Abstract： Communication optical cables play an important role in the electromechanical system of expressways. The quality of optical cable laying and welding construction will affect the operation and function of expressway communication. Taking a highway construction project as a research case, the article discusses the specific process of highway communication optical cable laying and welding construction process, so that the research can provide a certain reference for the construction of subsequent similar projects.
Keywords: highway; communication optical cable; construction technology; laying
0 Introduction
Compared with ordinary highways, the highway is more convenient and comfortable to drive, mainly because the civil parts of the highway are designed with high specifications, and its supporting facilities are more complete [1]. As an important part of the highway electromechanical system, communication optical cable is an important channel to realize information transmission, and also the information foundation to ensure the operation and management of China’s expressway [2]. At this stage, China’s highway communication optical cables are basically laid inside the pipeline, so this article focuses on the research on the engineering technology of pipeline optical cable laying facilities [3].
1 Project Overview
This article takes the Pengda Expressway as a research case. The total length of the highway is designed to be 89.852 km, with a two-way four lanes, a design speed of 80 km/h, a roadbed width of 25.5 m, and a separated subgrade width of 12.75 m. The project requires a new special bridge with a length of 300 meters, a middle bridge and a small bridge with a length of 100 meters. The road along the road is asphalt paved. The electromechanical system in the project is mainly distributed in the K0+000-K50+260 section, of which the design length of the right line of the Pancheng Tunnel is 2,101 m, and the design length of the left part is 2,105 m; the length of the right line of the Caowan Tunnel is designed to be 795 m, and the length of the left part is designed to be 802 m; the length of the right line part of the Mayukou Tunnel is designed to be 1,832 m, and the length of the left part is designed to be 1,874 m.
2 Communication optical cable laying facilities technology
2.1 Communication optical cable installation
The communication optical cable laying in this project is divided into two types: main line optical cable laying and branch optical cable laying. The specific steps of laying optical cables are shown in Figure 1.
(1) The main line optical fiber laying is to complete the optical cable laying task with the help of air compressor and blown cable equipment. The specific method is the air blowing cable laying method. The laying method is a new laying technology. Its core principle is to promote the slow movement of the optical cable with the help of the driving force of high-pressure airflow. The details are shown in Figure 2.
Before laying the main line optical cable, the construction personnel should check the quality of the silicon core tube. After the silicon core tube is laid, check whether it has the operating conditions of the blowing cable laying method. If the main line silicon core tube is only laid for a certain length, at this time, the construction team can be directly organized to enter the site, and the optical cable laying task can be completed with only 2 days. This means that the construction team will be free, which indirectly brings additional economic losses to the construction unit, but these problems can be solved in coordination. Therefore, construction management personnel should know the construction site in advance and organize all parties to enter the construction site in an orderly manner according to the specific situation .
Before the official laying of the optical cable, a comprehensive inspection of the optical cable should be carried out on the basis of the design drawings, that is, the opening test. When the cable blowing application method meets the construction conditions, the cable blowing application operation can be started. At this time, sufficient pipe wearers, cable blowing equipment, brackets and other tools should be prepared.
When laying optical cables, the number of joints should be minimized and the joint position should be arranged in a place that is easy to operate. The movement of the optical cable should be consistent with its rotation, and there should be no “surge” phenomenon. In addition to construction quality, safety issues at the construction site should also be considered to avoid safety accidents.
(2) Optical cable laying can be laid manually or by cable-wearing device. The use of cable piercing device in the process of optical cable laying can effectively improve the construction efficiency of optical cable laying. The commonly used cable threading devices have 150 m and 180 m specifications.
The main function of the cable threader is to make preparatory preparations and provide convenience to the construction personnel, so as to improve the construction efficiency and shorten the construction period. For example, before laying the optical cable, the construction personnel should have a clear understanding of the laying direction of the pipeline, check the integrity of the pipeline, and determine the laying distance of the pipeline in combination with the specifications of the cable-wearer, determine whether it needs to be optimized through calculation and analysis, and calculate the corresponding construction team equipment. After the preparation work is completed, the optical cable will be laid.
(3) Construction of traction communication optical cable. Communication optical cable traction laying usually has two methods: mechanical traction laying and manual laying. When the optical cable is laid, it is necessary to ensure that the optical cable is released from the cable plate in a relaxed curved state, and there is no twisting, surge and buckle. When mechanical traction is adopted, the speed of the tractor should be controlled within 20 m/min, and the speed of manual traction should be controlled within 10 m/min.
