(or UGV) can bring a lot of trouble both during construction and pose a danger to already finished buildings.

It is imperative to lower the groundwater level in the garden and the city, since the site will become swampy and unsuitable for growing cultivated plants. When the groundwater level is half a meter from the soil surface, it is imperative to organize an artificial drainage system on the site. There are many ways to solve this problem.

Application of pipes and trenches

Lowering the groundwater level can be achieved with a drainage system. In this case, a method known in hydrodynamics is used. When laying a collector of perforated pipes at a given depth of flooded soil, the water layer is sucked up by the pipe by forming a concave funnel in the cross section of the pipe. Thus, a drained soil zone on the site is obtained. You can use special pottery pipes with holes or asbestos cement. In asbestos-cement pipes, it is necessary to create transverse cuts, the width of which will be 1-2 mm, and the length - 3-5 cm with a step speed of 20-25 cm. Cuts can be made using a drill and a jigsaw. To begin with, holes are drilled with a drill with a small drill, into which it will then be possible to pass with a blade from a jigsaw.

The cheapest way to lower the water level is to dig trenches throughout the site or around the house with the soil sloped towards the spillway. The slope will allow water to naturally leave the site. In the middle of the trenches, it is worth laying bundles of brushwood, smeared with plastic clay, tightly. But it is better to fill the trench with large construction debris, broken bricks, concrete, large stones.

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Catchment ponds and basins

It is possible to lower the groundwater level by creating ponds in the center or along the edges of the site, depending on the terrain. This method requires minimal investment, but to increase the effect, it is necessary to create a complex of ponds in combination with additional catchment basins. If there is excess moisture at the base of the house or in the cellar, it is correct to make a water collector in the front garden. It is more expedient to organize it near the basement in order to quickly reduce the level of groundwater and sedimentary water, as well as to divert them from the foundation part of the buildings. The shape of the pool may be different. Groundwater is collected through a drainage well. The level of collected water is regulated by installing a pipe from the side of the pond, which leads into a ravine or ditch.

For gravity flow of water, the pipe must be laid with a slight decrease - a slope towards the ravine. In this case, it is better to use a PVC pipe with a larger diameter, as more water will pass through it and it will be less clogged. But, in order to protect yourself from a significant amount of fallen leaves and other debris that can clog the pipe, you can attach a metal mesh with a small cell at the base of the pipe (from the side of the pond) or simply put on a colander. The bottom of the pond must be covered with concrete slabs. To reduce the cost of the event, you can use clay. Clay mashed with water is laid in a layer of 15 cm and carefully compacted. After the first layer has dried, repeat the procedure twice. The edges of the pool also need to be strengthened with clay with a calculation of 15-20 cm from the edge of the water level. Crushed stone is poured onto the top layer of clay and tamped down. The last layer consists of fine gravel or sand 5-8 cm thick.

The selection of methods for dewatering and lowering the groundwater level is implemented mainly on the basis of taking into account the composition of the soil and the saturation of the groundwater inflow. When erecting the underground part of the structure with water-saturated soils, open dewatering is used. This method is simple and economical, but it is effective in soils where the water inflow is less than 10-12 m 3 /h. Groundwater is pumped out by a pump from water collectors with a size of 1 × 1 m. For quick use, the water collector can be an ordinary dug pit, and to increase reliability, it should be a backup pumping system. The downside in this system is that in fine-grained soils, open drainage will lead to shedding of the slopes of the trenches and the pit, as well as loosening the soil at the base of the buildings.

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Dewatering by wellpoints

Lowering the groundwater level can be achieved using wellpoint installations, consisting of metal pipes with a filter block in the lower part of the structure, an electric motor, a self-priming vortex pump and a catchment collector. The installation of a wellpoint consists in immersing metal pipes into the soil of the site along the trench or along the perimeter of the pit. The filter block consists of an inner solid and an outer perforated pipe. The lower part of the outer pipe has a tip of ball and ring valves. On the surface of the soil, the wellpoints are attached to a water collector and then to a pumping unit. Wellpoints are installed in the ground by hydraulic immersion, by supplying water under pressure of 0.3 MPa. Leaving under pressure from the tip of the filter block, the pressure of water erodes the soil around it and allows the wellpoint to be immersed in depth.

