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TRANSCRIPT
!"#$%&'()$*%+',%(%+#)-.)/%012)3'$+1)/'+14%'($)01'4)!"#$%&'(!)*+),%(-$*+,&#"&(./,($*)("%(&(0&1"##&,2(3&,,"),(
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Patrick Dunne School of Environmental Systems Engineering, University of Western Australia Supervisors: W/ Prof Carolyn Oldham School of Environmental Systems Engineering, University of Western Australia W/ Prof Andy Fourie School of Civil Engineering, University of Western Australia Alan Tandy Toro Energy Limited 2012
Patrick Dunne
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Patrick Dunne
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This thesis is presented in partial fulfilment of the requirements of the Bachelor of Engineering
(Environmental) at The University of Western Australia
Patrick Dunne
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Abstract
A capillary barrier forms part of the tailings cover system proposed by Toro Energy for use at its
Centipede uranium mine near Wiluna, Western Australia. If successful, the capillary barrier,
which consists of a layer of high-suction fine material overlying a layer of low-suction coarse
material, will limit both the infiltration of rainfall and the upward movement of contaminants
through capillary forces.
Toro wishes to use locally available mined waste materials for the construction of its tailings
cover. In order to determine the suitability of these materials for use in a capillary barrier, a
variety of materials from the Centipede site were selected, collected and analysed in order to
determine their grain size distributions and water retention properties (based on a model
developed by van Genuchten (1980)).
Inputting this data into a simulation created by Heiberger (1996) using Hydrus-2D software
revealed that a simple capillary barrier constructed using unsorted mined waste from the
Centipede site is unlikely to be effective. Thus, it is probable that grain sorting will be required if
Toro wishes to use mined waste materials in its capillary barrier.
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Acknowledgements
I would like to acknowledge and thank my supervisors, Prof Carolyn Oldham, Prof Andy Fourie
and Alan Tandy for their guidance and support throughout this project
Thank you to Muhammad Suradi for his assistance with running my pressure plate tests. This
project couldn’t have been completed without your help.
Thanks to Toro fieldies James Schlipalius and Lindsay Ashwin for help collecting and sending
off my samples. And a huge thank you to Alan Tandy (again), Vanessa Guthrie, Sebastian Kneer,
Adrian Yurisich, John Baines, Greg Shirtliff, Lisa Chandler, Brendan Vagg and everyone else at
the Toro office for their help setting up this project and getting it off the ground.
Also thanks to all my family and friends who have been there throughout my thesis year and my
entire engineering degree.
Patrick Dunne
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Table of Contents
Abstract!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#!
Acknowledgements!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!$!
List of Abbreviations!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!%!
List of Figures!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!%!
List of Tables!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!&!
1. Introduction!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!'(!
2. Background and Literature Review!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!''!2.1 About Toro Energy!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!''!2.2 Wiluna Uranium Project!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!''!2.3 Local Lithology!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!')!2.4 Wiluna’s Climatic Conditions!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!')!2.5 Sonic Drilling Program!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!'$!2.6 Toro’s Tailings Cover Design!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!'*!2.7 Context!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!'&!2.8 Tailings Cover Design Practice!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+(!2.9 Basic Capillary Barrier Design!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+'!2.10 Risk of Preferential Flow Pathways in Capillary Barriers!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!++!2.11 Complex Capillary Barrier Design!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+)!2.12 Modelling in Capillary Barrier Design!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+)!2.13 The van Genuchten Model!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+$!2.14 The Fredlund-Xing Fitting Curve!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+*!2.15 Other Important Material Properties in Capillary Barrier Design!"""""""""""""""""""""""""""""""""""""""""""!+,!
3. Approach and Methodology!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+%!3.1 Sampling!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!+%!3.2 Sample Preparation!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!)(!3.3 Grain Size Distribution Testing!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!))!3.4 Pressure Plate Testing!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!))!3.5 Determining Permeability Values!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!)$!3.6 Capillary Barrier Modelling!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!)$!
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4. Results!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!),!4.1 Grain Size Distribution Results!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!),!4.2 Pressure Plate Test Results!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!)%!4.3 Modelling Results!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!)&!
5. Discussion!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#+!5.1 Sample Properties and Identification!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#+!5.2 Capillary Barrier Performance!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#)!5.3 Limitations!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!##!
6. Conclusions!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#$!
7. Recommendations!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#$!
8. References!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!#,!
Appendices!""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!$'!Appendix A: Full Grain Size Distribution Results!"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""!$'!Appendix B: Full Pressure Plate Testing and Fredlund-Xing SWRC Results!"""""""""""""""""""""""""""""""""!$)!
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List of Abbreviations SWRC Soil water retention curve
Toro Toro Energy Limited
TSF Tailings storage facility
UWA University of Western Australia
VWC Volumetric water content
List of Figures
Figure 1: Wiluna Project location map (Toro Energy 2011) .................................................. 12
Figure 2: Centipede stratigraphy: typical cross-section (Yurisich 2012) ............................... 13!
Figure 3: Tailings storage facility, Centipede minesite (Yurisich 2012) ................................ 17!
Figure 4: Centipede tailings cover design, post-closure (Dunne 2012) ................................... 19!
Figure 5: Drill cores collected, Centipede site (Dunne 2012) .................................................. 29!
Figure 6: Finite elements mesh for a capillary barrier model (Heiberger 1996) .................. 36!
Figure 7: Grain size distribution curves; Wiluna mined waste samples (Dunne 2012) ........ 37!
Figure 8: Fredlund-Xing SWRCs for Wiluna waste samples (Dunne 2012) ......................... 38!
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List of Tables Table 1: Rainfall and evaporation averages for Wiluna, WA (BOM 2012) .......................... 14!
Table 2: Extreme storm events; Wiluna, WA (Knight Piesold 2010; ARR 1987) ................. 14!
Table 3: Sample locations and observed properties (Schneider/Toro Energy 2011) ............ 30!
Table 4: Prepared samples (Dunne 2012) ................................................................................. 30!
Table 5: Pressure plate testing apparatus (Dunne 2012) ......................................................... 34!
Table 6: Grain size distribution testing on Wiluna mined waste samples: key figures
(Dunne 2012) .................................................................................................................. 37!
Table 7: Van Genuchten parameter, dry density and permeability values; Wiluna waste
samples (Dunne 2012) ................................................................................................... 38!
Table 8: Capillary barrier simulations: water content after 10.5 hours runtime (Heiberger
1996; Dunne 2012) ......................................................................................................... 39!
Table 9: Capillary barrier simulations: Velocity vectors after 10.5 hours model runtime
(Heiberger 1996; Dunne 2012) ..................................................................................... 41!
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1. Introduction
As part of its proposed Centipede uranium mine near Wiluna, Western Australia, Toro Energy
must design a tailings cover system that is capable of containing radioactive tailings for 10,000
years (Yurisich 2012). A capillary barrier forms a part of Toro’s tailings cover design, as it
serves the duel purpose of limiting infiltration of rainfall (Parent & Cabral 2006) and preventing
upward movement of contaminants through capillary forces (Mudd & Patterson 2010).
A capillary barrier consists of two layers. The upper layer is fine grained, with a compromise
between strong suction and high hydraulic conductivity. The lower layer is coarse grained, with
weak suction. The contrast in suction between the two layers restricts water movement across the
interface (Khire et al 2000). The whole system is built on a slope- allowing infiltrating water to
drain through the upper layer away from the tailings (Parent & Cabral 2006). Toro Energy
wishes to use mined waste and non-mineralised overburden to construct its tailings cover system,
including the capillary barrier (Yurisich 2012). However, no studies have been done to determine
the suitability of using such materials for long-term tailings storage.
The project aims were to determine whether a capillary barrier is suitable for Toro’s tailing cover
system; to determine the grain size and water retention (i.e. suction) properties of several mined
waste materials; and to assess the suitability of these materials for use in the construction of a
capillary barrier.
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2. Background and Literature Review
2.1 About Toro Energy Toro Energy Limited is an Australian-based, publicly traded company engaged in the exploration
of uranium. It was formed through the amalgamation of the uranium interests of Oxiana Limited
and Minotaur Exploration Limited in South Australia. The company’s corporate office is located
in Norwood, South Australia.! The Wiluna and Theseus Uranium Projects, both located in
Western Australia, are Toro’s most major and advanced projects (Toro Energy 2012). Toro is
also a significant explorer in Western Australia, the Northern Territory, and in Namibia (Toro
Energy 2012). !
