The device and types of sewerage networks. SNIP external sewerage networks External sewerage networks

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The smallest depth at which it is possible to lay a street network of domestic and fecal sewerage can be determined, given the possibility of connecting the longest line of the network within the quarter with a slope of 0.007 to its system. The smallest depth of laying the initial elements of the intra-quarter network is taken 30 cm less from the depth of soil freezing and not less than 50 cm from the surface.

If the sewer network becomes clogged, it is necessary to inspect, rinse and clean it. For this, inspection wells are arranged wherever there are changes in the diameter and slope of pipes, where there are turns, and on straight segments of the sewer line having the same diameter. In places where rivers, ravines, railway tracks, etc. intersect with the network, overpasses or siphons are installed. Dukers are made of metal pipes, placed on the bottom of a ravine, river or under railway tracks. Dukers work under the natural pressure of escaping wastewater. Overpasses have the form of a bridge overlapping an obstacle, along which a sewer pipe with a rear slope is laid in a protective box.

Flushing of the sewer network from the sediments constantly forming at the bottom of the sewer pipes (in areas where the flow rate of sewage is insufficient) is carried out by accumulating the inflowing sewage in inspection wells (the bottom hole of the well is closed with a portable shield) and quickly emptying them into the sewer network (when the flap opens ). Thanks to these actions, a high speed of water movement is created, with the help of which all accumulated sediments are removed.

If the section of the network has an insufficient inflow of wastewater, then the inspection well is filled with water through the fire hose of the hydrant available in the water supply network. In some cases, at the initial sections of the network, special flushing wells with a capacity of up to 2 m³ are installed. They are filled with water from the water supply and connected to the sewer line.

Creation of a small sewerage network for individual buildings

Tools and materials required to create an individual sewer network: earthmoving tools, pipes, gravel, sand, tees, oblique crosses, tow, measuring instruments and tools for plumbing work.

During the construction process, it is necessary to take into account a number of sanitary and hygienic requirements and provide the ability to remove wastewater from toilets, sinks, washbasins, showers, baths, etc.

To receive wastewater in all rooms on the site, sewer pipes are used with a nominal bore of at least 25 mm. All pipes and fittings for the device of the internal sewage system must comply with all technical conditions, meet sanitary standards.

External sewerage networks are located outside residential premises. The system is designed for wastewater disposal and further treatment. Installation of an external sewerage system is strictly regulated by regulatory enactments - SNiPs.

Classification of external sewer networks

External sewer networks, depending on the method of their organization, are divided into several types:

systems where domestic wastewater is transported separately and to different collectors, and rain or melt water is called separate;
networks where rainwater and domestic wastewater are transported separately, but enter a common collector, are called semi-separate;
systems without dividing water into domestic and rainwater are called general alloy.

The most efficient, in terms of ecology, is a separate sewerage system. It is more expedient to install the same sewage system for household needs on a personal plot.

The main elements of external sewer networks

The external sewer network is a complex structure. As a rule, it includes:

metal or polyethylene pipelines of various diameters, designed for the passage of liquid;

for different purposes: for viewing, for turning the system, for arranging a level difference. In most cases, reinforced concrete is used for devices, but strong plastics can also be used;

collectors, which are large-diameter pipes into which water flows from the storm sewer network or household systems;
specialized. Installed in places where it is impossible to equip the passage of liquid by gravity;

various local types intended for primary wastewater treatment;

discharges of water into external sewerage networks or water bodies, for example, ponds.

DIY outdoor sewerage installation

Sewerage is being installed: external networks and structures are quite simple, if you adhere to the basic rules:

trenches to be dug for must contain a slope sufficient for the gravity of the fluid. If these standards are not met, then it will be necessary to additionally install pumping stations, which will complicate the work and negatively affect the cost of the system.
before the installation of the pipeline, the necessary equipment is installed: local cleaning systems, wells provided for by the project.
on a long straight section of the pipeline, the distance from one well to another must be at least 15 - 18 meters.
It is more convenient to start the installation of the pipeline with the last outlet pipe.
it is more expedient to connect pipes by welding into a socket.

Subject to the above rules, the sewer system will work flawlessly for a long time.

Sewerage project

Like many other types of construction work, the installation of an external sewer network begins with a project. It is best to entrust this work to specialists, but you can develop it yourself.

At the first design stage, it is necessary to establish where the wastewater will flow in the future. It can be:

centralized external sewerage network. To connect to this system, it is necessary to collect the documentation established by the legislation. This connection is considered to be the best;
special sealed wastewater storage tank. Such a system is periodically cleaned by machines, therefore, it is advisable to install the tank closer to the fence and the roadway for the convenience of equipment access;
local treatment facilities for further use of water, for example, for watering a vegetable garden or for discharging treated water into a nearby reservoir.