The use of wellpoints is very effective in sandy gravel soils. When using one tier of wellpoints, it is possible to reduce the groundwater level to 5 m. To increase the level of soil drainage, it is worth using a multi-tiered system. Also, wellpoints can be immersed in the ground by drilling wells with special equipment. To increase the reliability of the installation, you can make a backup system of pumps.

When arranging a septic tank in a country house or for a private house, additional work has to be carried out, such as draining the site. A similar need arises if the GWL is too high. In order for the installation of a septic tank to be carried out, it is necessary to use special equipment and drying technologies. In addition, there are other situations when such work is necessary.

The need for land reclamation

The drying procedure is called melioration. Its essence is the diversion of liquid or groundwater from the surface of the earth into a drainage well or reservoir, if it is located nearby. Drying required:

• With a high occurrence of groundwater.
• If the UGV rises to floor level in the basement.
• For clay and loamy soils with dusty sands, if the absorption of precipitation is difficult.
• There are many paved paths and buildings on the site, which leads to difficulties with the absorption of precipitation into the soil.
• The site is located in a lowland, that is, water comes to it from the territories located above.
• There is a reservoir nearby. Which leads to swamping of the area.

Important! These aspects provoke difficulties with the creation of a sewerage system and, in particular, the installation of a septic tank on the site. Therefore, it is necessary to organize the drainage of water.

Techniques and methods

Drainage of a summer cottage can be carried out in different ways, but there is a classification into groups:

• open.
• Conditionally closed.
• Closed.

The choice of one or another option with a high level of groundwater depends on many nuances. The first two types have an important drawback - this is the ingress of precipitation into the discharge system - rain and snow, which makes the load on it more intense.

superficial

Surface drainage of any site with a high water table is an option where the water will be drained quickly. This method is simple, it will be possible to systematically drain water from the site with your own hands. It is used as an option to divert seasonal precipitation. To make it work, you need to dig grooves with a downward slope.

Important! Although this method is simple, it will not help to cope with other causes of waterlogging. Also, trenches, including near the house, should be regularly cleaned of leaves that can retain water.

This option has a number of significant disadvantages:

• Water flows erode the soil, which leads to a loss of fertility.
• The accumulated water below leads to even greater difficulties in work.
• The walls of the pit need to be further strengthened.
• The foundations of buildings located nearby may be weakened.

Important! Ditch with drainage must be calculated. The depth depends on the intended purpose, and the width is 1/3 less than the depth.

Artificial downgrade

Artificial lowering of the groundwater level requires the use of special equipment and certain knowledge and skills in this area. Planning the installation of this system must be carried out even before creating a house project and building a foundation. The actual water removal is carried out by submersible pumps to the required level. Pumps are immersed in shaft wells or wells, which are always near the working pit.

When the water is pumped out, the soil supersaturated with it receives natural moisture, which makes it easier to manipulate it.

Closed drainage

Perforated pipes are installed throughout the site. The depth of their laying is not less than the freezing level - this is a mandatory requirement, otherwise the pipes will burst. They are laid on a sand cushion and rubble. Geotextile, which is laid on the bottom of the trench, helps to exclude silting.

Note! This option of lowering the groundwater level on the site does not affect the appearance of the site itself. Of course, you need to think about the arrangement of this system in advance.

Drainage of a site with a high level of groundwater

natural method

Trees are ready to answer the question of what to do if there is a high GWL. If it is not possible to use the above methods, then the folk, traditional method will help. Part of the territory, especially the lowland, should be taken under water-loving trees. Among the most convenient:

• Poplar. This tree is not the best, because its roots are weakly held in the soil, there is a risk that with a strong gust of wind it will collapse with the root.
• Fluffy birch, willow. Suitable for landing on the border of the site. These trees intensively take moisture from the soil, they are especially useful in swampy areas.
• Alder, maple, larch, ash. In addition to effectively draining the garden plot, they are of decorative interest for landscape design.
• Plum. The only fruit tree that easily gets along with high soil moisture.

When planting trees in order to dry the soil, you need to use the following scheme:

• The diameter of the pit is 1.5 m.
• Depth 80-100 cm.
• To make a pour of gravel at the bottom is drainage.
• After, a layer of fertile soil and then a seedling.

Of course, the results of such a dehumidification system will have to wait a long time.

