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James Penman, Terence Jibiki, Len Murray, and Mark Rynhoud

Two earthfill embankments are being constructed to form an impoundment in a mountainous region with a tropical climate. The embankment abutments are underlain by tropical weathered rock/soil including a significant thickness of residual soil. Previous slope failures within the area, including a 150 m wide failure of a construction access road, have been potentially due to weakness of the residual soil. In order to quantify the potential risk to the embankments, a geotechnical characterisation program consisting of in situ and laboratory testing was completed to determine the shear strengths and loading response within the residual soil material. This paper summarises the geotechnical investigation program and characterisation of this tropical residual soil in the context of the embankment stability.

Results of laboratory direct simple shear testing are presented and compared to common empirical methods for estimating the undrained shear strength of both over-consolidated and normally-consolidated materials using index properties and/or over-consolidation ratios. Methods used for comparison include those proposed by Skempton (1952 & 1957), Bjerrum-Simons (1960), Lambe & Whitman (1969) and Wroth & Houlsby (1985) for normally consolidated material and Ladd (1977) and Jamiolkowski et al. (1985) for over-consolidated material.

The results of in situ testing, including pocket penetrometer data and field shear vane data, are also presented.

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2016 Papers

2016 – Geotechnical Characterisation of a Tropical Residual Soil in an Embankment Abutment
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James Penman, Terence Jibiki, Len Murray, and Mark Rynhoud

Two earthfill embankments are being constructed to form an impoundment in a mountainous region with a tropical climate. The embankment abutments are underlain by tropical weathered rock/soil including a significant thickness of residual soil. Previous slope failures within the area, including a 150 m wide failure of a construction access road, have been potentially due to weakness of the residual soil. In order to quantify the potential risk to the embankments, a geotechnical characterisation program consisting of in situ and laboratory testing was completed to determine the shear strengths and loading response within the residual soil material. This paper summarises the geotechnical investigation program and characterisation of this tropical residual soil in the context of the embankment stability.

Results of laboratory direct simple shear testing are presented and compared to common empirical methods for estimating the undrained shear strength of both over-consolidated and normally-consolidated materials using index properties and/or over-consolidation ratios. Methods used for comparison include those proposed by Skempton (1952 & 1957), Bjerrum-Simons (1960), Lambe & Whitman (1969) and Wroth & Houlsby (1985) for normally consolidated material and Ladd (1977) and Jamiolkowski et al. (1985) for over-consolidated material.

The results of in situ testing, including pocket penetrometer data and field shear vane data, are also presented.
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2017 Papers

2017 – The Hamata Tailings Dam Design and Construction at the Hidden Valley Mine in Papua New Guinea
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Mark Stephen Rynhoud, David Johns and Len Murray

The Hamata tailings storage facility at the Hidden Valley mine is being constructed in a remote, high rainfall, tropical environment in a mountainous region of Papua New Guinea. Implementation of the design hasrequired adapting the design in response to various challenges encountered on the site during the ongoing construction period, based on observations by the designers and site monitoring data which is continuously collected and compared against design assumptions. This paper describes some of the design and construction modifications which have been implemented since construction of the tailings facility started and provides a case history of some of the challenges facing designers and construction crews when mining in remote, tropical conditions.
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2008 Papers

2008 – Towards responsible management of tailings facilities
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Elizabeth Gardiner, Len Murray, David Gladwin

Abstract: The Mining Association of Canada has worked over the past 12 years to improve the management of tailings facilities. This effort began out of a realization that tailings present a major business risk to the mining industry, and that a series of major tailings failures around the world in the 1990’s were fundamentally indicative of need for improved care and management practices by tailings dam and facility owners and operators. MAC established and continues to sponsor the Tailings Working Group, which has assisted in development and publication of a three-volume set of guides to improve tailings management:

•“A Guide to the Management of Tailings Facilities”, initially published in 1998, updated edition published in 2008;

•“Developing an Operation, Maintenance and Surveillance Manual for Tailings and Water Management Facilities”, published in 2003; and

•“A Guide to Audit and Assessment of Tailings Facility Management”, published in 2008.
The three guides provide a strong message that the key to safe and environmentally responsible management of tailings is consistent application of sound engineering capability within an effective management framework.

The documents are almost directly applicable to all forms of dams and are widely used for water dams. Also, because the documents are available in Spanish and French they have found wide use in International projects.

A brief comparison with published ANCOLD guidelines is provided.

Keywords: Management of tailings facilities and water dams, Operation, Maintenance and Surveillance, Auditing, risk, safety, guides
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2010 Papers

2010 – Hidden Valley – Design and Construction of Highland Papua New Guinea First Tailings Dams
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Rick Friedel, Len Murray, Gerrad Suter, James Penman, James Watt, Hendra Jitno

The Hidden Valley tailings storage facility (TSF) has set a new precedent in environmental management of tailings in Papua New Guinea (PNG). Modern mining in PNG arguably began with the development of Bougainville Copper in the late 1960s, and continued through to Ok Tedi, Porgera, Lihir, Misima (and others). These mines have proceeded with deep sea or riverine tailings deposition, rather than construction of a tailings dam to retain the mine waste within an impoundment; as is the practice throughout the majority of the mining industry.
The Hidden Valley TSF is comprised of two large earth and rock fill dams, raised by the downstream method. Starter dam construction was completed in 2009. At final height the Main Dam will be one of the highest tailings dams in the world. The dams are constructed of pit waste and therefore have the dual function of storing tailings and waste rock.
Construction of the starter dams and subsequent raises is complicated by conditions at the site. Water management was, and remains, the dominant issue. High rainfall, weak erosive soils, material availability, dense vegetation and remoteness of the site provide constant challenges to construction. The Observational Approach to construction was recommended by the designers and adopted by the mine operator. This involves a knowledgeable pre-assessment of what is likely to change and having contingency plans to deal with possible major issues. This approach allows changes to the design during construction so the “as-built” product is suited for the site, fit for purpose, and remains consistent with the overall intent of the design.
The TSF has been in operation since August 2009 and monitoring data of the structures has been collected during construction and operation. This data is reviewed to confirm design assumptions and assess dam performance.
Personnel involved with this project combined their experiences working in the PNG environment and dam building from other locations. This process led to close interaction between the mine operators, designers and construction teams. Team work and diligent construction practices were and will continue to be necessary to construct and operate the pioneering TSF in PNG.
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