Underground pipeline communications have become an indispensable attribute of the engineering systems of modern megacities. Due to the lack of free space underground, sewer networks, water supply lines, heating mains, and piping of electrical cables are located underground. Over time, the problem arises of replacing worn-out pipelines or repairing them. In conditions of dense urban development, it is very difficult, and sometimes even impossible, to dig a trench or a foundation pit for repair work. Therefore, trenchless laying of engineering networks has become a real technical breakthrough and helped solve a lot of problems in a big city.
Description of trenchless pipe laying technology
Under urban conditions, underground pipeline routes run under busy city streets, motorway roadways, green spaces, transport interchanges and other objects. If we carry out the replacement and repair of underground engineering networks directly underground and do not carry out the opening of the soil, then this work production technology is called «trenchless laying of engineering pipelines». This method is based on the principle of through passage of pipe structures through soil layers, laid in any direction. The production technology itself is simple, however, for such a laying in a closed way, special equipment and technological equipment are needed. Installation is carried out using a special metal cylindrical nozzle of the required diameter and a stackable hose. If there is a need for closed laying on long underground highways, then in this case the use of special equipment and technological equipment is required.
Advantage of trenchless technology
The main advantages and benefits of this technology, due to which trenchless pipeline laying should be preferred, are:
- Compared to the open method of laying utilities, the trenchless method will require a significantly smaller amount of material and technical resources.
- Reducing the time of work due to the lack of excavation and high speed of installation.
- The laying of pipelines is provided by a link of workers, consisting of three to four workers.
- The technology of laying a pipeline without trenches does not damage the surrounding area.
- The possibility of laying and repairing communications at any time of the year. If in winter it is very difficult to change and lay engineering networks in an open way, then trenchless technology is successfully used in frozen ground conditions.
- Safety installation.
- Reducing environmental pollution by several times.
Another important argument in favor of this technology is the exclusion of additional costs for restoring the integrity of the asphalt pavement, removing the land and reconstructing the disturbed adjacent territory.
The principle of the puncture and punching method
With this technology, the laying of communications is carried out by the method of piercing and punching. It should immediately be noted that these methods of trenchless underground laying exclusively new engineering pipe communications.
The puncture method is used for pipe lines up to 60 meters long. Such a small length is due to significant efforts of 150 — 3000 Kn, which are necessary for the equipment to pierce the soil. Tractors, bulldozers, winches and hydraulic jacks are involved in the organization of the puncture. Piercing of the soil is carried out by a pipe structure equipped with a protruding tip in the form of a cone with cutting knives installed on it. Due to the pressure received from the equipment, the tip, together with the tubular structure, moves forward in a circular motion. At the same time, the soil around the pipe is compacted and does not sprinkle, and the structure itself is connected by welding as it moves. Thus, it is possible to lay underground pipelines with a diameter of up to 600 mm. When laying a small-diameter engineering communications route, the puncture is carried out directly by the pipe without installing an additional tip.
It is important to be aware that deviations from the piercing line may occur if a conical tip is used. These errors arise due to the possible collision of the cone with natural obstacles and, therefore, errors from the calculated exit point of the puncture.
Depending on the category of soil and the technical capabilities of the equipment, the speed of piercing the soil in one hour is from 4 to 6 meters. If vibration forces are applied to the circular movements of the tubular element, then it is possible to increase the speed of puncture up to 20 — 40 m/h.
For soils with good water permeability, the hydropuncture method is used. In this case, the laying of communications is carried out with a powerful stream of directional water, which erodes the soil and forms a tunnel for laying pipelines.
The principle of the punching method is similar to a puncture, only it is carried out with one pipe without a special nozzle. In this case, earth masses fall into the inside of the pipe cavity and remain there until the entire structure is removed.
Soils for which the punching method is recommended should belong to categories I–IV and are represented by clay, loam, sandy loam or sand.
Engineering networks laid by the punching method can have dimensions from 600 to 1720 mm, and the maximum allowable section length is 100 meters.
