Application of Concrete-Filled Steel Tube Props in Kilometer-Deep Dynamic-Pressure Mine Roadways

Literature Overview

The paper by Gao Yanfa, Liu Keming, He Xiaosheng, Xie Hao, Gao Kunpeng, Chen Binghui, and Zhang Fengyin (2015), published in Coal Science and Technology (Vol. 43, No. 8, pp. 7-12), addresses the challenging problem of roadway support in kilometer-deep mine tunnels subjected to dynamic pressure. Funded by the National Natural Science Foundation of China (51474218; 51134025), the research is conducted at the School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing). The study proposes a high-strength composite support system based on concrete-filled steel tube (CFST) props for the Hua Feng Mine at the -1100 m level, where rock deformation is large and persistent.

Core Technical Content

Problem Analysis

At the -1100 m horizontal roadway of the Hua Feng Mine, the surrounding rock exhibited excessive deformation with prolonged deformation duration, leading to repeated failures of conventional support systems. The research team conducted on-site geological surveys, theoretical calculations, and field monitoring to analyze the deformation characteristics and instability mechanisms. The key finding was that the asymmetry of the surrounding rock structure leads to asymmetric deformation, requiring support systems capable of accommodating and resisting non-uniform loading conditions.

CFST Prop Design

Based on the bearing ring reinforcement theory for deep mine roadways, the proposed support system features an arc-wall semi-circular arch cross-section. The main steel tube is specified as φ194 mm × 8 mm seamless steel pipe, filled with C40 steel fiber reinforced concrete (SFRC). The system is supplemented with anchor-net-spray support and surrounding rock reinforcement grouting. This composite approach combines the high strength and ductility of the steel tube with the compressive capacity and energy absorption of the concrete infill.

Performance Results

The support system provides a support reaction force exceeding 0.93 MPa, effectively restraining the inward movement of surrounding rock into the roadway space. After support stabilization, the final surrounding rock deformation is less than 150 mm, meeting the roadway deformation requirements. The study emphasizes that asymmetric deformation requires enhanced monitoring of critical deformation locations, with support bearing capacity monitoring data guiding adaptive control measures.

Material and Manufacturing Specifications

Welding and Fabrication Considerations

From my perspective in steel pipe manufacturing and welding engineering, the selection of seamless steel pipe for the CFST props is well justified. At depths exceeding 1000 m, the confining pressure and rock burst potential create extreme loading conditions that demand the highest material quality and structural integrity. Seamless pipes offer uniform microstructure throughout the cross-section, free from the weld seam discontinuities inherent in ERW, HFW, or LSAW welded pipes. This uniformity is critical for the prop to function as a bearing ring, where localized weakness at a weld seam could initiate catastrophic failure under dynamic loading.

The concrete filling process inside the φ194 mm diameter tube presents practical challenges. The relatively small diameter compared to the tube wall thickness (8 mm) requires careful attention to concrete flowability and compaction. Steel fiber reinforcement in the C40 concrete improves post-cracking ductility and bond strength at the steel-concrete interface, which is essential for the composite action of the CFST prop. The welding of prop segments during assembly must be performed with full-penetration butt welds using suitable filler metals (e.g., E7018 or equivalent per AWS A5.1), with post-weld inspection by ultrasonic testing (UT) to ensure complete fusion and absence of internal defects.

Bearing Ring Theory Application

The bearing ring reinforcement theory posits that a continuous ring of high-strength material surrounding the roadway opening redistributes stress away from the tunnel perimeter, creating a stable bearing arch in the surrounding rock. The CFST prop system implements this theory by providing a continuous, high-stiffness ring that can sustain the radial and tangential stresses imposed by the deep overburden. The asymmetric deformation observed in the field underscores the importance of the prop's ability to maintain its circular geometry under non-uniform loading, which is a direct consequence of the tube's high bending stiffness and the composite action with the concrete infill.

Study Insights and Implications

This research demonstrates the effectiveness of CFST props as a solution for extreme deep mining conditions where conventional support systems fail. The combination of seamless steel pipe and steel fiber reinforced concrete creates a composite member with exceptional compressive strength, ductility, and energy absorption capacity. For engineers in steel pipe manufacturing, the study validates the importance of seamless pipe quality in critical structural applications, where material uniformity and the absence of weld-related defects are non-negotiable. The field monitoring approach, which uses support bearing capacity data to guide adaptive deformation control, represents a best practice for managing risk in deep mine roadways.