Plot lifting options

In some cases, drainage tips do not help, so you need to look for options on how to raise the site. This process is carried out in several stages:

• Removal of a fertile layer of earth 10-20 cm thick.
• Installation of pegs to control the height of the rise.
• The distribution of areas where the filling will be carried out.
• The soil level can be raised by 30 cm, but the rise will be gradual by 5-10 cm.
• The earth is alternated with a sand and gravel layer, each layer is carefully compacted.

This technique will perfectly help to cope with the problem of high groundwater levels.

Construction of any objects in conditions of high GWL is difficult. A number of measures that can be taken help to cope with the problem. Almost all methods can be implemented by hand, but this requires a lot of time and resources.

Earlier we talked about the fact that your designer should study in detail the features of the area in which you decide to build a house (see article ). Particular attention should be paid to the study of hydrogeological conditions (groundwater level).

Groundwater is formed mainly due to the seepage of atmospheric precipitation, waters of rivers, lakes, reservoirs, etc.

The main types of groundwater are:

• top water,
• ground water,
• pressure (artesian) water.

Verkhovodka called water located at a depth of 2-3 m from the surface of the earth above the waterproof layer. In places where the water-resistant layer ends, the perched water also disappears, flowing into the underlying layers of permeable rocks (sands, fractured limestones, etc.). In dry weather, as well as in winter, perched water usually disappears.

Ground non-pressure water- this is groundwater located above the first impermeable layer of rocks. The main source of their formation is atmospheric precipitation. The level of such groundwater is maintained at the depth at which they appeared, since there is no pressure in groundwater.

Pressure (artesian) water located between two impermeable layers. When constructing a pit, such waters rise above the level at which they were.

The fundamental difference between perched water and free-flowing groundwater is that, depending on weather conditions, perched water may either appear or disappear. While ground free water is in the ground constantly at the same level. It is these waters that must be diverted from the site during construction work.

Pressurized water, on the contrary, is unlikely to interfere: they must be used to supply the cottage with water.

When conducting engineering-geological surveys, the following is determined:

• availability of groundwater
• their character,
• chemical composition,
• expected water inflows (the amount of water and the rate of filling the pit, trench, etc.).

The presence of groundwater in the rock layer is determined by drilling exploratory wells.

Such research is necessary for a number of reasons:

First, because groundwater in some cases change the properties of the soil. For example, clay slates become unstable when exposed to water. Sands saturated with water easily give up water and require preliminary drying. Fine-grained sands with an admixture of silt particles are able to retain water and turn into quicksand. Some clays swell when wet and are difficult to work out.

When calculating design estimates, it is important to take this point into account. Because otherwise, during the construction process, the cost of the zero cycle may instantly increase (in particular, the development and construction of the foundation pit): it will be necessary to attract additional equipment and workers, increase the time frame for the work, and bear unplanned expenses.

Secondly, in the presence of groundwater, the soil becomes loose, loses its original properties, including bearing capacity. This means that unforeseen ground subsidence may occur. Which in turn leads to uneven subsidence of the foundation. As a result - the occurrence of cracks and destruction.

Thirdly, in the presence of groundwater, when laying the foundation, "washout" of concrete may occur. That is, with constant contact of water with concrete, cement is washed out of concrete. This leads to the fact that the material from which the foundation is made becomes heterogeneous. Therefore, the finished foundation cannot bear the design load.

Thus, in order to ensure the strength and durability of your foundation in particular and the house as a whole, it is necessary to remove groundwater (lower the groundwater level) from the construction site.

In private construction, the following methods are used to lower the level of groundwater:

1. Open methods of dewatering (surface drainage);
2. Closed dewatering methods:
   1. Drainage arrangement (pipeless and pipe);
   2. Dewatering with light wellpoints;
   3. Dewatering with the help of ejector wellpoint installations.

The following factors influence the choice of groundwater level lowering method:

• dimensions and shape of the pit being constructed;
• soil permeability;
• the required depth of dewatering;
• duration of dewatering;
• conditions for the movement of groundwater before the start of work;
• the presence of existing structures near the pit.

So, the essence of all methods of lowering water is the same- collect groundwater from the surface or from the depths of the soil and remove it from the construction site using various devices.

