fill is a popular and relatively
new minefill that is used for backfilling underground voids created in the process of
mining. The binder used in paste fill, typically at dosage of 3% - 5%, contributes
significantly to the cost of backfilling. While Ordinary Portland cement (OPC) has been
the typical binder in paste fills, there is an increasing trend to replace OPC with
blended cements that include OPC mixed with fly ash, slag and lime at different
proportions in an attempt to minimize the cost.

This research presents a study that utilizes a laboratory model and the two and three-
dimensional finite difference packages FLAC and FLAC3D to investigate the arching
effects including the consideration of interface elements between rock and backfill,
stope geometry and shear strength parameters. An arching effect instrument was
developed and was used to investigate the stress developments within circular and
square stopes, which were found similar to the results of numerical modeling. Stress
values in the circular stopes were approximately 85% of square stopes from the
experimental model.

Further, an analytical solution was developed from Marston’s solutions for investigating
stress developments within rectangular, square/circular and narrow stopes. The
research was extended to develop models for narrow and rectangular stopes using
FLAC and FLAC3D, respectively. The improved model of narrow stopes was verified
against Aubertin et al. (2003) and extended further by incorporating interface elements
between rock and backfill. FLAC axi-symmetric model for circular stopes was
compared with Rankine (2004) FLAC3D model. Finally, the findings for narrow stopes
were verified with Knutsson’s (1981) in situ measurements.

Blended cements are generally characterised by very slow early strength development,
followed by the attainment of good ultimate strength. Blends comprising of 100% OPC,
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75% OPC & 25% fly-ash and 30% OPC & 70% slag were tested, adding 3%, 3.5% and
4% binder to tailings having solids contents of 7%, 80% and 81%. The specimens
were subjected to uniaxial compressive strength after curing periods of 7, 14, 28, 56
and 90 days. The short-term flow characteristics of 3.5% paste fill mixes with each type
of binder were investigated using yield stress tests. The results provided an
understanding of the effect of solids contents, binder contents and curing period in the
selection of optimal paste fill mixture. It was observed that slag-based paste fill had
higher strength compared to the other two paste fills, however after considering the
cost of binders, the 3% slag-based binder with 79% solids content in the paste fill and
3.5% Flyash-based binder with 80% solids content in the paste fill were chosen as
optimal mixtures for strength and flow properties. Also, long term strength was
investigated on Cannington mine tailings using Portland cement, but only for 79% and
83% solids content in the paste fill.

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List of Publications
JOURNALS

“Optimization of Paste fills using Blended cements with Cannington tailings
mines”
Pirapakaran, K. and Sivakugan, N. (2008). Canadian Geotechnical Journal (under
review).

“A Laboratory Model to Study Arching within a Hydraulic Fill Stope”
Pirapakaran, K. and Sivakugan, N. (2007). Geotechnical Testing Journal, ASTM, 30 (6),
200-210.

“Arching within Hydraulic fill stopes”
Pirapakaran, K. and Sivakugan, N. (2007). Journal of Geotechnical and Geological
engineering, Springer, 25(1), 25-35.

CONFERENCES

“Numerical and experimental studies of arching effects within mine fill stopes”
Pirapakaran, K. and Sivakugan, N. (2006).
Proceedings of the International Conference on Physical Modeling in Geotechnics
(ICPMG), Hong Kong, 555-563.

“Geotechnical Characteristics of Australian Mine Fills”
Pirapakaran, K, Singh, S., and Sivakugan, N (2006).
Proceedings of the Northern Engineering conference, Mackay, Australia.

“Investigations into strength of Cannington paste fill mixed with blended
cements”
Pirapakaran, K. and Sivakugan, N. (2007)
Proceedings of the 10th ANZ conference, Australian Geomechanics society, Brisbane,
Australia, 144-149.

“Hydraulic Fill Research at James Cook University in the new Millennium”
Pirapakaran, K., Singh, S., and Sivakugan, N. (2007)
Proceedings of the 9th International Symposium on Mining with Backfill, Montreal,
Quebec, Canada (CD Rom).

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Contents

Statement of Access ii
Statement of Sources iii
Acknowledgements iv
Abstract v
List of Publications vii
Table of Contents viii
List of Figures xiv
List of Tables xxi
List of Symbols xxiii

1. Introduction 1
1.1 General 1
1.2 Problem statement 3
1.3 Scope of Research 4
1.4 Relevance of the Research 4
1.5 Thesis Overview 5

2. Literature review 7
2.1 General 7
2.2 A review of mining methods 8
2.2.1 Surface mining 9
2.2.2 Underground mining 9
2.3 A summary of backfill materials 12
2.3.1 Hydraulic fills (HF) 12
2.3.2 Paste fills (PF) 13
2.4 Concept of arching 16

3. Analytical Models and In situ Measurements on Arching Effects 18
3.1 General 18
3.2 Necessity for Arching Consideration in Backfills 19
3.3 Arching in Geotechnical and Mining Applications – Analytical solutions 21
3.3.1 Vertical stope 21
Marston’s theory 22
Terzaghi’s theory 22
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Limit equilibrium Wedge 23
Winch analytical model 24
Free standing vertical face 26
Modified Marston’s theory 27
Extended 3-dimensional Marston theory 28
Extended solution from Marston theory by the Author 30
Comparison of analytical solutions 33
2-dimensional solutions 33
3-dimensional solutions 35
3.3.2 Inclined stope 38
Caceres modified analytical approximation 39
3.4 Arching in Geotechnical and Mining Applications – In situ measurements 41
3.5 Summary and conclusions 45

4. Experimental Models on Arching Effects 46
4.1 General 46
4.2 Laboratory tests for friction angles 47
4.2.1 Determination of friction angle of hydraulic fills 47
Direct shear tests 47
Grain size distribution and grain shape of hydraulic fills 50
4.2.2 Determination of interfacial friction angles 58
Modified direct shear tests 60
Effect of wall roughness and packing density 61
4.3 Arching in geotechnical and Mining Applications - Physical models 71
4.4 A laboratory model to study arching within a hydraulic fill stope 74
4.4.1 Parametric study of critical stope parameters 74
Stope geometry 74
Wall roughness 75
Filling materials 75
4.4.2 Instrument 76
4.4.3 Methodology and interpretation 80
4.4.4 Proposed models 81
When completely filled 82
During filling 82
4.4.5 Effect of stope geometry 82
4.4.6 Scaling 88
4.4.7 Effect of wall roughness 89
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