About 70% of the population of Russia now lives in cities with a population of more than 100 thousand people. At the same time, the tendency towards the consistent inclusion of rural settlements in the urban area is clearly progressing.
Reliable functioning underground communications of the city, which provide its population with communications and the Internet, water, electricity, gas, heating, and sewage, are an important factor in ensuring social progress.
They are extremely saturated and branched. Their characteristic structural components are collectors, pipelines, as well as low and high voltage cables. In addition to settlements, enterprises and organizations also have their own engineering support structures.
It is noteworthy that the balance sheet value of the communications economy sometimes exceeds one third of the entire aerial construction. Its development and systematic improvement can stimulate or, conversely, restrain the development of megacities.
The existing urban development, on the other hand, also affects acceptable methods of constructing engineering networks and communications. Today, for the most part, they are laid in a closed way without first laying trenches.
Definition and concept of communications (PC)
Thus, underground utilities functionally provide the population with services of electricity and heat supply, water supply and drainage, communications, signaling and the Internet. Their main veins are most often placed under street and road routes.
Thus, the structural elements of a PC are:
- Steel, ceramic, concrete, polyethylene, asbestos-cement pipelines. They are laid, guided by hydraulic calculations. They are pressure (water, gas, oil pipelines) and gravity (drainage, sewage, water drainage).
- Cable communications of power supply of high and low voltage.
- Cable communications communications, alarm.
Classification of underground utilities
By the method of providing services, PCs are divided into transit, trunk, distributing. The first pass through the city to other settlements (gas and oil pipelines). The second ones are the main channels for providing the entire city or districts of the metropolis, while the third ones directly bring services to the houses.
According to the depth of occurrence, the networks are subdivided into those laid down to the freezing ground of the soil and below it (SNiP 2.05.02.85).
In turn, water and heat supply schemes are subdivided into those having forced and natural circulation, having lower and upper distribution, with associated water movement and dead ends, two- and one-pipe ones.
Underground power supply and communication schemes consist of cable shafts, switchgears and substations.
PC design
The underground communications plan is an important and mandatory component of any complex construction project. Typically, communications to avoid excessive mechanical stress are located outside the areas of pressure on the ground of buildings.
In terms of a PC, laying methods are necessarily reflected. Consider their options.
With a separate method, this or that communication is brought individually to the construction object. The terms of its construction are also individual, independent of the laying of other PCs. This is an outdated method, since in the conditions of a saturated urban development, excavation work to repair one communication line can damage another. It is used now in a narrow focus, in cases of refinement of existing PCs.
The combined method involves the location of several communications simultaneously in one trench. It is used in conditions of limited funding and a critical need for specific PCs.
The most common and promising in conditions of mass development is the collector method (CM), in which various PCs are placed in a standard common collector. This method greatly simplifies PC repair and maintenance. However, the collector method cannot be called universal. It is impossible to combine in one collector with other communications sewer, pressure water supply.
The collector itself is a concrete box. It can be different in height. Growth and half-growth (up to one and a half meters) suggests the presence of ventilation. In the box itself, the temperature regime is observed from 5 to 30 degrees Celsius.
PC building security requirement
Errors in the construction of underground utilities lead to accidents, injuries, fires, breakdowns of devices and equipment that are powered from them (STO 36554501-008-2007). During the construction of the construction complex, the geological and hydrogeological properties of soils must be taken into account, and the possible seasonal dynamics of their changes must be predicted.
The electrical equipment used in the laying of trenches and pipes must be made explosion-proof. Tunnels and mines in the areas of electric welding work for the duration of their execution are mandatory provided with a local exhaust.
Staying of workers - laying workers in pipelines is permissible if the diameter of the structure exceeds 1.2 meters and the length is not more than 40 m. For a pipe length of more than 10 m, forced ventilation of 10 cubic meters per hour is provided.
By time, the stay of workers in the pipeline is limited to one hour during breaks of 0.5 hours.
Typical PC construction
The modern construction of underground utilities is carried out in accordance with the location of city streets, terrain, large users of services. The transverse profile of streets that are being built or repaired is taken into account.