At the next stage, it is necessary to study the climatic conditions of the area in which it is supposed to place the external sewage system:

find out the depth of freezing of the ground, on which the depth of the network depends. If it is not possible to lay pipes and structures below the freezing layer, then you will need to purchase a special insulation for pipes, for example, glass wool.

survey the terrain. Is it possible to install a gravity sewage system on the site or is it mandatory to use pumping stations.
find out the type of soil and the level of occurrence of groundwater. If the waters are located close to the surface, then the possibility of laying pipes below the freezing depth is completely excluded. The type of soil affects the layer of the protective pipe cushion, which is constructed from sand. If the site has heavy soils, then the protective layer should be larger.

At the last stage, some indicators are calculated that are necessary for the correct operation of the sewer network:

the amount of waste water. It is estimated that one person needs about 200 liters of water per day.
the slope of the pipeline. According to the requirements of SNiP, for pipes with a diameter of not more than 200 mm, it is enough to make a slope of 2 cm for every 2 m of the pipeline.
the required volume of a septic tank for autonomous sewerage. The average course of wastewater disinfection takes place within 3 days.

It is more expedient to entrust the design of an external sewage system to specialists. As a last resort, you can carry out the design work yourself, strictly adhering to the recommendations.

Sewerage installation

It is somewhat easier to mount a sewer than to design it. You can do this work yourself. For this:

trenches are dug for pipelines and foreseen structures. The minimum margin for dimensions should be at least 20 cm, which is necessary for the convenience of laying the network.

a layer of sand is laid on the bottom of all trenches.
structures are installed: pumps, treatment facilities, wells, and so on.
an external sewerage network is being installed.

pipelines are laid in trenches and covered with a layer of sand.

the soil is laid by the backfilling method.

An external sewerage network is required on the personal plot. This system of structures will allow preserving the ecology of the environment and without additional efforts to obtain water for irrigation of garden plants.

Wastewater classification and sewerage systems

SEWERAGE AND SANITARY CLEANING OF SETTLEMENTS

Chapter 10

Sewerage is a necessary form of wastewater treatment in populated areas. Its task is to remove water, liquid waste generated as a result of household activities of the population of cities and towns and the work of industrial enterprises. Together with surface water (irrigation, atmospheric, groundwater) that ended up on the surface of urban and rural areas, liquid waste is a contaminated liquid and is called sewage. They contain chemical, biological and organic components. They must be removed, cleaned, disinfected and sent to nearby bodies of water. For this, the sewerage system and gutters are used.

Wastewater is classified into the following categories:

Household or household - from houses, industrial buildings, formed as a result of human activity. Contains organic mineral, bacterial contamination;

Manufacturing - from industrial enterprises formed as a result of technological processes. Contains organic, mineral, toxic contaminants;

Atmospheric - from the territory of the city, roofs of houses, rain and melt water. Contains mineral, chemical contamination.

Drainage systems depend on the composition of the wastewater. The degree of pollution is characterized by the amount of pollution per unit volume. The concentration of pollution depends on the rate of water consumption in the settlement, the nature of production, the place of collection of sedimentary waters, and their amount. The wastewater sewerage system provides reception, transportation, purification, disinfection, utilization of useful substances and discharge into a reservoir. There are two types of sewerage: export and floatable.

Export sewerage based on the removal of individual volumes of liquid to aeration fields.

Floatable sewerage consists of a system of underground pipelines and devices transporting waste water to the treatment plant. This system is most common in large settlements. For its installation, it is necessary to have an internal water supply with a consumption rate of at least 60 l / day per person.

The floatable sewerage system consists of internal devices, external networks, pumping stations, treatment facilities and wastewater discharge devices.

Floating sewerage, depending on how the issue of wastewater disposal is resolved, is subdivided into storm sewage, fecal (household), common-fusion, separate (full, incomplete), semi-divided and combined.

The common sewerage system carries out the drainage of storm wastewater by one system of pipelines, which comes after rain from urban areas through storm inlet grilles, and household and fecal wastewater coming from residential buildings and industrial buildings. With a separate sewerage system, two independent wastewater drainage systems are used: storm sewerage (drain) and household and fecal. Wastewater from industrial enterprises is discharged by a separate system to purify them from specific contaminants. Currently, a separate sewerage system is most applicable.

