Segment Bolt

Segment Bolt — Product Introduction

The segment bolt is a key fastener used in shield tunneling construction to connect precast lining segments. Through straight or curved designs, it assembles segmented blocks into a tunnel structure, fulfilling the core functions of ensuring overall tunnel stability and controlling ground settlement. By structure, products are divided into double-end straight type, double-end curved type, hex-head curved type, etc. Common strength grades cover 5.8, 6.8, and 8.8; materials include Q235 carbon steel, 45# steel, and 40Cr alloy steel. To cope with underground humid environments, hot-dip galvanizing, Dacromet coating, and other surface treatments are commonly adopted to enhance corrosion resistance.

I. Product Features

• Strong structural adaptability: The straight bolt has a linear shank, mainly used for longitudinal segment connection; the curved bolt’s shank curvature matches the inner/outer arc curvature of the segment, used primarily for circumferential segment connection, avoiding stress concentration at the bore and fitting narrow curved installation spaces.
• Complete range of strength grades: Commonly 5.8, 6.8, and 8.8 grades; depending on geological conditions and load requirements, grades 4.6, 4.8, 5.6, and 10.9 can also be selected.
• Diverse materials: Commonly Q235 carbon steel, 45# steel, and 40Cr alloy steel; after quenching and tempering, 40Cr can reach a tensile strength above 800 MPa.
• Comprehensive anti-corrosion process: Hot-dip galvanizing (zinc coating thickness ≥85 μm), Dacromet coating, nano-composite powder zinc infiltration, and other surface treatments are commonly used; salt spray test can reach 720 h without red rust, with anti-corrosion life ≥50 years.
• High thread precision: Thread precision reaches grade 6g, ensuring good matching with nuts; diameter range typically M24–M36.

II. Product Advantages

• High load-bearing capacity: Uses high-strength alloy steel, tensile strength ≥800 MPa, yield strength ≥640 MPa (grade 10.9), meeting the complex load requirements of shield tunnels.
• Excellent fatigue resistance: Under cyclic load (0.2–0.6 times ultimate load), fatigue life ≥2 million cycles, adapting to alternating stress during long-term tunnel operation.
• Reliable anti-loosening: Used with anti-loosening washers or thread-locking adhesive, effectively preventing preload loss caused by vibration and ensuring connection stability.
• Adaptable to complex geology: Through material upgrades and structural optimization, it can adapt to complex geological conditions such as soft soil, hard rock, and high water pressure.
• High construction efficiency: Supports a two-stage tightening process — initial tightening immediately after segment assembly, re-tightening after shield advancement — ensuring structural sealing.

III. Application Scope

• Metro tunnels: Segment connection in urban rail transit shield tunnels — the most core application scenario.
• Highway and railway tunnels: Highway river-crossing shield tunnels, railway shield tunnels, and other large tunnel projects.
• Water conservancy and energy tunnels: Power plant water-intake shield tunnels, cooling-water circulation shield tunnels, hydropower transmission tunnels, etc.
• Municipal and civil defense works: Sewage discharge tunnels, municipal pipeline tunnels, civil defense works, etc.
• Special engineering tunnels: West-East Gas Pipeline shield tunnel, gas pipeline projects, subsea ocean tunnels, military dedicated works, etc.
• Steel and concrete segment connection: Suitable for connection of steel segments and concrete segments; common specifications such as M24×531, etc.