Drainage systems in dacha and house areas are often designed “by eye”. This is not correct and often leads to flooding and other problems. In order to make a drainage system correctly, it is necessary to follow the requirements of regulatory documents.
The basic document is SP 104.13330.2012 - this is an updated version of SNiP 2.06.15-85 “Engineering protection of the territory from flooding and flooding.” Unfortunately, it contains little useful information regarding drainage systems used to protect low-rise buildings.
There is another document - “Guidelines for the design of drainage of buildings and structures” from the Moskomarkhitektura, published in 2000 (hereinafter referred to as the “Manual”). It contains a lot of useful information, but like any other piece of legislation, the guidance is difficult to read and redundant in places. Therefore, the site brings to your attention a summary that outlines all the most important things from this document.
When is it permissible to install an open drainage system?
According to SNIP, an open drainage system of horizontal ditches can be used to drain areas with one- and two-story low-density buildings, as well as to protect roads and other communications from flooding (clause 5.25). In this case, to strengthen the slopes of the canals, concrete or reinforced concrete slabs or rock fill should be used.
Obviously, this point relates to the general drainage systems of settlements or neighborhoods. In relation to a specific private house on its own land plot, the creation of an open drainage system cannot be considered appropriate, since a ditch on the site takes up space and poses a potential danger.
What materials can be used as a filter and filter mat in closed drainage systems?
The following can be used as a filter and filter mat in drainage systems:
- sand and gravel mixture;
- slag;
- expanded clay;
- polymer materials;
- Other materials.
What pipes can be used to create drainage systems?
According to SNIP, to create drainage systems it is allowed to use:
- ceramic pipes;
- polymer pipes;
- concrete, asbestos-cement, reinforced concrete pipes and pipe filters made of porous cement can be used in soils and water that are non-aggressive towards concrete;
How to determine the maximum depth of pipes in closed drainage systems?
The depth of pipes in closed drainage systems depends on their material and diameter. Data on the maximum depth of pipe installation are presented in the table.
How to determine the depth of installation of pipe filters made of porous concrete?
The maximum depth of installation of pipe filters made of porous concrete is determined in accordance with VSN 13-77 “Drainage pipes made of large-porous filter concrete on dense aggregates.”
How to determine the size of the hole in drainage pipes and the distance between them?
The size of the holes in the drainage pipes and the distance between them is determined by calculation.
How to determine the thickness of the filter around drainage system pipes?
The filter around the pipes of the drainage system should be in the form of sand and gravel coating or wraps or polymeric water-permeable materials. The thickness of the filter and the composition of the coating are determined by calculation in accordance with the requirements of SNiP 2.06.14-85. “PROTECTION OF MINING WORKS FROM GROUND AND SURFACE WATER.”
Is it possible to discharge drainage water into a storm drain?
SNiP allows the discharge of drainage water into storm sewers, provided that the storm sewer is designed for such a load. In this case, back-up of the drainage system at the points of discharge into the storm sewer is not allowed.
How to determine the maximum distance between inspection wells of the drainage system?
The maximum distance between drainage system wells in straight sections is 50 meters. In addition, wells should be located at turning points, changing angles and intersections of drainage pipes.
What should a drainage system inspection well be made of?
According to SNiP, inspection wells must be prefabricated from reinforced concrete rings. They must be equipped with settling tanks with a reinforced concrete bottom. Sump depth - at least 50 cm
What data is needed to create a drainage system project?
To design a drainage system you need:
- technical report on the hydrogeological conditions of construction (in common parlance “hydrogeology”);
- site plan with existing and planned buildings and structures. The scale of the plan is not less than 1:500;
- plan with floor marks in basements and subfloors of buildings;
- layouts, plans and sections of the foundations of all buildings located on the territory;
- plans and profile sections of underground communications;
What should a hydrogeological report include?