The external sewerage system consists of underground pipelines through which water is diverted by gravity from houses to pumping stations. The intra-quarter network joins the street one. At the junctions, control wells are built, located at the red lines of the streets. The canalized territory of the city is divided into separate basins along the border of the watersheds. Street sewerage is combined within one pool and directed to the main sewer. In the lowered sections of the collectors, pumping stations are arranged to raise wastewater and ensure their further gravity fusion (pressure header). Large collectors are called ducts.

Sewer networks are designed on the basis of the general plan. On the absolute horizontals, the boundaries of the sewerage basins along the watersheds and the directions of laying the main collectors with a natural slope are found on the terrain. Then the connections to them and the intra-quarter networks are designed.

Sewerage schemes are chosen depending on the terrain conditions: perpendicular, crossed, parallel, zone (belt), radial.

The sewerage route is selected using a feasibility study of possible options. When several pressure pipelines are laid in parallel, the distances between the outer surface of the pipes to structures and utilities should be taken in accordance with SNiP 2.04.03-85 based on the conditions for protecting adjacent pipelines and performing work.

The smallest laying depth is taken in accordance with SNiP 2.04.03-85 for sewer pipes with a diameter of up to 500 mm, 0.3 m less than the maximum depth of penetration into the ground of zero temperature, but not less than 0.7 m to the top of the pipe, counting from the planning marks, for pipes of large diameter - less by 0.5 m.

The diameters of the sewer pipes of the system depend on the amount of wastewater, which is determined by the degree of improvement, that is, the rate of water consumption, the presence of hot water supply. So, the rate of waste water consumption per 1 person. with centralized hot water supply and the presence of a bath - 400 l / day, and with gas heating installations - 300 l / day. ...

For sewer networks, cast iron, asbestos-cement, plastic, concrete, reinforced concrete and ceramic pipes are used, depending on the presence of pressure and the composition of the wastewater.

For pressure collectors, cast iron, reinforced concrete, steel and asbestos-cement pipes are used; for gravity and gravity collectors - cast iron, asbestos-cement, plastic, concrete, reinforced concrete and ceramic pipes. Collectors are laid from round reinforced concrete pipes and prefabricated elements.

A properly executed project and installation of external sewerage networks determines the duration and quality of their operation. The main provisions and rules for the construction and repair of the external sewerage network are determined by SNiP 2.04.03-85. The document regulates the full cycle of work on the construction of the engineering system from the installation of the pipeline to the construction of treatment facilities. SNiP sewerage external networks and structures will help you choose the best material and build an effective system for draining waste and rainwater.

What is outdoor sewerage

External sewerage includes branched pipelines and system elements necessary for transporting wastewater from residential buildings and other facilities to treatment facilities. The design of the utility network is carried out simultaneously with the preparation of water supply plans. The systems are interconnected by the need to maintain a balance of water consumption and disposal. Installation and maintenance of the city's outdoor sewerage system is entrusted to public utilities. The maintenance of the autonomous sewage system in private houses is carried out by the owners themselves.

There are two ways to transport wastewater:

gravity or gravity;
pressure head, requiring the installation of pumping equipment.

Sewerage types

To ensure the safety of the functioning of the external sewage system, SNiP offers several ways:

duplication of communications - ensuring the ability in the event of an emergency to switch the flow to a parallel pipeline or channel;
reliable power supply, availability of an alternative (backup) source;
stocking in the design of network bandwidth

Attention. When installing sewerage facilities, a certain sanitary zone must be observed up to the construction sites of residential and public buildings.

Structural diagrams

According to SNiP, the external sewage system is divided into several systems by the method of installation:

General-purpose - according to this installation scheme, all drains - domestic, storm, thawed - are sent to one sewer collector or container.
Separate - the system is arranged so that household wastewater and melt (rain) water are transported through various pipelines and enter various treatment facilities or storage facilities.
Semi-separate waste water and storm sewage are directed through different highways into one container.

Alloy scheme

Attention. It is forbidden to dump sewage into water bodies that is not purified to the established standards.

Sewer system classification

External engineering communications are arranged in various places and have their own purpose.

Yard network - used to service one building. Consists of the following elements: small diameter pipes (150 mm), building outlets, receiving and inspection chambers. This concept is used for a system connected to a central sewerage system, it is not used for an autonomous system.

Yard network

Intra-quarter - the network is arranged inside the quarter, it consists of the same elements as the courtyard.

The street network is designed to transport wastewater collected from all quarters. Such a pipeline is called a collector, its function is to collect waste water and divert it to a pumping station or treatment plant.

Attention. Laying the sewer pipeline on the ground in settlements is not allowed.

