6.58. At the intersection of main roads and railways (as well as streets with improved surfaces), the cables must be pulled into asbestos-cement free-flow or plastic pipes laid in a closed (horizontal puncture, drilling, pushing) or open way. Laying of pipes, as a rule, should be done before laying cables in the intersection area.
6.59. Pipes at crossings over railway lines and local roads, with the consent of their owners, are laid in open trenches.
6.60. At intersections with electrified railways, in addition to underground metro lines, cables must be laid in asbestos-cement pipes coated with bitumen or asphalt or in other non-metallic pipes.
6.61. The ends of the laid pipes must be located at a distance of at least 1 m from the base of the embankment or from the field edge of the ditch (Fig. 6.14). The ends of the pipes immediately after installation must be closed with wooden, concrete or plastic plugs.
Rice. 6.14. Laying a pipeline under the railway
6.62. When crossing permanent dirt unprofiled roads, including exits from highways, cables may be laid without pipes and covered with bricks or reinforced concrete slabs. At intersections with field (summer) roads, cable coverage is not provided.
At the intersection of local roads with dirt or cobblestone surfaces, it is allowed to lay the cable directly into the ground using a cable laying machine, followed by laying a backup pipe next to the cable and restoring the roadway.
6.63. When entering and exiting the pipe at the other end of the intersection at a length of 5 - 7 cm, the cable should be tightly wrapped with cable tape or yarn to avoid sharp bends at the edges of the pipe due to possible soil settlement.
At the points where the cable enters and exits the pipe, the soil must be tightly packed under the cable.
The gaps between the wrapped cable and the pipe should be carefully sealed with putty.
6.64. The construction of horizontal wells with a diameter of up to 250 mm, as a rule, is carried out by a hydraulic drill BG-3M (Fig. 6.15), usually part of the complex KM-170 machine mounted on the basis of a ZIL-157 vehicle, or other similar mechanisms.
Rice. 6.15. Trenchless pipeline laying using a hydraulic drill type BG-3M
6.65. Work on the installation of horizontal wells should be carried out, as a rule, in the summer. In winter, work is carried out under frozen ground.
6.66. To carry out work and install a hydraulic drill, it is necessary to dig a rectangular working pit with a length of 2200 mm and a width of 1600 mm.
The bottom of the pit should be located 500 mm below the axis of the pipelines being laid (determined by the project).
Fastening the walls of the pit must be done using inventory panels or separate boards 40 mm thick and racks of fastening timber driven into the corners of the pit.
The posts should be driven into the ground of the pit bottom to a depth of 500 mm.
At the bottom of the pit, it is necessary to arrange a flooring of edged boards 40 - 50 mm thick, which should be supported by three transverse beams measuring 150 × 100 mm.
6.67. The hydraulic drill must be installed strictly horizontally (level).
To obtain the correct direction of the well, it is necessary to pull the cord in the required direction and install the press so that the plumb line lowered from the cord coincides with the center of the distance between the cylinders. The base plates must be installed parallel and vertical.
Using a hydraulic cylinder block and a high-pressure pump, the first steel rod with a screwed-on steel cone-shaped tip is pushed into the ground. As the rods are pressed, they are screwed onto each other until the rod comes out with a tip on the opposite side of the transition.
6.68. To find the exit point of the end of the rod with the tip on the other (receiving) side of the structure being intersected, a trench 1.5 - 2 m long must be dug perpendicular to the axis of the well. After the rod exits, a pit is torn off on the receiving side to pull pipes into the well.
6.69. The initial puncture is carried out with a tip with a diameter of 70 mm. If the first puncture deviates significantly from the given direction, another puncture should be made at a distance of 0.5 - 0.7 m from the first.
6.70. After the end of the first rod enters the trench, the tip should be unscrewed and an expander (usually 130 mm in diameter) should be screwed in instead. Then the rod with the expander is pulled in the opposite direction, and a well (channel) is formed in the ground.
Depending on the soil group and the desired diameter of the well, the expander should be pulled 2 - 3 times, and the diameter of the expander can be gradually increased (130; 170; 210; 250 mm) by pushing and retracting the collapsible rod in the right and reverse direction.