The hydrogeological report consists of several sections:
The section “Characteristics of groundwater” includes the following information:
- groundwater recharge sources;
- reasons for the formation of groundwater;
- groundwater regime;
- mark of the calculated groundwater level;
- mark of the established groundwater level;
- height of the capillary soil moisture zone (if dampness in the basement is unacceptable);
- results of chemical analysis and conclusion about the aggressiveness of groundwater in relation to building structures.
The geological and lithological section includes general information about the land plot.
Soil characteristics include:
- geological sections and soil columns from boreholes;
- bearing capacity of soils;
- granulometric composition of sandy soils;
- filtration coefficient of sandy and sandy loam soils;
- coefficients of fluid loss and porosity;
- angles of natural repose of soils.
Is foundation waterproofing necessary if there is a drainage system?
The Moskomproekt “Manual” clearly requires the use of coating or painting waterproofing of vertical wall surfaces in contact with the ground - regardless of the presence of a drainage system.
Are there other ways to protect buildings from flooding and areas of soil flooding (besides creating drainage systems)?
Such methods exist. The Moscoproject manual for the design of drainage systems also recommends:
- soil compaction during the construction of pits and trenches;
- the use of closed outlets of drainage systems that collect water from the roofs of buildings;
- the use of open drainage trays with open outlets of drainage systems. The size of the trays is not less than 15*15 cm, the longitudinal slope is not less than 1%;
- installation of blind areas around the perimeter of buildings. The width of the blind area is at least 1 m, the slope away from the building is at least 2%;
- sealing of all openings with utility system connections located in external walls and foundations. Simply put, if you lead a sewer pipe through a foundation or wall, the holes must be sealed tightly;
- creation of a surface drainage system from the territory.
The construction of a drainage system, an integral part of any private house, must be based on the requirements of SNiP: drainage that meets all the rules will be able to fully prevent the negative impact of precipitation and groundwater on buildings and plantings on the site, because this is precisely its obligation.
We will talk about these rules, as well as the features of designing a drainage system, in this article.
Drainage system design
What should the project contain?
The start of drainage installation should be preceded by the development of a system design. The drainage design is created based on engineering hydrological studies of the site. Its purpose is to determine and describe the fundamental technical characteristics of the drainage system.
Typically, the project contains the following data:
- schematic representation of the laying of drainage pipes (deep and surface systems);
- design parameters of drains - cross-section, slope, assembly of the wellhead part, depth of installation in the ground and distance relative to each other;
- standard sizes of drainage system components (drains, wells, connecting elements, etc.);
- list of building materials required for installation of the structure.
The project must take into account the following factors:
- landscape of the site;
- average annual precipitation volume;
- composition and characteristics of the soil;
- ground water level;
- location of nearby natural reservoirs, etc.
What should the estimate include?
Before constructing a drainage system, a local estimate for drainage installation is drawn up, which consists of the cost of the operations listed below:
- dismantling of reinforced concrete foundations;
- manually creating trenches 2 m deep in the soil, installing fasteners across the entire width and laying a waterproofing layer of polymer film;
- installation of transverse drainage with double-sided outlet;
- laying a sewer pipeline from polyethylene pipes;
- backfilling the base for crushed stone pipelines;
- installation of drainage communications, strengthening of underlying layers and concrete layers (reinforcement);
- dismantling of existing asphalt concrete pavements;
- creation of new asphalt concrete pavements;
- installation of bridges, passages, decking, etc. made of wood;
- soil preparation for crops (filling a layer of soil up to 20 cm thick);
- manual sowing of various lawns and other plantings.
To install a drainage system, you will need the following materials:
- crushed stone;
- sand;
- corrugated drainage pipes, wrapped in geotextile;
- geotextiles (needle-punched non-woven fabric used to create an additional filter that may be required depending on the characteristics of the soil at the site);
- inspection wells.
