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Tunnel Segment Bolt

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Introduction
Overview of Tunnel Segment Bolts
A tunnel segment bolt is a kind of special fastener used to link and fasten segments of shield tunneling machines during tunnel excavation. Through this kind of bolt connection, severkal arched segments can be connected into a circle, thereby supporting the entire tunnel surface. During excavation, the ground settlement can be effectively controlled, the impact on the ground buildings can be reduced, and the construction underwater can be effectively controlled. When digging, it does not affect the characteristics of water surface traffic. This kind of fastened connection piece designed as a straight line or a certain arc is called a tunnel bolt or segment bolt.

Tunnel Segment Bolts Type
According to various factors such as the size of the segment, the diameter of the shield tunneling machine, and the location of the tunnel where the segment is located, the design of segment bolts is also diverse. At present, the main types of tunnel segment bolts are:
(1) Double-headed straight tunnel segment bolts
(2)  Double-ended arc-shaped tunnel segment bolts
(3) Hexagonal arc tunnel segment bolts
(4)  Hexagon head arc threaded tunnel segment bolts
(5)  Hexagonal flange surface arc threaded tunnel segment bolts
(6) Non-standard tunnel segment bolts



    
Technical Support
Grade, Material and Surface Treatment of Tunnel Segment Bolts
Tunnel segment bolts, like other bolts and fasteners, are designed with different strength levels according to the application environment and different forces.
The commonly used grades are: 5.8, 6.8, and 8.8.
The corresponding production materials are: Q235, 45# steel, 40Cr and other materials.
Common surface treatments for tunnel segment bolts include hot-dip galvanizing (hot-dip galvanizing), Dacromet (commonly known as zinc-based Chromate), powder sherardizing, multiple composite powder sherardizing, etc. The quality of the surface treatment of the tunnel segment bolts is very important. Because the tunnel segment bolts are installed underground, they play a role in connecting the segments. The environment where it is located in humid, which can easily cause corrosion of bolts and cause rust. Therefore, if the surface treatment of the bolt fails to meet the design requirements, causing the bolt to rust during use, the corrosion to the inside of the bolt will affect the mechanical properties and tensile strength of the bolt. In relatively harsh environments, composite coatings, such as thermal spray zinc alloy or powder sherardizing + zinc-based chromate + alkali-resistant coating, can be used to enhance the corrosion resistance and alkali resistance of the product.

Mechanical and Physical Properties of Bolts and Studs
No. Mechanical and Physical Properties Performance Level
3.6 4.6 4.8 5.6 5.8 6.8 8.81) 9.8 10.9 12.9
d≤163) d>163)
1 Nominal Tensile Strength  N/mm2 300 400 500 600 800 800 900 1000 1200
2 Minimum tensile strength N/mm2 330 400 420 500 520 600 800 830 900 1040 1220
3 Vickers hardness HV F≥98N min 95 120 130 155 160 190 250 255 290 320 385
max 2206) 250 320 335 360 380 435
4 Brinell hardness HB F=30 D2 min 90 114 124 147 152 181 238 242 276 304 366
max 2096) 238 304 318 342 361 414
5 Rockwell hardness HR min HRB 52 67 71 79 82 89 / / / / /
HRC / / / / / / 22 23 28 32 39
max HRB 95.06) 99.5 / / / / /
HRC /   32 34 37 39 44
6 Surface hardness HV 0.3 max / 7)
7 Yield point N/mm2 Nominal 180 240 320 300 400 480 / / / / /
min 190 240 340 300 420 180 / / / / /
8 Specified non-proportional elongation stress N/mm2 Nominal / / 640 640 720 900 1080
min / / 640 660 720 940 1100
9 Guaranteed stress N/mm2 0.94 0.94 0.91 0.93 0.9 0.92 0.91 0.91 0.90 0.88 0.88
180 225 310 280 380 440 580 600 650 830 970
10 Breaking torque MB,N.m min / according to GB/T3098.13 regulations
11 Elongation after breaking % min 25 22 / 20 / / 12 12 10 9 8
12 rate of reduction in area % min / 52 48 48 44
13 Shock absorption work Aku,min   25   30 30 25 20 15
14 Head firmness No break
15 Minimum height of undecarburized thread E / 1/2H1 2/3H1 3/4H1
16 Maximum depth of fully decarburized layer G,mm / 0.015
17 Hardness after tempering / The difference between the average hardness before and after tempering is not more than 20HV
18 Surface defects According to GB/T 5779.1 or GB/T 5779.3 regulations
 
The characteristics of tunnel segment bolts
The main feature of double-headed arc-shaped tunnel segment bolts is: compared with straight bolts, its arc-shaped form adds a bending process, such as improper process of the processing factory or the operator who does not pay attention to the details of the processing. It is easy to happen that the bolt cannot pass through the tube during installation due to the improper machining of the bolt radian. All arc-shaped products of Anyang Railway Equipment Co., Ltd. use molds to control the arc of the bolts, and each one passes the mold for inspection to ensure that each tunnel segment bolt that leaves the factory can pass through the segment smoothly. At the same time, it prevents the construction unit from During the construction process, it was found that the bolts could not pass through the segments, which affected the construction speed and helped the construction company reduce costs.
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