6.71. Asbestos-cement pipes should be pulled into the prepared well gradually while sealing the joints.
6.72. To lay pipes with a diameter of up to 250 mm in sandy, sandy loam, loamy and clayey soils, you can use reversible pneumatic punches of the IP-4603 or IP-4605 type. Compressed air to pneumatic punches, as a rule, is supplied from mobile compressor stations such as PK-10, ZIF-55.
6.73. To insert a pneumatic punch into the ground, it is necessary to dig two pits: a rectangular working pit, 2 m long and 1 m wide; a rectangular receiving pit 2 m long and 1.5 m wide.
The depth of the working pit should correspond to the depth of the well, and the depth of the receiving pit should be 0.5 m greater than the depth of the working pit.
6.74. To avoid a significant deviation of the well from the given direction, the pneumatic punch must be carefully oriented in the given direction, using the simplest devices: a level, a plumb line and a cord stretched on pegs above the axis of the well (Fig. 6.16).
Rice. 6.16. Orientation of the pneumatic punch along the axis of the future well:
1, 6 - extreme pegs; 2 - intermediate peg; 3 - cord; 4 - plumb line; 5 - pneumatic punch
6.75. Multichannel hidden transitions, as a rule, are carried out by the method of pushing (Fig. 6.17) a steel pipe using hydraulic installations of the KM-1200 type or by horizontal drilling of a well (Fig. 6.18) with simultaneous supply of pipes into it using an installation of the UGB type.
6.76. To carry out work with a KM-1200 type installation, it is necessary to dig two pits: a) a working one, rectangular in shape, 12 m long and 4 m wide; the bottom of the pit should be 0.5-0.6 m below the pipe being pressed; b) reception room, size 4x4 m.
In the opposite direction of pushing the part of the working pit, it is necessary to build a strong thrust wall from wooden beams; Secure the side walls of the pit with boards. A thrust metal plate and hydraulic jacks should be installed at the bottom of the pit close to the wall.
Rice. 6.17. Laying pipes using the pushing method:
1 - cartridge pipe; 2 - guide frame; 3 - replaceable pressure elements; 4 - hydraulic jack; 5 - thrust wall; 6 - pumping station for driving the hydraulic jack; 7 - crane
Rice. 6.18. Scheme of operation of the horizontal drilling unit (HDU):
1 - cutting head; 2 - pipe-cartridge to be laid; 3 - roller bearings; 4 - screw conveyor; 5 - coupling device; 6 - power plant; 7 - traction winch; 8 - pipe layer; 9 - block system; 10 - anchor device
6.77. On the surface near the working pit, a high-pressure pump with a drive, a welding unit, a truck crane of the KS-2561K type, spare thrust plates and replaceable pressure elements - nozzles should be placed.
6.78. The section of pipe 1 prepared for pushing must be lowered by crane 7 into the pit and installed on the guide frame 2 (see Fig. 6.17).
To transfer forces from the jacks to the pipe, it is necessary to use replaceable pressure elements 3 with a length of 0.8; 1.6 and 2.4 m. Initially, a small pressure element with a length of 0.8 m should be installed. At the end of the first cycle, a middle element with a length of 1.6 m must be installed and at the end of the second cycle, a length of 2.4 m. Then the elements must be connected each other and continue pressing the first section of pipe until it is almost completely embedded in the ground. After this, the pressure elements should be removed and the second section of the pipe should be placed on the guide frame, welded to the first one and pressing continued in the same sequence.
Soil from the pipe should be removed mechanically or manually. Lifting soil from a pit is usually carried out using a crane
After the end of the first pipe section enters the receiving pit, the excavation stops and the installation is dismantled.
Installation of a cable line on the street is divided into overhead lines and. If with overhead lines everything is clear - cables are laid on supports or in cable galleries on trays, then with an underground line everything is a little more complicated. Especially if you have to do it under the road. The difference is that the conductor is affected not only by the weight of the soil, but also by the passing traffic flow. Let's look at the general rules of underground installation, and then we'll figure out how to lay cables along the road.
Which cable can I use?
You cannot use the usual variants of cable products used in electrical wiring, such as AVVG, VVG, PUNP, PUGNP and others. They collapse in the ground if they are not laid in pipes. The insulation of these conductors is not intended to protect the conductors from destructive mechanical and chemical influences. To lay cables under the road, you need to use protected products, such as:
- , AAB2l;
- AAShv, AAShp;
- AAPl, AAP2l;
- ASpl;
- , AVBbShp, APvBbShv.