Construction of drainage
Rules for arranging drainage
You can protect buildings and plantings from excess moisture by knowing the rules for drainage:
- A closed drainage system involves creating a trench in the ground, the depth of which is 70-150 cm and the width is 25-40 cm. A slope directed towards an artificial or natural water intake must be provided. The slope following which drainage systems are installed is described by SNiP as follows:
- the slope value is 2 cm per 1 linear m if the soil is clayey;
- 3 cm per 1 linear m if the soil is sandy.
Option of a drainage system with a slope angle of 2 cm per 1 m (i=0.02)
- The bottom of the resulting depression is covered with a cushion of crushed stone. Drains are laid on it, then everything is covered again with crushed stone. Next, the system is backfilled with soil.
- Wastewater flows through drainage pipes, collects in a collector and ultimately ends up in a receiving water body (river, ravine, pond, etc.).
- Control over the operation of the drainage system is carried out through inspection wells built from reinforced concrete or polymer rings.
Pro tip: If the drainage system is installed correctly, the groundwater level does not rise above the permissible point, but, on the contrary, begins to decline. This leads to increased soil fertility on the site. If the drainage system is not built, the soil may become oversaturated with moisture, which has a negative impact on buildings and crops.
The construction of the drainage system must be made from high-quality, durable materials. Their quality requirements are regulated by the following state standards:
- GOST 8411-74. Ceramic drainage pipes. Technical conditions;
- GOST 1839-80. Asbestos-cement pipes and couplings for non-pressure pipelines. Technical conditions.
Methodology for constructing a drainage system
Measures for installing a drainage system consist of several stages:
- A trench is dug about 70 cm deep and about 50 cm wide. It should be located on a slope, above the house, to collect melted snow and precipitation from the site. Water is discharged outside the territory through drainage pipes.
- The bottom of the trench is first lined with gravel and it is thoroughly compacted.
- Drains are placed on the gravel bed - perforated corrugated pipes with a diameter of 100 mm. In this case, the slope is maintained (2-3 cm per linear meter), and the pipes are wrapped in geotextile - it prevents large particles of soil from getting into the system.
- The drainage is covered with a layer of material that allows water to pass through well, for example, expanded clay.
- Backfilling with soil is carried out.
As a result, a drainage system is formed on the site, which effectively collects precipitation and meltwater, which otherwise would simply flow down the slope.
For any construction process, it is very important to comply with the rules and established standards. According to the requirements of SNiP, drainage must be located at a certain distance from the building, and its device must meet all technical standards.
What is SNiP?
SNiP is an abbreviation derived from “Building Norms and Rules”. According to these codes, the requirements of various organizations for the implementation of sewerage, drainage, various buildings and other engineering structures are determined. SNiP takes into account ergonomic, economic, architectural, and technical characteristics that must be met.
Why comply with SNiP if sewerage, drainage or any other communication works like this:
- Any construction must be legalized, be it the construction of an extension near the house or the installation of a sewer pipeline. If you did not comply with the standards stated in the regulatory document, then the project will not be legal. Government organizations can force you to rebuild the pipeline or even fine you;
- SNiP not only helps to build drainage systems correctly, but also contributes to certain savings. The document identifies many ready-made solutions for drainage design that are least expensive for the owner;
- Communication carried out according to certain standards is more effective and durable. It is less susceptible to the negative effects of groundwater, seal failure or other factors.
What should be in the project
Before starting any construction, it is necessary to develop a drawing. According to SNiP requirements, the foundation drainage project must include:
The resulting diagram will help to calculate the materials used, develop an estimate and approve the project in certain government agencies. In addition, according to SNiP, wall drainage of the foundation also takes into account the general slope of the site, the amount of average annual precipitation, the level of freezing of the earth and groundwater.
The next step is to install drainage according to the diagram. Regardless of whether a closed or open drainage system is used, the following operations must be performed before installing the drain:
Geometric design
Installation of the drainage system is also carried out according to certain rules. The design of the system is controlled not only by SNiP, but also by GOST 1839-80. What is stated in the standards:
When installing drainage, the location of other communications must also be taken into account. With an allowable pipe height of 50 mm, the distance between the underground electrical network wire (if any) or the sewer system must be about 150 mm.