Drainage network diagrams

Depending on the features of the terrain, one of the external drainage schemes is selected:

perpendicular - used for rainwater drainage collectors for the fastest transportation of water to the general flow;
zone - a rare option, applied to objects with a significant difference in height, a pump is installed in the lower manifold;
cross-country - the main collector is installed along a river or other body of water to intercept wastewater;
radial - wastewater is directed to various treatment facilities.

Components of the external sewerage system

The engineering network consists of several main parts:

Pipeline - a line of pipes of various lengths and diameters, laid with a slope.
Wells - structures differ in purpose, they are - drainage, observation, drop and rotary. The wells are equipped with brackets for lowering repairmen and hatches with covers.

Pipeline and well
Outlets to water intakes are elements that ensure the free outlet of wastewater from the pipeline to the reservoir.
Collectors - underground tunnels in the form of large diameter pipes (from 2000 mm), through which waste is transported to the end point of the network.

Collector
Local treatment facilities - installations used for the treatment and discharge of wastewater into water bodies. These include septic tanks, biological treatment plants and other equipment. The number of homes maintained depends on the size and performance of the facility.
Pumping stations are installed at separate facilities that need a metered supply of wastewater.

The choice of a method for the disposal of household and rainwater effluents depends on a whole list of factors that are taken into account even at the design stage:

properties and nature of the soil;
climatic features such as freezing depth;
the volume of transported wastewater;
groundwater level;
the distance from the point of release from the building to the treatment plant.

Attention. The smallest permissible pipeline slope depends on the minimum sewer flow rate.

The choice of material for the pipeline

The materials used for the installation of highways and channels must be resistant to the effects of an aggressive environment and the effects of abrasive particles contained in the liquid. To prevent gas corrosion of the upper part of the collector, ventilation is installed to exclude gas stagnation.

SNiP of external sewerage provides for the use of pipe networks for the installation of the following materials:

polyethylene;
polyvinyl chloride;
polypropylene;
steel;
asbestos cement;
cast iron;
reinforced concrete.

Polymer pipes

Cast iron pipes

Reinforced concrete pipes

In rare cases, when installing a network, pipes made of ceramics and glass are used; such materials are permissible by the rules.

Polymer products are the best choice for the installation of external engineering networks. They have all the qualities that ensure reliable and long-term operation of the system:

resistance to mechanical stress;
frost resistance;
high throughput due to smooth surface;
corrosion resistance;
durability.

Installation rules for sewerage networks

Pipe diameter

The capacity of a free-flow network depends on the size of the pipes. Building codes define the minimum pipe diameter for a gravity engineering system:

street network - 200 mm;
autonomous sewerage - 110-150 mm;
intra-quarter - 150 mm;

The size of the rainwater and all-alloy street system is 250 mm, the intra-block system is 200 mm.

Speed

The SNiP contains tables that determine the speed of movement of wastewater, depending on the size of the pipeline or flume. These indicators help to avoid siltation of sewer networks. The flow contains suspended particles, which, if the speed is insufficient, settle on the surface of the line.

Basic design data:

diameter 150-250 mm - 0.7 m / s;
600-800 mm - 1 m / s;
more than 1500 mm - 1.5 m / s.

The smallest speed of movement of the clarified wastewater along the trays and pipes is 0.4 m / s. The maximum value of the speed of transporting wastewater:

for metal and plastic pipes - 8 m / s;
on concrete and reinforced concrete - 4 m / s.

For rainwater drainage, the indicators are:

metal and plastic pipes - 10 m / s;
concrete and reinforced concrete - 7 m / s.

Pipeline slope

One of the basic rules when laying a pipeline is compliance with the slope norm. For systems where fluid moves under the influence of gravitational forces, this parameter is critical. The negative consequences of errors in installation in the direction of decreasing or increasing the slope lead to malfunctioning of the network, blockages and breakdowns.

Attention. The standard indicator is calculated for 1 running meter of the pipe.

For autonomous sewage pipes that are smaller than central networks, the following standards apply:

In special conditions associated with the terrain, a decrease in the slope is allowed:

pipes 150 mm to 0.008;
pipes 200 mm to 0.007.

Storm water inlets are connected to the general system with a slope of 0.02.

Depth of the network

The minimum depth of the sewer pipeline depends on the heat engineering calculation. Also take into account the practice of operating utilities in the area. The pipes are laid 0.3-0.5 m below the freezing point of the soil. The maximum depth depends on several factors:

pipe material;
type of soil;
pipeline diameter;
way of laying.

Well requirements

Wells are an integral element of the sewer network, therefore the rules and regulations for their installation are described in SNiP.

Inspection wells

For the inspection of the pipeline, special elements are installed - inspection wells. Their installation is carried out in two cases:

at the joints of pipes;
at the section where the direction of the pipeline changes.

