Drainage inspection wells: types, device and installation features
The high level of groundwater is a hydrogeological situation that adversely affects the technical condition of underground structures. Contacting with concrete structures, water gradually but extremely persistently destroys them.
To reduce the GWL and to drain the water is a drainage system. One of its functional parts are manholes for drainage, the types of which are analyzed in the article.
Types of drainage manholes
The drainage manhole is a hydraulic underground structure designed to monitor and periodically clean the system.
The shape of the well in the plan can be rectangular or round. Used for pressure and non-pressure drainage system, but with some differences.
Most of the sewer drainage circuits are arranged according to a free-flow scheme. They are a network of interconnected drainage collectors, along which floodwater and infiltrated groundwater collected by drains flows by gravity. The force of gravity stimulates the movement of flows to the collection and disposal sites.
The pressure system is characterized by the forced movement of wastewater, the transportation of which is carried out through the operation of pumping equipment. The pressure system is arranged where their spontaneous movement to the drives for removal and disposal or to the treatment plant for processing is impossible. For example, if it is not possible to install the drive below the level of the gasket drains.
Both types of sewer systems are constructed according to SNiP 2.0403-85 “Sewerage. External networks and facilities.
Inspection wells for gravity nets
When constructing free-flow drainage, all pipelines are straightforward and are connected to each other by wells. It is necessary to provide for inspection drainage wells in the following cases:
- on straight sections of the drainage pipeline for inspection and maintenance;
- in the areas of connection and branching of the drainage pipeline;
- in places of changing the diameter of the drainage pipe;
- in places of change of the slope of the drainage pipeline;
- in places where the flow direction changes (rotary well).
For straight sections of the drainage pipeline, a maximum length is set on which the device of the manhole is mandatory. This length depends on the diameter of the pipeline:
- 35 m for pipelines of Ø 150 mm and less;
- 50 m for pipelines from Ø 200 to 450 mm;
- 75 m for pipelines from Ø 500 to 600 mm;
- 100 m for pipelines from Ø 700 to 900 mm;
- 150 m for pipelines from Ø 1000 to 1400 mm;
- 200 m for pipelines from Ø 1500 to 2000 mm;
- 250-300 m for pipelines over Ø2000 mm.
Such a dependence of the length of the pipeline on the diameter is given in the regulatory documentation governing the rules for the construction of all types of sewer systems.It is based on long-term practice of construction, control and maintenance.
The size of the manholes (working chamber in the plan) also depends on the largest diameter D of the drainage pipe. For rectangular wells:
- up to Ø 600 mm, 1000mm for length and width;
- Ø 700 mm and more, D + 400 mm for length and D + 500 mm for width.
Most manholes have a round-shaped working chamber.
The dependence of the diameter of the well Ø from the diameter of the pipe D:
- up to D 600 mm - Ø 1000 mm;
- D 700 mm - Ø 1250 mm;
- From D 800 mm to 1000 mm - Ø 1500 mm;
- D 1200 mm - Ø 2000 mm.
The dimensions of the rotary well can be increased to ensure the minimum turning radius of the trays.
There are several reservations on the size of the manhole associated with the depth of the bottom of the structure:
- if the depth of the manhole is 1.2m and less, for pipelines no more than 150mm, a well with a diameter of 700mm is allowed, for other pipelines not 1000mm;
- for wells with a depth of 3 m and more, the minimum size of the working chamber is at least 1500 mm.
Shallow manholes, maintenance and inspection of which can be done from the surface, are called inspection. Well structures that require the performer to dive to a depth of over 1 m are classified as serviced.
The height of the working chamber of the manhole is measured from the bottom (base plate) to the upper face of the neck. It depends on the depth of the drainage system and its purpose: the removal of groundwater from the foundation or the drainage of a private site.
The neck of the well provides access for the person and the equipment to the inside of the working chamber, the most suitable diameter for this is 700 mm. For descent into the working chamber, the manhole is equipped with brackets or a ladder.
When arranging trays for drainage pipes, the height of the shelf shelf is determined by the largest pipe diameter. The upper lines of the tray shelves should be flush with the top of the pipe.
Inspection wells for pressure networks
Pressure pipelines do not need to comply with slopes. In addition to standard functions, pressure manholes form rational places for installation, adjustment and maintenance of equipment.