At the same time, cable networks are laid along roads and streets. Moreover, main communications run along the main streets, while residential microdistricts are equipped with receiving and distributing PCs powered by them.
Passing collectors and heat pipes are located under the sidewalks. At the borders of the sidewalk and streets, sewers, a gas pipeline, and a water supply system are equipped.
Modern methods of laying a PC
The laying of underground utilities is now increasingly carried out trenchlessly. This method allows high-precision and time-efficient envelope of obstacles in the relief.
The first method of trenchless laying begins with pilot drilling using a drill rod to bypass obstacles along their lower edge. Then, the drilled hole is enlarged using an expander.
The second is based on the use of a self-propelled tunneling mechanism called a shield. The latter is placed in a specially open starting pit, and then put into action. He punches a canal in the ground to the finish pit, which was also previously opened for him.
The third is also performed between the channels, but at a shorter distance and with the help of a pipe horizontally clogged with a pneumatic punch.
PCs often form an intersection with each other, underground communications in this case are separated from each other vertically according to the requirements of SNiP II-89-80, see table 1.
Table 1. Regulatory distances during the construction of PCs to roads, foundations of buildings, etc.
PC detection problem
Modern urban construction, carried out in areas with existing buildings, involves a preliminary search for underground utilities. It is carried out using specialized equipment. The most commonly used route detector underground utilities. He determines the configuration of the PC, the depth of the location and even the location of the damage, the location of its individual cores, hidden communications.
Neglect of such a search is fraught with PC crashes. The desire of individual construction companies to save money by not paying certified firms the services of determining third-party communications in the earth-moving zone often leads to accidents and, as a result, to a compelled increase in the costs of their elimination.
About shooting a PC
Surveying underground utilities is advisable if there is no primary executive documentation for them (i.e., documentation that is produced directly in the process of their construction). It is important for linking PCs to a new infrastructure.
Such works are most in demand in large cities, where their density is highest. Surveying underground utilities is a specialized area of work of specialized electrical measuring laboratories that exist with organizations involved in pipe and cable laying.
The proper level of their conduct allows you to determine not only the direction and depth of the entire communication route as a whole, but also each of its segments separately.
Its mandatory elements are the essential functional parts of each type of PC:
- pipe and water supply (valves, hydrants, turning angles, plungers, pipe diameter);
- cable networks (transformers, switchgears);
- sewers (pumping stations, overflow and inspection wells);
- drains (overflow and storm water inlets, water outlets);
- drains (perforated pipes);
- gas pipelines (trunk and distribution sections, shut-off valves, pressure regulators, condensate collectors);
- heat supply networks (compensators, cameras with gate valves, condensing devices).
High accuracy of PC shooting is ensured by the competent use of high-precision equipment for PC diagnostics, specialized software,
An underground communications locator, cable detector, metal detector, multiscanner allow you to diagnose a PC with high accuracy in determining all of their structural elements. In passive shooting mode, it is possible to determine with sufficient accuracy communications located at a depth of up to 2.5 m.
However, the rich structure of communications, especially if they are located from each other, as well as the significant depth of their occurrence (up to 10 m), significantly complicates a more detailed search for underground utilities. In this case, an active determination mode is practiced. Around the cable or pipe under study, a special generator initiates an electromagnetic field, measuring which, determine the necessary characteristics of the PC.
PC repair
It is obvious that the existing underground utilities are subject to major repairs and reconstruction exclusively by organizations and enterprises that have the appropriate permits, within the timeframes approved in the consolidated plans of municipal communal governing structures. Every year, until November 30, operating companies submit their plans for such work to the municipal housing and utilities department for coordination and accounting.
If in the process of such work a violation of the integrity of the lawns, removal of the roadbed is required, then permission from the local authorities is mandatory. When replanning existing PCs in connection with the construction of new facilities, their re-equipment is carried out by the general contractor according to the project. Each specific PC repair project must be agreed upon by the general contractor with all business entities whose underground communications are in the work area.
