An integral part of a private house or cottage is a storm drainage system, which provides an aesthetic appearance to the residential building and the area adjacent to it. It also prevents premature destruction of the foundations of buildings and the roots of plants growing on the site. To an inexperienced person in the field of "water disposal", this moment may seem like a dark forest. In this article we will look at everything point by point: drainage of surface, storm and melt water, from buildings and site.

To create a storm drainage system, also known as a surface water drainage system, basic knowledge in construction and data about the area being developed are required. Storm sewerage is gravity-flow, i.e. is arranged at an angle and includes the following elements:

1. Roof drainage;
2. Drainage drainage system;
3. A sewer or drainage discharge point.

Roof drainage receives precipitation at the roof level, through trays, gutters, funnels and sends it to the surface drainage system.

Design of a surface water drainage system

For design you need to know:

• the average amount of precipitation (both in the form of rain and in the form of snow, melt water), you can find this out in SNiP 2.04.03-85;
• roof area;
• the presence of other communications and facilities in the territory being developed.

For design, it is necessary to decide in what places they will be located. drainpipes and how many there will be. A diagram is drawn up that shows the differences in elevation of the surface of the site and the buildings on it. The diagram indicates the location of all storm sewer elements, including pipes, inspection wells and water discharge points. During design, the amount of required materials and their costs are also calculated.

Drainage of water from the roof

The roof drain material is varied: steel, copper, steel with polymer coating, aluminum, etc. Plastic is especially popular. It is economical, resistant to damage, and is soundproofing material, hermetically sealed, light in both weight and installation. To properly design a roof drain you will need:

1. Metal bracket;
2. Hairpin with a special nut;
3. Adjustable mount;
4. Gutter bracket;
5. Tip;
6. Connecting coupling;
7. Knee;
8. Funnel plug;
9. Gutter plug;
10. Corner element;
11. Funnel;
12. Gutter connector;
13. Gutter;
14. Drain pipe.

The quantity and type of each element depends on the perimeter of the roof and the amount of pumped liquid, because too powerful a drainage system is irrational from the point of view of financial costs, and a weak one will not cope with the task. Need to find best option. The figure shows the required dimensions specific to middle zone Russia.

Installation of a water drainage system from the roof of a house

Installation is carried out after developing the design of the entire drainage system and reading the instructions supplied by the supplier store (each system has its own design features that must be taken into account). General installation sequence and work performed:

1. Installation begins with attaching the bracket from the side of the rafter wall or frontal board, taking into account the slope of the gutters.
2. Then the gutters themselves are laid using special plates and fastened to each other using the cold welding or rubber seals. The cold welding method is preferred for joining gutters due to its resistance to deformation.
3. An additional bracket is installed in corner connections and connections with funnels.
4. The pipes are installed, maintaining a distance of 3-4 cm from the wall. The vertical brackets are attached at a distance of 1.5-2 m. The drain itself should be located half a meter from the ground surface.

Tips from the professionals:

• The gutters begin to be laid from the funnel so that the edges of the gutter are below the edge of the roof.
• If you use a pipe to collect gutters from three directions (if the roof non-standard shape), it is necessary to provide tees instead of standard funnels.
• The distance between the brackets should be no more than 0.50-0.60 m.
• It is recommended to mark the slope of the gutters in advance. For example, a guideline can be a rope stretched from the starting point to the ending point.
• Plastic ebbs are mounted at a temperature of + 5°, otherwise the material will crack when cutting. Flashings made from other materials can be installed at any ambient temperature.

Construction of a surface water drainage system

Surface water drainage system or surface drainage consists of point drainage systems and linear channels.

Point drainage They are small wells locally connected to roof drainage. The trays are laid below the freezing level of the pipes. The installation of such drainage is similar to the installation of a roof drain. A trench is being prepared (lower than the freezing depth of the pipes, you can find out everything in the same SNiP) at a slope towards the collector. Sand is poured in a layer of 20 cm. Pipes are laid using fittings. If the sealing is maintained, the pipes are backfilled.

Linear channels come in two types - open or closed, equipped with grates or meshes to retain large debris. The gratings should be predominantly made of metal, because... withstand heavy loads (especially in places at the entrance to the garage).

