Evaluating Pit Rock as an Alternative Rehabilitation Material
Services: Rehabilitation performance assessment, UAV LiDAR and multispectral surveying, electromagnetic surveying, field sampling and vegetation assessment
Location: Queensland
Date: 2020 - 2021
Carrying out a drone-based asssessment to document surface condition
Our Scope
Rock mulching can help protect mine rehabilitation surfaces from erosion, but sourcing suitable quarry rock can add significant cost through additional drilling, blasting and haulage.
In 2017, this client established a 10,000 bank cubic metre trial to investigate whether rock extracted during mining could provide a practical alternative.
For pit rock to perform effectively in rehabilitation, it must remain sufficiently competent when exposed to weathering, resisting breakdown and erosion, and avoid releasing salts or other materials that could constrain vegetation establishment. Verterra was engaged to assess the trial and determine whether the material could be a viable alternative to quarry rock.
PROVE
A multi-method assessment approach was developed to examine spatial variation across the trial and establish relationships between rock type, material properties, erosion and vegetation performance.
The assessment included:
Electromagnetic surveying to characterise spatial variation in spoil and sub-surface properties
UAV-based multispectral surveying to assess variation in vegetation cover and differentiate between sandstone and mudstone areas, and high-resolution UAV imagery to document surface condition and visible rehabilitation features
Experimental high-density UAV LiDAR to measure the trial surface and identify landform and erosion characteristics
RTK GPS ground-control surveying to accurately locate prominent sandstone and mudstone rocks and validate the remotely sensed data. This included sampling at six representative locations across the trial, followed by laboratory assessment
Ground-based photography documenting notable erosion and areas of successful rehabilitation
Vegetation assessment to examine establishment across different trial conditions
This comprehensive approach considered how differences in rock and spoil properties corresponded with erosion patterns and vegetation establishment across the trial.
IMPROVE
Verterra integrated the spatial, laboratory and field evidence into a quantitative evaluation of the pit rock trial.
The integrated assessment gave the client a basis for evaluating:
Whether the pit rock remained sufficiently competent after three years of weathering
The extent and distribution of erosion across the trial
Differences in performance between sandstone and mudstone materials
How spoil and rock variability influenced vegetation establishment
Whether observed problems were localised or indicative of broader material limitations
The suitability of pit rock for future rehabilitation applications
Where material-selection or rehabilitation specifications may need to be refined
Rather than making a decision based solely on visual inspection, the approach provided multiple lines of evidence for assessing performance and identifying the factors responsible for variation across the trial.
VALUE
The project provided a defensible assessment of whether locally available pit rock could offer a practical alternative to quarried material.
Evaluating the trial after three years helped the client avoid making future rehabilitation decisions based only on the initial appearance or short-term performance of the material, provided evidence about how the rock responded under actual site conditions, and whether its use could introduce longer-term rehabilitation risks.
The assessment supported better-informed decisions about:
Future selection and use of pit rock
Rehabilitation material specifications
The need for alternative or supplementary treatments
The trade-off between upfront material costs and long-term performance
The risk of erosion, repair and rehabilitation rework
The potential to scale the approach to other areas of the mine