About 70% of Russia's population now lives in cities with more than 100 thousand people. At the same time, the trend of the consistent inclusion of rural settlements into the city is clearly progressing.
A significant factor in ensuring social progress is the reliably functioning underground communications of the city, which provide its population with communications and the Internet, water, electricity, gas, heating, and sewerage.
They are extremely rich and branched. Their characteristic structural components are manifolds, pipelines, and low- and high-voltage cables. In addition to settlements, enterprises and organizations also have their own engineering supporting structures.
It is noteworthy that the book value of the communications economy sometimes exceeds a third of all above-ground development. Its development and systematic improvement can stimulate or, conversely, hinder the development of megacities.
Existing urban development, for its part, also affects the allowableways of building engineering networks and communications. Today, most of them are laid in a closed way without first laying trenches.
Definition and concept of communications (PC)
Thus, underground utilities functionally provide the population with the 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, sewerage, water drainage).
- High and low voltage power cable communications.
- Cable communication communications, signaling.
Classification of underground utilities
According to 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 latter are the main channels for providing the entire city or areas of the metropolis, while the third ones directly bring services to homes.
According to the depth of the network, they are subdivided into those laid up to the border of soil freezing and below it (SNiP 2.05.02.85).
In turn, water and heat supply schemes are divided into those with forced andnatural circulation, with lower and upper distribution, with the associated movement of water and dead-end, two- and one-pipe.
Underground power supply and communication schemes consist of cable shafts, switchgear and substations.
PC Design
The underground utilities plan is an important and mandatory component of any complex construction project. Usually, communications, in order to avoid excessive mechanical stress, are located outside the areas of pressure on the ground of buildings.
In terms of PC, laying methods are necessarily reflected. Consider their options.
With a separate method, one or another communication is brought to the construction site individually. The terms of its construction are also individual, independent of the laying of other PCs. This is an outdated method, because in conditions of saturated urban development, earthworks to repair one communication can damage another. It is now used narrowly, in cases of refining existing PCs.
The combined method involves the location of several communications at the same time in one trench. It is used in conditions of limited funding and a critical need for specific PCs.
The most common and promising in the conditions of mass development is the collector method (CM), in which various PCs are placed in a standard common collector. This method greatly simplifies the repair and operation of the PC. However, the collector method cannot be called universal. It is impossible to combine sewerage in one collector with other communications,pressurized water supply.
The collector itself is a concrete box. It may vary in height. Growth and half-height (up to one and a half meters) suggests the presence of ventilation. In the box itself, the temperature regime is from 5 to 30 degrees Celsius.
Security requirement in building a PC
Mistakes in the construction of underground utilities lead to accidents, injuries, fires, breakdowns of devices and equipment powered by them (STO 36554501-008-2007). During the construction of the PS, the geological and hydrogeological properties of soils must be taken into account, as well as the possible seasonal dynamics of their change.
Electrical equipment used in the laying of trenches and pipes must be made explosion-proof. Tunnels and shafts in the areas of electric welding work must be provided with local exhaust for the duration of their execution.
Stay of workers - layers in pipelines is permissible if the diameter of the structure exceeds 1.2 meters and the length is not more than 40 m. With a pipe length of more than 10 m, forced ventilation is provided from 10 cubic meters per hour.
In terms of time, the stay of workers in the pipeline is limited to one hour with breaks of 0.5 hours.
Typical PC construction
Modern construction of underground utilities is carried out according to the location of city streets, terrain, large users of services. It takes into account the cross profile of the streets that are being built eitherbeing renovated.
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 fed from them.
Pass-through collectors and heat pipes are located under the sidewalks. On the borders of the sidewalk and streets, sewerage, gas pipelines, and water pipes are being equipped.
Modern PC laying methods
The laying of underground utilities is now increasingly performed trenchless. This method allows you to accurately and efficiently go around terrain obstacles in time.
The first method of trenchless laying begins with pilot drilling with a drill rod around obstacles along their lower edge. The drilled hole is then enlarged with a reamer.
The second is based on the use of a self-propelled tunneling mechanism called a shield. The latter is placed in a specially opened starting pit, and then put into action. He breaks a channel in the ground to the finishing pit that was also previously opened for him.
The third one is also performed between the channels, however, at a shorter distance and with the help of a horizontally driven pipe with a pneumatic punch.
PCs often form an intersection with each other, underground utilities in this case are separated from each other vertically in accordance with the requirements of SNiP II-89-80 see table 1.
Table 1. Normative distances for the construction of PCs to roads, building foundations, 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 locator of underground utilities. It determines the configuration of the PC, the depth of location and even the location of damage, the location of its individual cores, hidden communications.
Neglecting such a search is fraught with PC crashes. The desire of individual construction organizations to save money by not paying certified firms for the services of determining third-party communications in the earthworks area often leads to accidents and, as a result, to a forced increase in the cost of their elimination.
About shooting PC
Shooting underground utilities is advisable if there is no primary executive documentation for them (ie, documentation that is produced directly in the process of their construction). It is important for tying the PC to the new infrastructure.
Such jobs are most in demand in large cities, where their density is highest. Shooting underground utilities is a specialized area of work of specialized electrical measuring laboratories that exist at organizations involved in pipe and cable laying.