Advice from professionals. To effectively collect surface water, a comprehensive arrangement of storm and point drainage is necessary. In case of heavy precipitation, the bulk of the water will be drained by surface drainage.

You can see what the process of installing a surface water drainage system looks like in the video:

Deep drainage system is provided if the area where the site is located is prone to prolonged rains. Such a system will protect the site from erosion, protect trees from premature death (due to rotting roots), and protect the foundation from the destructive effects of water.

Groundwater drainage system

Drainage groundwater differs from the systems described above in that it is installed at a greater depth and in the case of groundwater close to the surface of the earth, which can flood a basement or underground garage. Drainage is combined with storm water, and storm water pipes are laid higher than the drainage. It is necessary to understand the difference between stormwater and drainage. Storm drainage for drainage of rain, melt water and floods, and deep drainage for drainage of groundwater and possible flooding. Surface and deep drainage are connected using special node connections to accumulate excess water in one place and its subsequent release, recycling or reuse. Drains are installed parallel to each other.

This is important: during heavy rainfall, water in large quantities passes through the storm drain in a short time. When such a flow of water enters the groundwater drainage system, this water flows from the pipes into the ground, thereby not draining it but flooding it, that is, it begins to perform the opposite function. Therefore, the surface water drainage system should be connected to the groundwater drainage system no earlier than the places where the water drainage and not drainage pipes pass, if you look at the direction of water movement into the systems. Soil drainage is carried out in places where perforated pipes are laid. Water is drained through sealed pipes.

According to the method of groundwater extraction, they are divided into: vertical, horizontal and combined drainage. Vertical drainage consists of vertical ribbed wells lowered into the groundwater layer. They are equipped with pumps and filters, respectively, for cleaning and pumping groundwater outside the territory. This scheme is quite complicated both in installation and in operation.

Horizontal drainage consists of perforated pipes laid on optimal depth pumping outlet in dug ditches lined with crushed stone. Ditches are dug throughout the site in a herringbone pattern.

The installation of drainage, regardless of the type of site, begins with the arrangement drainage well in the farthest part of the site, away from the house. You can use ready-made plastic wells.

In places corner connections inspection wells are installed to facilitate communication maintenance.

The depth of drainage is selected based on its objectives: if the goal is to collect groundwater to protect the basement, then the depth should correspond to the level of the basement floor; if the goal is to drain abundant waters descending into soil - depth corresponds to the depth of the foundation.

The pipes are wrapped with a special material () to prevent sand and gravel from getting into the pipes, with which the pipe is covered with a layer of 20-30 cm. After this, the pipe can be covered with ordinary soil. Unlike vertical drainage, water collected through holes in pipes is discharged by gravity and not by pumps.

Horizontal drainage is more popular than vertical or even combined drainage due to its cost-effectiveness and ease of installation.

You can read more about the design of the groundwater drainage system in the article:

Discharge of collected water

Excess water is removed outside the site, into a ditch or reservoir. If this is not possible, then a well or reservoir is installed within the site, from where the water can be reused.

Advice:

It is recommended to lay drainage in ditches with V-shaped walls with a wall slope of 30◦ in the cross section of the ditch. Width 50 cm. Recommended ditch slope1-3 cm per meter of length. Wells can be equipped from any material that is not subject to corrosion.

Maintenance of drainage systems

Maintenance of the above systems is not difficult if they are properly designed and constructed. Main points in service:

1. Once every ten years, use a pump to thoroughly flush the pipes to prevent deposits on their walls.
2. Regular visual inspection wells, collectors and cleaning if necessary.

The shelf life of a properly designed, installed, and maintained drainage system is on average fifty years, or even much more.

Tips from the professionals:

1. Be sure to check that the pipes are laid on a slope. The slope should be away from the house.
2. If it is impossible to install a gravity drainage system, a pressure outlet equipped with a pump is installed.
3. Do not forget about optimal design and price = quality.Very often you want more, better, but the budget does not always allow you to realize your plans. That's why It is recommended to design, compare the project with prices, make purchases and install in accordance with the recommendations given here.

Lecture on the topic: Engineering organization of populated areas.
Part 11: Organization of surface water flow.