Before laying the communication optical cable by traction method, it is necessary to ensure penetration and insertion of the hole. For the long optical cable, the penetration process from the middle to both sides should be adopted. The hole with a higher position should be selected in the middle penetration hole, and the pipe hole should be checked in combination with the construction drawing, and the pipe hole should be cleaned with steel wire. Before formal traction, place the cable plate on the side of the optical cable pipe to be transmitted, and release the optical cable, so that the optical cable can be sent into the pipe hole in a relaxed curved state. When the cable plate enters the hole, a horn protection tube should be added, and lubricant should be applied evenly on the outer layer of the optical cable at intervals of 2 to 4 holes. Each hole is usually arranged with 1 to 2 pull personnel, and the personnel hold the optical cable up with both hands to assist the traction.
During the whole traction construction process, if the length of the optical cable exceeds 800 m, or the angle of the pipe is less than 150°, and the traction operation cannot be completed at one time, it should be pulled through from the middle to two ends in sections. After the traction to a certain length, the word “∞” is poured from the hole, and then the word “∞” should be turned over to make the optical cable Move the end to the outside and continue to be laid. After one end is laid out, put it into the hole one by one from the hole of the traction head along the direction of the hole wall to the cable disk. At the other end, the word “∞” is inserted into the hole from the cable plate. After completion, it is reserved from the hole of the cable plate to the direction of the traction head. By inverting the “∞” lifting method, it can effectively prevent the optical cable from being dragged on the ground and protect the optical cable.
2.2 Optical cable test
After the laying of the optical cable, the construction personnel shall test the optical cable to ensure that the performance of the optical cable meets the requirements. Optical cable test includes optical cable line loss test, attenuation equalization test, optical fiber attenuation coefficient test and other tests.
The loss test of optical cable lines is a relatively important one in the optical cable test project. By measuring the total loss of optical cable lines and the wavelength loss of a single optical fiber, the quality and performance of optical cables can be judged. In the test, construction workers need to use optical cable test instruments to measure and record data. According to the test results, the optical cable and optical power can be adjusted to improve the quality of information transmission. In the loss test of optical cable lines, it is very important to control the wavelength loss of a single optical fiber within 0.1 dB. Optical fiber wavelength loss refers to the phenomenon that the energy of the optical signal gradually decreases with the increase of distance during the transmission of optical signals in optical fibers. The size of the wavelength loss directly affects the transmission distance and quality of the optical signal. Therefore, it is necessary to ensure that the wavelength loss of the optical cable line meets the requirements to ensure the performance and transmission quality of the optical cable.
3 Communication optical cable welding construction technology
3.1 The method of optical fiber connection
Optical cable connection is the process of connecting two optical cables to transmit optical signals. Generally speaking, there are three main ways of optical cable connection: melting connection, mechanical connection and active connection.
Melting connection is a common connection method, that is, the bare optical fibers of two optical cables are welded by a welding machine to form a continuous optical path. Mechanical connection is also a common connection method, that is, the bare optical fiber of two optical cables is accurately connected by mechanical joints to form a continuous optical path. Compared with the melting connection, the mechanical connection is simple to operate and does not require electricity, but the connection loss is greater than the melting connection. Active connection is a connection method that can adjust the connection loss, that is, the bare optical fiber of the two optical cables can be connected with adjustable connectors, and different degrees of connection loss can be achieved by fine-tuning the position of the connector.
Among them, the welding method has small loss, good reliability, and relatively higher frequency of use.
3.2 Principles to be followed in optical fiber connection
If the number of cores is the same, the optical fiber corresponding to the same bundle tube should be used to connect; if there is a difference in the number of cores, the construction shall be carried out in standard order, first connecting the optical fiber with a large number of cores, and then the optical fiber with a small number of cores.
Specific technical requirements for construction using the welding method: the optical cable connection should be carried out in a clean environment; the excess optical cable should be placed in the tray to prevent the bending and damage of the optical cable; the connection loss of a single optical cable should be controlled within 0.05 dB; it is strictly forbidden to leave the joint part in the bridge part; try to keep the joint part Set at a high level to avoid water washing.
3.3 Machinery and equipment
The construction tools required for this project include generators, cutters, connecting vehicles, etc.
3.4 Optical fiber connection method
(1) Open the optical cable. Construction personnel should fix the optical cable in the connection box to ensure that the beam tube is not damaged. The length of the optical cable peeling should be controlled at 1 m. After peeling, it should be wiped clean and then put into the connection box. When fixing the steel wire, the steel wire must be pressed tightly and not loosened.
(2) Optical fiber penetrates into the heat-shrinkable tube. According to different colors and different bundle tubes, the optical fibers are sorted and placed into the heat-shrinkable tube in turn. Peel off the coating layer of the optical fiber and wrap it in a heat-shrinkable tube, which can play a role in protecting the joint.
