Septic tank made of concrete rings in clay soil. Installing a septic tank on clay soil. For biological treatment
Perhaps the first thing you should take care of when starting to build a house or cottage is the septic tank. Those owners of plots with clayey soil will find it more difficult to install a flawlessly functioning sewage drainage system. But with due diligence and knowledge of how to install a septic tank in clay, this is quite possible. In such soil, you can install both a factory-made autonomous treatment station and a homemade container with or without a bottom.
The homeowner should know that in some respects he is lucky: clay is the best soil filter.
The ability to pass water and purify it are two different things. Therefore, in such soil you can safely install a septic tank without a bottom. All sewage outlets will be effectively cleaned, but this process is quite slow. Therefore the device sewer system under these conditions, it has its own characteristics that prevent overfilling of the container.
Types for installation in clay
Storage containers
Most often, they are used as plastic containers, in particular Eurocubes of various sizes. But barrels and homemade welded cubes can be installed of stainless steel. The storage container can be made of brick or concrete. Such septic tanks are often found in villages and towns. They are easy to set up: just dig a pit the right size, after which its bottom and walls are laid out with bricks. Or they install concrete rings with a diameter of 1 m and concrete the bottom of the pit.
For biological treatment
They are the most reliable and modern. These products are autonomous biological wastewater treatment stations capable of producing water that can be used for watering a garden or discharged into a pond with fish. The operating principle of such septic tanks is to separate fractions into heavy and light. This is facilitated by the design of the station.
The main work of wastewater treatment is performed by aerobic or anaerobic bacteria. The life activity of the former is possible only under the condition of constant air pumping. The latter live in silt or soil and do not need additional stimulation. These stations can be installed on heavy soils, including clayey ones.
With soil purification
These are the simplest wastewater storage tanks to set up. They are arranged in a similar way to storage tanks, but without concreting the bottom. That is, you can use all the same materials: brick, concrete, plastic or iron, but at the bottom you need to arrange drainage layer. It is made of sand and crushed stone. Here, large fractions are filtered, after which the wastewater penetrates the clay and receives better purification.
Such septic tanks are good because the sewer truck needs to be called less often than in the case of storage tanks. However, in clayey soil the process of filtration and wastewater removal will be hardly noticeable. Therefore, you will have to pump out sewage with the same regularity as if you have a container with a concrete bottom. Such a septic tank can be built quite quickly with your own hands.
Installation technology
- You need to decide what will be used for the device storage capacity. In order to speed up cleaning and make it more effective, it is recommended to build a two-chamber structure with a filtration field. This will allow you to avoid overfilling the main tank and obtain the most purified wastewater at the output.
- 2nd step - determining the location of sewage receivers. Here you need to focus not only on the convenience of their placement on the site, but also on sanitary and hygienic standards. Since clay does not allow water to pass through well, the risk of runoff entering a well or well is small. Therefore, it is possible to install a septic tank with your own hands at the minimum distances from water intake points and residential premises - 7 m.
- Once the location of the tanks has been determined, excavation work begins. It would be a good idea to ask your neighbors in advance about the depth at which the clay/soil boundary lies. If it is located below 3 m from the soil surface, the work will be complicated by the need to install a drainage system at a fairly large depth. When digging pits, take into account that one container should be separated from another at a distance of no more than 2 m.
- After installation concrete rings, plastic cubes or brick laying along the walls of the pits, they begin to install a drainage layer directly in the containers themselves. To do this, backfill with sand and crushed stone. For the first, a layer of 10-15 cm is enough. For the second - 25-30 cm. If used as reservoirs plastic barrels, then during installation it is recommended to strengthen them with chains or otherwise. This is necessary because during floods and when the soil freezes, the container can be squeezed out of the hole.
- Both containers need to be connected with a pipe so that it hits 40-50 cm lower sewer pipe, which goes from the house to the main wastewater tank. This device allows wastewater to flow into the 2nd chamber and promotes the separation of fractions. Heavier ones settle in the first container.