SNiP determines the diameters of the wells depending on the size of the pipes:

main line up to 600 mm - well 1000 mm;
pipeline from 700 mm and more - pipe size + 400 mm in length and 500 mm in width.

Inspection well

On straight sections of the gravity network, observation structures are located after 35 m, for medium-diameter highways (500-600 mm) - 75 m, for large pipes (1500-2000 mm) - 200 m. The working part of the structure is equipped with a hinged ladder for descent.

Rainwater drain

Stormwater drainage is used to quickly drain rain and melt water. It can be open, closed and mixed. An open network consists of trays and channels, a closed network consists of storm water inlets and an underground pipeline, a mixed network is a combination of pipes and trays. To reduce the length of the system, the discharge is carried out into the nearest body of water or ravine.

When installing a rainwater drainage system, it is necessary to provide for the installation of facilities for the treatment of the most polluted effluents generated during heavy rains. For this, sand traps, sedimentation tanks and filters are installed. It is also recommended to design the possibility of using treated rainwater for irrigation and industrial needs.

Wastewater treatment devices

18 July, 2016
Specialization: Capital construction works (laying of foundations, erection of walls, construction of a roof, etc.). Internal construction work (laying of internal communications, rough and final finishing). Hobbies: mobile communications, high technologies, computer technology, programming.

It's no secret that in the near future I'm going to build a house in the country for my son. And now I design engineering communications for the future structure. In particular, outdoor sewerage is on the agenda.

The device of this system, although it seems rather simple, especially in comparison with the branched pipelines laid inside the house, has many nuances. Violation of certain requirements can lead not only to the inoperability of the system, but also dangerous consequences for others. And then there should be a smaller estimate, because I'm still going to spend my own money, not government money.

In general, I had to tinker a lot. But as a result, I can provide you with detailed instructions on how to correctly design and install this system with your own hands. Read carefully.

Building code requirements

To begin with, let's consider what an external sewage system is according to SNiP. After all, you do not want your future home not to meet the established standards and not be accepted into operation by the relevant services. So I don’t want something like this for giving my offspring, so I’ll dwell on the coverage of the issue raised in more detail.

Elements of external sewerage

The outer part of the sewage disposal system is necessary for transporting sewage to the places of their processing and cleaning them from various contaminants.

It consists of several elements:

Pipelines of various cross-sections and lengths... They are made of different materials and serve to deliver wastewater from the drain pipe of the internal pipelines of the house to the treatment facilities (centralized or autonomous).
Wells... They are an obligatory part of the sewage system and are necessary to perform certain actions.

In my practice, I have come across the following types of wells:

to inspect communications (through them, clogged pipes are cleaned);
for arranging pipe bends;
for laying pipes with a difference in height;
drainage.

Collectors... They are a kind of large-diameter pipelines that serve to accumulate and transport sewage water in centralized waste disposal systems.
Wastewater treatment plant... They are central (to the settlement or part of it) and local (used to clean the sewage system in a private house). In the latter case, the sewage treatment plant can be replaced with a storage tank, which is periodically emptied using sewage equipment.

Swap stations... An intermediate link of the treatment system, which accumulates wastewater and gradually supplies it to the treatment plant. Such units are used in centralized networks or privately, if a biological treatment plant with aerobic bacteria is installed on the site.

Above, I have listed the main elements of the system. But in order to mount an external sewer network, you will need many more materials and tools, which I will discuss below.

polymer - polypropylene, polyethylene, polyvinyl chloride;
steel and cast iron pipes are an outdated option, since the price of such parts is high, and the performance properties leave much to be desired;
asbestos-cement and reinforced concrete channels - they are used only in centralized sewerage systems, I have not met them in private houses.

I also heard that there are pipes made of ceramics and glass, but in practice I haven’t come across them, so I cannot tell you anything concrete. But this is a very exotic material that will certainly not be useful in private construction.

General installation rules

Regardless of the size, performance and other parameters, when creating local external sewage systems, it is necessary to adhere to certain sanitary and building rules.

A lot of information is indicated in the regulatory documents, but for an ordinary master who makes a sewage system in his own dacha, it is enough to take into account the following factors:

groundwater level at the site;
soil properties;
the climate of the area in which the construction is carried out;
the average volume of sewage that is planned to be disposed of per day;
the distance from the house to the central sewer collector or an autonomous septic tank.

One of the main requirements that should be strictly observed (otherwise your external sewage system simply will not work) is the slope of the pipelines. The specific value depends on the diameter of the parts. To make it clearer for you, I have compiled a small table.