With surface drainage groundwater, seeping through the slopes and the bottom of the pit, enters the drainage ditches and through them into the pits, from where it is pumped out by pumps. In fine-grained soils, drainage ditches, and sometimes slopes of the pit, are loaded with a sand-gravel mixture, which serves as a good water-conducting medium that protects ditches and slopes from slumping. Drainage ditches are usually arranged with a depth of up to 1.5 m. The width of the ditches along the bottom is made at least 0.6 m, and the slopes are usually 1:1.5 steep (that is, with a trench depth of 1 m, the width to which the slope will depart will be 1.5 m).

The arrows show the direction of water movement.

The device of drainages is one of the methods of closed dewatering.

The following apply types of drainage:

- pipeless drains- deep trenches filled with filter material (brushwood, gravel, coarse sand, stone).

Filling in pipeless drainages is arranged from several layers of filler of various sizes. To isolate the drainage from the penetration of surface water, the drainage trench is clogged from above with a waterproof layer (clay or clay mixed with sand) 0.5 m thick.

To protect the filler from contamination, a layer of moss or peat is laid between it and the waterproof blocking.

- pipe drains from polymer pipes. Such pipes must be perforated (holes are made along the pipe in the required quantity for the penetration of groundwater into the pipe) and corrugated (to maintain shape and volume). The drainage pipe is laid in the ground to a depth of 1.5-2 m.

1 - local soil; 2- fine-grained sand; 3 - coarse sand; 4 - gravel; 5 - pipe; 6 - sealing layer.

When installing pipe drainage, a manhole should be arranged. Inspection wells should be installed in places where pipes and collectors turn, change the slope and diameter of pipes, where pipes flow into closed collectors, as well as in places necessary for flushing drainage lines. Manholes must be arranged for periodic cleaning and inspection of drainage pipes.

1 - pipe; 2 - drainage well; 3 - soil; 4 - the bottom of the well; 5 - well cover.

Light Wellpoints are used to lower the level of groundwater to a depth of 4-5 m. Such installations are a pipe, at the end of which there is a wellpoint. A lightweight wellpoint is connected to a pump located on the surface using a rubber hose and a vacuum manifold.

1 - pipe; 2 - clutch; 3 - wellpoint (perforated pipe); 4 - protective filter mesh; 5 - tip; 6 - air flushing pipe; 7 - nozzle; 8 - traffic jams; 9 - air valves; 10 - air pipeline; 11 - water separator; 12 - valve; 13 - float; 14 - tees; 16 - pipeline; 17 - water ring vacuum pump; 18, 19 - control valves; 20 - manometers.

To lower the water level to a great depth, I use two - three-tier installations.

Ejector Wellpoints consist of wellpoints with ejector water lifts, a distribution pipeline (collector) and centrifugal pumps. Ejector water lifts placed inside the wellpoints are driven by a jet of water pumped into them by a pump through a collector.

It can be seen from the diagram that the water ejected from the wellpoint enters the tray and then drains into the circular tank. From the tank, part of the water is again sucked in by the pump, the rest is discharged by the pump or discharged by gravity outside the construction site.

As can be seen from Table 1, it is ejector wellpoints that make it possible to lower the groundwater level to 20 m.

I would like to draw your attention to the fact that you should not independently conduct geological surveys of the site and design a method of dewatering. Studying the geology of the site is a rather delicate matter and it is better to entrust it to a professional (see article).

In this case, your task is to draw up the terms of reference for the project in the design organization that you have chosen.

Further, the designer himself will directly issue an application for engineering and geological surveys. Such surveys can be carried out both by specialists of the design organization that creates the project for you, and by a third-party organization. It is important that this organization has a license to conduct engineering and geological surveys. It is also possible that the project will use ready-made surveys of the area. Such information can be obtained from the Office of Land Resources.

Once again, I would like to emphasize that you should not worry about organizing geological surveys. It is the designer's responsibility to obtain the correct data for your site! Because, if something happens to the built cottage within 20 years (for example, the house sags because the bearing capacity of the soil and the presence of groundwater were not correctly calculated), then the designer who created this project will be responsible in accordance with the Civil Code of Ukraine.

Only after receiving engineering survey data on your site, your designer will tell you which method of dewatering will be most effective in this situation. Also, the recommended method of dewatering will be indicated in the design and estimate documentation. These recommendations will be used by the construction organization that will carry out construction work on your site.

