What to do if the drain pit rings sag: troubleshooting methods

Nikolay Fedorenko
Checked by a specialist: Nikolay Fedorenko
Author: Tatyana Zakharova
Last update: April 2019

Concrete ring drains have become popular due to their affordability and low cost. If the structure is assembled and arranged correctly, it has been serving without repair for more than a decade. However, sometimes the concrete elements are displaced, and the cesspool ceases to fulfill its function - the collection of sewer flows.

We will tell you what to do if the drain pit rings sag, and how to prevent further displacement of parts. In our article, we describe methods for stopping subsidence and effective actions to restore the shape of the drain pit. Recommendations are given on the prevention of such processes.

Concrete ring drain pit designs

To understand the reasons for the displacement and determine the method of repair, it is necessary to have a good idea of ​​the structural features of the sewer structures. Most of them are buried in the ground, therefore, you need to be able to understand the characteristics of the soil. First, recall the technology of mounting drives made of concrete rings.

How to build a drive for sewage?

There are many options for constructing a drain pit, without which a local sewer system would be inferior.

A volumetric tank buried in the ground at some distance from the house is used to collect wastewater. As a building material for the assembly of the structure, cement pouring, ready-made concrete rings, brickwork and even rubber automobile tires are used.

Scheme of cumulative sewer capacity
The scheme of the accumulative sewer capacity, during the assembly of which 2 standard concrete rings were used, and the concrete slab performs the function of the bottom

Let's dwell on the accumulation well from reinforced concrete or concrete rings. Large (with a diameter of 1 m and more) parts have a rather large weight, therefore, transportation and installation of components is carried out using special equipment and workers.

But strong and sufficiently wear-resistant elements of a cylindrical shape have a low cost, so half of all cesspools in summer cottages and small cottages built precisely from them. For the construction of an underground structure, 2-3 rings of factory production will be required.

It is difficult and irrational to do similar parts on your own, while on sale there are all the constituent elements of a storage tank:

  • standard diameter rings;
  • closed element for bottom device;
  • round floor slabs;
  • necks of smaller diameter (additional);
  • plates with a hole for the hatch.

Rings for assembling a sewer well in a summer cottage can be made with one's own hand. Walkthrough for their manufacture given hereWe recommend that you familiarize yourself with very useful information.

After preliminary calculations, the necessary kit is purchased, from which the sewer well is assembled. Before installing concrete parts, it is necessary to dig a pit, in width and depth slightly larger than the dimensions of the cesspool.

Concrete slabs for the bottom
A part closed on one side and functioning as a bottom can be replaced by a reinforced concrete slab. It is placed on a leveled base and stapled to the bottom ring.

The first element is put on an even base - the bottom of the structure, then 1 to 4 rings are placed on top of each other, carefully sealing the joints. To protect concrete on both sides (external and internal), put mastic or other waterproofing.

After backfilling, only a part of the neck and the technical hatch remain visible on the surface. It is needed for regular maintenance - pumping out accumulated waste.

With traditional schemes and rules for calculating the depth of the drain pit will introduce the article, parsing all possible options for construction.

Features of the device without a bottom bottom

A drain pit without a bottom is no longer a drive, but a construction with partial filtration of drains. The lower part of the cesspool is not clogged, but is equipped with a kind of filter - a thick layer of sand and gravel. A loose “cushion” passes through itself a liquid medium directly into the ground, trapping solid and large particles.

If you want to build a simple treatment plant, you need at least two tanks: the first is the same drive, and the second is filter well.

In the first, solid waste settles and is partially processed, and the settled liquid flows into the next tank. It is followed by further anaerobic cleaning and the penetration of liquid into the soil.

Scheme of a septic tank made of concrete rings
Scheme of a septic tank made of concrete rings, consisting of 3 chambers: a drive and two filter wells. When subsiding or shifting elements of one of the parts, the entire system will fail

If the only container is made filtering, the treatment will be ineffective, and the wastewater will remain just as harmful to the environment. In addition, the filter - a sand-pebble mixture - will have to be changed over time, since pollution and clogging of its waste will occur quite quickly.

If you want to make a pit without a bottom, in order to less frequently call for sewage trucks, one tank is not a way out. The construction of a cesspool with a soil filter occurs in the same sequence as a conventional storage, with one exception.

Instead of arranging a sealed bottom, you need to pour a thick layer of sand, and then gravel. Do not forget about two important requirements: the enclosing soil should be sandy, in the extreme case sandy, and the groundwater should be 1 m or more lower than the bottom filter covering the bottom.

Reasons for subsidence of concrete rings

If, after some time after the start of operation, you notice that the neck of the tank has settled or slightly shifted to the side, then a subsidence or displacement of the structure has occurred.

It’s worthwhile to be wary even if, at ordinary volumes of water consumption, the rate of accumulation of drainage water has sharply decreased: it seems to be time to call the sewage system, and the tank is half full. Most likely, the joints between the rings diverged, as a result of which the drain occurs directly into the ground.

