In modern infrastructure construction, the laying and crossing of underground pipelines are increasingly frequent. Traditional construction methods often face problems such as greater interference with ground traffic and the surrounding environment, as well as the difficulty of construction under complex geological conditions. Horizontal Directional Drilling (HDD) technology has emerged to provide an efficient, environmentally friendly and economical solution for underground pipeline crossing projects. In this paper, the working principle, technical characteristics and wide application of HDD horizontal directional drilling system will be discussed in depth.
一.HDD horizontal directional crossing system Working Principle
Planning and Survey: Before the construction, the drilling paths are planned based on factors such as engineering requirements and geological conditions. It is necessary to carry out surveys and underground investigations to clarify the distance to be traversed, the burial depth of the pipeline or facility, the geological structure of the underground, and the possible environmental influences, etc., so as to provide an accurate basis for the subsequent construction.
Opening the surface entrance: Setting up the drilling rig at the selected starting position to create a surface entrance point, which is the starting point of the whole traversing process and the beginning of the subsequent drilling operations.
Pilot Hole Drilling: Starting from the surface entry point, a pilot hole is created by drilling with a small diameter drill bit. The drill bit is usually equipped with a mud motor, etc. During the drilling process, the thrust and torque provided by the drilling rig will advance the drill bit along a pre-planned path in the ground. At the same time, a mud pump delivers prepared mud to the drill bit through the drill pipe. The mud lubricates and cools the drill bit, as well as carries the drill cuttings back to the surface, and also stabilises the hole wall to prevent it from collapsing.
Real-time monitoring: During the pilot hole drilling process, a variety of sensors and navigation tools are used to monitor the position and direction of the drill bit in real time. These tools include gyroscopes, magnetic sensors, inclinometers and accelerometers, etc., which can accurately measure the attitude and position information of the drill bit in the ground and transmit these data to the control system on the ground in real time.
Guiding and deviation correction: Based on the real-time monitored data, the operator determines whether the drill bit has deviated from the predetermined path. If deviation is found, it can be corrected by adjusting the angle of the drill bit or changing the drilling parameters, etc. to ensure that the drill bit always advances along the planned path, so as to achieve the purpose of precisely controlling the drilling direction.
Reaming: After the pilot hole is completed, its diameter is usually smaller than the diameter of the pipe or facility to be laid. A reaming operation using a reamer is required to enlarge the pilot hole to accommodate the target pipe or facility by gradually replacing the reamer with one of a larger diameter. During the reaming process, the reamer cuts the soil from the borehole wall and mixes it with the slurry to form a slurry solution that is discharged out of the borehole.
Pipeline back dragging: When the reamed hole reaches a predetermined diameter, the pipeline to be laid is connected to the reamer, and then through the back dragging device of the drilling rig, the pipeline is dragged along the reamed hole from the exit point until the pipeline laying is completed. During the back dragging process, the pulling force and speed should be controlled to avoid the pipe being overstretched or damaged.
Exit and recovery: After the pipe laying is completed, carry out the final connection and fixing work at the exit point. At the same time, clean up the remaining drilling mud, backfill and restore the area around the borehole, so that it can be restored as much as possible to its pre-construction state and reduce the impact on the surrounding environment.
二.HDD horizontal directional crossing system Technical Features
1.Non-excavation construction with low impact on the environment
One of the greatest advantages of the HDD horizontal directional traverse system is its trenchless construction method. Compared with traditional excavation construction, HDD does not require extensive destruction of ground roads, buildings, vegetation, etc. This not only reduces disturbance and damage to the surrounding environment, but also reduces noise and dust pollution during the construction process. This not only reduces the disturbance and damage to the surrounding environment, reduces noise and dust pollution during construction, but also avoids social problems such as traffic congestion caused by excavation. The environmental advantages of HDD technology are especially prominent when underground pipeline crossing projects are carried out in areas with high environmental requirements, such as city centres, nature reserves, rivers and lakes.
2.High-precision guidance, adaptable to complex terrain
With the advanced guidance system, HDD can achieve high-precision control of the drilling trajectory. Whether in the horizontal or vertical direction, the drilling can be carried out precisely according to the design requirements, and the error can be controlled within a small range. This enables HDD technology to adapt to a variety of complex terrain conditions, such as crossing rivers, lakes, roads, railways and buildings and other obstacles. In complex urban underground spaces, HDD can also accurately avoid existing underground pipelines and other infrastructure, ensuring safe and smooth construction.
