Zhuojin Pipe Fitting Co., LtdJack-Up Shrinkable CFST Support Test and Engineering Application
Literature Overview
This study, published in the Journal of the China Coal Society in 2022 by researchers from Shandong Jianzhu University and Shandong University of Science and Technology, presents a comprehensive investigation of jack-up shrinkable concrete-filled steel tubular (CFST) supports for roadway support in coal mining. Supported by the National Natural Science Foundation of China (Grant 51704176), Shandong Postdoctoral Innovation Fund (202003080), and Shandong University Civil Structure Disaster Prevention and Mitigation Collaborative Innovation Center (XTP201923), the research addresses the challenges of long-term roadway stability in the immediate surrounding area of mined-out panels.
Core Technical Contributions
The study proposes a novel jack-up shrinkable CFST support system that combines high bearing capacity with controlled deformability. The system is designed to resist roof pressure while allowing controlled compression to accommodate strata movement, making it suitable for the demanding conditions of roadway support in the immediate surrounding area of mined-out panels.
Support Structure Design
The jack-up shrinkable CFST support consists of a steel tube filled with concrete, a jack-up mechanism for initial roof contact, and a shrinkable structure that provides controlled compression resistance. The shrinkable structure options include yang wood, pine wood, and steel wire mesh, each with different compression characteristics.
| Shrinkable Structure | Compression Stage Bearing Capacity (kN) | Ultimate Bearing Capacity (kN) | Maximum Compression Rate |
|---|---|---|---|
| Yang wood | 200 | 700 | Moderate |
| Pine wood | 500 | 900 | 77.7% |
| Steel wire mesh | 400 | 750 | Lower than pine wood |
The test results clearly demonstrate that pine wood is the most suitable shrinkable structure, offering the highest compression rate of 77.7% and a good balance between compression stage bearing capacity and ultimate bearing capacity. The high compression rate means that pine wood can absorb significant strata movement before reaching its ultimate capacity, providing a longer warning period before failure.
CFST Column Bearing Capacity Tests
The study conducted bearing capacity tests on both short and long CFST columns to verify the high bearing capacity characteristics of the support system. The test results were used to correct the slenderness ratio reduction factor and optimize the bearing capacity calculation formula for the jack-up shrinkable CFST support.
The corrected slenderness ratio reduction factor accounts for the composite action between the steel tube and the concrete core, which provides enhanced stability compared to hollow steel tubes. The optimized bearing capacity formula incorporates the jack-up mechanism, the shrinkable structure, and the CFST column properties to provide a comprehensive prediction of the support's load-deformation behavior.
Roadway Support Resistance and Compression Calculation
The study analyzed the roadway support resistance and compression requirements using literature-based methods. The case study of the Luoxi Coal Mine 3_(lower)A02 working face roadway demonstrated the practical application of the support system. The calculated support resistance and compression were used to determine the appropriate number and arrangement of supports.
Engineering Application Results
The engineering practice demonstrated that a single row of φ299 mm × 10 mm jack-up shrinkable CFST supports, combined with a row of φ21.6 mm × 10300 mm roof control anchor cables, along with a wind curtain and mesh spraying layer for mined-out area isolation, can ensure long-term roadway stability. The system exhibited excellent initial roof contact through the jack-up mechanism, strong resistance-increasing deformation capacity, and high support bearing capacity.
Engineering Practice Implications
The jack-up shrinkable CFST support system offers several advantages for roadway support in coal mining:
- The jack-up mechanism ensures immediate roof contact upon installation, eliminating the gap that can occur with conventional supports and reducing the risk of roof caving.
- The shrinkable structure provides controlled deformation capacity, allowing the support to accommodate strata movement without sudden failure.
- The CFST column provides high bearing capacity and durability, making it suitable for long-term roadway support in heavily stressed areas.
- The combination of CFST supports with roof control anchor cables and mined-out area isolation provides a comprehensive support system that addresses multiple failure mechanisms.
The study also suggests that combining the jack-up shrinkable CFST support with roof cutting stress relief on the mined-out side and recovery and reuse of the outer steel tube would further improve the effectiveness of the roadway support system. These additional measures would reduce the stress concentration on the support and provide economic benefits through material recovery.
Study Insights and Reflections
This research demonstrates the practical application of CFST technology in a challenging underground mining environment. The jack-up shrinkable CFST support represents an innovative integration of structural engineering principles and mining support requirements. The controlled deformability provided by the shrinkable structure is a key feature that distinguishes this system from rigid support solutions, which may fail catastrophically under excessive strata movement.
The choice of pine wood as the shrinkable structure is noteworthy. While wood is a renewable resource, its use in underground mining applications requires careful consideration of moisture content, decay resistance, and long-term performance. The high compression rate of pine wood suggests that it can undergo significant plastic deformation before failure, which is desirable for a support system that needs to accommodate unpredictable strata movement. However, the long-term durability of wood in the humid underground environment should be monitored, and replacement procedures should be established.
The engineering case study provides valuable real-world validation of the support system. The successful application at the Luoxi Coal Mine demonstrates that the theoretical design and experimental results can be translated into practical engineering solutions. The combination of CFST supports, anchor cables, and isolation measures provides a robust system that addresses the complex loading conditions in the immediate surrounding area of mined-out panels.
Future research directions should include the long-term performance monitoring of the support system under actual mining conditions, the development of predictive models for support life and maintenance intervals, and the optimization of the support system parameters for different geological conditions. The integration of monitoring technologies to provide real-time feedback on support performance would enhance the safety and efficiency of the system.
In conclusion, this study presents a comprehensive investigation of the jack-up shrinkable CFST support system, from structural design and experimental testing to engineering application. The results demonstrate that this system is a viable and effective solution for roadway support in coal mining, offering high bearing capacity, controlled deformability, and long-term stability. The research contributes to the advancement of underground support technology and provides practical guidance for the design and implementation of CFST-based support systems in mining engineering.