List of used literature:

1. Knaupe V. Construction of pits and dewatering / Per. with him. M.F. Gubin; Ed. V.N. Burlakova and V.V. Sorokin. - M.: Stroyizdat, 1988. - 376 p.
2. Handbook of the master builder. Chief editor Kazachek G.A. - Editorial board of scientific and technical literature. Minsk, 1955.
3. Reference book on general construction works. Foundations and foundations. Under total ed. M.I. Smorodinov. M., Stroyizdat, 1974, 372 p.
4. Fizdel I.A. Defects and methods for their elimination in structures and structures. - M.: Publishing house of literature on construction, 1970.

The rise of groundwater often leads to flooding of the local area, garden or vegetable garden. Excess moisture contributes to the washing out of the soil, as a result of which the foundation sags, the house collapses. Constant dampness interferes with the development of cultivated plants, provokes the growth of lichens, molds.

The question arises, how to drain the site from groundwater if the water has nowhere to go? To prevent such a phenomenon, it is necessary to make drainage in an area with a high groundwater level (GWL). A number of reclamation works on the site can be done with your own hands, using purchased materials and improvised means.

Melt or rainwater passes through the upper aquifer, reaches the water-resistant layer (clay) and rushes through its recesses to the lowest point - there a zone of excess moisture is formed. When the runoff of the aquifer cannot cope with large volumes of precipitation, the upper layers of the soil overflow with moisture, and groundwater rises. Their impact is especially destructive if there is fine sand above the waterproof clay: in this case, quicksand can form.

An external inspection of structures and terrain will help to assess the state of the local area in terms of the proximity of groundwater. The following facts indicate the rise of the water horizon and the need for drainage:

• plaster is peeling off the walls, door and window frames are warped, cracks appear in the glass for no apparent reason - these are evidence of a loss of strength due to leaching of calcium from cement;
• there is a constant smell of dampness - it accompanies mold, which negatively affects wooden and concrete structures and is harmful to health;
• nettle, coltsfoot, horsetail, hemlock, reed, wormwood, licorice are developing the territory;
• the number of mosquitoes, snails and frogs increased, snakes appeared;
• the basement or cesspool is filled with water.

If you need to check an empty building plot, trial sounding will help clarify the situation with the groundwater level. The data obtained on the composition and quality of the soil will give an accurate answer to the question of whether it is necessary to drain the site. . This is usually recommended when groundwater occurs at a depth of 1-2 meters. Drainage channels of open and closed type, arrangement of a drainage pond, production of artificial embankments, pumping out with a special drainage pump will help to lower their level.

open system

For partial drainage of a site with a high level of groundwater, it is possible to equip a simple network of sewage ditches laid along the entire perimeter of the territory and between the ridges. Rain and melt water is collected in shallow catchment arms, directed to the main canal, and then transported to a drainage well or soaked into the ground outside the site.

Here are the basic rules for making open drainage with your own hands:

1. The main trenches are dug to a depth of at least 40 cm, additional ones are enough to be deepened by 15 cm. The width of the channels depends on their location, usually it is 1/3 of the depth. Be sure to withstand a slight slope of the system to ensure gravity flow.
2. Near buildings and various structures, the channel is deepened in relation to the foundation and supporting elements by 25-30 cm.
3. Since the walls of the ditches are not reinforced with anything, they cannot be dug along the perimeter of the structures so that the foundation does not deform over time.

Open drainage cannot divert groundwater - it only prevents the oversaturation of aquifers with atmospheric moisture. The disadvantage of this option is the reduction of the usable area for planting cultural plantings.

An improved version of the open system is backfill drainage. The trenches are covered with a wide strip of geotextiles, coarse gravel is covered up to half the depth. From above, the ditch is filled with gravel of a fine fraction, not reaching the soil level by 10-15 cm. The edges of the geotextile are wrapped, sand or gravel crumbs are poured over it.

closed system

This option provides effective groundwater drainage and allows you to significantly reduce the humidity in the area with high GWL. The system is a network of drains - pipes buried below the soil freezing line (so that there are no gusts in winter) and connected to a drainage well.

Work on the arrangement of drainage is carried out in this order.