3.High construction efficiency and short construction period
The HDD system adopts mechanised operation, and the drilling, reaming and hauling back processes are carried out continuously, resulting in relatively fast construction speed. Compared with the traditional excavation construction, HDD greatly shortens the construction period. Especially in long-distance crossing projects, the construction efficiency of HDD is more obvious. The shorter construction period not only reduces the overall cost of the project, but also reduces the impact of construction on the surrounding environment and social life.
4.Wide range of applicable pipe diameters
HDD technology is applicable to the laying of pipelines of various diameters. From small-diameter communication cables and gas pipes to medium-diameter water supply and drainage pipes to large-diameter oil and natural gas pipelines, HDD is capable of handling them all. By selecting the appropriate drilling equipment, reamers and construction techniques, it is possible to meet the crossing requirements of pipelines of different diameters. This wide applicability makes HDD technology widely used in all kinds of underground pipeline projects.
5.Remarkable cost-effectiveness
Although the purchase and maintenance costs of HDD equipment are relatively high, HDD technology has significant cost-effectiveness in terms of overall project costs. By reducing the costs of ground excavation, road repair, traffic diversion and compensation to the surrounding environment, as well as shortening the construction period and reducing labour and equipment rental costs, HDD is able to achieve a lower total cost of ownership than traditional excavation in many cases. The cost advantages of HDD are especially prominent in projects with complex geological conditions and difficult construction.
三.HDD Horizontal Directional Traversing System Application Areas
1.Oil & Gas Pipeline Crossing
In the oil and gas industry, HDD technology is widely used in projects where pipelines cross rivers, lakes, roads, railways and other obstacles. For example, HDD horizontal directional traversing technology is widely used in large-scale energy transmission projects such as West-East Gas Transmission and West-East Oil Transmission to achieve safe and efficient laying of long-distance and large-calibre pipelines, which not only ensures the stability and reliability of the energy transmission pipelines, but also minimizes the impact on the ecological environment along the pipelines.
2.Urban underground pipeline network construction
With the acceleration of urbanisation, there is an increasing demand for the construction and upgrading of urban underground pipeline networks, and HDD technology plays an important role in the laying and renovation of underground pipeline networks such as water supply and drainage pipelines, gas pipelines, power cables and communication fibre optic cables in urban areas. In the city centre area, due to the dense population and busy traffic, the traditional excavation construction is often subject to many limitations, and the non-excavation construction method of HDD can efficiently complete the construction and renovation of underground pipeline network without affecting the normal operation of the city, so as to ensure the normal operation of the urban infrastructure.
3.Water conservancy engineering
In the field of water conservancy engineering, HDD technology can be used to cross rivers, dams and other obstacles, laying irrigation pipelines, drainage pipes and diversion pipes of hydropower stations. For example, in the construction of some large-scale irrigation districts, the HDD technology is used to cross the rivers and highways with irrigation pipelines, which realises the rational deployment and efficient use of water resources. In flood control projects, HDD technology can also be used to lay drainage pipes to improve the city’s flood control and drainage capacity.
4.Environmental protection project
In environmental protection projects, HDD technology can be used for laying inlet and outlet pipelines of sewage treatment plants, impermeable membrane anchoring trenches of landfills and underground collection pipelines of hazardous waste treatment sites, etc. HDD’s non-excavation construction method can reduce the secondary pollution of the surrounding environment and protect the integrity of the ecological environment. Meanwhile, in some ecologically fragile areas, such as nature reserves and wetlands, HDD technology can complete the necessary infrastructure construction without damaging the ecological environment.
HDD Horizontal directional traversing system, as an advanced underground pipeline laying technology, plays an increasingly important role in modern infrastructure construction with its unique working principle and remarkable technical features. It not only provides efficient, environmentally friendly and economic solutions for underground pipeline crossing projects in the fields of oil and gas, urban underground pipeline network, water conservancy engineering and environmental protection, but also promotes the continuous innovation and development of underground engineering construction technology. With the continuous progress of science and technology, HDD technology will continue to improve in terms of equipment performance, guiding accuracy, construction technology, etc., and its application areas will be further expanded to create more powerful value for the industrial field.
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