Excavation of concrete rings
A minimum of repair work is required if only the upper ring has moved. It is necessary to put it in place and additionally fix it with brackets. But for diagnosis, you have to dig out all the rings

There can be several reasons for subsidence, displacement and destruction of the structure.

Factors worth considering include:

  • groundwater level and mobility;
  • mobility of the soil surrounding the reservoir;
  • lack of concreted (or fixed in another way) bottom;
  • violation of installation technology (uneven base, insufficient sealing of joints, lack of staples, etc.).

The level of water occurrence is determined even at the stage of designing the project. To do this, measure the distance from the soil surface to the aquifers. The best time to check is rainy autumn or spring snowmelt, when the maximum amount of water is in the ground.

To determine, you just need to look into your own well and measure the water level in it. Indeed, most of the mine water intake structures at the dachas are buried in the upper water pipe, in extreme cases, in the first aquifer from the surface.

If an official drilling company drilled and equipped a well in your neighborhood or in a neighboring section, then it should have provided the customer with a report with documentation on the work done. The papers issued by her must have a geological section with hydrogeological marks of the water source.

It happens that high groundwater does not manifest itself immediately, but after some time. Under their influence, layers of porous and subsidence soils are also deformed, which can also violate the stable position of the sewer tank.

Sandy soil is especially good for water. A layer of loose sand or loess sand that has settled down under a heavy tank can cause subsidence or rupture of the joint of concrete rings.

Scheme of a septic tank with a filtering well made of concrete rings
Scheme of a septic tank with a filtering well made of concrete rings.If the groundwater under the well is higher than prescribed by the standards, over time they will wash the foundation, and the structure will sag

During subsidence, the entire structure is lowered, while at break the upper part remains in the same place, sandwiched with gravel-sand sprinkling or sand-cement mixture, and the lower part comes off and "goes" down. Often, soil movements are the result of nearby construction work.

Errors in sealing joints or arranging the bottom are common causes for the repair of cesspools. Especially if the bottom is not equipped with a concrete slab or at least a properly made filter. To determine the exact cause of subsidence or slip of the rings, and then choose a repair method, you must completely empty the pit.

The methods for repairing a drive, a filtering structure without a bottom and even a water well, which are made from factory concrete rings, are similar.

Methods for stopping the subsidence process

Repair work should always begin after the tank has been completely cleaned. To do this, they call the sewers and with the help of special equipment they remove all contents from the pit. The solid sediment adhering to the bottom also needs to be cleaned with shovels or scrapers and raised to the top with a bucket on the rope. Let us consider in more detail ways to recover a cesspool.

Dismantling of the structure and installation of the bottom

If subsidence is not a temporary phenomenon, but a permanent one, the structure must be dismantled and solved as soon as possible and the problem of the bottom structure is solved. Most likely, before the construction of the sewer station, there was no work on tamping and compaction of the base, on which it was planned to install a column of concrete rings.

Action plan:

  • Digging drive from all sides.
  • Stitching and lifting rings up.
  • Assessment of the condition of the bottom of the pit.
  • Concrete slab installation.
  • Reassemble drive.

If after digging or at the next stage, the pit quickly fills with water, repair work will not work.

There is a way out - you need to move the cesspool to another place and conduct a full cycle of required measures sewer well, including ramming the bottom or strengthening it with cement mortar. The unstable position of the soil layers sooner or later will again cause the destruction of the prefabricated structure.

Dismantling concrete rings
Excavation is best done with ordinary shovels - due to a lack of free space and the possibility of harming the structure. To dismantle heavy concrete elements will have to rent a crane

After thorough cleaning and digging, the cause of subsidence will be visible. Most often, it is a violation of the technology of the bottom device. Therefore, it is necessary to strengthen and level the base, fix the bottom.

A layer of sand is poured onto an even base, rammed, then a layer of gravel or gravel. The thickness of each layer is 0.35-0.45 m. Again they are leveled and only then a concrete slab is laid.

The second option is reinforcement followed by concrete pouring. The bottom of the pit is reinforced with a mesh of metal reinforcement. The diameter of the rods is not less than 10 mm, the mesh size is not more than 0.2 m. The mesh is poured with cement mortar with a plasticizer added for strength. The drying time of the screed depends on the weather, but you will have to wait at least one week.

When it becomes clear that the bottom is firmly fixed, you can again build the tank, simultaneously closing the joints and waterproofing the rings.

Securing the bottom concrete ring

In more rare cases, the base under the well is done correctly, but the lower ring is still shifted to the side. It is necessary to fix it - fix it on a concrete wall and pour cement mortar on the sides. If subsidence occurs downward, the lower link should be blocked with the help of additional devices.

One of the simplest options is a tie-in to the walls of the ring of steel pipes, which are firmly fixed in the ground and will serve as insurance against further subsidence, even if the base moves slightly.

To do this, holes are made in the walls of the lower link (from 4 to 6 pieces) and pipes with a diameter of at least 0.05 m are inserted into them. The cavity of each pipe must be filled with a solution to prevent water from entering.