1. Layout. Draw the optimal "route" of water drainage. Pipes should run along the perimeter of buildings and in the gaps between trees. When draining a garden plot with a high level of groundwater, they make sure that there is at least 2.5 m to the trunks. The position of the drainage well is applied on the plan: it should be in the lower position.
2. Site marking according to the plan. It is performed with the help of pegs and twine.
3. Digging trenches. They are located below the freezing boundary of the soil, and for drainage of the building - below the base of its foundation by 15 cm.
4. Making a sand cushion. A layer of coarse-grained sand (10-15 cm) is covered at the bottom of the ditches, it is filled with water, but it is not heavily rammed. The upper edge of the pillow is formed according to the level, maintaining a constant slope of 1-2 mm per 1 meter - from the top point to the well.
5. Geotextile laying. Its stock in width is 25 cm on each side.
6. Backfilling of the filtering layer of gravel (5-10 cm).
7. Pipe laying. You will need ready-made polymer corrugated products in a geotextile sheath (silting protection). For main channels, pipes of 100 mm are needed, and for auxiliary channels - 75 mm. Laying is preferably done with a herringbone. At all turns of the route, sand traps are installed into which the ends of the pipes are inserted, but they are not connected to containers (to make it easier to clean the system).
8. Backfilling of the filter layer. The space of the ditches is filled with large and medium gravel, not reaching the ground level by 20-30 cm.
9. Shelter system. Gravel is covered with free edges of geotextiles, covered with gravel chips or soil left over from digging a trench.

To prevent clogging of perforations with clay particles and salt deposits, the system is flushed every 2-3 years by running water from a hose into it under pressure.

Plot lifting

Even if deep drainage did not help to completely get rid of the negative manifestations of GWL, you will have to deal with the planning and backfilling of a site with a high level of groundwater.

This method is expensive, but provides a real and lasting effect. Regardless of the elevation of the site, the work plan is approximately the same.

1. Territory planning. They draw up a detailed plan of the site with the designation of the level of heights, the location of the surface aquifer, the thickness of the fertile layer. This will help determine where, how much and what exactly to add. If the geology of the area is complex (bogginess is combined with a high GWL, there is a clay layer or voids), it is better to entrust the planning to a specialist.
2. Demolition of old buildings (if any).
3. Site clearing. It is freed from vegetation, debris, roots are uprooted.
4. Laying the drainage system (if it does not already exist). Dumping alone will not solve the problem of excess moisture. It still needs to be removed in a closed or open way, as described earlier.
5. Site clearing. A low strip foundation is laid around the territory so that the poured material is not washed away by rains. After the concrete hardens, layer-by-layer dumping of materials (10-15 cm each) is carried out. Each layer is compacted with a vibrotamper. After laying all the lower layers, they withstand a couple of weeks for natural shrinkage by 2-3 cm, only then comes the turn of fertile soil. So that the layers do not mix, they are separated by geotextiles.

To fix the backfill, the site is sown with cereals with a branched root system.

Here you will find answers to the most popular questions from readers regarding land reclamation and drainage facilities.

1. What material is best to fill the area?

For a rise of 20-30 cm with a small area, fertile soil can be used. If a meter layer of backfill is required, the base is made of compacted sand, secondary crushed stone or broken brick is placed in the middle (for drainage), and soil is laid on top. On beds and lawns, you can do without crushed stone, paths and platforms are sprinkled with excavated soil instead of soil. Experts believe that it is better to place the earth from the site down. This prevents heavy gravel from sinking into light sand or light sand from sliding off loam.

1. Are asbestos or used steel pipes suitable for closed deep drainage?

It is better to use special drainage pipes for draining groundwater with ready-made holes and wrapped with geofabric. Other product options quickly become clogged, and the drainage fails. As a last resort, asbestos-cement pipes with a diameter of at least 100-150 mm are taken. For water to enter them, holes are drilled or cuts are made, in order to avoid silting, they are wrapped with geofabric.

1. What material can be used for drainage instead of gravel?

In open systems, it can be replaced by viscous brushwood. Bundles with a diameter of 30 cm are formed as follows: large branches are placed in the center, and small twigs are placed outside. Moss is laid over the laid knittings. On peat soils, such a system remains operational for up to 20 years.

1. Is it possible to carry out an artificial lowering of the groundwater level?

To reduce the level of excess moisture to 5 m, a wellpoint installation is used. It includes a ground vacuum manifold for water discharge, pumps to reduce pressure in it and vertical pipes, at the ends of which wellpoints are located. Sometimes expensive complexes with injector water lifts are used, which can increase the depth of groundwater up to 20 m.