To receive it, the customer submits the following documentation package:
- a letter agreed with the municipal authorities;
- project of work and plan of PC route;
- guarantee of restoration of the road surface;
- confirmation of the availability of equipment and materials necessary for repair;
- an order to appoint a person responsible for repairs.
The customer also pays for the rental of the repair area, after which he receives permission.
If, when performing work, the contractor discovers a PC that is not specified in the project, he is obliged to stop the work and notify the customer. That, in turn, calls the employees of the project company, who on this occasion draw up an act and formulate an official decision.
In case of damage to the PC, the architecture department, with the participation of all interested parties, draws up an act and a decision is made on compensation for damage. The culprit is determined, and the deadlines are set.
PC service
PC maintenance is carried out with the aim of safe and uninterrupted supply of electricity and water, gas, communication services, drainage, sewage, etc. to the population and business. This task is complicated by the visual inaccessibility of communication routes. Thus, the operation of the PC is reduced to their preventive maintenance and current repair.
The purpose of preventative maintenance is to identify potential damage leading to leaks and other supply disruptions. Its first part is the inspection and measurement of basic indicators directly on the external elements of communications (transformers, switchgears, manholes, condensing devices). However, the basic indicators are the pressure of water and gas, the voltage of electricity. The frequency of inspection is determined by the organizations providing utility services to consumers, it is finally approved by their superior management bodies.
Description of one type of service
Route maps are created for the main gas pipeline with water traps and condensate tracers applied to them. In the latter, condensate is pumped out with the help of motor pumps. Only certified specialists are allowed to do such work. Safety precautions prohibit the use of open fire and smoking is strictly prohibited.
To determine the operation modes of gas pipelines at least twice during the period of maximum winter and minimum summer load, pressure is measured in them.
The tightness of these communications is carried out by periodic drilling and shufrovye inspections. For this purpose, a well with a diameter of 20-30 cm is drilled at each joint of the gas pipeline. The drill plunges into the depth to a distance of 20 cm before reaching the gas pipeline. Next, the presence of gas in these wells is checked.
If the soils in which the gas pipelines are laid have increased corrosion ability, then the integrity of the structures is checked at least 1 time in 2 years, with neutral soils 1 time in 5 years.
Thus, the areas with the highest pressure drops are determined. Most often, the cause of their formation is the sagging gas pipeline caused by a violation of the homogeneity of the soil. Therefore, at the same time as repairing the integrity of the pipe, a thorough tamping of their soil bed is carried out.
PC organizations (enterprises)
Underground communications of the organization are designed comprehensively as part of a single master project together with buildings and structures. PCs are located in area-optimized technical bands.
Directly on the territories of the enterprises themselves, exclusively overhead and ground communications are used.
Pre-factory communications are laid underground. They are placed together in common tunnels. The PC length of leading industrial enterprises is up to several tens of kilometers. The complexity of laying various communications (in percent) is: sewage - 65%; water supply - 20%; heat pipelines - 7%; gas pipelines - 3.5%, electric and communication cables - 3%; technological pipelines - 1.5%.
Technological pipelines can be placed together with a gas pipeline, heat pipe, reverse water supply. It is forbidden to place pipelines with explosive and flammable liquids.
Conclusion
The problem of replacing underground utilities is now becoming very urgent. Its root cause is the systemic shortcomings of the state financing mechanism according to the obviously failed residual principle. Thus, objective reality is actually neglected: the fact that each design laying of underground utilities involves specific terms for their replacement, in accordance with the materials of their manufacture and the conditions of occurrence in the ground.
PC replacement should be planned as part of the state economic policy. Unfortunately, the inconsistent economic function of the state actually impedes the creation of full-fledged and efficient funds for regular capital economic investments.
In this regard, there is a positive global experience. An example to follow is the Norwegian PC system, which is clearly regulated by the focus of the country's budget on compliance with relevant state standards.
We constantly observe a vicious closed cycle: how, in the absence of such an established economic mechanism, managing monopolistic organizations continually initiate an increase in already overstated utility tariffs, motivating this with 90% outdated PCs.