For regions where there are severe frosts (far north), PvKShp is used.
The basic requirements are described in clause 2.3.83-2.3.101
Options for protecting cables under the road
When laying the cable under the road surface, avoid placing the line near trees - you need to retreat from them by a radius of 2 m, and around bushes you can reduce it to 0.75 m (clause 2.3.87). If you cannot retreat this distance, lay it closer, but place it inside a metal pipe. You should also avoid places with increased load on the ground, such as various parking lots, roads, and entrances. They need to be walked around the perimeter. We'll talk about how exactly they lay it under the road later.
If places with increased load cannot be avoided, then you need to use pipes, for example, a smooth HDPE pipe, a corrugated pipe or an asbestos-cement pipe, they are called cases. If there are no harmful factors, you can lay the line without pipes.
The cable is laid in a trench, it is dug to a depth of 70-80 cm. If a single cable is laid, then its width is 20-30 cm. If there are several lines, there should be a distance of 10 cm between them. The bottom of the trench is covered with a cushion of sand 10 cm high. When backfilling it, you need to remove all stones, debris, bricks, and other sharp and dangerous objects from the soil. Their presence in the ground can puncture the insulation.
There is no need to pull the cable, it needs to be laid freely, in waves, as shown in the picture:
It is necessary to provide for possible future land works. To avoid damaging the line when digging, it is worth laying down a warning tape, for example this:
Avoid connecting the conductor underground; this should be done in special couplings. If you do not have the skills to install such couplings, you should not do it yourself; if possible, try to do the installation without connections - with a single cable.
In any case, it is better to use a protective pipe of any type as additional protection, this will increase the reliability of the line. In addition, similar grades can be laid in this way for not too critical electrical installations. As an option, you can use corrugation, it has a probe (metal wire) for pulling wires. If it is not there, then it will not be possible to push through a long soft wire.
Methods for laying a line under the road surface
When connecting a site, say a dacha, to electricity, it sometimes happens that the supports with electric lines are located on the opposite side of the road. How to bring electricity into the house in this case? Let's start with the fact that you do not have the right to unauthorizedly lay a line under the road; this must be agreed upon with the administration of the city or village or other responsible body.
The first option for laying a cable line under the road is simple and does not require destruction of the asphalt. It is called the puncture method or the HDD method. Stands for “horizontal directional drilling”. The technology is that the soil under the road is drilled with special installations, thus avoiding opening the asphalt surface. It is used for laying communications under railways, under reservoirs, under buildings.
The second option is simpler, but leads to certain destruction. You need to dig a trench by removing the top layer of asphalt.
According to PUE standards, the depth of the trench must be at least 1 m, and the cable must be located in a protective pipe.
Materials
Crossing a cable line with a non-electrified railway (A5-92-35)
2. When laying cables using the open method, asbestos-cement free-pressure pipes should be used; when laying cables using the puncture method, thick-walled steel pipes should be used.
3. The number, length and diameter of pipes are indicated in a specific project.
4. Seal the cables at the ends of the pipes according to the drawing.
Designation |
Rice. |
Nature of the intersection |
A5-92-35 |
||
If there is an exclusion zone |
||
Laying a cable line in an open way at the intersection with an electrified railway (A5-92-36)
1. The drawing shows the minimum dimensions.
2. Asbestos-cement free-flow pipes must be impregnated with tar or bitumen.
3. The number, diameter and length of pipes are indicated in a specific project.
Designation |
Rice. |
Nature of the intersection |
A5-92-36 |
In the absence of an exclusion zone and the presence of a drainage ditch |
|
In the absence of an exclusion zone and drainage ditch |
||
If there is an exclusion zone |
||
Laying a cable line using the puncture method at the intersection with an electrified railway (A5-92-37)
1. The drawing shows the minimum dimensions.
2. After the puncture, an asbestos-cement or plastic pipe is inserted into the steel pipe. The number, diameter and length of pipes are indicated in a specific project.
3. Asbestos-cement free-flow pipes must be impregnated with tar or bitumen.
4. The intersection must be provided at an angle of 75-90°C to the axis of the track.
5. The intersection must be at a distance of at least 10 m from the beginning of the frames, the tail of the crosspieces and the points where the suction cables are connected to the rails.
6. Seal the cables at the ends of the pipes according to the drawing.