Drainage of groundwater, including flood water, from buildings and soil on a site is one of the most common hydrogeological tasks. However, before proceeding with its solution, it is necessary to determine the required sewerage capacity, and this will require drainage calculations. How to carry it out, what factors are taken into account, and what types of groundwater drainage systems there are - later in the article.
Attention! It should be taken into account that, depending on the specific conditions, when laying a ring drainage, the distance between the wall of the trench in its upper part and the wall/foundation of the house must be at least 3 m. The filler (gravel and sand) must be poured to such a depth as to prevent swelling of the soil when water freezes around the foundation. We should not forget about the mandatory organization of a concrete blind area under the walls, extending at a distance of at least 1 m of the building.
Methods for organizing drainage
It could be:
- simple backfilling of the trench with sand and gravel
- installation of drainage trays
- installation of drainage pipes
- laying drainage mats
Sand and gravel backfill is attractive in its simplicity; it is enough to dig a trench and add filler in a layer of 15-40 cm. As a rule, the rest of the volume is filled from above with previously excavated soil.
But these quickly enough (within 2-3, maximum 5 years) lose their effectiveness as a result of silting. Filling the space between the aggregate grains prevents water from being directed into the drain.
Concrete or polymer concrete trays can be laid in the trench, also on a gravel-sand base, which are covered on top, for example, with cast iron gratings. This method is used, as a rule, near garden paths, vehicle entrances and similar objects.
The most common method now is to lay a drain - a special smooth-walled or corrugated pipe with perforation. The advantage of this method is that with proper organization, especially with the use of geotextiles (for wrapping pipes), it ensures long and reliable operation of the system.
Drainage mats are a three-layer material made from a combination of polymers, which has a high ability to drain water even under high soil pressure.
The mats are laid either in ordinary trays or trenches, or directly on the soil surface, which is used in large and excessively wet areas. In addition to their high drainage capacity, the mats also create a frost-protective layer that prevents soil heaving.
All these methods are applicable both for organizing the drainage of groundwater from the foundation of a building, and for drainage of the territory of the land plot itself.
Any serious construction work requires preliminary drawing up of a plan and performing calculations. The importance of design is especially noticeable when arranging a drainage structure on a site. Only compliance with all the nuances when drawing up the scheme and correct calculation of drainage will allow you to achieve maximum efficiency of the drainage system.
- protection of buildings and homestead areas from flooding by rain and melt water;
- improving the drainage of surface water flowing from waterlogged areas and hard surfaces;
- reduction of groundwater levels under construction sites and fertile areas;
- interception of pressure waters that come from the aquifer.
Important! Drainage of the territory allows you to protect a residential building and outbuildings from premature destruction and optimize soil moisture for the proper growth of garden crops.
Site drainage – a set of measures to protect the territory from waterlogging
What to consider when designing drainage
Design work, which includes the development of a scheme and calculation of site drainage, is carried out taking into account the condition of the soil and climatic conditions in the area.
Classification of soils by degree of moisture
Each soil has a certain percentage of moisture content, the value of which depends on the throughput of the upper layers of the soil and the depth of the aquifers. In this regard, three categories are distinguished:
- Dry. Due to the good water permeability of the upper soil layers, stable surface runoff is ensured. Groundwater is at a sufficient depth and does not have much effect on the level of humidity.
- Raw. The upper layers have low permeability, so water slowly leaves the surface. At the same time, groundwater does not moisten the upper layer of soil. Such soils have signs of surface waterlogging, which are especially evident in the spring and autumn periods.
- Wet. Taking into account the low permeability of the soil and the close location of the aquifer, water in such an area can remain on the surface for more than 20 days. Wet places include peat and gleyed soils, as well as salt marshes.