Arrange them in places of installation:
- locking equipment;
- pumping stations;
- in places of accession to highways.
The size of the working chamber depends on the mounted equipment. The depth should be 0.5 m deeper than the penetration of zero temperature. If this is not possible, provision should be made to insulate the wellbore to the indicated depth.
The distance from the walls of the working chamber to the pipeline must be at least:
- 0.3 m for pipes Ø 400 mm and less;
- 0.5 m for pipes from Ø 500 to 600 mm;
- 0.7 m for pipes Ø 700 mm and more.
The height of the working chamber should be at least 1.5 m. For descent into the well equipped with iron brackets or stairs.
Types of drainage manholes
Inspection wells designed for free-flow drainage system are divided into the following types:
- node with one or two nodes of accession.
The standard structures of prefabricated concrete inspection wells are designed according to the series 3.003.1-1 / 87 “Prefabricated reinforced concrete whole-shaped wells for underground pipelines”.
Linear wells are arranged on straight sections of the pipeline, they have two pipes: supply and discharge.
Rotary wells are characterized by the allowable angle of rotation of the pipeline, which depends on the diameter of the pipe and the size of the working chamber.
Nodal wells are built in such a way that the connected pipelines have an acute angle with the main pipeline in the direction of fluid flow.
Materials manufacturing manholes
Inspection wells can be industrial or self-made. As a rule, the project of a well is coordinated with the operating organization.
The industry offers various options for ready-made drainage wells made of: concrete, polymers or composites. Self-made wells can additionally be made of bricks, rubble. Each material has its pros and cons.
The vast majority of drainage wells are made of reinforced concrete. The use of concrete has its advantages:
- excellent resistance to buoyancy of water;
- the ability to hold large loads;
- the possibility of manufacture by hand on-site facilities;
- low price
Reinforced concrete has a density of about 2.5 times more than water. It has a large mass and a high coefficient of friction with the surrounding soil, which well compensates for the buoyancy force of water.
However, a large mass of concrete has its disadvantages:
- the need to use lifting equipment;
- the complexity of the hole for the input and output of drainage pipes;
- the need to arrange access roads for the period of installation works;
- the inability to achieve full waterproof.
Composite and polymeric manholes for prefabrication can be used on pipelines up to 400mm.
Modern urban planning is increasingly using polymer drainage wells. There are several reasons for this:
- ease of installation;
- a wide range of fittings;
- high speed of construction;
- low weight
Transportation of polymeric or composite wells is carried out by ordinary freight transport. For the assembly and installation of the well enough for three people. However, such wells also have disadvantages:
- high price;
- insufficient resilience;
- Production on individual design data is very expensive.
When purchasing a plastic well, it is necessary to pay attention to withstand loads, especially if the well is mounted within the roadway.
Brick wells have pros and cons similar to concrete wells. An additional advantage of a brick well can be attributed to the simplicity of achieving the specified size.However, such a well requires more time for construction.
How to mount an inspection well
By the time of the start of work on the installation of a drainage well, the pipeline should be laid, but not filled.
The general progress of construction work:
- digging the pit;
- base device;
- installation or production of the bottom;
- manufacture or installation of the tray;
- installation of the working chamber of the well;
- mounting the top of the working chamber and the neck;
- waterproofing of the working chamber;
- backfilling and installation of the hatch.
Consider the option of building a readiness well. With self-construction construction stages are similar.
Development of the pit and its size
Before starting the development of the pit, make sure that there is no ground water at the bottom of the well. If there is water, then it is necessary to build a temporary drainage pit or carry out periodic pumping.
The pit is produced according to the size of the planned well to the device.The bottom of the pit should be larger than the base of the future structure. The less dense the soil and the less clay particles it contains, the less its ability to “hold” the shape of the mine.
During the development of a pit in loose, easily crumbling sandy soils, the work on dumping is usually much greater than in the development of a pit in sandy loams and loams. If the shedding of waste rock will interfere with the development of the excavation, the walls of the mine will need to be strengthened.
The depth of the pit is more than 35-40 cm lower mark of the drainage pipe. Mark the pipes checked level.
Device of the basis of a drainage well
After the excavation has been dug, coarse gravel or crushed stone of 10-20 mm fraction is poured at the bottom. A thickness of 20 cm is sufficient.
