ACARP ACARP ACARP ACARP
Open Cut

Shear Strength Characterisation of In-pit Mud to Ensure Low Wall Stability

Open Cut » Geology

Published: June 19Project Number: C25040

Get ReportAuthor: David Williams | The University of Queensland

High wet season rainfall totals between 2008 and 2013 resulted in the extensive flooding of open cut coal mines, particularly in the Bowen Basin and the formation of in-pit “mud” up to 10 m deep.  To re-start mining and spoiling in-pit, it has proved necessary to remove the mud, which is incurring a very high cost.

This project addressed the high potential for the geotechnical instability and failure of low wall spoil dumped on in-pit, water-softened spoil or floor material (known in the industry as “mud”), specifically:

  • Minimisation of geotechnical risk with a focus on deeper excavations and higher spoils; including the improved understanding, modelling, monitoring and management of principal hazards; and
  • Improved assessment and evaluation of hydrogeology on mining, including impacts on slope stability and degradation of material parameters.

Not having to remove undegraded wet-up spoil and floor materials will produce very significant cost and time savings, particularly in situations where the cleaning out of pit bases presents logistical problems.  The results of the project will also lead to generally improved characterisation of spoil and floor materials subjected to wetting-up by rainfall runoff and groundwater inflow accumulated in the pit, and to improved estimates of the degraded shear strength parameters of spoil and floor materials susceptible to water-softening.

The objectives of this project were to:

  • Sample and collect fresh spoil and degraded mud that had formed in-pit from mines within the Bowen Basin;
  • Characterise the material, to determine its shear strength; and to
  • Investigate the impact these results have on low wall design.

The laboratory testing involved physical, chemical, mineralogical, geochemical and geotechnical characterisation of all spoil and mud samples, tested as sampled and after degradation.  The testing included moisture content, total suction, Atterberg limits, specific gravity, electrical conductivity, pH and Emerson class testing.  Particle size distributions were determined dry and after 24 hours of soaking.  For spoil materials, the influence of prolonged saturation and wetting and drying cycles were also investigated.  The geotechnical testing included standard consolidation and direct shear testing as sampled and after 24 hours of saturation.  Select mud samples were also investigated using a large slurry consolidometer, simulating in-pit spoiling and the measuring the influence the loading rate had on pore water pressures and consolidation.

Results were used to identify relationships between the determined material characteristics and their geotechnical parameters, and to understand the degree of degradation.  A modified slake durability test was developed allowing for the rapid identification of degradable materials.  Comparisons of the shear strength results were made to the current BMA spoil strength framework using the program Slide 7.0 for four scenarios typical of Australia open pit coal mining operations.  A model was also developed using particle size distribution results to estimate the shear strength of in-pit mud.

Underground

Health and safety, productivity and environment initiatives.

Underground

Open Cut

Safety, productivity and the right to operate are priorities for open cut mine research.

Recently Completed Projects

C19024Establishing Ecologically Sustainable Mine Water Release Criteria In Seasonally Flowing Streams

Extreme rainfall conditions in the Fitzroy Catchment over an approxi...

C25030Coal Mine Open Pit Final Void Closure And Relinquishment - Addressing Uncertainty In Coal Mine Environmental Planning

This report addresses uncertainties faced by coal mine operators whe...

C27046Estimation Of True Deformation Vector From Slope Radar Monitoring

Slope deformation radar monitors are now widely used in open cut coa...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27004Improving Coal Flotation With Oscillatory Air Supply

This report provides detailed information on coal flotation with os...

C25018Improving Solids Recovery And Moisture Reduction In Ultrafine Coal Dewatering

This report provides detailed information on fine coal dewatering in...

C27028Lab Froth Flotation Testing Guide With Coal Quality

Correct outcomes from laboratory froth flotation testing in coal bor...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C26039Nanoporosity In Cokes: Their Origin, Control And Influence On CO2 Reactivity

This project using the outcomes of previous project C24060, examine...

C28063A Comprehensive Technical Review Of High-Efficiency Low-Emission (HELE) Pulverised Coal Combustion Technologies For Power Generation

Research and development has been undertaken worldwide to realise co...

C28064Carbon Structure Transformation During Coking Of Australian Coking Coals: Better Understanding The Coke Formation

Carbon structures of coke that are formed during the plastic layer a...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C28076Selective Absorption Of Methane By Ionic Liquids (SAMIL) - Phase 2 Demonstration In A Packed Bed Reactor

An alternative approach to high temperature oxidation of ventilation...

C26004CFD Modelling Of Reverse Thermal Oxidisers For VAM Abatement - CFD Modelling Of Fixed-Bed RTO Devices

The project is part of a larger multi‐phase program of study a...

C27058Technological Assessment Of A Recycle Reactor For VAM Abatement

Underground coal mining emits high volumes of methane, diluted in ve...

Mine Site Greenhouse Gas Mitigation

Low Emission Coal Use

Step-change technologies aimed at reducing greenhouse gas emissions.

Recently Completed Projects

C17060BGasification Of Australian Coals

Four Australian coals were trialled in the Siemens 5 MWth pilot scale ga...

C17060AOxyfuel Technology For Carbon Capture And Storage Critical Clean Coal Technology - Interim Support

The status of oxy-fuel technology for first-generation plant is indicate...

C18007Review Of Underground Coal Gasification

This report consists of a broad review of underground coal gasification,...

Low Emission Coal Use

Mining And The Community

The relationship between mines and the local community.

Recently Completed Projects

C16027Assessing Housing And Labour Market Impacts Of Mining Developments In Bowen Basin Communities

The focus of this ACARP-funded project has been to identify a number...

C22029Understanding And Managing Cumulative Impacts Of Coal Mining And Other Land Uses In Regions With Diversified Economies

The coal industry operates in the context of competing land-uses that sh...

C23016Approval And Planning Assessment Of Black Coal Mines In NSW And Qld: A Review Of Economic Assessment Techniques

This reports on issues surrounding economic assessment and analysis ...

Mining And The Community

NERDDC

National Energy Research,Development & Demonstration Council (NERDDC) reports - pre 1992.

Recently Completed Projects

1609-C1609Self Heating of Spoil Piles from Open Cut Coal Mines

Self Heating of Spoil Piles from Open Cut Coal Mines

1301-C1301Stress Control Methods for Optimised Development...

Stress Control Methods for Optimised Development and Extraction Operations

0033-C1356Commissioned Report: Australian Thermal Coals...

Commissioned Report: Australian Thermal Coals - An Industry Handbook

NERDDC