How is trenchless pipe laying: the features of the method + example of work
In the construction of new pipelines, as well as in the repair or replacement of old lines of communications, trenchless pipe laying is actively used.
A variety of methods allows you to choose the best way - depending on the complexity of the site or building density.
Benefits and features of BPT
Obvious advantages compared to excavation when digging trenches are the following aspects:
- reduction of terms of work;
- minimization of costs for restoration of improvement;
- preservation of infrastructure facilities in the normal mode;
- reducing the impact on environmentally sensitive areas.
The choice of the method of trenchless laying of the pipeline depends on the diameter of the required well, the characteristics of the landscape and the soil, the material of the pipes being laid, the presence or absence of effective communications.
There are many implementation options, but among them there are four main methods: sanation, punching and puncture of the soil, horizontal directional drilling.
Reconstruction and replacement of the pipeline method of rehabilitation
The method of rehabilitation is applied in cases where during the audit process it was revealed the need for a full or partial replacement of the existing pipeline.
With the help of rehabilitation, the following problems are effectively solved:
- clogging of pipeline sections and the formation of cracks;
- destruction of local branches of communications by tree roots;
- risk of pipe breaks due to corrosion.
Depending on the state of communications and the tasks they set, they resort to the technology of relining or renovation.
Relining technology or "pipe in pipe"
Relining is a rehabilitation option used for pipelines in which an insignificant reduction in diameter is possible. If the actual service life of metal pipes is exhausted and there are concerns that they work before the next breakthrough, then they are preliminarily cleaned of deposits of calcium, rust and sand.
A polyethylene liner is prepared, having the form of a sleeve, which is preliminarily filled from the inside with a polymeric composition uniformly distributed over the entire length. This polymer stocking under the pressure of water or air straighten inside the pipe, at the same time turning it inside out so that the previously applied composition adjoins the walls of the pipeline.
After the sleeve has filled the entire segment of the worn-out pipeline, under the influence of temperature, the polymerization process is carried out. As a result, both the strength of communications and their throughput increase.
Another technology of relining implies laying of new polypropylene pipes from the inside of existing ones. In this way, steel, ceramic, asbestos-cement, cast iron, concrete and reinforced concrete pipelines with a diameter of 200-315 mm are replaced.
At the same time, it is necessary to take into account that at the joints of PVC pipes a seam of about 15 mm is formed, and it is necessary to measure out the gap between the inner diameter of the old pipe and the outer surface of the new pipe.Due to the low hydraulic resistance of plastic pipes, the throughput does not deteriorate even with decreasing diameter.
Renovation of pipelines by renovation technology
Another option for rehabilitation is renovation. It differs from relaining by a much less gentle attitude to the existing communications, which are destroyed and compacted into the ground, creating a protective sheath for a new pipeline, which is often of a larger diameter.
For such a trenchless pipe laying, specialized equipment is needed - a pneumatic impact machine with a cone-expander equipped with cutting ribs is used. The video below the article clearly shows how the cone handles a 6 mm steel pipe.
The working mechanism is fixed to the traction cable, after which modules of PVC pipes, the length of which can vary from 600 to 1000 mm, are connected in stages, depending on the width of the well.The pneumatic hose is connected to the compressor, after which it is passed through the attached modules together with the safety cable.
The entrance to the replaced pipeline expands and a pneumatic impact machine is inserted into it. Moving through the communications, she breaks them, at the same time pulling the laying material behind her.
Ground punching methods
Ground punching is also performed with a significant number of variations. This is a microtunnelling technology, the use of pneumatic punches, directional auger drilling, controlled and uncontrolled puncture. Each of these methods of trenchless laying is demanded and relevant depending on the location of communications.
Pipe Case or Unmanaged Puncture Method
In this method, the casing pipe is crushed into the ground, while simultaneously being sampled. Screws are more often used for sampling, less often - compressed air and washout with water. An uncontrolled puncture is used in any type of soil, although there may be difficulties in the case of non-cohesive soils and in the presence of large stones, when the casing is compressed by the soil or its progress is blocked.
At the preparatory stage, the casing is set up in the pit clearly along the axis of the puncture. Due to possible obstacles, the trajectory of movement can be corrected using two pipes, one of which is chosen to have a larger diameter than is required, and a lash of pipes of the desired diameter is laid inside it.
The outer pipe serves as a peculiar case and protects the working pipeline, which is important in cases where the installation is done under railway or tram lines, as well as under heavy traffic.
The difference in diameter is usually 150-250 mm, and the annular distance should be packed with a cement-sand mortar. This reduces the pressure of the soil on the working tube, reduces the load on it from transport, and also provides protection from the effects of other communications located nearby. The length of the casing segments ranges from 3 to 12 meters; in the process of laying they are successively welded.
Managed puncture differences
This method differs from uncontrolled puncture by the additional use of diverters - steel plates fixed in front of the casing. They are raised using hydraulic cylinders, thereby correcting the direction of the puncture.
In both cases, a bentonite solution is used to reduce friction, which, after laying the pipeline, is pumped out and can be reused after filtration.
Involvement of pneumopunches in dense soils
The use of pneumatic punches for the puncture of the soil is the most inexpensive, fast and efficient way, due to the relatively high accuracy of trenchless penetration. This method does not require the manufacture of additional stops for hydraulic jacks, it uses a small and easy-to-transport equipment, and the minimum requirements for the preparation of the construction site.
Due to compressed air, sufficient impact energy is developed, under the influence of which an open steel pipe with a length of up to 80 meters is plugged into soils of high strength. The average speed of laying at the same time is 15 meters per hour. After laying the pipe is cleaned of soil with water and compressed air. Large diameter pipes are cleaned by hand.