Before starting work on the creation of an external drainage system, I advise you to order exploration work for the study of soils, laying the pipeline route, calculating the necessary details and the cost of work.
If you don’t want to do all this, at least ask for advice from those neighbors who have already completed work on the arrangement of engineering systems.

External piping requirements

Before choosing a specific type of pipes and starting work, I want to list the most important requirements that apply to external sewage systems (they are fixed in SNiP under the number 2.04.03-85):

The outer part of the sewage system should be constructed of materials that have the longest possible service life and are not subject to corrosion. After all, it will be operated in very aggressive conditions.

When laying pipelines, it is imperative to take into account the nature of the soil in order to avoid movement of the soil after backfilling. Otherwise, a leak will appear, which can become a source of groundwater contamination.
In the project of an external drainage system, it is necessary to provide for the presence of mandatory elements: revision holes, valves, nozzles, pumps, and so on. Believe me, all the rules were created for a reason, and you will greatly regret in the future if you cannot clean the pipes due to the lack of revisions.
It is imperative to install inspection chambers and hatches at the points of pipe bends, intersections of individual pipelines and revisions. Otherwise, in the event of an accident, earthworks will have to be carried out. Wells must have safety features (hatches, fences, ladders, and so on).

Arrangement of external sewerage

So, let's look at how an external sewage system is done. I divided all the work on the arrangement into several parts. But remember that the specific instructions depend on whether you are connecting the pipelines in the house to a central sewer or building your own sewage treatment plant.

But first things first.

Pit preparation

Installation of an external sewage system begins with the preparation of a foundation pit, more precisely, a trench for laying pipes. You can simply dig it with a shovel (if the length is not very long) or order an excavator.

The depth of the hole directly depends on the depth of soil freezing in the area where you live. External sewerage pipes should be laid 50 cm below that mark. You can find the necessary information in special tables.

The approximate depth of soil freezing in different regions of Russia is:

in the northern regions of the Russian Federation - from 3 to 3.5 meters;
in the middle zone of our country - from 2.5 to 3 meters;
in the southern regions on the Black Sea coast - from 1.2 to 2 meters.

The values shown are approximate. That is why I advise you to conduct a soil survey in the area where your house is built.

Most often, pipes with a diameter of 110 mm are used for the installation of the outer part of the sewage system. For them, I advise you to dig a 60 cm wide trench (for easy installation). Depth - freezing level + 50 cm according to SNiP + 10 cm for arranging a shock-absorbing cushion.

In addition, when digging a ditch for laying sewer pipes, I pay attention to several other features:

I always carefully level the bottom of the groove and make the slope, which I already mentioned above. It is necessary to ensure a free flow of water towards the collector or your own treatment plant.

Once I have leveled the bottom, I carefully tamp the ground at the bottom to avoid shifts. Then I sprinkle a 10 cm thick sand pillow on top, which I also very carefully compacted.
The fact is that pipes are assembled using sockets, so ground movements can lead to a depressurization of the system. And I, for example, do not want to dig three meters of earth again to find a leak. Moreover, you will have to dig along the entire length.
In those places where the pipe enters the collector or, you need to make a wider platform (at least two meters), the bottom of which is also carefully tamped and covered with sand.

Sockets and fittings are slightly larger than the pipe itself. Therefore, in those places where they will be installed, I always make pits so that the central axis of the pipe is always at the same level (naturally, with a slope from the house).

Pipe laying

Having finished with the pit, you can safely proceed to laying pipes. However, before that, I want to say a few words about the choice of a suitable material.

Now I will not mention citywide networks, since large companies are engaged in their construction. And for a private house or summer cottage, I used polymer pipes in my practice:

polyethylene;
polypropylene;
polyvinyl chloride.

If the pipes will be laid at a very great depth or frequent and significant dynamic loads will affect this section of soil, it is better to buy corrugated high-strength pipes made of polyethylene or propylene. They are joined together using shaped parts.

In all other cases, I use PVC pipes with sockets. If you have designed an internal sewer system, then you know what I mean. Only you need to take not the familiar gray parts, but those varieties that are colored orange.

They are strong enough, have a smooth inner surface and are perfect for the construction of external engineering systems for wastewater disposal. The maximum to which these pipes can be buried is 3 meters, which is quite enough for most cases.

I lay pipes according to the following scheme:

First, I lay out all the pipes at the bottom of the trench without cutting. I put revisions, tees, crosses and other necessary fittings in the right places.
Then I start the assembly, which I start from the manifold inlet or local septic tank. To do this, I take the parts cut to the required size and clean them of dust and dirt.