2.2 Wiluna Uranium Project
Toro’s Wiluna project is centred around two uranium deposits, Centipede and Lake Way, both
located near Wiluna in the northern Goldfields Region of Western Australia (Figure 1). The
Centipede deposit, located 30km south of Wiluna, is expected to be mined first, with an
estimated mine life of approximately 14 years. Toro Energy expects to mine up to 2Mt of ore
and between 6 and 8 Mt of non-mineralised waste per year. The uranium ore will be processed
using agitated leach methods producing approximately 1000 tonnes of uranium oxide
(UO4.2H2O) per year (Toro Energy 2011).
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Figure 1: Wiluna Project location map (Toro Energy 2011)
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In May 2012, Western Australia’s Environmental Protection Authority recommended that the
state Environment Minister approve the Wiluna project and, in October 2012, state government
approval was granted. This marks the first approval for a uranium mine in Western Australia
since the ban on uranium mining in the state was lifted in 2008 (Kean 2012). Subject to federal
government approval, financing outcomes and board decisions Toro anticipates construction of
its first mine, Centipede, through 2013 and 2014 with first uranium sales in the 2014/15 fiscal
year (Toro Energy 2012).
2.3 Local Lithology
The local lithology consists of a sequence of layers of calcrete, sand and clay, illustrated in
Figure 2, below.
Figure 2: Centipede stratigraphy: typical cross-section (Yurisich 2012)
2.4 Wiluna’s Climatic Conditions
Wiluna’s climate can be described as semi-arid desert (BOM 2012). The Shire of Wiluna is an
area of low rainfall, high evaporation and extreme temperatures. The daily temperature can vary
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from highs of well over 40 degrees in the summer months to nightly lows in the winter months
below zero (BOM 2012). Rainfall is low, as shown in Table 1, below.
Table 1: Rainfall and evaporation averages for Wiluna, WA (BOM 2012)
Month
Rainfall
Evaporation mean (mm) median (mm)
January 35 18 490
February 38 17 395
March 35 14 365
April 29 13 240
May 26 15 165
June 24 12 115
July 15 9 120
August 10 5 155
September 5 2 225
October 7 2 325
November 10 4 365
December 21 12 450
Annual 255 - 3410
The majority of Wiluna’s precipitation falls in storm events and it is during these events that
water infiltration to the tailings is most likely to occur. Knight Piesold (2010) made predictions
of extreme storm events in Wiluna based on Australian Rainfall and Runoff (1987) data,
summarised in Table 2, below.
Table 2: Extreme storm events; Wiluna, WA (Knight Piesold 2010; ARR 1987)
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Gee et al (1994) suggest that, in arid and semi-arid regions, recharge can be as much as 60% of
precipitation. This, combined with the fact that Wiluna experiences extreme storm events, means
rainwater infiltration into the tailings is a major concern at Centipede despite the low rainfall
(Khire et al 2000).
2.5 Sonic Drilling Program
Toro Energy (Toro) conducted a sonic drilling campaign on its Centipede Uranium deposit in
September and October 2011. Samples from the drill cores obtained were taken for use in this
project.
The aims of this drilling program were to obtain density data and to convert a portion of the
Centipede uranium resource from the ‘indicated’ resource category to the ‘measured’ category
and therefore increase confidence in the ore body (Schneider 2011). 73 holes were drilled in
total, and each drill hole was of 100mm diameter and between 5 and 15m deep (Schneider 2011).
Toro determined a variety of soil properties for the drill cores taken during this drilling program
(Schneider 2011):
• Density profile
• Observed geological formation
• Permeability (for five drill core samples)
• Gamma radiation profile
• Geochemical assays: U, Sr, Ca, Mg, S, Va (for 350 drill core samples)
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2.6 Toro’s Tailings Cover Design
Toro engaged Knight Piesold Pty Ltd to undertake the design of the tailings disposal system for
the Wiluna project.
The objectives of the design were defined as follows (Knight Piesold 2010):
• Permanent and secure containment of all solid waste materials
• Capacity of 12 million cubic metres
• Maximisation of facility storage capacity
• Minimisation of seepage
• Excess capacity to contain a 1 in 100 year storm event
• Rapid and effective rehabilitation
• Minimisation of impact of radioactivity
• Ease of operation
The tailings storage facility (TSF) will be established in the void developed from mining the
Centipede ore body. This area will be divided into three facilities, only one of which will be
active at any one time. Each facility will be divided into three cells for deposition control
purposes, however these cells will be interconnected to allow equalisation of water levels
(Knight Piesold 2010). The layout of the TSF is shown in Figure 3, below.
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!
Figure 3: Tailings storage facility, Centipede minesite (Yurisich 2012) !!
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It is envisaged that the tailings cover systems would comprise the following elements (starting
from the base of the cover) (Figure 3):
• Radiation control layer – nominal 600mm thickness of sandy / gravelly waste rock and
overburden.
• Shaping layer – variable thickness of non-mineralised waste rock and/or overburden to
produce a profile that will blend with local landforms and prevent ponding.
• Capillary break layer – A coarse-grained capillary break layer (potentially forming part
of the shaping layer) will be included to limit upward movement of soluble tailings
constituents. This layer is the bottom (coarse) layer of the capillary barrier.
• Surface water shedding layer - A fine-grained water shedding layer will be built over the
capillary break layer to reduce infiltration of rainfall into the tailings mass. The layer will
be sloped so that the top surface drains. This layer makes up the top (fine) layer of the
capillary barrier.
• Growth medium and topsoil - Any topsoil that has been stripped from the pit area will be
placed back over the top of the growth medium layer. The growth medium layer will
consist of non-mineralised overburden stripped from the pit area.
• Engineered clay base and TSF perimeter walls – Since the TSF is partly below the
water table; its base and perimeters will be constructed using impermeable clays. It is
envisioned that this will prevent groundwater flow into and out of the tailings confinement
system.
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Figure 4: Centipede tailings cover design, post-closure (Dunne 2012)
!
Toro Energy wishes to use mined waste material and non-mineralised overburden from its
Centipede mine to construct this tailings cover, including the two layers of the capillary barrier.
However, prior to this project no testing had been done to determine the suitability of these
materials, based especially on their hydraulic properties, for constructing a capillary barrier.
2.7 Context
If the Centipede mine becomes operational, it will be the first ever uranium mine in Western
Australia. This fact creates challenges for Toro Energy. The performance of the mine, including
its tailings cover system, will set a precedent for future uranium mines in the region and the state.
In a state where the public remains sceptical about the safety and environmental impact of
uranium mining, the success or failure of Toro’s tailings cover could also have huge social and
political ramifications that would affect the entire uranium industry in Western Australia.
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This project also has national context, given the importance of tailings storage in Australia’s
many uranium mines. Due to insubstantial tailings cover designs in the past, Australian uranium
mines do not have a particularly good track record when it comes to storing radioactive mine
tailings. Several poorly designed cover systems (such as at the Rum Jungle and Mary Kathleen
mines) have resulted in unacceptable levels of uranium being released into ground and surface
water (Mudd & Patterson 2010; Lottermoser & Ashley 2005). While cover design has improved
since these past failures, Australian uranium mines are under increased scrutiny from the
government, regulatory bodies, the media and the public, to store tailings safely (ARPANSA
2012).
The recent Fukushima incident in Japan has lead to recent worldwide scrutiny being placed on
the global nuclear industry (Moeller 2011) and thus Toro’s Wiluna project, including its tailings
cover, has increased global context. The Fukushima accident occurred due to an unprecedented
tsunami inundating emergency cooling systems at the Fukushima Daiichi nuclear power station,
causing fuel to melt in three reactors and resulting in large releases of radioactive material
(Moeller 2011). A global increase in anti-nuclear sentiment followed this disaster; uranium price
dropped dramatically and several countries (including Germany and Japan) scaled down or
abandoned their nuclear energy programs (Maeda & Sheldrick 2012). This global concern over
the safety of nuclear power has ramifications for Toro Energy’s Wiluna project as it means that
any environmental damage or breach in safety as a result of the project could cause a massive
public backlash against Toro with potentially damaging effects on the Australian uranium
mining industry.