(3) Start the control power supply and carry out the welding operation according to the procedure. The construction personnel should remove the dust in the welding equipment. There should be no debris or dust in the fixture and groove. The optical fiber used in this project can be divided into conventional single-mode optical fiber and dispersion displacement single-mode optical fiber. Optical fibers can be divided into 1 310 mm and 1 550 mm according to the difference in wavelength.
(4) Optical fiber end face. The processing quality of the optical fiber section directly affects the connection quality, so before welding operation, it is necessary to ensure that the quality of the end surface meets the requirements of the management specification. After peeling off the coating layer of the optical fiber surface, wipe it clean and finally cut it. If the thickness of the optical fiber coating is 1.25 mm, the cutting length is 8-16 mm. If the coating thickness of the optical fiber is 0.9 mm, the cutting length should be 16 mm.
(5) Place the optical fiber. The construction personnel put the optical fiber into the V-shaped groove, and then slowly crush the fixture and the pressure plate. The position of the optical fiber in the pressure plate should be determined in combination with the cutting length. After the above process is completed, the windshield will be closed, and the welding equipment will automatically carry out the welding operation. The welding operation time is about 11 s.
(6) Heat-shrinkable tube heating. The construction staff opened the windshield, took out the optical fiber from the welding equipment, and placed it in the bare fiber center for heating. Heat-shrinkable casing is used for heat gas, and the heating time of heat-shrinkable casing is controlled: if the specification of the heat-shrinkable casing is 20 mm, the heating time should be 40 s; if the specification of the heat-shrinkable casing is 60 mm, the heating time should be 85 s.
(7) The disk fiber is fixed. The connected optical fiber is placed in the storage disk. In the process of the coil, if the radius of the coil is larger, it means that the radian will also increase, and the loss of the line will be lower. Therefore, the radius of the coil should be strictly controlled to avoid more losses.
(8) Seal and hang. In the open environment, the connecting box should be sealed to ensure that the connecting box will not be soaked. Once water enters the connecting box, the performance of the optical fiber will be affected.
During continuous operation, construction personnel should ensure that the optical fiber is always clean. Use a stripper to peel off the coating on the surface of the optical fiber, then wipe it clean, and cut the end surface of the optical fiber with a cutter. If the cutting quality does not meet the requirements, it should be reworked. After the continuous construction is completed, observe whether there are quality defects in the optical fiber connection image, and the secondary connection construction should be carried out if it is not qualified. When welding optical fiber, it is necessary to ensure that the bending radius of the optical fiber is not less than 40 mm. Wipe the junction box and seal with alcohol and install it as required. During the installation process, the construction personnel need to do a good job of corresponding protection.
(9) Quality requirements: The end surface of the optical fiber should be cut flat and vertical, and there should be no quality defects. The loss of a single optical fiber connector cannot be greater than 0.1 dB, and the image of the welding contact must meet the requirements of the design drawing. At the same time, ensure that the coating thickness of the optical fiber is not less than 10 mm, and there are no bubbles in the pipe; the bending radius of the optical fiber cannot be less than 40 mm, and the optical fiber cannot be twisted and compressed.
3.5 Precautions
(1) After the coating layer on the surface of the optical fiber is peeled off, wipe it with acetone.
(2) Use a stripper to peel off the coating on the surface of the optical fiber, wipe it clean, and cut the end surface of the optical fiber with a cutter. If the cutting quality is not up to standard, it should be reworked.
(3) Check the optical fiber connection image. If it is not qualified, the secondary connection construction should be carried out.
(4) Detect the monitoring point of optical fiber connection. If the requirements are not met, it should be returned to the previous process.
(5) Slowly remove the completed optical fiber and ensure that the thickness of the fiber coverage is not less than 10 mm after shrinking.
(6) Use alcohol to wipe the junction box and seal, and install it according to the established requirements. During the installation operation, the construction personnel should do a good job of corresponding protection.
(7) Corresponding safety protection measures should be taken during open-air operation.
4 Conclusion
To sum up, because highway communication pipelines have good construction conditions and the technology of blown cable laying facilities has matured, more and more construction units choose to use the blown cable method for construction. The total length of the optical fiber laid in this project is 2,450 m. After practical demonstration, four people are assigned to the air blowing end control during the air blowing construction process, and two people are assigned to observe the condition of the pipe end, which can greatly improve the construction efficiency, shorten the construction period, the construction safety is in a controllable state, and the construction quality reaches the expected goal. Engineering practice has proved that the welding construction technology has a good technical feasibility.