- Further, if free-standing containers were used as containers, they must be insulated. This can be done using polystyrene foam. Such a septic tank, insulated with your own hands, will not freeze in the most severe frosts.
Filter field
In clay conditions, if the groundwater level (GWL) is below 1.5 m, semi-buried filters or filter cassettes are installed. At high groundwater level It is rational to arrange surface filtration using gravel-sand pillows.
The dimensions of the post-treatment field depend on the type of daily consumption water. If the volume of wastewater does not exceed 0.5 m³, according to established standards, a filter area of 1 m² will be sufficient. If the daily volume of wastewater is more than 1 m³, a field measuring 1.5-2 m² will be required. There are ready-made designs of filter wells available for sale. The price of these products is low, and installation is simple. The role of the main filter in them is played by geotextiles. But if you buy finished design There is no desire or opportunity; you can do the post-treatment field yourself.
After the soil is removed, a pipe is laid connecting the second container with the filtration field. As a rule, the laying depth is 0.7-1.2 m from the ground surface, but not lower than 1 m from the groundwater level. The bottom of the pit is leveled and a drainage mesh is installed on it. After which sand and crushed stone are poured. The height of the pillow should be such that its top rises above the inlet pipe by at least 5 cm. We should not forget that the pipes are installed taking into account the required slope. It must be at least 1* per 1 m. Pipes must be insulated using a wooden box and polystyrene foam.
Drainage device
Since such soil is not capable of good fluid permeability, a drainage system will be required to remove rain and flood water from the tanks for receiving sewage. To do this, not wall drainage, but ring drainage is performed. To install the pipeline you will need drains. You can use purchased perforated pipes or make your own from sewer pipes. plastic pipes diameter 110 mm. Perforation is carried out with a drill 1.5-2 mm thick at a distance of 2-2.5 cm from each other. The holes should be staggered.
A trench is formed around the septic tank so that its bottom is 20-30 cm below the freezing point of the soil. Next, the bottom is leveled with a slope that should be at least 1 cm per 1 m towards the storage well. After this, they fill it with 5-7 cm of sand and 10-15 cm of gravel. Then geotextiles are laid on the bottom of the trench. A pipeline is installed inside the ditch and the pipes are wrapped with previously laid material. Then they begin backfilling.
Device Feature
Clay is a highly heaving soil. This property is especially evident if it is wet rather than dry. During seasonal freezing and thawing, such soil can easily push a plastic or other container placed in it out of the hole. Therefore, during the installation of containers for sewage drainage, provision should be made for their fastening in the pit.
This can be done using metal rods, which can be used as corners or pipes of small diameter. The purpose of the rods is to fix the location of the container and prevent it from moving during soil heaving. For this purpose you can use steel chains, 1 end of which is firmly fixed in the soil.
For deeper wastewater treatment, two-stage trenches can be made for the filtration field. In the upper part of such a ditch there are pipes through which wastewater is discharged, and in the lower part there is a sand and gravel cushion up to 30 cm thick. Using such trenches, you can build a full-fledged filter system and remove wastewater outside the site.
The depth of the pits should be such that the liquid in the pipes does not freeze in winter, that is, below the freezing point of the soil. Each pipe will need to be perforated in the same way as a drainage pipe, but the holes should be larger, since the liquid will include small fractions. To prevent clogging of the holes with soil, each pipeline element is wrapped with geotextile.
When installing septic tanks, the following nuances must be taken into account:
Groundwater level and soil type.
The location of the place to install the septic tank relative to the house, well, fence.
Is there drainage from this area (ditches, drainage).
The depth at which a pipe passes from a building.
The degree of slope of the site.
In absolutely ideal conditions, the installation of a septic tank can be carried out at a depth of at least 75 cm from the surface layer of the earth, in order to protect the container from freezing in winter. For example, in some regions of Russia, the depth of ground freezing in winter according to SNiP is 140 cm, but in reality for a septic tank 75 cm will be more than enough.