2.8 Tailings Cover Design Practice
Early radioactive tailings cover designs relied on compacted soil layers to limit water infiltration
and radon release. However, soil fracturing and root intrusion by plants severely compromised
these systems by increasing the saturated hydraulic conductivity several orders of magnitude
above design targets (Waugh 2004). In Australia, preferential flow pathways have been largely
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responsible for the failure of compacted earth covers at the Rum Jungle (Mudd & Patterson
2010) and Mary Kathleen mines (Lottermoser & Ashley 2005).
Modern tailings covers are designed to mimic a natural soil-water balance, incorporating a fine-
grained growth medium overlying a two-layered capillary barrier (Waugh 2004).
2.9 Basic Capillary Barrier Design
The limitations of simple compacted soil tailings covers are overcome through the inclusion of a
capillary barrier, which serves the duel purpose of limiting infiltration of rainfall (Yanful et al
2005; Parent & Cabral 2006) and preventing upward movement of contaminants through
capillary and evaporative forces (Mudd & Patterson 2010). In Wiluna, with its extreme rainfall
events and high evaporation, both of these factors are a huge concern and thus incorporating a
capillary barrier in Toro’s TSF is instrumental. Furthermore, the moisture-retaining upper layer
of a capillary barrier can provide added benefit by functioning as an oxygen barrier, reducing the
generation of acid in mine tailings (Nicholson et al 1989).
The capillary barrier consists of two layers. The lower layer (capillary break layer) is
characterised by a weak suction and is constructed from coarse-grained material. The upper layer
(surface water shedding layer) is characterised by a compromise between strong suction and high
hydraulic conductivity and is built using fine-grained material. The contrast in unsaturated
hydraulic properties between the two layers restricts movement of water across the interface
between the layers (Khire et al 2000). The high hydraulic conductivity of the upper layer allows
flow of infiltrating rainfall to the edges of the system, away from the waste (Khire et al 2000).
Most capillary barriers (including Toro’s proposed capillary barrier) are sloped in order to assist
this diversion of water (Tidwell et al 2003). Indeed, Fala et al 2005 found an unsloped capillary
barrier to be completely non-effective for a tailings cover in Canada, while a sloped system was
successful in diverting infiltrating water. In an inclined system such as this the barrier can only
divert water so far downslope under saturated conditions before the upper layer can hold no more
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water and water infiltrates the coarse layer (Parent & Cabral 2005). The point that this happens is
called the critical distance (or diversion length) from the top of the slope.
The performance of the capillary barrier depends on several variables. Thickness and hydraulic
properties of the upper layer significantly affect the water balance of capillary barriers, while the
thickness of the lower layer has a much smaller impact (Khire et al 2000). Tidwell et al (2003)
found that in Yucca Mountain, Arizona, where soils are frequently dry, capillarity difference
between the two layers was required to be small (limited by the need of a fine-grained material
that does not filter into the coarse material under dry conditions). Given Wiluna’s arid climate,
material selection for the Centipede tailings cover’s capillary barrier is more than likely to be
limited by this factor also.
2.10 Risk of Preferential Flow Pathways in Capillary Barriers
Based on a review of relevant literature, it is unclear whether preferential flow pathways will
cause a problem for a capillary barrier in Toro’s TSF. Current literature on this topic is
conflicting. Walter et al (2000) suggest that capillary barriers can, under certain circumstances,
cause funnelled flow into the coarse layer at their critical distance, leading to groundwater
contamination. Meanwhile, it has been suggested that root intrusion into a capillary barrier can
lead to its long-term failure by facilitating preferential water flow through root pathways, albeit
at a lower rate than a simple compacted soil barrier (Suter et al 1993; Bowerman & Redent 1997;
Kampf & Montenegro 1997). Burrowing fauna may also cause long-term problems to a capillary
barrier in much the same way (Bowerman & Redent 1997; Kampf & Montenegro 1997).
Conversely, Tidwell et al (2003) determined that the effect of preferential flow pathways on the
performance of a capillary barrier at Yucca Mountain, USA, would be minimal.
Despite the potential long-term problems caused by the development of preferential flow
pathways, there is a general consensus that a capillary barrier can be very successful if long-term
monitoring is conducted and that inclusion of a capillary barrier is current best practice in
tailings cover design (Parent & Cabral 2005; Bowerman & Redent 1997; Khire et al 2000;
Waugh 2004).
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2.11 Complex Capillary Barrier Design
While a simple capillary barrier consists of two layers, several more complex systems involving
three or more layers have been envisioned. Mallants et al (1999) proposed a four layered
capillary barrier for a radioactive tailing cover in Belgium. This system consists of a coarse layer,
overlying a fine layer, overlying a second coarse layer, overlying a layer of very fine clay. This
arrangement allows the diversion of any water that infiltrates through the upper fine layer to flow
away from the tailings through the lower coarse layer (Mallants et al 1999). Essentially, the
system functions as two capillary barriers overlying each other and hence provides an extra
degree of safety against rainfall infiltration.
A complex, multi-layered capillary barrier such as the one proposed by Mallants et al has
potential for use as part of Toro’s tailing cover, if the increased performance is worth the added
construction and design costs. While in theory a simple capillary barrier will be adequate, the
added level of protection brought by using a complex capillary barrier should be analysed as an
option in the design of Toro’s TSF.
2.12 Modelling in Capillary Barrier Design
A numerical computer model is a useful tool when designing a tailings cover. Hydrological
water balance models have seen use around the world in the design of radioactive tailings covers
(Khire et al 2000; Parent & Cabral 2005). Hydrus 2D, the modelling software used in this
project, is a two-dimensional modelling environment for analysis of water flow and solute
transport in variably saturated porous media (Radcliffe & Simunek 2010). The software package
includes the two-dimensional finite element model HYDRUS2 for simulating the movement of
water, heat, and multiple solutes (Radcliffe & Simunek 2010). The model includes a parameter
optimization algorithm for inverse estimation of a variety of soil hydraulic and/or solute
transport parameters (Radcliffe & Simunek 2010). It is supported by an interactive graphical
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interface for data processing, generation of a structured mesh, and graphic presentation of the
results (Radcliffe & Simunek 2010).
Hydrus-2D is an effective tool in the simulation of water flow above simple and complex
capillary barriers (Radcliffe & Simunek 2010; Heiberger 1996; Mallants et al 1999) and has seen
use assisting the design of many tailings covers throughout the world; including the Laronde
waste rock pile in northern Canada (Fala et al 2005) and the Texas low-level radioactive waste
disposal site (Simunek et al 1999). In this project, the Hydrus 2D software was used to analyse
water flow in unsaturated media across a finite element mesh representing a capillary barrier.
In order to numerically model a capillary barrier, the following parameters are required (Yanful
et al 2005; Rabozzi 2005; Parent & Cabral 2005; Khire et al 2000):
• Layer thickness
• The dip and length of slope (if any)
• Physical properties of materials (permeability, water retention curve, bulk density etc.)
• Climate data, especially infiltration rate
• Water table elevation (not necessarily relevant for Toro, due to impermeable base and
walls of the TSF)
• Maximum acceptable infiltration rate
In a Hydrus 2-D capillary barrier simulation, all these factors are included. Capillary barrier
shape and slope are determined through a 2D finite element mesh, infiltration rates are included
as an upper boundary condition and water retention properties of the materials can be determined
using a range of ‘water retention curve’ models (Radcliffe & Simunek 2010). In this project,
solutions to a water retention curve model developed by van Genuchten (1980) were used as
input parameters into the capillary barrier simulation.
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2.13 The van Genuchten Model
The model stipulated by van Genuchten (1980) gives an equation for the soil-water content-
pressure head curve, ! (h). This particular form of the equation enables one to derive closed-form
analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the
predictive conductivity models of Burdine (1953) or Mualem (1976),both of which use pore size
distribution as a tool to predict hydraulic conductivity.
