Stabilization of Unsealed Mine Haul Roads Using MSWI Fly Ash under Seasonal Moisture Variation
Creators: name: Abdul Majeed, Zarafath Zimar
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400502
subject: Civil geotechnical engineering

description: The mining industry contributes significantly to the global economy. Australia holds a prominent position in the global mining sector and consistently receives recognition for its continuously expanding industry. Mine haul roads are a significant component of the mining industry and are used by heavy trucks and machinery. Typically, the operating and maintenance cost of the haul roads are higher compared to the design and construction costs. These mine haul roads are often constructed as unsealed roads using marginal materials. Direct exposure to rainfall causes significant challenges to mine haul roads, especially when the existing subgrade is expansive clays or collapsible soils. The calcium-based stabilisation approach is generally used to treat this soft soil.

Common additives like cement, lime, and coal fly ash are traditionally used to treat problematic soils. However, there is a growing interest in exploring more sustainable and cost-effective alternatives to these additives, which are often destined for landfills. One such alternative is municipal solid waste incineration (MSWI) fly ash, a by-product of waste incineration in waste-to-energy (WTE) plants. This study focuses on evaluating how MSWI fly ash compares to coal fly ash in stabilizing expansive clay on mine haul roads, particularly in response to seasonal moisture variations. Therefore, this study investigated the performance of MSWI fly ash treated expansive clay on mine haul roads for the seasonal moisture variation compared to the coal fly ash. 

The study employs a comprehensive approach, incorporating laboratory testing and numerical simulations to assess the performance of untreated and MSWI fly ash-treated pavements. The study explores several factors, including the mechanical, hydraulic, durability, microstructural, and environmental aspects. Mechanical properties are evaluated through various strength tests under varying moisture conditions and cyclic loading. Hydraulic behaviour is assessed through tests for shrinkage, swelling, consolidation, and soil water characteristics. Durability performance is assessed through cyclic wet and drying tests. Results from the study indicate that MSWI fly ash treated expansive clay outperforms untreated samples and those treated with coal fly ash in both mechanical and hydraulic aspects. Microstructural tests provide insights into the chemical transformations and structural changes during the stabilization process, highlighting the crucial role of cation exchange in MSWI fly ash treated clays. 

Furthermore, the study evaluates the environmental impact of the treated samples, including leachate testing, which conforms to state regulatory limits. Additionally, a life cycle assessment examines the environmental advantages of using MSWI fly ash in pavement applications. Using the experiment data, finite element 3D models were created using the Abaqus finite element package. These models are validated with field data for both static and dynamic scenarios. Once validated, they are employed to predict the performance of control soil and MSWI fly ash stabilized mining haul roads under operational traffic and changing moisture conditions to understand the rutting behaviour of these pavement models.

This research contributes significantly to the mining industry's efforts to enhance the sustainability and cost-effectiveness of mine haul road construction and maintenance, with MSWI fly ash emerging as a promising alternative for soil stabilization.