The problem of flooding the site or excessive accumulation of water after showers is familiar to many owners of suburban real estate. When water stands at the foundation of the house or turns the lawn into a swamp, the question arises about the need to create an effective drainage system. One of the most affordable and time-tested solutions is drainage-holeIt can be built independently without the use of heavy machinery. A properly designed water catchment can protect the foundation from destruction and save the crop from rotting roots.
However, just dig a hole is not enough - you need to take into account the type of soil, the level of groundwater and the volume of drains. Errors in the design phase can lead to wall collapse or rapid siltation of the system, which will require expensive rework. In this article, we will discuss how to correctly calculate the parameters, select materials and perform all the stages of work to make the system work for decades.
Creating an effective drainage requires precision and compliance with technological nuances. You will know how different it is. filter-well From the storage tank, why it is important to do the right filling of the bottom and how to avoid common mistakes. Competent approach will allow you to save significant money on the services of professional builders, while getting a reliable result.
Selection of the place and calculation of the volume of drainage pit
The first and most critical step is to determine the location of the future water catchment. The pit should be located at the lowest point of the site so that water flows into it by gravity through the laid pipes. The distance to the foundation of the house should be at least 5-7 meters, otherwise there is a risk of washing the base of the building, especially during spring floods. Also, the distance to the neighboring borders should be taken into account - according to sanitary standards, it should not be less than 3 meters.
The volume of the pit directly depends on the area of the site, the amount of precipitation and the type of soil. For clay soils that do not allow water to pass through, a larger tank will be required, since absorption will occur slowly. If we are talking about sandy soils, water will go away faster, but there is a risk of rapid silting of the walls. The calculation formula usually comes from the volume of water falling during a heavy rainstorm, multiplied by the stock factor.
The level of groundwater deposits must also be taken into account. If the water is high, digging a deep hole makes no sense - it will just be filled from below. In such cases, surface drainage ditches are used or pumps are used for forced pumping. The depth of freezing of the soil also plays a role: the bottom of the pit should be below this mark so that the system does not freeze and fail in winter.
- 📍 Choose the lowest relief point on the site for natural runoff.
- 🏠 Keep a safe distance from the foundation (at least 5 meters).
- 📏 Check the depth of groundwater before starting the digging.
- 🌧️ Calculate the volume based on the average rainfall in your area.
Necessary tools and materials for construction
For the quality implementation of the project, you will need a set of building materials and a specialized tool. The main element of the design are the walls, which should not crumble. Most often used concrete-ringbrickwork or ready-made plastic containers. Concrete rings (wall) with a diameter of 1 meter or 1.5 meters are the most popular solution due to their strength and durability.
As a filtering material used crushed stone of various fractions. Large crushed stone (40-70 mm fraction) is laid on the bottom and near the walls to create a buffer zone, and small (20-40 mm) is used for the final filling. An important element is geotextile This material prevents mixing of soil with rubble, prolonging the service life of drainage. Without geotextiles, the filter pores will quickly clog with silt.
To supply water, drainage pipes (usually PVC or PHD with perforation) and connecting fittings will be required. Don’t forget to use sand to create a leveling cushion and cement mortar if you use concrete rings. The tool set is standard: shovels (bayonet and sow), level, roulette, tamping and, possibly, a concrete mixer for preparing a solution.
| Materials | Appointment | Recommended volume/quantity |
|---|---|---|
| Granite gravel | Filtering backfill | 2-3 cubes. m (depends on the size of the pit) |
| geotextile | Separation of soil layers | Density 200-300 g/m2, by area of walls and bottom |
| Concrete rings | Wall strengthening | 3-5 pieces (height 0.9 m) |
| The drain pipe | Water supply | The length of the trench to the pit |
Use the rubble of granite rocks, not limestone. Limestone dissolves over time in acidic water, which leads to filter drawdown and siltation of the system.
Cocking and pitting technology
The digging of the pit is the most time-consuming stage of work, requiring physical effort and compliance with safety precautions. The dimensions of the pit in the plan should exceed the diameter of the rings used or the dimensions of the plastic container by 30-40 cm on each side. This gap is necessary for easy installation of elements and organization of lateral filtration. The walls of the pit are desirable to do vertical or with a slight slope to prevent the fall of the soil in the process of work.
The depth of the pit is determined by the calculated volume and level of the waterproof layer. If you use concrete rings, the bottom of the pit should be carefully aligned. To do this, a fertile layer of soil is removed, and a sand cushion 10-15 cm thick is created. Sand must be poured with water and tightly tamped to exclude the drawdown of the rings in the future. Uneven shrinkage can lead to depressurization of joints and distortion of the structure.
⚠️ Attention: When digging deep pits (more than 1.5 meters) in loose soils, be sure to use temporary wall fastenings or work in special formwork to avoid falling of the soil on a person.
If groundwater begins to actively arrive during the digging process, the work should be suspended and a temporary outflow of the pump is organized. Working in the water is extremely difficult and dangerous. In such cases, it is advisable to dig a hole in the dry season or use ready-made concrete rings with a bottom, installing them immediately after excavation of the soil so that the walls do not have time to swim.