The van Genuchten model was developed specifically as a tool to provide parameters for the
governing transfer equations in numerical models of unsaturated flow. Hydrus-2D represents a
modern version of the numerical models that van Genuchten had in mind when developing his
water retention curve equation.
The curve can be fit to experimental data, including results derived from a pressure plate test
(Kazimoglu et al 2005). This means that results from pressure plate testing (as conducted in this
project) can be used as input values into a Hydrus-2D capillary barrier simulation by way of the
van Genuchten water retention curve equation.
The equation is as follows:
(1)
Where:
• !(") is the water retention curve [L3L#3];
• |"| is suction pressure ([L#1] or cm of water);
• !s is saturated water content [L3L#3];
• !r is residual water content [L3L#3];
• $ is related to the inverse of the air entry suction, $ > 0 ([L#1], or cm#1); and,
• n is a measure of the pore-size distribution, n > 1 (dimensionless)
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2.14 The Fredlund-Xing Fitting Curve In this project, Fredlund-Xing water retention curves were developed (in addition to solutions for
the van Genuchten equation) in order to give a graphical representation of the water retention
properties (i.e. suction) of non-mineralised waste samples from Wiluna.
Like the van Genuchten model, the Fredlund-Xing equation (developed in 1994) gives a soil-
water retention curve that can be used to estimate various parameters used to describe
unsaturated soil behaviour. The equation is in the form of an integrated frequency distribution
curve and is based on the assumption that the shape of the SWRC is based upon the pore size
distribution of the soil (Fredlund & Xing 1994). Best-fit parameters for experimental water
retention test data, such as pressure plate test data, can be determined through least-squares
computation (Fredlund & Xing 1994). In this project, this computation was performed using a
spreadsheet on Microsoft Excel.
The Fredlund-Xing SWRC model is based on several sub-equations combined to give the
following equation:
(2)
Where:
• ! is Volumetric water content (VWC)
• a5 is a curve-fitting parameter based on equations in Fredlund & Xing (1994)
• b5 is a curve-fitting parameter based on equations in Fredlund & Xing (1994)
• " is Applied pressure / matric suction (kPa)
• m is a curve-fitting parameter related to slope at inflection point
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2.15 Other Important Material Properties in Capillary Barrier Design
While this report focussed on the hydraulic properties of the materials used in capillary barrier
design, there are other material properties that can influence the performance of a barrier.
As is the case with all other sections of the tailings cover, stability is important to consider when
selecting materials to construct Toro’s capillary barrier. Both layers of the capillary barrier must
remain stable for more than 1000 years in order to ensure the long-term effectiveness of the
tailings cover (Toro Energy 2011).
Long-term stability of a material is complex and based on many variables. Nonetheless, stability
can be predicted through modelling based on several factors, including the following (Smithson
2008; Riley 2006; Goudie & Viles 1997):
• Soil erosion parameters based on the USDA’s Universal Soil Loss Equation
• Thresholds of rilling and gullying
• Insolation weathering
• Salt weathering (this is of particular concern due to the Wiluna TSF’s location in a saline
environment)
• Slaking
• Aggregate stability (for the top layer of the tailings cover)
Geochemical properties of materials used in a tailings cover can have an effect on its long-term
performance, due to the chemical processes of weathering. Weathering of all or part of a tailings
cover (including a capillary barrier) can cause major change in its stability or hydraulic
properties and thus negatively affect its performance (Yanful et al 1999). Weathering has been
responsible for the failure of many tailings covers throughout the world. The sulphide
weathering of tailings covers at the Banska Stiavnica and Smolnik mines in Slovakia resulted in
the release of Iron oxyhydroxides from the tailings into the surrounding environment (Lintnerova
et al 2007). In Australia, weathering has been identified as a potentially major risk in the storage
of uranium mill tailings in Alligator Rivers, Northern Territory (East 1986).
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Weathering is often exacerbated by the chemistry of the tailings themselves (Yanful et al 1999).
Thus, in sections of the tailings cover that may be in contact with tailings, it important to select
materials that will not react with the tailings. In Toro’s tailings cover design (Figure 4), it is
possible that the lower (coarse) layer of the capillary barrier will come into contact with tailings.
Therefore, it is important that the material geochemistry is considered when selecting adequate
materials for its construction (although this task falls outside the scope of this project).
3. Approach and Methodology
3.1 Sampling Three drill cores from Toro Energy’s September 2011 sonic drilling program were selected.
These cores were inspected at the Wiluna site on June 15th, 2012, and sent via courier to the
UWA Civil Engineering Workshop. The cores ranged from 5 to 9 metres in length, were 100mm
in diameter. Five smaller (approx. 1kg) samples were selected from these drill cores and used for
laboratory analysis.
The cores and samples were selected based on a variety of factors.
The samples:
• Included all major local soil types in various observed percentages (sand/clay ratio)
• Did not contain any mineralisation (radiation above 600ppm U3O8 equiv.)
• Were undamaged from any previous analysis by Toro
• Had similar observed properties to those used in permeability testing conducted by Knight
Piesold
These factors meant the choice of viable drill cores samples was limited to areas where little or
no uranium mineralisation was present, due to both transport restrictions and the requirement for
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non-mineralised waste samples in the capillary barrier construction. Since the sonic drilling
program was conducted in order to assess the uranium resource, most drill cores contained too
much mineralisation for use in this project and thus the range of viable sonic cores was limited to
a relatively small region of the Centipede deposit. However, the layered nature of the geological
formations around Centipede (Figure 2) meant that a variety of representative waste material
samples could still be collected from the three drill cores selected, despite the comparatively
short distances between them (200 – 500m).
Figure 5: Drill cores collected, Centipede site (Dunne 2012)
As part of the drill program, the Toro geologists recorded the observed properties of each drill
core. These observations included an observed clay/sand ratio, grain size, colour and a brief
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description of the material. The observed properties of the five samples used for this project
were:
Table 3: Sample locations and observed properties (Schneider/Toro Energy 2011)
Sample no. Drill core Depth of sample
% clay (observed)
% sand (observed)
Colour Description
1 CPS150 3 – 3.5m 40 60 red/brown Very fine to fine sand, secondary clay 2 CPS150 4.5 – 5m 100 0 red/brown Clay 3 CPS170 7 – 7.5m 80 20 grey/yellow Grey clay with secondary coarse sand 4 CPS153 4 – 5m 75 25 red/brown Red/brown clay with secondary
med/coarse sand 5 CPS170 3 – 3.5m 30 70 red/brown Medium grain sand with clay
3.2 Sample Preparation
Prior to testing, the five samples were kiln-dried, and their particles were separated using a
mortar and pestle. The prepared samples are shown in the photographs below.
Table 4: Prepared samples (Dunne 2012) Sample Photograph
Sample 1
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Sample 2
Sample 3
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Sample 4
Sample 5
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3.3 Grain Size Distribution Testing
The grain size distribution of the five samples was tested in order to ensure sample identification
was based on experimental rather than observed data, and to determine whether observed
sand/clay percentages are a useful predictor of actual grain size and hence a useful tool for the
identification and collection of non-mineralised mined waste materials.
A 300g segment of each sample was tested for grain size distribution using 4.75-0.075mm sieves
in the University of Western Australia’s Civil Engineering Workshop. The amount of material
remaining on each sieve was weighed and recorded. If more than 10% of a sample was found to
be of a grain size finer than 0.075mm (the smallest sieve size used), a hydrometer test was
conducted in order to find the size distribution of the fine particles.
The weights recorded from the sieving and the results from the hydrometer testing were used to
construct a grain size distribution curve for each sample. From these curves D10 and D60 values
were determined, as were the relative percentages of sand and silt/clay in each sample based on
the Australian geological definition (sand particles are 0.0625mm – 2mm in size, silt/clay
particles are smaller than 0.0625mm) (Pain 2008).
3.4 Pressure Plate Testing
Three of the five samples were tested for their water retention properties using a pressure plate
apparatus in the UWA Civil Engineering Workshop, with assistance from PhD student
Muhammad Suradi. A small amount of each sample was used to fill a 55mm diameter, 20mm
deep ring. Each sample ring was saturated, then placed on a porous ‘pressure plate’. This plate
was placed inside a pressurised apparatus, onto which pressures ranging from 5-200kPa were
applied. The apparatus, pressure plate and a sample inside a ring are shown in Table 5, below.