Organization of surface water flow

The organization of surface (storm and melt) water flow is directly related to the vertical layout of the territory. Surface runoff is organized using a general territorial drainage system, which is designed in such a way as to collect all surface water runoff from the territory and divert it to possible discharge sites or treatment facilities, while preventing flooding of streets, low-lying areas and basements of buildings and structures.

Rice. 19. Schemes for organizing surface runoff depending on the topography of the territory.

The main parameters characterizing rains are intensity, duration and frequency of rains.
When designing rainwater drainage systems, they take into account rainwater giving highest expenses drain. That. For calculations, average rain intensities for periods of various durations are taken.
All calculations are carried out according to the recommendations:
SNiP 23-01-99* Climatology and geophysics.
SNiP 2.04.03-85 Sewerage. External networks and structures
Surface drainage is organized from all urban areas. For this purpose, open and closed city drainage systems are used, which remove surface runoff outside the city area or to treatment facilities.

Types of rain network (closed, open)
Open network- this is a system of trays and ditches included in the transverse profile of streets, supplemented by other drainage, artificial and natural elements.
Closed- includes supply elements (street gutters), an underground network of pipes (collectors), rain and inspection wells, as well as special-purpose units (outlets, water wells, drop wells, etc.).
A mixed network has elements of an open and closed network.

Closed rain network

Special structures of a closed rainwater network include: rainwater inlets and inspection wells, storm drains, rapid flows, water wells, etc.
Stormwater wells are installed to ensure complete interception of rainwater in places where the design relief is lowered, at exits from blocks, in front of intersections, on the side of water inflow, always outside the pedestrian traffic lane (Fig. 20).
In residential areas, rainwater wells are located at a distance of 150-300m from the watershed line.
Along highways, rainwater wells are placed depending on the longitudinal slopes (Table 4).

Rice. 20 Layout of rainwater wells at intersections .

Rice. 21. Location of rainwater wells in the highway plan.
1 – collector, 2 – drainage branch, 3 – rainwater well, 4 – inspection well.

The storm (rain) collector located along the highway is duplicated if the width of the roadway of the highway exceeds 21 m or if the width of the highway in the red lines is more than 50 m (Fig. 21, c). In all other cases, use the circuits shown in Fig. 21, a, b.
For ease of operation, the length of the storm sewer branch is limited to 40 m. There can be 2 rainwater wells on it, at the junction of which an inspection well is installed, however, in areas with a large volume of runoff, the number of rainwater wells can be increased (up to 3 at one point). With a branch length of up to 15 m and travel speed Wastewater not less than 1 m/s, connection without a manhole is allowed. The diameter of the branches is taken within the range of 200-300 mm. Recommended slope – 2-5%, but not less than 0.5%
If necessary, rainwater wells are made combined: to receive water from the roadway and to receive water from drainage systems (drains).
Inspection wells are located in places where the direction of the route changes, the diameter and slope of pipes, pipeline connections and intersections with underground networks at the same level, in accordance with the terrain conditions (slopes), the volume of runoff and the nature of the laid storm sewer collectors, on the storm (sewer) network.
On straight sections of the route, the spacing of inspection wells depends on the diameter of the drainage pipes. The larger the diameter, the greater the distance between the wells. With a diameter of 0.2÷0.45 m, the distance between wells should be no more than 50 m, and with a diameter of more than 2 m - a distance of 250 -300 m.
The storm sewer, as an element of the storm sewer, is located in the built-up area of ​​the city, depending on the general layout of the entire storm network.

Storm drain depth depends on the geological conditions of the soil and the depth of freezing. If the soil in the construction area does not freeze, then the minimum depth of the drain is 0.7 m. The depth of installation is determined in accordance with the requirements of SNiP standards.
A conventional drainage network is designed with a longitudinal slope of 50/00, but in flat terrain conditions it is reduced to 40/00.
In flat areas they accept minimum slope collector equal to 40/00. This slope allows for the continuity of movement (constancy) of storm water in the collector and prevents its siltation.
The maximum slope of the collector is taken to be such that the speed of water movement is 7 m/s, and for metal collectors 10 m/s.
At large slopes, collectors may fail due to water hammer.
Possible structures on the drainage network include drop wells, installed in areas with a large drop in relief, to reduce the speed of water movement in the collector, which exceeds the highest permissible standards. If there are significant extreme slopes of the terrain along the collector route, rapid flows, water wells are installed, or cast iron or steel pipes.
For sanitary reasons, it is advisable to arrange outlets of the drainage network outside the boundaries of city buildings in treatment facilities (septic tanks, filtration fields).