If you are cutting pipes with a saw and not with a pipe cutter, the end of the part must be deburred and a small chamfer removed, otherwise the rubber O-ring may be damaged. I also recommend making sure that the cut is exactly 90 degrees to the surface of the pipe.

After cleaning, I insert the smooth part of one pipe into the socket of the other until it stops. To provide additional sealing and extend the life of the seal, I always apply a silicone sealant to it.
I do the same with the rest of the parts along the entire length of the pipeline.

I want to give one free piece of advice. If your external sewer layout has sharp bends, do not use 90-degree bends. Better to set two at a 45 degree angle. And be sure to put a well with a revision in this place.

This will save you from trouble and will allow you to quickly clear a difficult area in case of it.

In this way, you need to collect all the pipes into one system and test them for tightness. To do this, you need to pour a bucket of water into the branch pipe of the internal sewage system and wait until it gets into the central collector or your own septic tank (more on that later).

Warming

Very often, when designing an external sewage system, I resorted to additional insulation of the plastic pipes used. Strictly speaking, if you dug a trench of sufficient depth (below the level of freezing of the soil), there is no need for insulation, but, as they say, it is better to play it safe.

As a heat-insulating material, you can use:

glass wool or basalt fiber;
polystyrene;
polyurethane foam;
heat insulating.

I advise you not to rack your brains over the choice of material and buy insulating shells made of extruded polystyrene. It has a fairly low coefficient of thermal conductivity, high water-repellent properties, long service life and increased strength.

Among other things, no tricks are needed to install it on pipes. It is enough to mount the halves of the shell on the pipe and snap them onto special locks, wrapping them on top for fidelity with adhesive tape.

It is much easier than wrapping pipes with mineral wool, then fixing it, then wrapping it with roofing material on top, and so on.

backfilling

The last stage in the design of the external sewer pipeline is backfilling of the trench. I do not advise to treat this stage with disdain, as this is where beginners often make a lot of mistakes.

For backfilling, you can use the soil that was removed from the trench. First, you need to make sure that there are no fallen clods of earth, stones and other objects in it that can damage the PVC pipe.

I highly recommend using sand for backfilling (at least until the pipe inside the trench is hidden under its layer). In this case, the pipe is more reliably protected from ground shifts and, accordingly, depressurization.

In any case, backfilling should be done in layers, especially on the sides of the pipe, with intermediate compaction of the soil. This, again, is necessary to protect the engineering system from damage. It is necessary to ram the soil only on the sides of the pipe, on top - in no case. Plastic may not withstand such intense exposure.

A small bump should be poured on top, which is needed to compensate for the shrinkage of the soil after the latter is wet.

By the way, if you plan to install a sewage treatment plant with some kind of electrical equipment (for example, a biological treatment plant), I advise you to immediately lay a shielded electrical cable into the ditch before backfilling. So as not to be smart about connecting electrical devices to the network later.

Construction of a sewage treatment plant

In addition to pipelines, a local sewage treatment plant is part of the external sewerage system. As the latter, I propose to use a septic tank made of concrete rings, which does an excellent job with the tasks and is done quite simply.

Calculations

At my son's dacha, I decided to build a three-chamber filtering septic tank. Of course, you can say that its capacity is excessive for a structure where people are not supposed to live permanently. But I decided to make a reserve for the future.

Moreover, this option has many advantages:

the construction and operation of a septic tank is cheaper than a biological treatment plant;
it can be built independently, without the involvement of outside specialists (looking ahead, I can say that I only needed an excavator to dig a pit and a crane to install concrete rings).

Of the shortcomings, I can only single out the possible appearance of an unpleasant odor (solved by installing a ventilation pipe) and the need to remove sludge from the bottom.

So, my septic tank will consist of three different chambers:

for the primary settling of sewage;
for cleaning liquids from biological contaminants;
to remove purified water through the filtering bottom of the chamber.

Some replace the last compartment with drainage fields, but I decided to limit myself to such a design so as not to carry out a large amount of earthwork.

If at the dacha you are not going to install a washing machine and invite a large number of people there to rest, you can limit yourself to one camera, which will serve to remove solid inclusions.

Now about the size of the chambers. Here are some calculations. Let's say that 5 people are supposed to live at the dacha (well, the calculation is to replenish the family). Each of them consumes about 200 liters of water within 24 hours, that is, the treatment plant should be able to receive 1000 liters of liquid per day.

According to regulatory documents and sanitary requirements, a local treatment plant should have such a volume to accommodate three times the volume of dirty water, that is, about 3 thousand liters.