The system was allowed to reach equilibrium at each applied pressure (i.e. water level in the
column (Table 5) reached a constant level), at which point each sample was weighed.
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Table 5: Pressure plate testing apparatus: UWA Civil Engineering Workshop (Dunne 2012)
A portion of Sample 3 inside a 55mm
diameter, 20mm deep ring placed on
the pressure plate.
The UWA Civil Engineering
Workshop’s pressure plate apparatus;
as used in this project. The pressure
plate and samples were enclosed
inside the metal cylinder, onto which
various pressures were applied. The
system was said to reach equilibrium
when the water level inside the
column (attached to the stand behind
the cylinder) reached a constant level.
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After the pressure plate test was run, the samples were kiln-dried and weighed again in order to
determine their dry weight and density.
The pressure plate results were analysed using PC-Progress’ RTEC program, giving parameter
values for the van Genuchten model. In addition to this, water retention curves were created
using a similar water retention curve model developed by Fredlund & Xing (1994).
3.5 Determining Permeability Values
The Hydrus-2D capillary barrier simulation used in this project required permeability (Ks) values
for each material. Originally, known permeability values (determined by Knight Piesold) of
materials similar to those used in this project were to be input into the model. However,
discrepancy between observed and actual soil properties meant using these values would result in
a grossly inaccurate simulation (Chapter 4.2). Instead, permeability (Ks) values were estimated
using Hydrus-2D’s permeability estimation tool, which gives an approximate result based on
grain size and density (Radcliffe & Simunek 2010).
3.6 Capillary Barrier Modelling
The model parameter values obtained for each of the three tested samples were then input into a
simple capillary barrier simulation developed by Heiberger (1996) using Hydrus-2D. This model
space consisted of a soil block 402cm long and 250cm deep with a 5% slope (Figure 6). The
coarse material began at a depth of 65cm below the surface and was 80cm thick, extending about
% of the distance across the model space. The finite element mesh contained a dense grid at the
interface between the coarse and fine layers. The steady infiltration rate at the soil surface (as a
boundary condition) was 4mm/h; while there was free drainage at the base and no drainage along
the side walls of the model area. The simulation’s runtime was 15 hours. This was approximately
analogous to a 1-in-25-year storm event in Wiluna assuming 60% of rainfall infiltrates the soil,
or a 1-in-100-year storm event assuming 30% of rainfall infiltrates the soil (Knight Piesold 2010;
Gee et al 1994).
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Figure 6: Finite elements mesh for a capillary barrier model (Heiberger 1996)
When the simulation was run using materials stipulated by Heiberger (Table 7), water was
diverted downslope along the capillary barrier and around the end of the barrier, away from the
location where tailing would hypothetically be stored (Tables 8 and 9).
Sample 2, which was found to contain the finest particles (Table 6), was used as the upper (fine)
layer of the capillary barrier in this simulation, while Samples 3 and 4 were used alternatively as
the lower (coarse) layer.
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4. Results
4.1 Grain Size Distribution Results
Grain size distribution testing and analysis on the five samples yielded the following results.
Table 6 shows the measured D60, D10, sand and silt/clay percentages of the five samples;
compared with the observed sand and clay percentages from Toro’s September 2011 drill logs.
Grain size distribution curves for each sample are shown in Figure 7.
Table 6: Grain size distribution testing on Wiluna mined waste samples: key figures (Dunne 2012)
Sample No. % clay
formation (observed)
% sand formation (observed)
D60 (mm)
D10 (mm)
% silt/clay (particles <
0.0625mm)
% sand (particles >
0.0625mm) 1 40 60 0.7 0.14 <2.2 >97.8 2 100 0 0.098 0.0011 45 55 3 80 20 0.94 0.18 <3 >97 4 75 25 0.45 0.084 <8.4 >91.6 5 10 90 0.64 0.075 <10 >90
Figure 7: Grain size distribution curves; Wiluna mined waste samples (Dunne 2012)
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4.2 Pressure Plate Test Results
Van Genuchten model parameter values (Table 7) and Fredlund-Xing water retention curves
(Figure 8) for Samples 2-4 were determined through analysis of results from the pressure plate
tests. Dry density (&d) and permeability (Ks) values are also included in Table 7, as are the van
Genuchten parameter values and permeability values of the materials used in Heiberger’s
capillary barrier simulation.
Table 7: Van Genuchten parameter, dry density and permeability values; Wiluna waste
samples (Dunne 2012)
Material !s !r n " (cm-1) #d (g/m2) Ks (cm/d) Sample 2 0.766 0.255 1.99 0.117 1.163 86.8 Sample 3 0.566 0.148 2.13 0.106 1.603 904.3
Sample 4 0.659 0.16 2.02 0.114 1.414 606.6 Heiberger
fine 0.348 0.02 12.18 0.045 258 Heiberger
coarse 0.348 0.012 7.35 0.151 1811
Figure 8: Fredlund-Xing SWRCs for Wiluna waste samples (Dunne 2012)
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4.3 Modelling Results
Running the capillary barrier simulation using the van Genuchten equation values determined
experimentally (with Sample 2 as the fine layer and Samples 3 and 4 as the coarse layer) gave a
poor result, with the barrier unable to prevent water flow across the interface between the two
layers. This is evident in Tables 8 and 9, which illustrate the water content and water velocity
vectors respectively after 10.5 hours of constant 4mm/hr water flux from the model surface.
Water content and flow velocity results of Heiberger’s simulation are also included in Tables 8
and 9 in order to give an indication of what would be expected in a successful capillary barrier
simulation.
In all three simulations, initial water content for each material was defined as being equal to its
residual water content term (!r in Table 7) in its respective solution to the van Genuchten
equation. Both the fine and coarse materials in all three simulations remained unsaturated for the
entire model runtime.
Table 8: Capillary barrier simulations: water content after 10.5 hours runtime (Heiberger 1996; Dunne 2012)
Water content of Heiberger’s capillary barrier simulation after 10.5 hours runtime. Infiltrating water does not cross the interface between the fine and coarse layers. Instead, it is diverted downslope, away from where tailings would hypothetically be placed.
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Water content of the capillary barrier simulation using Sample 2 as the fine material and Sample 3 as the coarse material, after 10.5 hours model runtime. This barrier is not effective, as water is clearly infiltrating through the interface into the coarse layer.
Water content of the capillary barrier simulation using Sample 2 as the fine material and Sample 4 as the coarse material, after 10.5 hours model runtime. This barrier is also not effective, as water is clearly infiltrating through the interface into the coarse layer.
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Table 9: Capillary barrier simulations: Velocity vectors after 10.5 hours model runtime (Heiberger 1996; Dunne 2012)
Flow velocity vectors of Heiberger’s capillary barrier simulation after 10.5 hours runtime. Infiltrating water does not cross the interface between the fine and coarse layers. Instead, it is diverted downslope, away from where tailings would hypothetically be placed.
Water flow velocity vectors of the capillary barrier simulation using Sample 2 as the fine material and Sample 3 as the coarse material, after 10.5 hours model runtime. This barrier is not effective, as water is clearly infiltrating through the interface into the coarse layer.
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Water flow velocity vectors of the capillary barrier simulation using Sample 2 as the fine material and Sample 4 as the coarse material, after 10.5 hours runtime. This barrier is also not effective, as water is clearly infiltrating through the interface into the coarse layer.
5. Discussion
5.1 Sample Properties and Identification
The results of the grain size distribution analysis confirmed that the clay system (Sample 2)
contained finer particles overall than any of the clay/sand system blends, which contained
coarser particles on average (Table 6; Figure 7).
The sand/clay blended soils, despite having wide-ranging observed sand/clay percentages, were
found to have very similar grain size distribution curves (Figure 7). Furthermore, there was a
lack of correlation between observed and measured grain size distribution. For example, the
coarsest material (Sample 3) had an observed 20:80 sand to clay ratio, while Sample 5 (with an
observed 90:10 sand to clay ratio) contained finer particles on average (Table 6; Figure 7).