Open rain network consists of street and intra-block. The network includes ditches and trays that remove water from low areas of the territory, overflow trays that remove water from low areas of the territory, and ditches that drain water from large areas of the basin. Sometimes open network complement the beds of small rivers and canals.
The cross-sectional dimensions of individual network elements are determined by calculation. At small areas drain, the cross-sectional dimensions of trays and ditches are not calculated, but are taken for design reasons, taking into account standard dimensions. In urban conditions, drainage elements are reinforced along the entire bottom or along the entire perimeter. The steepness of the slopes of ditches and canals (the ratio of the height of the slope to its foundation) is set in the range from 1:0.25 to 1:0.5.
Trays and ditches are designed along the streets. The routes of drainage canals are laid as close as possible to the relief, if possible outside the building boundaries.
The cross-section of ditches and trays is designed to be rectangular, trapezoidal and parabolic, and ditches - rectangular and trapezoidal. The maximum height of ditches and ditches is limited in urban environments. It is made no more than 1.2 m (1.0 m is the maximum depth of the flow, 0.2 m is the smallest excess of the edge of the ditch or ditch above the flow).
The smallest slopes of roadway trays, ditches and drainage ditches are taken depending on the type of coating. These slopes provide the lowest non-silting speed of rainwater movement (at least 0.4 - 0.6 m/s).
In areas of the territory where the terrain slopes are greater than those at which maximum current speeds occur, special structures, fast currents, and stepped drops are designed.

Features of designing a rainwater network during reconstruction.

In the area being reconstructed, the designed rainwater network route is tied to existing underground networks and structures. This allows maximum use of the stored reservoirs and their individual elements.
The position of the network in plan and profile is determined by specific design conditions, as well as the height and layout of the territory.
If the existing collector cannot cope with the estimated costs, the drainage network is reconstructed. In this case, the design solution is chosen taking into account the reduction in the drainage area and the estimated water flow due to the installation of new collectors. Additional pipelines are laid at the same elevations as the existing network or at deeper elevations (if the existing network is not deep enough). Pipes of insufficient cross-section are partially replaced with new ones with a larger cross-section.
In sections of the existing network that are shallow, it is necessary to strengthen the strength of the drainage structure and its individual elements, and, if necessary, provide thermal protection. Continuation of the lecture on the topic: Engineering organization of populated areas.
Part 1: Vertical planning of urban areas.
Part 2:

Water is one of the most common reasons damage to earthen structures. In addition, if a large amount of water gets into a pit or excavation, its development becomes very difficult. Therefore, water drainage should, as a rule, be carried out before starting production. earthworks.

Surface water drainage

Surface water drainage can be carried out in the following ways:

1. installation of ditches on the upland side near the excavations and embankments of upland ditches that collect water flowing down the slope (Fig. 5b);
2. installation of ditches in recesses that drain water falling onto the surface and slopes of the recess (Fig. 5b);
3. arrangement of correctly laid out reserves near the embankments (Fig. 5a) and correctly arranged cavaliers near the excavation (Fig. 5b);
4. correct planning of the strip of land between the embankment and the reserve or between the excavation and the cavalier with a slope of the surface of this strip (berm) away from the structure;
5. constructing a roller of earth on the upland side when digging a trench;
6. strengthening the slopes of embankments, excavations, dams and other structures.

If excavation work needs to be carried out in a swampy area, then before starting work it is necessary to carry out a series of works to drain the area, sometimes with the whole system(a network of) drainage ditches that collect water from the swamp and drain it into the nearest river, stream, lake, etc. etc.

Groundwater drainage

Groundwater can lie at different depths.

If the groundwater is shallow and its layer is thin, it can be drained away from the structure by open ditches that collect water.

Sometimes groundwater lies deep and its layer is thick. Then they resort to installing drains.