If the volume of the concrete ring is 0.6 cubic meters of water, then about 5 rings will be needed to build a septic tank. We divide into three sections - it turns out that 2-3 rings will go to each camera. I'll do three to be sure.

Choosing a location

The second important point after calculating the required volume is the choice of a place for installation. Moreover, this is done not of their own free will, but in accordance with the existing sanitary requirements.

Be sure to consider the following requirements:

The minimum distance from a residential building to a septic tank should be 5 meters or more.
If you make a septic tank at a distance of more than 15 meters, you will have to pull a long pipe and make an inspection hole on it with a well for inspection. So I do not recommend digging a pit too far.
The distance from the source of water intake (well or well) to the treatment plant must be at least 30 meters.

By the way, one such moment. No matter how well and for a long time the septic tank works, sooner or later it will be necessary to clean it from bottom silt deposits using sewage equipment. Therefore, you need to think about how this unit will drive up to your structure.

Excavation

The next stage is earthworks again. This is not a narrow ditch, you will have to take out a fairly large amount of soil, therefore I immediately advise you to either hire workers or order an excavator.

The size of the pit should be slightly larger than the diameter of the concrete rings used. That is, if we take rings with a diameter of 2 meters, the foundation pit should have a width of 2.5 meters. Then this space will be covered with clay in order to exclude the seepage of sewage into the ground when the well is depressurized.

The depth of the well depends on the number of concrete rings used. Fold the height of the parts and go deep into the ground so that after the installation and arrangement of the concrete floor, only the inspection hatch is visible from above to check the operation of the septic tank.

Installation of rings

For the installation of reinforced concrete parts, you will definitely need a crane. Otherwise, construction will take away the last remaining health from you. Despite the fact that the work of special equipment requires additional costs, you will get a durable, strong and sealed treatment plant, which is well worth the money spent.

The installation itself is as simple as possible. You just need to lay the parts one on top of the other, making sure that the walls are oriented strictly vertically. The joints must be reinforced with cement mortar. If in the country the soil is subject to shear and swelling, metal brackets can be used to strengthen the treatment plant.

To prevent the concrete rings from slipping, the bottom of the trench should be prepared before installing them. It is necessary to make a cushion of rubble there, carefully tamping it.

Most of the trouble will be with the arrangement of the bottom. In the first two chambers, it must be completely sealed in order to exclude the seepage of waste into the soil, and in the third well it will be necessary to leave a filter cushion made of rubble.

I'll tell you more about arranging a sealed bottom:

The bottom of the first two wells should be carefully tamped again, after which a reinforcing frame made of metal mesh or reinforcing bars should be made at the bottom. I always drill down the walls a bit to insert the reinforcement pieces into the concrete rings and ensure a good floor-to-wall connection.
After that, prepare a concrete solution from sand, crushed stone and cement, with which to pour the lower part of the well, leveling the surface with a trowel.
It is possible to continue work on the arrangement of septic tanks only after the concrete solution has completely solidified. This usually takes 2 to 3 weeks, depending on the ambient temperature.

In hardware stores, sections of concrete rings are sold, already equipped with a concrete bottom. You can buy yourself two such parts and not waste time and effort on concreting the bottom of the treatment plant. But the pillow at the bottom is still needed so that the entire structure does not shift during operation.

Sealing

To prevent the seepage of sewage into the soil, the inner walls of the well should be carefully sealed. For this, I recommend using a special mixture, for example, Aquabarrier.

For reliability, I decided to seal the surface with a bitumen-based coating waterproofing. Some go even further by installing plastic liners inside concrete tanks that keep water out.

Simultaneously with the sealing, overflow pipes must be installed. This is done according to the following scheme:

The first pipe, which connects the septic tank to the residential building, is installed in the first chamber of the septic tank at a distance of about 50 cm from the top of it. Although this is purely subjective, it all depends on the depth at which the pipes are laid.
The second pipe (between the first and second chambers) should also be installed at the top, but slightly lower than the first. The bottom line is that the already settled water that accumulates at the top of the chamber pours out through it.
The second and third chambers are connected in the same way.

The photo shows an approximate layout of pipes in a septic tank.

backfilling

The last stage in the construction of the treatment plant and the entire external sewerage system is the backfilling of the septic tank. You can use the soil that you took out when preparing the pit, but I additionally bought oily clay and filled the space around the wells with it. Thus, I created an additional barrier for the seepage of sewage into the soil.

Output

External sewerage is perhaps a more important component of the waste disposal system at a summer cottage than the inner part of this utility network. To clearly see the installation process, you can watch the video in this article. And if you have any questions or your own advice, you can leave them in the comments to the material.

July 18, 2016

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