Let's consider the option of installing a septic tank with clay soil and an extremely high groundwater level. In this case, the installation of a septic tank must be done so that the filtration field (drainage) made after the septic tank is slightly higher than the water level, otherwise the runoff will not be absorbed very well in the soil, which means that such a septic tank installation will not be considered correct. The septic tank should be installed shallowly and lightly sprinkled with earth on top to form a slide. It can also be insulated using polystyrene foam, insulation, for example, K-flex-ST or its analogues. When installing a septic tank in water, it is required to anchor it using concrete beams. The septic tank itself will almost always be full of water, and therefore, to prevent it from floating, too much mass is not required to strengthen the septic tank in the soil. If the septic tank is installed in very difficult conditions, for example, in a swamp, then the septic tank must be installed using concrete slab(in this case, the septic tank is mounted on the slab using metal strips), with the further lowering of this structure using a manipulator into the pit.
When installing septic tank in clay very difficult to do required field dispersion, because drainage from crushed stone will begin to collect all the water from the site 
from rain, and therefore the drainage will be in the liquid and it will not drain well. This means that the drain can be made into a ditch, or a special well can be made at the very end of the dispersion field in order to install a drainage pump in it, with further pumping of water into the drainage ditch.
A septic tank consists of one or more separate chambers. Waste liquid passes through them. The configuration of the septic tank and the depth of its placement depend, first of all, on the performance of the structure and its overall dimensions. It is necessary to lay the septic tank on a soil that is not subject to swelling and other deformations during severe freezing or thawing.
If cold winter the soil freezes significantly, then the container is placed in a sufficiently deep pit, and its bottom should be in a non-freezing layer of soil, or on a special foundation in the form of a concrete cushion. The simplest septic tanks, like the “Tank” or “Triton” system, are usually buried so that the thickness of the soil from the soil surface to the septic tank body is no less than half a meter.
For normal stable operation of any treatment plant of this type it is extremely important that flood waters in no case did they stagnate, and the height of the groundwater was certainly more than one meter. If your site is poorly drained, then the septic tank is laid shallow and covered with soil so that a small hill about 50-70 cm high is formed. All technological openings must be left free access. It is worth considering that the angle at which the liquid flows through the chambers of this septic tank must be at least 50.
In addition, for a septic tank to work well in clay or other dense soil (heavy loam) that does not allow water to pass through well, it is necessary to install two-stage filter trenches. The first trench is equipped sand and gravel cushion 30 cm thick. A perforated filter pipe is laid in it at a depth of approximately 0.5-1 m. In another trench - at a depth of 1.5-2 m.
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Such soil belongs to the category of problematic soil and is considered “heavy”, not only literally, but also figuratively. Excavation, carried out in areas with clay soil, are characterized by their specificity. How is it expressed in relation to installation biorefinery stations?
Local structures of this category can be installed on any soil. And this is one of the advantages of such septic tanks for autonomous sewerage. However, there is a point that is not taken into account by all land owners who, in an effort to save money, try to carry out the entire cycle of activities on their own. Installation biorefinery stations It is carried out on clay soils only after a series of engineering calculations. Therefore, inviting a specialist (at least for professional consultation) is more than rational decision. Otherwise, during the operation of a deep cleaning septic tank, problems may arise that cannot be dealt with on your own.
So what are the features of clay soil? The main difficulty is the minimal absorption of liquid due to the increased density of the earth. What does this mean in practice?
- The removal of clarified liquid must be carried out forcibly. On clay soils it is not advisable to organize a natural discharge. Or rather, it’s impossible. Therefore, when choosing a biorefinery station model, you need to take this nuance into account.
- Groundwater is located quite high. Since it is necessary to prepare a pit for the installation of the station, there may be a problem with its constant flooding. Even with forced drainage, it is unlikely to be completely resolved.
- Any on clay soil septic tank, including station, does not fit to significant depth. This means that you will need additional insulation housings. For most regions of the Russian Federation, this topic is more than relevant, considering how low the thermometer drops in winter. In relation to a biorefinery station, another difficulty lies in the fact that for bacteria to function normally, they need to be provided with maximum favorable conditions. Consequently, on this point, it is necessary to correctly calculate everything - the type of heat insulator, the thickness of the layer, the method of laying it.