A drainage is a narrow closed ditch filled with materials that allow water to pass through well. Pipes are laid at the bottom of these ditches to collect groundwater or large crushed stone material that conducts water well.

The purpose of drainage varies:

1. Water drainage together with an open ditch(sub-cuvette drainages); in this case, the ditch is given a minimum cross-section, and drainage is arranged under the bottom of the ditch. Drainage pipes can be wooden, plastic, steel, stone, concrete or pottery (Fig. 35). To prevent drainage from becoming clogged through the wells, the latter are covered with gratings on top.
2. Lowering groundwater levels. This decrease occurs most strongly near the drainage; As you move away from the drainage, the level rises again (Fig. 36). In order to drain a large area, it is necessary to place drains in several lines at a certain distance from each other in plan.

Each drainage must have a longitudinal slope (0.0025-0.015). It is necessary to ensure that the water from the drainage has an outlet to a low point in the area, an open ditch or another deeper drainage. Drains are installed below the soil freezing line.

Drainage ditches are dug with special narrow shovels. In the absence of such shovels, digging is done with ordinary shovels, and then the width of the ditch has to be greater, which increases the volume of work.

If groundwater appears in the pit while working, you have to resort to pumping out the groundwater (drainage). In this case, water is excavated into the pit (with tongue and groove fastening).

These two types of work are usually done simultaneously with the development of the soil itself and are not preparatory, but auxiliary work and are described below.

Procuring tools and equipment for work, storing them and organizing their repairs

Before starting work, all the necessary tool and equipment (wheelbarrows, grabs, etc.) according to the number of workers, with a reserve in case of breakdown. The tool must be suitable for the soil and type of work.

Tools, such as shovels, should be prepared with handles of different heights, and crowbars - of different weights, so that the worker can select the appropriate tool. Tools and equipment must be assigned to a specific team, unit or individual worker responsible for their safety and condition.

To store tools, you should have storage rooms at the place of work, and sheds are needed to store wheelbarrows, rakes and trolleys.

Timely repair of tools and all equipment must be ensured.

In addition to the listed preparatory work, before starting the main work, it is necessary:

• provide workers with housing and food at the place of work;
• ensure water supply;
• at the site of future work, examine the soils and accurately determine their category, the presence of groundwater, etc.;
• determine the exact scope of work;
• assign methods of work production and their organization;
• distribute workers among teams and units.

Surface water (storm and melt water) is formed from atmospheric precipitation. There are “foreign” surface waters, coming from elevated neighboring areas, and “our own”, formed directly at the construction site. To prevent “foreign” surface waters from entering the site, they are intercepted and diverted off-site. To intercept water, upland ditches or embankments are made along the boundaries of the construction site in its elevated part (Fig. U.2). To prevent rapid siltation, the longitudinal slope of drainage ditches must be at least 0.003.

To drain “their” surface waters, they give an appropriate slope when planning the site vertically and arrange a network of open or closed drainage.

Each pit and trench, which are artificial catchment basins to which water actively flows during rains and snow melting, must be protected by drainage ditches or embankments With upland side.

In cases of heavy flooding of the site with groundwater with a high horizon level, the site is drained using open or closed drainage. Indoor drainage is usually arranged V in the form of ditches up to 1.5 m deep, torn off With gentle slopes (1: 2) and longitudinal slopes necessary for water flow. Closed drainage is usually trenches with slopes towards the discharge of water, filled with drainage material (Fig. U.Z). When the device is more effective drainage At the bottom of such a trench, pipes perforated in the side surfaces are laid - ceramic, concrete, asbestos concrete, wooden. Such drains collect and drain water better, since the speed of water movement in the pipes is higher than in the drainage material. Closed drainages must be laid below soil freezing levels and have a longitudinal slope of at least 0.005.