These results imply that the observed material properties from Toro’s September 2011 drilling
program are an inaccurate guide for identifying and collecting soils. Likewise, the discrepancy
between observed and actual soil properties meant that the results from permeability testing
conducted by Knight Piesold on Toro’s sonic drill core samples could not be used as inputs into
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the capillary barrier model.
From Table 6 it can also be noted that observed ‘clay’ and ‘sand’ percentages were based on
local soil formations rather than the geological definitions for ‘sand’ and ‘clay’. Using the
Australian geological definitions for sand (0.0625mm – 2mm), silt (0.002mm – 0.0625mm) and
clay (<0.002mm) (Pain 2008) it can be seen that all four of the sand/clay system blends (Samples
1,3,4 and 5) were technically defined as being predominantly sand, while the 100% clay system
sample (Sample 2) was roughly half sand, half silt/clay.
The pressure plate testing results implied that, despite the fact that the magnitude of volumetric
water content differs between the three samples tested, their water retention properties were not
significantly different. This is illustrated in Figure 8, which shows the Fredlund-Xing water
retention curves for Samples 2, 3 and 4. While it was clear that Sample 2 had higher all-round
volumetric water content than Samples 3 and 4, the similarity between the shapes of the curves
showed that the each sample had similar suction (Fredlund & Xing 1994). This was also the case
for the van Genuchten parameters determined through the pressure plate testing. It is clear that
the materials did not have significantly varied water retention properties, especially when
compared the materials used in Heiberger’s capillary barrier simulation (Table 7).
Despite the wide variety of ‘observed’ properties, and the fact the samples were taken from
different locations and soil systems, the clay/sand blended samples had very similar grain size
distributions; and all samples had similar water retention properties. The similarity between the
physical properties of these materials suggested that waste materials collected from Centipede
were not likely to be ideal for use in a capillary barrier, which relies on difference in capillary
forces between its two layers to limit flow. However, the similarity of the tested materials could
have positive implications- as it means a blended waste material with relatively uniform physical
properties could potentially be easily collected from the Centipede site.
5.2 Capillary Barrier Performance
The results from the pressure plate tests and modelling suggest that unsorted waste materials at
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Centipede do not have sufficiently different water retention properties for use in a capillary
barrier. This is illustrated in Tables 8 and 9, which show water passing through the interfaces of
the Sample 2/Sample 3 and Sample 2/Sample 4 capillary barrier simulations. The results from
these two simulations are in stark contrast to Heiberger’s simulation, which diverts water to the
edge of the barrier.
The relative lack of uniformity in the grain size of the tested samples could explain the result, as
many capillary barrier designs (including that of Heiberger (1996)) utilise more uniform
materials in the fine and coarse layers (Parent & Cabral 2006). Thus, if Toro Energy wishes to
use mined waste materials in its capillary barrier design, it is recommended that some kind of
material sorting process be examined for feasibility; and the water retention properties of these
sorted materials be tested.
5.3 Limitations
The need to select non-mineralised drill cores for use in this project meant that the sample size
was small and the samples were not significantly spatially distributed around the Centipede
deposit (Figure 5). Furthermore, accessibility issues in the drill program meant that drill cores
were only obtained from the lakebed system; no suitable samples from the nearby dune system
were obtained (Schneider 2011). While the results of this project showed that a range of
materials from Centipede are unsuitable for use in capillary barrier construction, it is not
inconceivable that materials from other parts of Centipede (such as the sand dune system) have
suitable hydraulic properties.
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6. Conclusions
The results from the laboratory analysis and modelling suggest that constructing a simple
capillary barrier using unsorted mined waste is not likely to be effective for Toro Energy’s
Centipede mine.
Designing and implementing a radioactive tailings cover system is a huge operation and
optimising its design relies on many factors. The results of this paper will be a valuable
contribution to the design of Toro’s tailings cover. The literature review confirms the fact that a
capillary barrier is a good idea for use in the tailings cover; while the results of the model
suggest that grain sorting will need to take place if Toro wishes to use mined waste material to
construct its barrier.
Additionally, as a result of this project Toro now has a record of the grain size distribution and
water retention properties of a range of waste materials- information that was previously
unknown. Data such as this is essential for the capillary barrier design to move beyond the
conceptual stage. The similarity in grain size and water retention properties of the samples could
also be a positive for Toro, as it suggests that a mixed waste material with relatively uniform
grain size and capillarity could likely be collected from the Centipede mine and used elsewhere
on site, such as in another section of the tailings cover or in dam construction.
7. Recommendations
Based on the findings of this project, it is strongly recommended that a capillary barrier be
included in the design of Toro Energy’s radioactive tailings storage facility in Wiluna. Including
a capillary barrier as planned will ensure that current best practice is incorporated in Toro’s
tailings cover design, limiting the risk of tailings release through groundwater or evaporative
forcing. However, the use of non-mineralised mined waste material from Toro’s Centipede mine
in the construction of this capillary barrier is not recommended unless the material is subject to
grain sorting, which may or may not be viable.
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This project can be seen as a first step of many in the fine-tuning of Toro’s capillary barrier
design and can thus be used as a basis for future studies. Some other issues that could be
considered are:
• The viability of using sorted mine waste material in the capillary barrier. A cost/benefit
analysis should be conducted, comparing grain sorting processes with collecting and
transporting material from elsewhere.
• Preferential flow pathways and their effect on the performance of the capillary barrier.
• Analysis of the stability and geochemistry of materials to be used in the tailings cover,
including the capillary barrier.
• Modelling the upwards transport of tailings through evaporative and capillary forces, rather
than just downwards water infiltration. Despite the fact that a review of the relevant
literature suggests that this is a problem that will not occur with a capillary barrier that
prevents infiltration (Tidwell et al 2003; Parent & Cabral 2006; Yanful et al 2006), it is
important to know for certain that tailings will not be transported upwards when designing
a radioactive tailings cover.
• Potential costs and benefits of using a more complex capillary barrier (such as the one
proposed by Mallants et al (1999)) in Toro’s tailings cover.
Studying any of these issues would build upon the work conducted in this project and bring Toro
Energy one step closer to completing the design of its radioactive tailings cover system.
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8. References
Australian Radiation Protection and Nuclear Safety Agency, 2012, Cradle-to-Grave Radioactive Waste Management, Australian Government, Canberra, Australia
Bowerman, A.G.; Redent, E.F., ‘Biointrustion of Protective Barriers at Hazardous Waste Sites’,
Journal of Environmental Quality, vol. 27 (3), pp. 625-632 Burdine, N.T., 1953, ‘Relative permeability calculations from pore-size distribution data’, Petr.