Advantages of microtunnelling technology
The microtunneling process is fully automated. Casing and working pipes are made not only of steel, but also of ceramics, fiberglass, cast iron and reinforced concrete. The average distance of penetration without reinstalling the jacking station is from 100 to 250 meters.
The distance varies from the type of soil, the power of the pushing frame, which the microtunnel complex is equipped with, as well as the material of the pipes used - depending on the compressive force that the pipe can withstand.
Use of directional auger boring equipment
The use of auger boring machines is a cheap alternative to microtunneling. Such installations allow the casing to be laid with high accuracy and compliance with the design slope, which is important for gravity communications. Restrictions on the use may be quicksies and large solid inclusions of soil. Driving distance usually does not exceed 80 meters.
The use of a screw with a hollow shaft allows drilling without the development of a receiving pit.
Horizontal directional drilling method
Perhaps this is the most costly method of all existing in trenchless pipe laying, but also the most high-tech. HDDs are resorted to not only when drilling is necessary for long distances and laying large diameter pipes, but also in cases where it is necessary to lay a small segment of a pipeline with a small diameter in close proximity to private properties or objects of cultural value.
The process uses a drilling fluid, which reduces friction when drawing pipes through the pipe, maintaining the developed soil in suspension to prevent compression of the laid material, cooling and lubricating the equipment, carrying the developed soil to the surface.
Drilling mud is prepared by diluting bentonite with water - a natural mineral with a complex of special additives. The resulting suspension prevents the collapse of channels, eliminates the need for partial or complete pumping of groundwater, as it can perform its functions even in permeable soils.
Horizontal directional drilling in water-saturated soils requires precise control of the pressure and flow of drilling mud, as well as the use of special additives in its preparation.
Since the water for the preparation of the solution is taken from water bodies located in the immediate vicinity, it is necessary to take into account the presence of mineral salts and the pH of the groundwater, since these parameters may affect the stability of the suspension. This approach avoids uncontrolled erosion.
The work of HDD can be divided into several stages:
- drilling trajectory planning;
- site preparation;
- pilot well execution;
- well expansion stage;
- reverse pulling;
- restoration of the territory.
Consider each item of the plan.
Planning phase and calculation of the well trajectory
Prior to drilling, it is required to calculate and plan the well trajectory. Take into account not only the length and depth of the path, but also possible obstacles, such as:
- compactibility of soil, its porosity and stickiness;
- moisture content and groundwater level;
- the presence of large stones and rocks;
- Subsurface structures adjacent to the drilling zone.
Possible risks are determined and notifications are sent to emergency services and to the traffic police department.
A drawing of the drilling trajectory is drawn up or markup is made directly on the surface of the territory. With a serious engineering approach, the angles of entry and exit of the drill, as well as the minimum allowable radii of curvature of the rod rods are taken into account.The greatest load on the installation occurs with the simultaneous expansion of the pilot well and the laying of the pipeline, so the calculations are made adjusted to the capacity of the equipment.
Organization of the venue for horizontal directional drilling
The HDD complex is delivered to the site, unloaded, and exhibited at the work site. It is necessary to align the angle of inclination of the drilling frame and anchor the installation. Without such an attachment, the drill itself, its drive and the drilling frame wear out faster, so you should not neglect fixation. Then it is necessary to carry out a test start of the mixer for the suspension and the engines of the installation, to ensure the stability of the connection of the hydraulic hoses.
Pilot well execution
Pilot drilling is the passage of the entire length of the trajectory of a well with a small diameter, sufficient for pulling a rod of rods. The first segment is loaded into the guide rod, the threaded connection is abundantly lubricated and connected to the drilling head - a device consisting of a transmitter of the location system, the drill blade itself, as well as a suspension supply filter.
Then, bentonite solution is supplied and pressure is adjusted to ensure that the suspension passes through the hoses into the drill rod, enters the barrel, the filter and the nozzles of the drill head, and then comes out with the necessary head.
The installation operator performs an inlet perpendicular to the ground surface relative to the longitudinal axis of the drill head, and then performs drilling, consistently increasing the rod of rods.
The operator of the location system marks the positions, depth and angle of drilling, compares with the planned trajectory and puts the actual trajectory on the plan if reorientation is required. After the drill head appears at the exit point, the pilot drilling is completed.
Stages of well expansion and tunnel laying
In the process of pilot drilling, a well of 75-100 mm wide is formed, which is sufficient when laying communications of small diameter. If the diameter of the well is narrower than it is required, then the expander is pushed to the opposite sideOften this stage is combined with the laying of communications equipment, then a swivel is installed behind the rotating expander so that the stacked material does not twist.
In some cases, taking into account the effort required for tightening, the well is expanded to the extent that the tunnel size provides for the laying of material of the desired diameter.
Reverse pulling is also performed with the supply of drilling fluid to reduce friction of the material against the borehole walls. As the lash is pulled along the length of the rod, the operator of the HDD turns off the suspension, stops the rotation and disconnects the rod, and then resumes the installation. The procedure is repeated until the expander appears from the well inlet.
Completion and restoration of landscaping
After the trenchless laying of the pipeline is completed, the installation engine is turned off, the laid communications whip is disconnected, the connectors, the swivel and the filter are removed. All devices are cleaned from the ground, treated with waterproof grease. The rest of the suspension is pumped out, the pit is filled up and, if possible, the natural or close to natural landscape is restored.
Conclusions and useful video on the topic
Drilling well with improvised tools on a private plot:
Video about applying the method of timing:
The principle of renovation - the destruction of the steel pipe:
Step-by-step instruction on the use of a compact installation of HDD:
The use of the trenchless method of laying communications implies the use of special equipment and certain devices. However, for short distances you can drill a hole with a diameter of 50-100 mm, having on hand the usual electrical appliances. The main thing is to make calculations correctly.