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Application of trenchless technology in electric power engineering construction

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With the rapid development of urban economy and the acceleration of urbanization, there are more and more electric power engineering construction projects. The electric power is transmitted by power cable, which covers a small area, does not occupy the ground space, is not affected by the road surface buildings, and does not need to set up poles and towers and wires on the road surface. It is easy to supply power to the city and make the city neat and beautiful. Therefore, now the cable project is also more and more. The construction of conventional cable engineering is to cut grooves to lay power pipelines. It is easy to damage the original pipeline when excavating and backfilling; The transportation of residual soil causes leakage and dust. It is easy to cause uneven settlement, subsidence or protrusion of road surface, and bring inconvenience to vehicles and pedestrians. And because use electricity application time is not consistent, often dig today, fill in tomorrow, the day after tomorrow and the day after tomorrow and "broken belly open", produced the road that makes the public loathe "zipper phenomenon". Therefore, the conventional construction technology is less and less suitable for the needs of urban development. 
In recent years, xiamen city increased the strength of urban planning, construction and management, "xiamen city road management method" also stipulated that the new road delivery use less than 5 years is not allowed to "cut open the belly". In January 2007, xiamen municipal general office of the people's government issued a notice on strengthening the management of urban road excavation and construction in the island. The new management measures strictly approved the authority of examination and approval. Those exceeding these limits shall be subject to joint examination and approval by the municipal bureau of parks and forests and the municipal urban management office, and major excavation projects shall also be submitted to the municipal government for examination and approval. In addition, xiamen city also established the road excavation plan pre-declaration system for the first time, stipulating that the next year's report should be submitted in December every year, and the next year's report should be submitted in May every year. Except in emergencies, excavation projects that have not been declared in advance shall not be approved. The road excavation construction site must standardize the establishment of public signs, and the road level jurisdiction of the municipal administrative departments of acceptance and acceptance of qualified before starting. These regulations also increase the difficulty of conventional cable construction. It is not easy to apply for it, and when you do, you have to pay a high fee for digging and repairing urban roads. Because it is to belong to punitive qualitative compensation, dig cement concrete road surface for example, no matter the size of actual excavation width, although dig only 30 centimeters wide, also be to press the area of whole board to calculate, compensation amount is very big. 
In this case, the advantages of trenchless technology are reflected. Trenchless technology refers to the new construction technology of laying, replacing or repairing various underground pipelines under the condition of no trench (groove) on the surface by using various technical means of geotechnical drilling and excavation. Instead of the traditional trenchless pipe laying and repairing construction method, it is drilling pipe laying and repairing. Compared with traditional excavated construction method, the trenchless technology has not affect traffic, do not damage the environment, short construction period, the advantages of social benefit is remarkable, especially suitable for can not be implemented excavation work in some areas, such as downtown, highway, railway, building, river, crops and vegetation areas, pipe laying, update, or repair. According to the construction technology, it can be divided into: guided drilling pipe laying technology, evading ground shuttle pipe laying technology, pipe jacking tunneling pipe laying technology, pipe jacking pipe laying technology. Among them, the advantages of guided drilling and pipe laying technology are: guided by a guiding instrument, guided detection combined with pipeline detection can effectively adjust the bit, avoid pipelines, suitable for construction under complex formation conditions; Pipe laying diameter, length and material range are wide, suitable for pipe diameter less than 1000mm, mainly using PE pipe laying and pipe laying; Small disturbance to the surface, fast construction speed, high construction accuracy, is the fastest development of a non - excavation construction method. In addition, because the underground pipe network of xiamen urban area is relatively complex, most of the bureau's trenchless construction adopts the method of guided drilling and pipe laying. The following is a detailed introduction of the construction technology of guiding drilling and pipe laying method. 
Firstly, the position and topography of the pipeline laid are measured, and the optimal curve of the borehole, working pit and acceptance pit are designed. 
Secondly, conduct the construction of guide drill. First, drill a guide hole that is much smaller than the diameter of the prelaid pipe according to the pre-designed pipeline laying line. Then, drag back the reaming head to expand the hole diameter to 1.2-1.5 times of the diameter of the prelaid pipe. Then, pull the pipe in to realize trenchless laying of new pipe. The construction of guiding drilling and laying pipe consists of three stages, namely drilling and guiding hole, reaming and reaming pipe. 