1. Is it necessary to make a drainage well?

The well is convenient in that water can be taken from it for irrigation or other needs. At the top there is a pipe from which water flows out when the container is full. If there is free space on the site, the role of a catchment reservoir can be played by a small pond, the bottom of which is covered with crushed stone and a sand and gravel mixture. Moisture-loving plants can be planted around the drainage reservoir, and a recreation area can be equipped.

Dewatering in the construction of subways is used in the construction of stations, tunnels and underground passages built in an open way, in the tunneling of station and distillation tunnels in a closed way, in the construction of mine shafts, as well as in the performance of various works associated with the construction of subway tunnels (relaying communications, supplying or strengthening foundations and etc.).

For dewatering, the following are used: light wellpoints, ejector wellpoints, vacuum and downhole dewatering units, as well as deep pumps installed in dewatering wells,

The essence of the method of dewatering is based on the fact that when pumping groundwater entering a well, pit or underground working, the surface of the water in the soil acquires a funnel-shaped shape with a slope towards the place of pumping (Fig. 86). The funnel-shaped (lowered) groundwater surface is called the depression surface, and the space between this surface and the non-lowered surface of the groundwater flow is called the depression funnel.

As the water is pumped out, the depression funnel increases in area and in depth. If the pumping intensity remains constant, then over time, stabilization sets in - a steady state, in which there is no further development of the depression funnel. With the cessation of pumping, the groundwater level is restored. The purpose of dewatering is the development and maintenance of a depression funnel in aquifers, i.e., their maintenance in a drained state during the entire period of construction of the structure. In some cases, dewatering is used to relieve excess pressure in the underlying aquifers, separated from the bottom of the pit by a layer of water-resistant soil.

Rice. 86. Scheme of dewatering: a - one well; b - two wells with an aquiclude below the dia of the pit; c - the same at the level of the bottom of the pit; 1 - the contour of the pit for the structure under construction; 2 - dewatering well; 3 - dry soil located above the groundwater level (GWL); 4 - depression funnel (soil drained by dewatering); 5 - depression surface; 6 - watered soil; 7 - submersible pump; 8 - waterproof layer; h is the maximum height of the residual water layer removed by an open drain

However, in some cases (for example, when impervious soils lie close to the bottom of the pit), it is not possible to completely drain the aquifers and a layer of water 0.5-1 m thick remains above the aquiclude. To remove it, open drainage is most often used using portable pumping units, pumping water from arranged temporary wells (sumps).

When choosing a dewatering method, the soil characteristics and conditions of their occurrence, the thickness of the aquifer, the filtration coefficient, the size of the drained zone in the soil, the methods of mining or construction work, the duration of the dewatering, the characteristics of the available technical means of dewatering are taken into account.

Dewatering wells are drilled outside the contour of the structures under construction. Their location in the plan depends on the size of the structure, as well as on the hydrogeological characteristics of the soil and can be: linear (in one or several rows in a straight line, for example, when driving distillation tunnels), contour (along the contour that envelops the structure, for example, a foundation pit, for the construction of an open-cut metro station), annular (for example, when sinking mine shafts), combined (for example, when one or more rows of the same wells are located inside the contour of water-reducing wells with wide pits).

Dewatering with light wellpoints. This method is based on the creation and maintenance of vacuum by self-priming pumps in a widely branched network of wellpoints immersed in the ground and connected by rubber hoses to a collector (Fig. 87). Groundwater is sucked through the filters into the suction manifold and pumped out of the drained area by pumps.

The light wellpoint is a string of pipes with a diameter of 46-50 mm and a length of up to 8.5 m, connected hermetically. In the lower part of the column there is a filter unit consisting of two pipes: an outer one, which has holes evenly distributed over the entire surface, and an inner one, with an open lower end. The outer pipe is wrapped in a spiral, over which a filter mesh is stretched. The link ends with a tip with a ball valve. Each wellpoint is immersed in the ground with the help of hydrojetting, using the pressure of a water jet.

With one tier of light wellpoints, it is possible to lower the groundwater level to 4.5 m. To lower groundwater to a greater depth, wellpoints are used, which have tiers. Light wellpoint installations of the LIU type are used in the development of pits and trenches in soils with a filtration coefficient of up to 1 m / day.