Creation of a geodetic alignment basis. At the stage of preparing the site for construction, a geodetic alignment basis must be created for planning and elevation justification when taking the project of buildings and structures to be erected onto the site, as well as (subsequently) geodetic support at all stages of construction and after its completion. A geodetic alignment basis for determining the position of construction objects in plan is created mainly in the form of: a construction grid, longitudinal and transverse axes that determine the location of the main buildings and structures on the ground and their dimensions - for the construction of enterprises and groups of buildings and structures; red lines (or other development control lines) and building dimensions - for the construction of individual buildings. The construction grid is made in the form of square and rectangular figures, which are divided into main and additional (Fig. U.4). The length of the sides of the main grid figures is 200...400 m, additional - 20...40 m. The construction grid is usually designed on the construction master plan, less often on the topographic plan of the construction site. When designing, the location of points is determined. grids on the construction plan (topographic plan), choose the method of fixing the grid on the ground. When designing a construction grid, the following must be provided: maximum comfort to perform marking work; the main buildings and structures being erected are located inside the grid figures; the grid lines are parallel to the main axes of the buildings being constructed and are located as close to them as possible; direct linear dimensions are provided on all sides of the mesh; grid points are located V places convenient for angular measurements With visibility of adjacent points, as well as in places ensuring their safety and stability.

The breakdown of the construction grid on the ground begins with the outlining of the original direction, for which they use the geodetic grid available on the site or near it (Fig. U.5). From the coordinates of the geodetic points of the grid, the polar coordinates 5, 5r, 5z and angles Pb p 2, P3 are determined, along which the original directions of the grid are brought to the area AB And AC. Then, starting from the original directions, a construction grid is broken out across the entire site and secured at the intersections with permanent signs with the planning point (Fig. U.6). Signs are made from pipe sections filled with concrete, from concreted rail scraps, etc. The base of the sign must be located at least 1 m (1000 mm) below the soil freezing line. The red line is moved and secured in the same way.

When transferring the main axes of objects under construction to the terrain, if a construction grid is used as a planned alignment base, the method of rectangular coordinates is used. In this case, the nearby sides of the construction grid are taken as coordinate lines, and their intersection is taken as the zero reference (Fig. U.7, A). Point position ABOUT main axes X 0-Y 0 is determined as follows: if it is given that X 0 =50 and Y 0 =40 m, then the point ABOUT is located 50 m from the line X towards the line Ho and at a distance of 40 m from the line U towards U 0. If there is a red line as a planned alignment basis on the construction plan, some data must be given that determines the position of the future value: for example, a point A on the red line (Fig. U.7, b), the angle p between the main axis of the building and the red line and the distance from the point A to the point ABOUT intersections of the main axes. The main axes of the building are fixed behind its contours with the signs of the above structure.

High-altitude justification at the construction site is provided by high-altitude support points - construction benchmarks. Typically, reference points of the construction grid and red line are used as construction reference points. The elevation of each construction benchmark must be obtained from at least two benchmarks of the state geodetic network or local network.

Creation of a geodetic alignment base is the responsibility of the customer. He must at least 10 days in advance. before the start of construction and installation work, transfer it to the contractor technical documentation on the geodetic alignment base and on the points and signs of this base fixed on the construction site.

During the construction process, the construction organization must monitor the safety and stability of the geodetic alignment signs.

The removal of surface water and lowering the groundwater level are carried out to protect construction sites and foundation pits of future structures from flooding by storm and melt water.

Work on drainage of surface and groundwater includes: construction of upland and drainage ditches, embankment; drainage device; surface layout of warehouse and assembly areas.

Ditches or trays are arranged along the boundaries of the construction site on the upland side with a longitudinal slope of at least 0.002, and their sizes and types of fastenings are taken depending on the flow of storm or melt water and the maximum values ​​of non-erosive flow rates.

The ditch is installed at a distance of at least 5 m from the permanent excavation and 3 m from the temporary one. The walls and bottom of the ditch are protected with turf, stones, and fascines. Water from all drainage devices, reserves and cavaliers is diverted to low places, remote from constructed and existing structures.

In case of heavy flooding of the site with groundwater with a high horizon level, use drainage systems open and closed types.

Open drainage is used in soils with a low filtration coefficient when it is necessary to lower the groundwater level (GWL) to a depth of 0.3–0.4 m. Drainage is arranged in the form of ditches 0.5–0.7 m deep, at the bottom of which a layer of coarse-grained sand, gravel or crushed stone 10–15 cm thick.

Closed drainage is usually deep trenches with wells for system inspection and with a slope towards water discharge, filled with drained material. Sometimes pipes perforated in the side surfaces are laid at the bottom of such a trench. On top drainage ditch covered with local soil.