On top of the coarse rocks fall asleep sand with a layer of 10 -15 cm.Then it is plentifully moistened and carefully tamped. A good level of density of the base can be considered a seal in which a person's foot does not sink into the sand (shoes do not leave fingerprints).
Installation or production of the bottom
The construction of the bottom is a crucial stage of the whole construction of the manhole, since it is the bottom that takes the entire weight of the structure and determines its verticality.
There are two options: make it on site by hand or mount it ready.
Option one. It is necessary to ensure that there is no water for at least 2 days, otherwise a large part of the binder will be washed out of the concrete. The bottom thickness should be at least 10-15 cm.
For the reinforcement of the bottom use Ø 6 mm reinforcement. A grid with a mesh size of about 10 cm is made of reinforcement.
First pour half the volume of concrete. After setting of the bottom part, the grid is laid and the concrete is poured to the required thickness of the well base. The ends of the reinforcement around the perimeter of the bottom should be covered with concrete. This design is suitable for wells up to 10 m deep.
Option two. The finished bottom is a reinforced concrete slab, mounted on a prepared and compacted base. The quality of the installation is verified using the construction level.
After performing all the operations, the bottom of the well should be 5-10 cm below the lowest point of the branch pipe.
Production of a receiving tray for pipes
A layer of cement mortar is laid on the mounted bottom and a bed for drainage pipes is formed. By means of a level marks are checked.
The bottom of the finished plastic well, as a rule, already has the necessary trays.
Installation of the first ring of the working chamber
Drainage pipes must be laid on the receiving trays beforehand. From the bottom of the first concrete ring opposite the receiving chutes, corresponding holes are cut out.
The installation of the shaped parts of the concrete well, the sealing of the joints and the holes is carried out with the cement mortar of mark 100.
The working chamber of a plastic well is mounted entirely.When there is a danger of flooding the pit, the well is placed under pressure until it is filled with soil.
Mounting the top of the working chamber and the neck
The top of the reinforced concrete well served is a slab. The standard access hole to the shaft of the storage or collector structure should be 700 mm in diameter. The opening of the manholes is accepted from 600 mm and more: it must ensure the free entry of devices for cleaning the network if necessary.
After installation of the top of the working chamber, the installation of functional equipment for pressure drainage is carried out.
Next is the arrangement of the mouth of the well. The number and size of rings is selected taking into account the required height.
The neck of some plastic wells is a cone-shaped short pipe, which can be easily cut to the required size.
The neck is blocked by a support ring under the hatch.
For a plastic well, the top and the neck are shaped parts mounted on the seal.
In the case of self-production, the top of the working chamber is carried out in such a way as to withstand the weight of the soil, pedestrians, and transport if the structure is arranged under the roadway. It is made of reinforced concrete, according to the manufacturing technology of the bottom.
Performance of a waterproofing of the working camera
In case the groundwater or flood water can come into contact with the manhole, the walls are waterproofed 500 mm above its level during the period of greatest rainfall.
To seal a concrete well, a coating waterproofing based on bitumen mastic is used, it is applied:
- on the bottom and working chamber of the well;
- on cement joints, drainage pipe entry points.
Additionally, the pipes are sealed with a clay lock on the outside of the well.
Instead of bitumen mastic, you can use specialized waterproofing compounds. Waterproofing is applied to the inner surface of the well. The composition of the masonry mortar add additives that increase the waterproofing properties of the solution.
Backfilling, sealing and installation of the hatch
The hatch is mounted on the neck of the well. The level of installation of the hatch depends on the type of coating:
- on the carriageway - flush with the carriageway;
- in the green zone - 50-70 mm above ground level;
- in the undeveloped part - 200 mm above ground level.
Backfilling around the well is done with a gravel-sand mixture. Lay a layer of about 20 cm at a time, after which the soil is compacted. To facilitate tamping it can be shed with water.
Partial hit of the soil and vegetation layer in the backfill is highly undesirable, since it includes organic matter. Over time, organic matter will decompose and decrease in volume, and the earth around the well will sow.
Conclusions and useful video on the topic
Installation of a plastic well:
Plastic wells comparison:
The manholes installed on the drains are part of the hydraulic system. With proper design and performance require one-time service in 5 years.At the same time service life is measured in decades.