Trans. Am. Inst. Mining Metall., vol. 198, pp. 71-77 Bureau of Meteorology, 2012, ‘Climate Statistics for Wiluna, Western Australia’, BOM,
Australian Government, Canberra East, J., 2007, ‘Geomorphological assessment of sites and impoundments for the long term
containment of Uranium mill tailings in the Alligator Rivers region’, Australian Geographer, vol. 17 (1), pp. 16-21
Fala, O.; Molson, J.; Aubertin, M.; Bussiere, B., 2005, ‘Numerical Modelling of Flow and
Capillary Barrier Effects in Unsaturated Waste Rock Piles’, Mine Water and the Environment, vol. 24 (4), pp. 172-185
Fredlund, D.G.; Xing, A., 1994, ‘Equations for the soil-water characteristic curve’, Canadian
Geotech Journal, vol. 31, pp. 521-532 Gee, G.; Wierenga, P.; Andraski, B.; Young, M.; Fayer, M.; Rockhold, M., 1994, ‘Variations in
water balance and recharge potential at three western sites.’ Soil Science Society of America Journal, vol. 58, pp. 63–72
Goudie, A.; Viles, H., 1997, Salt Weathering Hazards, Wiley Publishing, New York City, NY,
USA Heiberger, T.S., 1996, ‘Simulating the effects of a capillary barrier using the two-dimensional
variably saturated flow model SWMS-2D/HYDRUS-2d’, PhD Thesis, Oregon State University, Corvallis, OR, USA
Kampf, M.; Montenegro, H., 1997, ‘On the performance of capillary barriers as landfill cover’,
Hydrology and Earth Systems Sciences Discussions, vol. 1 (4), pp. 925-930 Kazimoglu, Y.K.; McDougall, J.R.; Pyrah, I.C., 2005, ‘Moisture Retention and Movement in
Landfilled Waste’, Proceedings of the International Conference on Problematic Soils, Famagusta, Cyprus
Kean, A., 2012, ‘Toro Energy receives milestone approval for Wiluna uranium project’,
Proactive Investors News, Australia
Patrick Dunne
Page | 48
Khire, M.V.; Benson, C.H.; Bosscher, P.J., 2000, ‘Capillary Barriers: Design Variables and Water Balance’, Journal of Geotechnical and Geoenvironmental Engineering, August 2000, pp. 695-708
Knight Piesold Pty Ltd, 2010, Wiluna Uranium Project Tailings Management Strategy and
Conceptual Storage Design, Knight Piesold, West Perth, Australia Lintnerova, O.; Sottnik, P.; Soltes, S., 2007, ‘Abandoned Smolnik mine (Slovakia) – a catchment
area affected by mining activities’, Estonian Journal of Earth Sciences, vol. 57 (2), pp. 104-110
Lottermoser, B.G.; Ashley, P.M., 2005, ‘Tailings dam seepage at the rehabilitated Mary
Kathleen uranium mine, Australia’, Journal of Geochemical Exploration, vol. 85, pp. 119-137
Maeda, R.; Sheldrick, A., 2012, ‘Japan aims to abandon nuclear power by 2030s’, Reuters,
<http://www.reuters.com/article/2012/09/14/us-japan-nuclear-idUSBRE88D05520120914>
Mallants, D.; Volckaert, G.; Marivoet, J., 1999, ‘Sensitivity of protective barrier performance to
changes in rainfall rate’, Waste Management, vol. 19 (7-8), pp. 467-475 Moeller, K., 2011, ‘Waste Safety Standards Committee 27th to 30th June 2011’, Revision of
Current WS-G-2.7 Safety Guide, International Atomic Energy Agency Mualem, Y., 1976, ‘A new model for predicting the hydraulic conductivity of unsaturated porous
media’, Water Resources Res., vol. 12, pp. 513-522 Mudd, G.M.; Patterson, J., 2010, ‘Continuing pollution from the Rum Jungle U-Cu project: A
critical evaluation of environmental monitoring and rehabilitation’, Environmental Pollution, vo. 158, pp. 1252-1260
Nicholson, R.V.; Gillham, R.W.; Cherry, J.A.; Reardon, E.J., 1989, ‘Reduction of acid
generation in mine tailings through the use of moisture-retaining cover layers as oxygen barriers’, Canadian Geotechnical Journal, vol. 26 (1), pp. 1-8
Pain, C.F., 2008, ‘Field Guide for Describing Regolith and Landforms’, Cooperative Research
Centre for Landscape Environments and Mineral Exploration, CSIRO Exploration and Mining, Bentley, WA, Australia
Parent, S.E.; Cabral, A., 2006, ‘Design of inclined covers with capillary barrier effect’,
Geotechnical and Geological Engineering, vol. 24, pp. 689-710 Rabozzi, C., 2005, ‘Evaluation of mineral barriers water retention curves using the vapour
equilibrium method’, Post-doc, Dipartimento di Ingegneria del Territorio, dell’ Ambiente e delle Geotecnologie, Torino, Italy
Patrick Dunne
Page | 49
Radcliffe, D.E.; Simunek, J., 2010, Soil Physics with Hydrus: Modeling and Applications, CRC
Press, Taylor & Francis Group, Boca Raton, Florida, USA Riley, S.J., 2006, ‘Geomorphic estimates of the stability of a uranium mill tailings containment
cover: Naberlek, Northern Territory, Australia’, Land Degradation & Development, vol. 6 (1), pp. 1-16
Schneider, A., 2011, ‘Sonic Drilling report 2011’, Toro Energy Limited, West Perth, WA,
Australia Simunek, J.; Sejna, M.; Van Genuchten, M.T., 1999, ‘The Hydrus-2D software package for
simulating two-dimensional movement of water, heat and multiple solutes in variably saturated media. Version 2.0’, IGWMC – TPS – 53, International Ground Water Modelling Center, Colorado School of Mines, Golden, Colorado, pp. 251
Stolberg, D.J.; Williams, D.J., 2004, ‘Cover systems for hypersaline tailings in an arid climate’,
in Stolberg, D.J.; Williams, D.J., 2004, Tailings and Mine Waste ’04, Proceedings of the Eleventh Tailings and Mine Waste Conference, October 2004, Vail, Colorado, USA
Suter, G.W.; Luxmoore, R.J.; Smith, E.D., 1993, ‘Compacted Soil Barriers at Abandoned
Landfill Sites are Likely to Fail in the Long Term’, Journal of Environmental Quality, vol. 22 (2), pp. 217-226
Tidwell, V.C.; Glass, R.J.; Chocas, C.; Barker, G.; Orear, L., 2003, ‘Visualization experiment to
investigate capillary barrier performance in the context of a Yucca Mountain emplacement drift’, Journal of Contaminant Hydrology, vol. 17, pp. 342-355
Toro Energy Limited, 2011, ‘Environmental Review and Management Program (ERMP)’, EPA
Assessment No 1819, Toro Energy, Norwood, SA, Australia Toro Energy Limited, 2012, ‘Environmental Review and Management Program (ERMP):
Response to Submissions’, EPA Assessment No 1819, Toro Energy, Norwood, SA, Australia
Van Genuchten, M.T., 1980, ‘A closed form equation for predicting the hydraulic conductivity
of unsaturated soils’, Soil Sci. Soc. Am. J., vol. 44, pp. 689-710 Walter, M.T.; Kim, J.S.; Steenhuis, T.S.; Parlange, J.Y.; Heilig, A.; Braddock, R.D.; Selker, J.S.;
Boll, J., 2000, ‘Funneled flow mechanisms in a sloping layered soil: Laboratory investigation’, Water Resources Research, vol. 36 (4), pp. 841-849
Waugh, W.J., 2004, Design, Performance and Sustainability of Engineered Covers for Uranium