Drainage installation must be carried out before the construction of buildings and structures begins.

Organization of drainage and artificial lowering

Groundwater level

Excavations (pits and trenches) with a small influx of groundwater are developed using open drainage.

If there is a significant influx of groundwater and a large thickness of the water-saturated layer, the water level is artificially reduced before the start of work.

Water reduction work depends on the adopted method of mechanized excavation of pits and trenches. Accordingly, the order of work is established both for the installation of drainage and water-reducing installations, their operation, and for the development of pits and trenches. When placing a pit on the bank within the floodplain of a river, its development begins after the installation of water-reducing equipment, so that the decrease in groundwater level is ahead of the deepening of the pit by 1–1.5 m. If the pit is located directly in the riverbed, then before dewatering work it is fenced off on the water side with special dams (lintels). Drainage work consists of removing water from the fenced-off pit and then pumping out the water that filters into the pit.

In the process of draining a pit, it is important to choose the correct pumping speed of water, since very rapid drainage can cause damage to the lintels, slopes and bottom of the pit. In the first days of pumping, the intensity of the decrease in water level in pits from coarse-grained and rocky soils should not exceed 0.5–0.7 m/day, from medium-grained soils - 0.3–0.4 m/day and in pits from fine-grained soils 0. 15–0.2 m/day. In the future, water pumping can be increased to 1–1.5 m/day, but in the last 1.2–2 m of depth, water pumping should be slowed down.

In an open drainage pumping of incoming water directly from the pit or trenches is provided. It is applicable in soils that are resistant to filtration deformations (rock, gravel, etc.). With open drainage, groundwater, seeping through the slopes and the bottom of the pit, enters drainage ditches and through them into pits (sumps), from where it is pumped out. The dimensions of the pits in plan are 1×1 or 1.5×1.5 m, and the depth is from 2 to 5 m, depending on the required immersion depth of the pump’s water intake hose. Minimum dimensions The pit is prescribed to ensure continuous operation of the pump for 10 minutes. Pits in stable soils are secured wooden log house from logs (without a bottom), and in floating ones - with a sheet pile wall and a return filter is installed at the bottom. Trenches are secured in approximately the same way in unstable soils. The number of pits depends on the estimated water flow to the pit and the performance of the pumping equipment.

The influx of water to the pit (or flow rate) is calculated using the formulas for the steady-state movement of groundwater. Based on the data obtained, the type and brand of pumps and their number are specified.

Open drainage is an effective and simple method of drainage. However, it is possible that the soil at the base may loosen or liquefy and some of the soil may be carried away by filtered water.

Artificial decrease in groundwater level involves the construction of a drainage system, tube wells, wells, and the use of wellpoints located in close proximity to the future pit or trench. At the same time, the groundwater level sharply decreases, the previously water-saturated soil and now dehydrated soil is developed as soil of natural moisture.

There are the following methods of artificial water reduction: wellpoint, vacuum and electroosmotic.

Artificial water reduction methods eliminate water seepage through the slopes and the bottom of the pit, so the slopes of the excavations are preserved intact, and there is no removal of soil particles from under the foundations of nearby buildings.

The choice of water reduction method and the type of equipment used depends on the depth of the excavation pit (trench), engineering-geological and hydrogeological conditions of the site, construction time, structure design and TEP.

Artificial water reduction is carried out when the drained rocks have sufficient water permeability, characterized by filtration coefficients of more than 1–2 m/day; it cannot be used in soils with a lower filtration coefficient due to the low speeds of groundwater movement. In these cases, evacuation or electrodehumidification (electro-osmosis) is used.

Wellpoint method provides for the use of frequently located wells with tubular water intakes of small diameter for pumping water from the ground - wellpoint filters connected by a common suction manifold to a common one (for a group of wellpoints) pumping station. To artificially lower the groundwater level to a depth of 4–5 m in sandy soils, use light wellpoint units (LIU). To drain trenches up to 4.5 m wide, single-row wellpoint units are used (Fig. 2.1, A), with wider trenches - double-row (Fig. 2.1, b).

To drain pits, closed-circuit installations are used. When the hydrocarbons are reduced to a depth of more than 5 m, two- and three-tier wellpoint installations are used (Fig. 2.2).