The proper level of their implementation allows you to determine not only the direction and depth of the entire communication route inas 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, angles of rotation, plungers, pipe diameter);
- cable networks (transformers, switchgears);
- sewers (pumping stations, overflow and manholes);
- water drains (overfall and storm water wells, water outlets);
- drainages (perforated pipes);
- gas pipelines (main and distribution sections, shut-off valves, pressure regulators, condensate collectors);
- heat supply networks (compensators, shutter chambers, condensing devices).
High accuracy of PC shooting is ensured by the competent use of high-precision equipment for PC diagnostics, specialized software, Underground utilities locator, cable detector, metal detector, multi-scanner allow you to diagnose PCs with high accuracy in determining all their structural elements. With 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 utilities, especially if they are located from each other, as well as their significant depth (up to 10 m) greatly complicates a more detailed search for underground utilities. In this case, the active detection mode is practiced. Around the investigated cable or pipe, an electromagnetic field is initiated by a special generator, measuring which,determine the desired characteristics of the PC.
PC Repair
Obviously, the existing underground utilities are subject to overhaul and reconstruction only by organizations and enterprises that have the appropriate permits, within the time frame approved in the master plans of municipal utility management structures. Every year, by November 30, operating enterprises submit their plans for such work to the city housing and communal services department for linking and accounting.
If in the process of such work it is necessary to violate the integrity of lawns, remove the roadway, then permits from local governments are required. When re-planning existing PCs in connection with the construction of new facilities, their re-equipment is carried out by the general contractor in accordance with the project. Each specific PC repair project must be coordinated by the general contractor with all business entities whose underground utilities are located in the work area.
To receive it by the customer, the following documentation package is submitted:
- letter agreed with municipal authorities;
- project of works and PC track plan;
- Guaranteed road resurfacing;
- confirmation of the availability of equipment and materials necessary for repair;
- order to appoint a person responsible for repairs.
The customer also pays the rent of the repair area, after which he receives a permit.
If, during the performance of work, the contractor detects a PC that is not listed inproject, he is obliged to stop work and notify the customer. He, in turn, calls the employees of the design company, who draw up an act on this occasion and formulate an official decision.
In case of damage to the PC, the architecture management, with the participation of all interested parties, draws up an act and makes a decision on compensation for damage. The culprit is identified, and the deadlines for elimination are set.
PC Maintenance
PC maintenance is carried out for the purpose of safe and uninterrupted supply of the population and business with electricity, water, gas, communication services, drainage, sewerage, etc. This task is complicated by the visual inaccessibility of communication routes. Thus, the operation of a PC is reduced to their preventive maintenance and current repair.
The purpose of preventive maintenance is to identify possible damage that leads to leaks and other supply disruptions. The first part of it is the inspection and measurement of basic indicators directly on the external elements of communications (transformers, switchgears, manholes, condensation devices). However, the basic indicators are the pressure of water and gas, the voltage of electricity. The frequency of the inspection is determined by the organizations that supply utilities to consumers, it is finally approved by their higher authorities.
Description of one of the services
Route maps are created for the main gas pipeline with water seals and condensate collectors applied on them. In recentcondensate is pumped out using motor pumps. Only certified specialists are allowed to perform such work. At the same time, safety precautions prohibit the use of open fire and smoking is strictly prohibited.
To determine the operating modes of gas pipelines, pressure is measured in them at least twice during the period of maximum winter and minimum summer load.
The tightness of these communications is carried out by periodic drilling and chute inspections. For this purpose, a well with a diameter of 20–30 cm is drilled behind each joint of the gas pipeline. The drill plunges into the depth to a distance of 20 cm, not reaching the gas pipeline. Next, the presence of gas in these wells is checked.
If the soils in which gas pipelines are laid have an increased corrosivity, 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 greatest pressure drops are determined. Most often, the reason for their formation is the sagging of the gas pipeline, caused by a violation of the homogeneity of the soil. Therefore, simultaneously with the repair of the integrity of the pipe, a thorough padding of their soil bed is carried out.
PC organizations (enterprises)
Underground communications of the organization are designed comprehensively as part of a single general project, together with buildings and structures. PCs are placed in space-optimized technical lanes.
Directly on the territories of the enterprises themselvesexclusively overground and ground communications are used.
Pre-factory communications are laid underground. They are placed together in common tunnels. The length of the PC of the leading industrial enterprises is up to several tens of kilometers. The complexity of laying various communications (in percent) is: sewerage - 65%; plumbing - 20%; heat pipelines - 7%; gas pipelines - 3.5%, electrical and communication cables - 3%; technological pipelines - 1.5%.
Technological pipelines can be placed together with a gas pipeline, heat pipeline, recycling water supply. At the same time, it is forbidden to place pipelines with explosive and flammable liquids.
Conclusion
The problem of replacing underground utilities is now becoming very relevant. Its root cause lies in the systemic shortcomings of the state financing mechanism according to a deliberately failed residual principle. Thus, in fact, the objective reality is neglected: the fact that each design laying of underground utilities implies specific terms for their replacement, according to the materials of their manufacture and the conditions of occurrence in the ground.
PC replacement should be planned as part of government economic policy. Unfortunately, the inconsistent economic function of the state actually prevents the creation of full-fledged and effective funds for regular capital economic investments.
In this regard, there is a positive world experience. The Norwegian PC system can serve as a role model, clearlyregulated by the orientation of the country's budget to comply with relevant state standards.
We are constantly observing a vicious vicious cycle: how, in the absence of such an established economic mechanism, managing monopoly organizations now and then initiate an increase in the already inflated tariffs for utilities, motivating this by 90% outdated PCs.