Installation of local treatment systems for sewage (septic tanks) is often complicated by mining and geological conditions (soil composition) and high groundwater levels.
These reasons create problems with the discharge of treated wastewater into the ground. The most difficult thing is to install a septic tank on clay, which has a minimum coefficient of filtration of liquids.
The main problem at this stage is related to the fact that almost all clays (90%) belong to soils prone to frost heaving. It is because of this reason that the installation can be squeezed onto the surface, so it is necessary to resort to additional fastening of the local treatment plant during the installation process. Most often, a so-called bandage made of steel strips or cables is used for this, which encircles the septic tank and is attached to concrete base
in the pit. Considering that on clay soils drainage systems (filter fields) in many cases only work in upper layers
soil, you have to resort to shallow placement of a septic tank.
In this case, it is necessary to provide measures for insulating the structure:
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- Insulating a septic tank with glass wool In the very simple case
- It is more effective to insulate the treatment plant with special heat-insulating materials, the choice of which is quite wide. The most affordable (cost) method is filling the container with expanded clay. The use of polystyrene foam (preferably extruded) or polyurethane foam is considered more effective. In addition, active protection systems against the effects of negative temperatures are increasingly being used. To do this, use a heating electrical cable, the thermal power of which will reliably protect the septic tank from freezing even in harsh climatic conditions.
Discharge of treated wastewater
The main problem for those who decide to install an autonomous sewage system and install a septic tank in clay soil is the difficulty of draining treated wastewater. Such soil has minimal filtering capacity, which creates whole line sometimes intractable problems.
There are several main ways to remove treated wastewater from a septic tank in such conditions.
It is used if the soil on the site does not accept water at all. In this case, the entire volume of treated wastewater enters a sealed container or well, from which it is then pumped out using sewage disposal equipment or drainage pumps.
The disadvantages of this method include the need to construct a large-volume container, otherwise pumping will have to be performed very often. But if there is no other way out, this technology has to be used.
Increasing the drainage area
There are several varieties of this technology, but they all boil down to the need to increase the filtration area in order to ensure the removal of the required volume of treated wastewater even with minimal drainage capacity of the soil.
- Construction of a number of sequential drainage wells, in which case it is necessary to use rings of the largest possible diameter.
In practice, systems of two or three overflow drainage wells are used, which can fully meet the needs of a family of 3-4 people.
To increase the filtering capacity of wells, they resort to drilling additional drainage wells. This method allows in some cases reach filtering soil horizons, which will help to significantly increase the productivity of the structure. Drilled wells must be protected with casing pipes, and a simple mesh filter must be installed at their mouth, which will prevent siltation of additional drainage.
- Install a septic tank in clay with your own hands It is also possible with the construction of filtration fields of a large area. This method is used at high GWL (groundwater level).
The most productive is a drainage system using corrugated plastic pipes and geotextiles. Pipes of this type are characterized by increased strength; they are able to provide effective removal of treated wastewater. And geotextiles prevent siltation of the system.
To increase the efficiency of the filtration field, laying two-level drainage is often used. In this case, a number of lines (drains) are laid close to the surface, and the main part is buried as deep as the groundwater level allows.
The filter line is laid in pre-prepared trenches, which are covered with geotextile fabric. For filling from crushed granite(it is not recommended to use another one due to the tendency to erode) with a thickness of at least 20 cm are laid drainage pipes. They are also covered with a layer of crushed stone on top, which can significantly increase the volume of discharged wastewater. The entire resulting system is covered with geotextiles, which will ensure the durability of the line.
To ensure filtration of wastewater in conditions clay soil it is necessary to lay out significant filtration fields.
Of course, installing septic tanks in clay involves a significant increase in the volume of work performed during installation. But to ensure efficient work installations of local wastewater treatment even in such conditions is quite possible.