In the case of using two-tier wellpoint installations, the first (upper) tier of wellpoints is first put into operation and, under its protection, the upper ledge of the pit is torn off, then the second (lower) tier of wellpoints is mounted and the second ledge of the pit is torn off, etc. After each subsequent tier of wellpoints is put into operation, the previous ones can be turned off and dismantled.

The use of wellpoints is also effective for reducing water in low-permeability soils, when a more permeable layer lies underneath them. In this case, wellpoints are buried in the lower layer with obligatory sprinkling.

Rice. 2.1. Water reduction with light wellpoint systems: A– one-

in-line wellpoint units; b– double-row wellpoint units;

1 – trench with fastening; 2 - hose; 3 – valve; 4 – pump unit;

5 – suction manifold; 6 – wellpoints; 7 – reduced groundwater level;

8 – water intake filter unit of the wellpoint

Rice. 2.2. Scheme of tiered water reduction of needle filters

trami: 1 , 2 – respectively, wellpoint filters of the upper and

lower tier; 3 – final decrease in depression

groundwater surface

In addition to wellpoints, the LIS also includes a water collection collector that combines the wellpoints into one water-reducing system, centrifugal pumping units and an outlet pipeline.

To lower the wellpoint into working position in difficult soils, wells are drilled into which wellpoints are lowered (at depths of up to 6–9 m).

In sand and sandy loam soils, wellpoints are immersed hydraulically, by washing the soil under the milling tip with water at a pressure of up to 0.3 MPa. After the wellpoint is immersed to the working depth, the hollow space around the pipe is partially filled with subsided soil, and partially filled with coarse sand or gravel.

The distances between wellpoints are taken depending on their arrangement, the depth of water drawdown, the type of pumping unit and hydrogeological conditions, but usually these distances are 0.75; 1.5 and sometimes 3 m.

Vacuum method Water reduction is based on the use of ejector water reduction units (EIU), which pump water from wells using water-jet ejector pumps. These installations are used to reduce groundwater level in fine-grained soils with a filtration coefficient of 0.02–1 m/day. The depth of the groundwater level depression in one tier ranges from 8 to 20 m.

EIUs consist of wellpoints with ejector water lifts, a distribution pipeline (collector) and centrifugal pumps. Ejector water receivers placed inside the wellpoints are driven by a jet of working water pumped into them by a pump under a pressure of 0.6–1.0 MPa through the manifold.

Ejector wellpoint filters are immersed hydraulically. The distance between wellpoints is determined by calculation, but on average it is 5–15 m. The choice of wellpoint equipment, as well as the type and number of pumping units, is made depending on the magnitude of the expected groundwater influx and the requirements for limiting the length of the collector served by one pump.

Electroosmotic water reduction, or electrodehumidification, is based on the phenomenon of electroosmosis. It is used in low-permeability soils with a filtration coefficient Kf of less than 0.05 m/day.

First, along the perimeter of the pit (Fig. 2.3) at a distance of 1.5 m from its edge and in increments of 0.75–1.5 m, wellpoint cathodes are immersed, with inside the contours of these wellpoints at a distance of 0.8 m from them with the same step, but in a checkerboard pattern, steel pipes (anode rods) connected to the positive pole are immersed, the wellpoints and pipes are immersed 3 m below the required water reduction level. When a direct current is passed, the water contained in the pores of the soil moves from the anode to the cathode, and the soil filtration coefficient increases by 5–25 times. Pits usually begin to be developed three days after turning on the electric drainage system, and in further work in the pit can be carried out with the system turned on.

Open (connecting to the atmosphere) water-reducing wells used for large depths of groundwater level depression, as well as

when the use of wellpoint filters is difficult due to large inflows, the need to drain large areas and tightness of the territory. For pumping water from wells, artesian turbine pumps of the ATN type are used, as well as deep well pumps submersible type.

Rice. 2.3. Scheme of electrical soil drainage:

1 – anode pipes; 2 – wellpoint cathodes;

3 – pumping unit; 4 – reduced groundwater level

The use of methods for reducing groundwater level depends on the thickness of the aquifer, the soil filtration coefficient, the parameters of the earthen structure and construction site, and the method of work.