Holes in concrete
To make holes in concrete using a punch. Pipes can be tried to drive into dense soil with a sledgehammer through holes from the inside

If the soil is not dense enough and it is impossible to drive in the supporting parts, they will be fixed in the future when backfilling with a sand-gravel mixture, into which dry cement can be added for reliability.

Sealing the space between the rings

If two concrete links have diverged, and a large space has formed between them, there are several ways to solve the problem. First you need to find out if the subsidence process has stopped. If not, you will have to disassemble the structure, strengthen the bottom and rebuild the structure.

When stopping the subsidence process, you can go in two ways:

  • Disassemble the structure to the place of repair, install the rings, fix them with brackets and seal the cracks.
  • To make repairs without disassembling, just filling up the gap with masonry.

Bricks are laid in the traditional way, with a shift in half a brick, on an ordinary cement mortar. To strengthen the masonry, it must be covered with plaster, and then with bituminous water-repellent mastic.

Brickwork for closing the gap
The scheme of the brickwork for repairing the gap in concrete rings. For more effective waterproofing, soil is removed from the outside and plastering is also carried out.

After repair, it is necessary to check the reliability of the structure and make sure that the tank does not continue to sag. If the original “patch” did not help, you will still have to disassemble and complete the repair with reinforcing the bottom, additional fixation of all joints with brackets and waterproofing walls sewer well.

Effective Joint Sealing Methods

Very often, the consequence of a small subsidence is the formation of gaps between the links. The reason is weak connections between the rings, insufficient sealing. It is clear that one seal of the formed cracks will not be enough.

First you need to fasten the links together with metal brackets (around the entire circumference), and only then produce joint sealing by all the rules.

Materials used for sealing joints:

  • plaster (based on cement and PVA);
  • rolled material coated with bitumen mastic (preferably for outdoor use);
  • putty from a bitumen-gasoline mixture;
  • sealing tape RubberElast;
  • Kiilto fibroresin FIBERPOOL;
  • Sealant Peneplag and others.

The use of fixing brackets makes any sealing reliable, but it is better to use not folk remedies, but modern materials.

Waterproofing a concrete structure
Bituminous mastics or resin-based mixtures are often used as a final seal. They completely cover the concrete structure in order to increase its resistance to moisture and chemicals.

Small cracks and gaps can be filled with any material that has the qualities of a sealant, for example, frost-resistant tile adhesive or polyurethane foam.

Preventing sagging

To protect yourself from the time-consuming and sometimes expensive process of repairing the storage tank, it is better to immediately provide options for protection against displacement and subsidence of the structure.

To do this, you must:

  • equip an even, strong, stable base;
  • fix the bottom or concrete slab that performs the function of the bottom;
  • fasten all the links together with metal brackets;
  • to make reliable sealing of joints;
  • fill the tank from the outside with a sand and gravel mixture with cement.

The larger the structure, the higher the risk of ring displacement, therefore protection measures should be more reliable.

Pipe sealing
When processing joints between rings, do not forget about sealing the places of contact of pipes with concrete links. Clearance in openings in the same way.

For high groundwater and loose sandy soil, we recommend installing an airtight container, not a filter well.

Introduces the repair of the sewer well by installing a plastic insert next article, the contents of which we advise you to read.

Conclusions and useful video on the topic

With the help of videos you will get acquainted with the ways to eliminate the consequences of subsidence or displacement of the concrete rings of the sewer store.

Video # 1. Sealing joints with repair mixture:

Video # 2. Waterproofing Testing Raberit:

Video # 3. Staple links:

Eliminating the causes of subsidence of the accumulation sewer tank is a laborious process that requires patience and professional skills. If you doubt the correct determination of the cause of the displacement or do not know how to repair the cesspool, contact a professional.

Want to talk about your own experience in repairing a drain pit with sagging rings? Do you know a proven way to restore its geometry? Please write comments in the block below, ask questions, a divider with useful information and a photo on the topic of the article.

Was the article helpful?
Thanks for your feedback!
No (13)
Thanks for your feedback!
Yes (84)
Visitors Comments
  1. Nalisher

    I have a private house, or rather a cottage, adapted for permanent housing. So, I myself built a septic tank from concrete rings, it has two wells. Septic is more than 10 years old and the rings are slightly sagged. So, next spring I will use advice. I especially liked the second option, which with reinforcing the bottom with a mesh of metal reinforcement. Then certainly everything will fall into place, it will be possible to make the third well immediately smaller, only immediately with reinforcement.

  2. Sergey Vasilevich

    I had it in my country house last year. One ring slipped into the cesspool (friends of mine advised me to make a well out of reinforced concrete rings, this is the most budget option for a summer residence). As I found out, I saw that the neck of the structure shifted to the side.
    He called the scavengers, the contents of the pit were completely pumped out.The problem was at the bottom of the well, the shift began due to the fact that the soil sank under the base. Strengthened, repaired, now everything is ok. I never thought that with a cesspool can be so much trouble.

  3. Sergei

    I am interested in how to determine whether it is temporary or permanent. Maybe the septic tank sank to a new level on a solid layer of soil and will not go any further. Just wait and watch?