How Carbon Fiber Wrapping Affects Coal Samples Under Compression

Jim Crocker
12th March, 2025

How Carbon Fiber Wrapping Affects Coal Samples Under Compression

The uniaxial compression testing setup (a) and strain gauge arrangement (b) used to measure axial and circumferential deformation of CFRP-confined coal cylinders under loading.

Image adapted from: Li et al. / CC BY (Source)

Key Findings

  • Researchers in China and Spain developed a carbon fiber method to strengthen abandoned coal pillars
  • Partially wrapped pillars matched the strength of fully wrapped ones, especially with closer spacing and more layers
  • This technique effectively prevents ground sinking, enhances safety, and is cost-efficient for mining areas
Ensuring the stability of abandoned coal pillars is crucial to prevent surface settlement, which can threaten nearby structures and infrastructure. In regions where coal mining has ceased, these pillars often lose their bearing capacity, increasing the risk of ground subsidence. Addressing this issue is vital for maintaining safety and reducing economic losses associated with structural damage. A recent study from Liaoning University of Technology, China, and the University of Vigo, Spain, explores an innovative approach to reinforcing coal pillars using carbon fiber reinforced plastic (CFRP)[1]. CFRP is a strong, lightweight material composed of carbon fibers embedded in a plastic resin, known for its high strength-to-weight ratio and durability. This research aims to develop a cost-effective method to enhance the mechanical properties of coal pillars, thereby mitigating the risks of surface settlement. The study focuses on partially-confined coal cylinders subjected to uniaxial compression, a test where force is applied along one axis to evaluate the material's response. By partially confining the coal cylinders with CFRP strips, the researchers aimed to improve their axial compression performance. The key parameters examined were the net spacing ratio, which refers to the distance between the CFRP strips relative to the size of the coal cylinder, and the number of CFRP strip layers applied. Varying these parameters allowed the team to assess their impact on the strength and deformation capacity of the coal pillars. Results from the experiments revealed that partially-confined coal cylinders exhibited mechanical properties comparable to fully-confined ones. The primary mode of failure in these partially-confined structures was the fracture of the CFRP strips and localized fracturing within the coal itself. Importantly, as the net spacing ratio decreased and the number of CFRP layers increased, both the peak strength and deformation capacity of the coal cylinders saw significant improvements. In some cases, the enhancement rate reached up to 409.36%, demonstrating the substantial effectiveness of CFRP reinforcement. Furthermore, the study observed the energy evolution pattern in CFRP-confined coal cylinders. Before reaching peak strength, energy predominantly accumulated as elastic energy, which is stored energy that can be released when the material deforms. After exceeding peak strength, the dissipation of energy increased sharply, indicating the material's ability to absorb and dissipate energy during failure. This behavior suggests that CFRP reinforcement not only enhances strength but also improves the material's resilience under stress. Considering the practical aspects of implementation, the researchers evaluated factors such as the equivalent thickness of the CFRP material used and the overall economic benefits. The optimal configuration identified was a net spacing ratio of 0.25 with six layers of CFRP wrapping. This arrangement provided the best balance between performance enhancement and material cost, offering a cost-effective solution for reinforcing coal pillars. This study builds on previous research, such as the development of pumpable standing supports using CFRP and sand-based materials in arid mining regions[2]. In that work, the combination of high-water cementing material with desert sand in a CFRP shell demonstrated effective strain hardening behavior and increased bearing capacity. Similarly, the current research leverages CFRP's confinement capabilities to enhance the structural integrity of coal pillars. By reducing the reliance on high-water cementing materials, both studies highlight CFRP's role in creating more sustainable and efficient reinforcement solutions. The integration of CFRP in mining applications presents several advantages. Its lightweight nature allows for easier handling and application compared to traditional materials like steel. Additionally, CFRP's resistance to corrosion and fatigue ensures long-term durability, which is essential in the harsh environments of underground mines. The ability to tailor the reinforcement by adjusting the net spacing ratio and the number of CFRP layers provides flexibility to meet specific engineering requirements. The implications of this research are significant for the mining industry, particularly in regions with extensive abandoned coal pillars. Implementing CFRP reinforcement can extend the lifespan of these structures, reduce maintenance costs, and enhance overall safety. Moreover, the optimized use of materials as demonstrated in the study aligns with sustainable engineering practices by minimizing resource consumption while maximizing performance. Future research could explore the application of similar CFRP reinforcement techniques in different geological settings and under varying stress conditions. Additionally, combining CFRP with other innovative materials could further enhance the mechanical properties and economic viability of reinforcement solutions. Investigating the long-term performance of CFRP-confined coal pillars in real-world mining operations would also provide valuable insights into their practical effectiveness and durability. In conclusion, the study conducted by Liaoning University of Technology and the University of Vigo represents a significant advancement in the field of mining engineering. By systematically analyzing the effects of CFRP confinement on coal cylinders, the research offers a promising method to address the critical issue of surface settlement caused by weakened coal pillars. Incorporating findings from earlier studies, this work underscores the versatility and effectiveness of CFRP as a reinforcement material, paving the way for safer and more sustainable mining practices.

Sustainability

References

Main Study

1) Mechanical behavior of CFRP partially confined coal cylinders under uniaxial compression

Published 10th March, 2025

https://doi.org/10.1371/journal.pone.0319491

Related Studies

2) Behavior of CFRP-Confined Sand-Based Material Columns under Axial Compression.

https://doi.org/10.3390/polym13223994


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