Dewatering with ejector wellpoints. Such wellpoints have a special device for lifting water - an ejector (water jet pump). One tier of such ejector wellpoints can lower the groundwater level to 18-20m in soils with a filtration coefficient of 0.5-1 m/day.

The design of ejector wellpoints is based on the principle of operation of a water jet pump, in which a jet of water moving at high speed takes with it some additional amount of water from a lower level and raises it to a higher one. The scheme of operation of the ejector wellpoint is based on the following (Fig. 88). In the wellpoint column 1, an ejector water lift (ejector) is lowered on the pipe 2. Working water is supplied to the ejector through the annular space between the outer and inner water pipes. Flowing out of the nozzle 6 at high speed under the action of the pump 4, the jet of working water draws water into the diffuser 5, which enters the filter unit 7 from the surrounding rocks. Groundwater pumped out by wellpoints mixed with working water through pipe 2 enters circulation tank 3, from which part of the excess water goes into the drain and sewerage, and the other part again enters centrifugal pumps to feed the wellpoints.

The immersion of the ejector wellpoints occurs when water is flushed through the ball valve 8. At great depths, as well as unfavorable geological conditions, special wells are drilled into which wellpoints are inserted.

In construction, ejector installations of the EY type are used. The set includes from 16 to 36 wellpoints, high and low pressure pumps with electric motors, distribution pipeline and circulation tank. Ejector wellpoint installations are used for dewatering when excavating soil for pits and trenches up to 10-12 m deep.

Rice. 87. Scheme of operation of a light wellpoint installation: 1 - pumping unit; 2 - wellpoint; 3 - collector; 4 - filter part of the wellpoint UGV - groundwater level

Rice. 88. Scheme of operation of the ejector wellpoint

Vacuum method of dewatering. The method is based on creating a stable vacuum on the outer surfaces of water intake devices (filter sections of pipes). Vacuuming of water-saturated soils is used to enhance the effect of dewatering in difficult hydrogeological conditions - in soils with filtration coefficients of 0.05-2 m / day, with low water permeability, low water loss and heterogeneous composition of soils, in particular when interbedding aquifers and water-resistant layers.

Vacuumization is achieved by using UVV vacuum dewatering units with a conventional wellpoint filter for lowering the groundwater level to a depth of 6-7 m, EVVU ejector vacuum dewatering units with vacuum concentric wells, which make it possible to carry out vacuum dewatering to a depth of 20-22 m in interbedded water-bearing and water-resistant soils, and installations bottomhole dewatering UZVM, designed for draining fine and silty sands in the bottomhole zone in open and closed methods of work.

In air-blast units, to create a stable vacuum in the cavity of the suction manifold, a water-air ejector is used, which mainly activates water, which is released from the water-air mixture coming from wellpoints. Water is pumped out by a water-water ejector. Both ejectors are fed with working water coming to them from a centrifugal pump. To ensure stable operation, each of the ejectors can take on the functions of the other.

Ejector vacuum dewatering installations with vacuum concentric wells differ from conventional installations with ejector wellpoints in the design of the wells.

The downhole dewatering plant, operating on the principle of vacuum dewatering (Fig. 89), when tunneling with a shield method, allows you to overcome areas with difficult hydrogeological conditions.

Deep water supply. This method is based on pumping water from aquifers with the help of deep centrifugal pumps installed in dewatering wells drilled around a future underground mine. Tubular filters are lowered into the wells to the level of the aquifer, and then the drill casing pipes are removed from the soil, thus creating direct contact of the filter with the surrounding soil. As a result of pumping water from the well with a deep pump, a depression funnel is formed, inside which the soils are largely drained. Deep dewatering is used when pumping water from depths of more than 20 m.

Rice. 89. Location of the downhole vacuum dewatering unit during the construction of the subway tunnel: 1 - wellpoints; 2 - wooden fastening of the face chest; 3 - lever for laying tubing; 4 - tubing layer; 5 - tubing lining of the tunnel; 6 - pressure gauge; 7 - vacuum gauge; 8 - water jet pump; 9 - pressure gauge; 10 - circulation tank; 11 - deflector; 12 - drop sleeve; 13 - centrifugal pump; 14 - electric motor; 15 - flexible connecting sleeve; 16 - stackable collector link; 17 - haulage ways; 18 - jack for moving the tubing layer; 19 - collector; 20 - rock loading machine; 21 - mobile track link