☑️ Dit readyness
Filtration floor and wall device
After preparation of the pit, they begin to create a filter "pie". The bottom of the pit is the main element through which water escapes into the deep layers of the soil. On the rammed sand pillow is poured a layer of large rubble thickness of 20-30 cm. This layer serves as a primary filter and distributes the load. A layer of geotextiles is laid over the rubble with overlap on the walls of the pit at least 50 cm.
When using concrete rings, it is important to ensure their tightness. The joints between the rings are smeared with a cement solution with the addition of liquid glass for waterproofing. However, if the purpose of the pit is to absorb water (filtering well), then the lower ring may not have a bottom or have a perforation, and only the upper joints are sealed so that dirty water from the surface does not get inside. For storage pits, the entire structure is sealed.
Around the established rings or walls, a reverse backfill is formed. The space between concrete and soil is filled with a mixture of sand and rubble. This creates an additional filtration zone and reduces the pressure of the soil on the walls of the structure. In the walls of concrete rings, you can punch holes for the entrance of pipes in advance or after installation, using a diamond crown punch or simply breaking concrete carefully.
Why do you need a back filter in the walls?
The reverse filter (sand + rubble around the pit) prevents the leaching of soil particles from the walls of the pit. Without it, small soil particles will gradually wash out with water, forming voids around the structure, which can lead to subsidence of the soil and even collapse of the walls of the drainage pit.
Installation of supply pipes and filling of the system
Connecting the supply pipes requires compliance with the slope. For a gravity system, the slope should be 2 cm per 1 linear meter of the pipe. The pipe is injected into the hole through the prepared hole. The entry point of the pipe must be carefully sealed with cement mortar or special cuffs to prevent soil from entering the pit and washing the walls.
After installation of pipes and checking their work, the final filling is made. Inside the pit (if it is a filtering well) the rubble is filled to the level of the supply pipe, and then to the top. On top of the structure is covered with geotextiles, which was left with a margin on the edges. This creates an “envelope” that protects the rubble from getting fertile land from above. Then the hole is filled with soil that was extracted during the digging.
The top of the pit is closed with a concrete slab with a hatch for maintenance. The hatch is necessary for periodic checking of water level and, if necessary, pumping silt by the drainer machine. If the hole is accumulative, then the presence of a hatch and a pump (drainage or fecal) is a prerequisite for operation. The land on top is better to sow grass so that the roots of plants strengthen the soil, but do not plant trees with a powerful root system.
- 📉 Observe the slope of the pipes at least 2 cm per 1 meter linear.
- 🔒 Seal the entry points of the pipes with cement solution.
- 🌿 Fill the hole from above with fertile soil and sow grass.
- 🚿 Leave access through the hatch for maintenance and silt pumping.
Typical errors and drainage life
One of the most common mistakes is to ignore geotextile. Many believe that you can just fill the pit with rubble, but without a tissue separator, the rubble quickly mixes with the soil, and the system stops letting water through. The service life of such a pit will be only 2-3 years, after which a complete dugout and replacement of the filter will be required. Using quality materials pays off in the long run.
Another mistake is the insufficient volume of the pit. If you calculate the system "back to the side", then in the rainy season it will overflow faster than the water will have time to absorb. This will lead to the release of water to the surface of the site. Always lay a stock of 30-40%. Also, do not save on the depth: if you make the pit too shallow, it will freeze in winter and stop working in the cold season.
With the correct design and use of high-quality materials (concrete rings, granite rubble, dense geotextiles), the service life of a drainage pit can reach 50 years or more. Plastic containers are less useful – about 20-30 years, since plastic is susceptible to deformation under soil pressure. Regular maintenance, including water level checks and pumping out bottom sediments every 3-5 years, significantly prolongs the life of the system.
⚠️ Warning: Do not discharge household wastewater from the toilet or kitchen into the drainage pit without first cleaning in the septic tank. This will lead to rapid silting of the pores and the formation of toxic sludge, which will poison the soil on the site.
The main secret of the durability of drainage is the use of geotextiles and granite rubble. These two components prevent the siltation of the system, which is the main cause of drainage failure.
Frequently Asked Questions (FAQ)
How often should water be drained from the drainage pit?
The frequency of pumping depends on the type of pit. If it is a filtering well for storm water, then pumping is rarely required, only if the bottom has silted and the water has stopped leaving (every 3-5 years). If it is a storage tank for household wastewater, then pumping is carried out as it is filled, usually 1-2 times a year, depending on the volume and number of residents.
Can I use old car tires for the walls of the pit?
The use of tires is possible for small drainage holes in the country. They are built on top of each other, creating walls. However, this method is suitable only for light soils and small volumes of water. Tires do not provide such tightness and strength as concrete rings, and can shift when the soil is swelling. The service life of this design is shorter.
What to do if the water does not leave the hole?
If the water is standing and not absorbed, there may be two reasons: the filter silted (crushed stone clogged with clay) or the groundwater level rose. In the first case, washing with a jet of water under pressure or silt pumping. In the second case, the drainage pit becomes ineffective, and the option of installing a pump for forced water discharge into the storm sewer or outside the site should be considered.
Do I need to clean the drainage hole for the winter?
The hole itself is not necessary to insulate if it is below the depth of freezing. However, the hatch and the upper part (head) should be insulated with polystyrene foam or covered with sawdust to prevent the formation of an ice plug in the neck, which can damage the structure when ice expands.