The laying of underground cables is a key technology in building modern urban infrastructure. It is related to the selection and application of multiple methods, each method corresponding to specific engineering needs and environmental conditions. Starting from classic direct burial laying to complex trenchless technology, the core goal is to ensure the long-term stable operation of cables while minimizing interference to the existing environment and urban activities. These technologies are directly related to the safety and efficiency of so-called "urban arteries" such as electricity and communications.
What are the technical requirements for direct buried cable laying?
A widely used cable laying method with relatively low investment is direct burial. Its first technical point is to ensure sufficient burial depth to prevent damage caused by external forces. For general areas, the depth of direct burial of cables should not be less than 0.7 meters. When crossing farmland, the requirements increase to no less than 0.7 meters. At the same time, the level must be treated, and about 100 mm of fine sand or soft sand should be laid as a cushion.
The handling of details during laying is very critical. The cable must leave a certain margin in the trench, usually 0.5% to 1% of the total length, to accommodate soil settlement and thermal expansion and contraction. When backfilling, it must first be covered with a protective layer, and then compacted in layers. In order to warn subsequent construction, it is recommended to lay colored strips with warning signs when the backfill reaches half the depth. After completion, permanent azimuth marking stakes must be set at key parts such as cable turns and joints.
What scenarios are suitable for cable duct laying?
The method of burying multiple cables in advance to form a pipe bundle system to protect the pipes is called cable duct laying. It is especially suitable for urban roads, commercial areas, etc., where underground space is limited or the pipe network is dense. This method can effectively reduce repeated excavation of the road surface and can significantly reduce the impact of construction on urban traffic.
There are clear specification requirements for the design and construction aspects involved in the duct system. The pipes are generally non-magnetic and smooth-surfaced types such as steel pipes and hard plastic pipes. The internal aperture of the power cable duct is generally not less than 100 mm in length. In this way, it is ensured that the cable will be able to pass through smoothly. In order to facilitate future cable threading and maintenance operations, cable inspection wells must be set up every 50 to 100 meters in the project area and at the turning position where there are necessary straight lines, and so on.
What is trenchless cable laying technology
Trenchless technology with special characteristics also has another specific name, which is called "no excavation" or "micro excavation" technology. The main significance of this technology is that when the surface is not excavated or the degree of excavation is controlled to a minimum, corresponding tunnels are constructed underground using specific methods such as horizontal directional drilling, and then pipes or cables are laid in the tunnels. This is its complete process. This technology can minimize environmental damage and social costs, and it is an economically superior alternative to traditional excavation methods.
The core of this technology lies in underground drilling and pipeline installation. Detailed geological survey and path planning are required before construction. During the drilling process, the drilling trajectory is accurately controlled by the guidance system. After drilling, the protective pipe or cable will be dragged into the tunnel. This method is extremely suitable for crossing rivers, crossing roads, crossing railways, crossing green belts and other sensitive areas where large-scale excavation is not suitable or cannot be carried out.
How to ensure safety during high-voltage cable tunnel construction
Construction of deep-buried high-voltage cable tunnels in urban areas faces severe challenges such as complex geological conditions and the protection of adjacent buildings. Take a cable tunnel project in Wuhan with a depth of 19 meters as an example. The construction team adopted the method of establishing an all-round "three-dimensional protection network" covering all day and night to deal with risks during the construction of this cable tunnel. This system integrates real-time monitoring technology for the actual situation of groundwater levels, real-time monitoring technology for harmful gas content, and real-time monitoring technology for settlement of surrounding buildings.
Through the linkage between the monitoring system and intelligent pumping and drainage equipment, underground hydrological conditions can be dynamically controlled. High-precision monitoring points were arranged throughout the construction process to track data in real time and dynamically optimize excavation parameters to ensure safe and controllable conditions for deep underground operations. When construction is close to existing live lines, a "graded protection" strategy must be adopted, such as moving the running cables as a whole and building a physical isolation area, so as to achieve a safe connection between the old and new projects.
What are the standards and specifications for underground cable protection pipe systems?
In order to ensure the long-term reliability and interoperability of underground cable protection tube systems, there are systematic standards and specifications at home and abroad. For example, the European standard EN 50626 series provides general and specific material requirements for buried cable conduit systems. This standard is applicable to conduit systems installed with the help of various technologies such as blowing cables and pulling cables.
Specifically, the standard clearly stipulates detailed performance indicators and test methods for solid-wall conduits and accessories made of different materials, such as polyethylene PE, polypropylene PP, and rigid polyvinyl chloride PVC-U. These specifications include the mechanical properties of the duct system, as well as key characteristics such as environmental stress resistance and sealing performance. They are an important basis for ensuring product quality and project life.
How to accept cable line construction projects
In order to ensure the final quality of the project, the acceptance of cable line construction after completion must be carried out in accordance with strict national and industry standards. Take the new specification "DL/T 5891-2024" released by the power industry at the end of 2024 and implemented in mid-2025. It clearly stipulates the construction and acceptance standards for cables and ancillary facilities with rated voltages of 500 kV and below.
The acceptance work is carried out throughout the entire process, not just at the end of the project. The specification clearly requires that from the moment the materials enter the construction site, all aspects of the construction period, all the way to the final testing link, must have corresponding basis for inquiry. The content included in the acceptance often covers the location and depth of the cable laying, as well as the protection measures for the cable. Whether the installation is in place, whether the process used in joint production meets the requirements, whether the integrity of the overall grounding system meets the standard, whether the test value of the insulation resistance is accurate, and whether the various indicators of the withstand voltage test meet the standards, etc. If there are some scenes with special requirements, such as mining environment, seabed environment, etc., then the acceptance also needs to strictly comply with the provisions of the relevant corresponding professional standards.
If you are planning an engineering project that involves complex underground pipeline crossings, and when faced with many different technical solutions such as direct burial, pipe drainage, and trenchless, what key factors will you give priority to when making the final choice?
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