Mill Tailings, Environmental Sciences Laboratory, SM Stoller Corporation, Grand Junction, Colorado, USA
Patrick Dunne
Page | 50
Yanful, E.K.; Mousavi, S.M.; De Souza, L.P, 2006, ‘A numerical study of soil cover performance’, Journal of Environmental Management, vol. 81, pp. 72-92
Yanful, E.K.; Simms, P.H., Payant, S.C., 1998, ‘Soil Covers for Controlling Acid Generation in
Mine Tailings: A Laboratory Evaluation of the Physics and Geochemistry’, Water, Air and Soil Pollution, vol. 114, pp. 347-375
Yurisich, A., 2012, ‘Response to questions from Ray Claudius, OEPA, 22 December 2011 & 5
January 2012’, Toro Energy, West Perth, WA, Australia
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Appendices
Appendix A: Full Grain Size Distribution Results Sample 1 Sieve size (mm) soil W (g) W % sum W % % finer
4.75 0.6 0.2 0.2 99.8 2.36 3.6 1.2 1.4 98.6 1.18 42.5 14.0 15.4 84.6 0.6 93.2 30.8 46.2 53.8
0.425 38.5 12.7 59.0 41.0 0.3 34.6 11.4 70.4 29.6
0.212 29.8 9.9 80.3 19.7 0.15 24.4 8.1 88.3 11.7
0.106 18.3 6.0 94.4 5.6 0.075 10.2 3.4 97.8 2.2
0 6.8 2.2 100 0 total weight 302.5
Sample 2 Including hydrometer results Sieve size (mm) soil W (g) W % sum W % % finer
4.75 0 0 0 100 2.36 0.1 0.0 0.0 100.0 1.18 0.1 0.0 0.1 99.9 0.6 12.8 4.3 4.4 95.6
0.425 15.4 5.2 9.5 90.5 0.3 18.4 6.2 15.7 84.3
0.212 17.1 5.7 21.4 78.6 0.15 14.1 4.7 26.1 73.9
0.106 32.9 11.0 37.1 62.9 0.075 43 14.4 51.5 48.5 0.054 36.5 12.2 63.8 36.2 0.039 7.1 2.4 66.2 33.8 0.028 8.1 2.7 68.9 31.1 0.021 11.2 3.8 72.6 27.4 0.015 10.2 3.4 76.1 23.9 0.011 8.1 2.7 78.8 21.2
0.0081 8.1 2.7 81.5 18.5
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0.0058 6.1 2.0 83.6 16.4 0.0042 6.1 2.0 85.6 14.4 0.0030 3.1 1.0 86.6 13.4 0.0021 3.1 1.0 87.6 12.4 0.0012 4.1 1.4 89.0 11.0 0.0011 2.0 0.7 89.7 10.3 0.0009 0 0 89.7 10.3 0.0007 0 0 89.7 10.3
0 30.77 10.30 100.0 0.0 total weight 298.6
Sample 3 Sieve size (mm) soil W (g) W % sum W % % finer
4.75 9 2.9 2.9 97.1 2.36 18.2 6.0 8.9 91.1 1.18 67.4 22.1 31.0 69.0 0.6 88.3 28.9 59.8 40.2
0.425 37.6 12.3 72.2 27.8 0.3 29.2 9.6 81.7 18.3
0.212 19.7 6.4 88.2 11.8 0.15 13.7 4.5 92.6 7.4
0.106 8.8 2.9 95.5 4.5 0.075 4.5 1.5 97.0 3.0
0 9.2 3.0 100 0 total weight 305.6
Sample 4
Sieve size (mm) soil W (g) W % sum W % % finer 4.75 0 0 0 100 2.36 2.8 0.9 0.9 99.1 1.18 18.5 6.1 7.0 93.0 0.6 58.8 19.3 26.3 73.7
0.425 51 16.7 43.0 57.0 0.3 47.4 15.6 58.6 41.4
0.212 35.2 11.5 70.1 29.9 0.15 24 7.9 78.0 22.0
0.106 25.1 8.2 86.2 13.8 0.075 16.5 5.4 91.6 8.4
0 25.5 8.4 100 0 total weight 304.8
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Sample 5 Sieve size (mm) soil W (g) W % sum W % % finer
4.75 6.8 2.2 2.2 97.8 2.36 8.3 2.7 4.9 95.1 1.18 36.5 11.9 16.8 83.2 0.6 78.7 25.6 42.4 57.6
0.425 37.1 12.1 54.5 45.5 0.3 36.6 11.9 66.4 33.6
0.212 27 8.8 75.2 24.8 0.15 21.2 6.9 82.1 17.9
0.106 14.7 4.8 86.9 13.1 0.075 9.7 3.2 90.0 10.0
0 30.6 10.0 100 0 total weight 307.2
Appendix B: Full Pressure Plate Testing and Fredlund-Xing SWRC Results
!"#$%%&#$!"'()$!)$%)!*$+,-)%!.+/&%!0+%1!*$+,-)!234! !
5678!29:;<4!!:==>689!=?8<<@?8! <:7=>8!A!B863C5! <:7=>8!D!B863C5! <:7=>8!E!B863C5!
FG":! HI! JJ! JAKI! L!LMG":! NJKL! JDKI! HNKA! A!AMG":! NE! HHKA! HLKH! D!FMG":! NMKE! HFKA! NNKF! N!LMMG":! IJ! HEKI! NIKE! LF!AMMG":! INKL! HDKA! NEKH! AA!O6P:>!9?;!B863C5! FFKD! NIKA! INKA!
!
Water retention curves were created using this data; and equations as described in Fredlund &
Xing (1994). Key Fredlund-Xing Fitting Curve results are as follows, where:
Mr : Mass of sample ring (g) Mr+s : Mass of ring & sample (g) Ms : Mass of soil sample (g)
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Md : Mass of dry soil sample (g) w : Water content V : Volume of soil sample (cm3) 'd : Dry density of soil sample (g/cm3) " : Applied pressure / matric suction (kPa) ! : Volumetric water content (VWC) !s : Saturated VWC a : Curve-fitting parameter m : Curve-fitting parameter n : Curve-fitting parameter related to slope at inflection point
Initial Conditions: Sample 2
Mr Mr+s Ms Md w V 'd 30.53 92.90 62.37 55.27 0.128460286 47.515 1.163
$ Mr+s Ms w ! 1 122.2 91.67 0.658585128 0.765934503 5 116.5 85.97 0.555455039 0.64599421 10 109.6 79.07 0.430613353 0.500803329 20 104.5 73.97 0.338339063 0.39348833 50 100.9 70.37 0.27320427 0.317736566 100 99.5 68.97 0.247874073 0.288277547 200 97.6 67.07 0.213497377 0.248297449
!"#$%&'$()*+,-*)*, .&))&(/,0%12$334,5*'#+$,6,
572)&1(8,9,:;0*<,=>?8,@, @,A&))&(/, :@,B,@,A&))&(/<6, 0*%*'$)$%3, C(&)&*+,=*+7$,, D$37+),
L! MKFII! MKFII! !! Q<! MKFII! EFGHH,F! MKEHM! MKEHD! LKADIFJ$RMF! :! H! GFEHE,LM! MKDII! MKDFH! IKEMDEH$RMF! 7! LKLHD! EFGIJ,AM! MKAFD! MKAIL! NKHIEJN$RMF! P! MKNHH! 6FH6G,FM! MKLHJ! MKLJF! DKDIHDN$RMF! !! !! !!LMM! MKLNN! MKLIN! JKIML$RMF! !! !! !!AMM! MKLEN! MKLEH! EKHIDJF$RMH! !! !! !!%&.!
! !MKMMMAHENJD!
! ! !
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Initial Conditions : Sample 3
Mr Mr+s Ms Md w V 'd 30.33 111.70 81.37 76.17 0.068268347 47.515 1.603
$ Mr+s Ms w ! 1 133.4 103.07 0.353157411 0.56611133 5 129.3 98.97 0.299330445 0.479826703 10 123.9 93.57 0.228436392 0.366183537 20 118.5 88.17 0.15754234 0.25254037 50 115.5 85.17 0.118156755 0.189405278 100 114.9 84.57 0.110279638 0.176778259 200 113.5 83.17 0.091899698 0.147315216
!"#$%&'$()*+,-*)*, .&))&(/,0%12$334,5*'#+$,J,
572)&1(8,9,:;0*<,=>?8,@, @,A&))&(/, :@,B,@,A&))&(/<6, 0*%*'$)$%3, C(&)&*+,=*+7$,, D$37+),
L! MKFII! MKFII! !! Q<! MKFII! EFGHH,F! MKEHM! MKEHD! LKADIFJ$RMF! :! H! GFEHE,LM! MKDII! MKDFH! IKEMDEH$RMF! 7! LKLHD! EFGIJ,AM! MKAFD! MKAIL! NKHIEJN$RMF! P! MKNHH! 6FH6G,FM! MKLHJ! MKLJF! DKDIHDN$RMF! !! !! !!LMM! MKLNN! MKLIN! JKIML$RMF! !! !! !!AMM! MKLEN! MKLEH! EKHIDJF$RMH! !! !! !!%&.!
! !MKMMMAHENJD!
! ! ! Initial Condition : Sample 4
Mr Mr+s Ms Md w V 'd 30.3 102.00 71.7 67.2 0.066964286 47.515 1.414
$ Mr+s Ms w ! 1 128.8 98.5 0.46577381 0.658604167 5 122.9 92.6 0.37797619 0.534458333 10 117.5 87.2 0.297619048 0.420833333 20 112.1 81.8 0.217261905 0.307208333 50 107.8 77.5 0.15327381 0.216729167
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100 106.7 76.4 0.136904762 0.193583333 200 105.1 74.8 0.113095238 0.159916667
Experimental Data Fitting Process: Sample 4
Suction, $ (kPa) VWC, !
! fitting (! - ! fitting)2 Parameters Initial Value Result
1 0.659 0.659 !s 0.659 0.659 5 0.534 0.537 6.22134E-06 a 7.000 4.885 10 0.421 0.416 2.27423E-05 m 1.087 0.727 20 0.307 0.310 5.27353E-06 n 0.338 1.881 50 0.217 0.224 5.33418E-05 100 0.194 0.186 5.54472E-05 200 0.160 0.160 1.52163E-07
SUM
0.000143178