The method of punching most often lays underground sewer lines.
Punching is carried out due to significant dynamic forces created by hydraulic jacks, which are symmetrically installed along the perimeter of the pipe circumference. Work is carried out in the following sequence:
- First, a small excavation is made.
- A persistent structure in the form of a wall is installed for attaching hydraulic jacks.
- The first links of the conductive pipe are attached to the jacks, securely fixed on the thrust structures. The other end of the tubular structure is in a free open position.
- Hydraulic jacks create the necessary forces that set the tubular element in motion, and it slowly penetrates through the thickness of the soil with a progressive motion.
The earth is removed from the cavity manually using shovels or compressed air with impact pneumatic devices.
Horizontal Directional Drilling Method
Manufacturing jobs by technology trenchless laying of engineering pipes by the HDD method consists in directional testing of the soil using special drilling rigs. With the help of horizontal directional drilling, it is possible to lay engineering networks in places with a developed transport infrastructure, as well as under highways and railways. HDN technology only fifteen years ago was considered an innovative breakthrough in the field of closed installation and was first tested in the United States in the 70s of the past century. The novelty successfully passed the test and already in the 80s this technology began to be used in Europe. Using this method, it is possible to lay pipes with a diameter of 76 to 315 mm with a route length of up to 300 meters.
The technology contains three stages of sequential work:
- Installation of a wired (pilot) well using a drilling rig for trenchless pipe laying. In order to correctly set the direction and subsequently monitor the correctness of the trajectory of movement, a special navigation device is installed on the drill head.
- Expansion of the original well to the design section. At this stage, the reamer with the principle of reverse action is included in the work, which, passing through the wire well, expands the well cavity to the desired size.
- Pipeline laying. At the final stage, the prepared sections of the pipeline are pulled by a special rod of the HDN machine. For laying, they mainly use modern HDPE pipes, which are widely used for the installation of engineering networks for sewerage, water supply and sanitation. Installation of polyethylene tubular structures with several lashes pre-welded into a single thread is possible. To reduce the rate of additional friction that occurs when pulling pipelines through a prepared horizontal tunnel, drilling mud is pumped into the well.
Thanks to the use of horizontal drilling technology, it is possible to significantly save material and technical resources and lay engineering communications in any urban area and industrial sites in a short time.
It is important to know that the perimeter of a drilled horizontal well should be 30% larger than the cross section of the underground pipelines being laid.
Scope of technology without a trench
Scheme of laying pipes PDN under the reservoir
Using the technology of laying networks in a closed way without carrying out a large amount of excavation allows you to perform the following types of work:
- Laying underground cable communications.
- Installation of technological pipe systems for pumping oil.
- Laying of underground gas pipelines and water mains.
- Laying of pipe sewerage.
- The device of underground heating mains.
- Repair of damaged pipes and their replacement.
In addition, the technology of horizontal directional drilling makes it possible to lay engineering communications in places where soil landslides are possible, where there is no free access for construction equipment. Trenchless technology methods are used when laying pipelines in difficult hydrogeological conditions, in protected areas and on the territory of architectural monuments.
The main criteria for choosing a laying method are the category of soil and its density, soil composition, length of the route, and the estimated diameter of pipelines.
Video about trenchless laying of communications:
cars and equipment
The laying of engineering communications can be carried out according to various methods, but their basic principle is the same: it is necessary to create certain efforts to push through pipe communications. Therefore, the most commonly used:
- Settings for trenchless pipe laying on pneumatic wheels or on caterpillar tracks;
- hydraulic jacks;
- Welding machines for joining tubular elements;
- Tractors and bulldozers;
- Drive diesel oil stations;
- Basic equipment: well expanders, pipes of the required diameter, rods;
- Additional equipment: surveillance cameras and monitors, remote control panels;
- Mortar mixing plants.
Laying pipeline systems without trenches and pits a few decades ago seemed like an unrealizable fairy tale. With the development of technological progress, the situation has changed dramatically and now we can safely say that this technology has a great future and great opportunities.