1 drill the guide hole
Use the guide bit to drill accurately from the predetermined entry point to the specified pipe line at a certain inclination Angle. The guide bit is an inclined asymmetric bit with jet nozzle at the front end, and a positioning signal emitter is placed inside. The jet effect of high-pressure mud ejected from the front end of the bit and the cutting effect of the bit jointly form the hole wall underground. The mud also plays the role of lubrication and cooling, and rapidly fix and shape the hole wall. The receiver on the ground can detect the longitude and latitude coordinates, depth, tilt rate, slope direction and other parameters of the drill bit in the ground, usually every drill pipe positioning. Drill pipe length varies with the type. The larger the type, the longer the drill pipe. Based on the measured parameters, rig operators judge the deviation between the drilling position and the design track, and make adjustments at any time to ensure the drilling along the design track. When the rotation and feeding are carried out at the same time, the drilling hole shows a straight line extension, and only when the feeding is not rotating, the drill hole deflects towards the direction of the drill bit inclined surface under the action of the inclined surface reaction. The drill pipe continues to be reattached until the bit reaches the receiving well or emerges from the target position. 
2. Retractable hole
After the guide hole is completed, the guide bit is replaced with a tapered reaming head with a diameter larger than the existing pipe hole in the receiving well or at the target position. The drill bit has a helical arrangement of high hardness tungsten carbide metal on its surface, so that it expands the hole under the action of pulling back the drill pipe. The holes distributed on the circumference of the drill bit can spray out high-pressure mud, which is similar to the process of drilling guide hole. In the return process of reaming, the mud pump will provide enough drilling mud slurry to the hole wall, in the loose hole wall surface quickly formed a layer of protective wall mud layer, the back of the reaming head in the back side of the continuous replacement of the drill pipe. After the reaming head reaches the drilling rig, a new reaming head is connected to the receiving well for reexpanding again. The expansion can be repeated many times, so that the diameter of the pipe hole is expanded successively, until the pipe hole meets the design requirements.
3. Retractable pipe
After reaming, the hole cleaner is used to clear the hole. Pay attention to the proportion of mud and ensure the quality of mud when cleaning holes. When the hole cleaning meets the requirements of pipe laying, the preparation before the backhaul shall be carried out to check whether the quality of pipe material and whether it is damaged in the process of handling, whether the welding (connecting) connection of pipe material conforms to the regulations, and the laying shall not be completed until the inspection is completed. When the pipe is pulled back, the product pipe is suspended in the hole of the enlarged hole, and the pipe wall is lubricated by mud between the holes, which not only reduces the resistance of the pipe to be pulled back, but also protects the corrosion layer of the pipe when it is pulled back. At this point, the operator should pay attention to control the tension and speed of the drill, to ensure that the laying pipe is not damaged. 
Finally, after the construction of the traction pipe is completed, the masonry inspection well is started. 
Take an engineering example below to illustrate the application of trenchless technology in power engineering construction. 
Example: the design of the newly built 110KV hubin south substation 10KV meiyuan line project is to feed a cable from the newly built 110KV hubin south substation to the hexiang meiyuan switch station 901. After the cable is drawn out from the substation, the cable is laid along the cable trench already built on the north side of hubin south road and the newly built pipe trench eastward to the meiyuan switch station 901. Among them, one section needs to cross hubin south road. And hubin south road belongs to urban main road, vehicles flow ceaselessly, underground pipeline crisscross-crossing, there are green trees on both sides of the road. As is known to all, conventional construction method is adopted for pipeline crossing the road. Large excavation should be adopted for half of the foundation groove of the highway, and the other half of the pipeline should be constructed after backfilling after pipeline laying is completed. Although the construction method is simple, it inevitably has a certain impact on traffic operation and urban environment: it is easy to cause noise, dust, vibration and exhaust gas during the construction; To obstruct traffic (blocking, interrupting, or rerouting); obstruct. Damage the environment (green belts, parks and gardens); Affecting the lives of citizens and the operation of shops; Poor safety; Comprehensive construction cost is high. These shortcomings are exactly the advantages of non - excavation technology. Therefore, the project adopts the technology of guided drilling and pipe laying to carry out the power pipeline crossing in the trenchless way. 16. This project has excavated 4M*2M*1M working pits and acceptance pits, with a reaming diameter of 500MM and a diameter of 160x4 PE tubes, with a length of about 46 meters and a maximum depth of 3m below the natural ground; The drill ground point is located at the north side of hubin south road, and the unearthed point is located at the south side of hubin south road. The grave Angle of 10 °, unearthed from 6 ° Angle. The project does not pollute the environment, does not affect traffic, construction cycle is short and other advantages.

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