For your information. Groundwater does not have a great influence on the degree of moisture in the upper layers of soil if its level in the pre-frost period is below the freezing depth by 1 m for sand and 2 m for clay.
Types of water supply of the site
Another indicator for correctly calculating the drainage of a site is the source of water supply. That is, the designer needs to find out how the soil is saturated with water.
- Atmospheric nutrition - showers and melt water. It is a source of waterlogging in areas with a low slope, where clayey rock predominates.
- Soil nutrition is the capillary rise of moisture from the lower soil layers.
- Ground-pressure recharge is the influx of pressurized water from the nearest aquifer.
- Heaving nutrition is the thawing in spring of ice crystals that accumulated in the ground during frosts.
Heaving soil is especially dangerous for construction sites
Drainage and drainage scheme
Taking into account the above characteristics, the type of drainage system is selected, which can be surface, vertical and deep.
Surface drainage performs the function of removing rain and melt water from the surface of the site. Designing and installing such a system is not difficult. Since the drains are located on the surface, there is no need to calculate the drainage depth, and accordingly, the volume of excavation work is insignificant.
Vertical drainage is a system of drainage wells located in places of greatest accumulation of moisture. The collected water is discharged either into the lower layers of the soil or pumped out using pumping equipment.
The deep system is the most effective because it allows you to protect the territory from almost all sources of water supply. It is a network of drainage pipes that are located at a certain depth. Such drainage is often used to protect foundations and basements, as well as garden areas from soil and ground-pressure feed.
Typical scheme of a drainage system: B – inspection outlets; K – inspection wells; PC – receiving well
Calculation of basic drainage parameters
Having designed the circuit, it is necessary to calculate the main parameters, such as:
- pipe diameter;
- geotextile density;
- trench depth;
- drain slope;
- distance between inspection wells.
Pipe diameter
To accurately calculate the diameter of the drainage pipe, you should know the required drainage intensity. In practice, pipes Ø100-110 mm are most often used, which have a throughput capacity of 7 l/s. This is quite enough to cope with large rainfalls and high water.
Note. The larger the diameter of the drain, the higher the filtration area. Therefore, when calculating wall and reservoir drainage, preference is often given to pipes Ø165 mm.
Drainage pipes of different diameters
Geotextile density
Geotextile fabric acts as a filter that protects the drain from clogging. The main indicator of this material is density. Experts pay special attention to calculating the density of geotextiles for drainage. If this characteristic is low, the fabric may tear during installation. On the other hand, excessive density reduces the moisture filtration coefficient. For drainage work, the optimal value is considered to be 100-150 g/m².
Geotextile fabric is an important element of drainage
Trench depth
The depth of installation of drainage pipes is influenced by two factors - the depth of soil freezing and the depth of the foundation (for wall drainage).
If the drain freezes in winter, then when the snow melts it will not be able to remove excess moisture, and the efficiency of the system will tend to zero. To prevent this, the trench must be developed taking into account the climatic characteristics of a particular area.
Calculating the depth of wall drainage is very simple: add 30 cm to the lowest point of the foundation. This will be enough to intercept groundwater during the rainy season or during a flood.
Drain slope
The correct slope of drainage pipes is of great importance for the functionality of the system. The absence of a slope will lead to stagnation of water, and too large an angle will contribute to the appearance of deposits in the internal cavity of the pipeline.
Important. The optimal indicator is 1%. That is, on 1 m of pipe the slope should be 1 cm.
The depth of the catchment area is calculated as follows. First, the distance from the top point of the drainage to the receiving well is measured, then the resulting sum is divided by 100. For example, the length of the drainage pipeline is 30 m, then the catch basin should be located 30 cm below the top point of the system.
Distance between inspection wells
The location of inspection wells is standardized by SNiP. According to the approved rules, points for maintenance and cleaning of drainage must be located at all turns of the pipeline. For straight sections that are long, wells are installed every 35 m.
Note. If the pipeline has the same diameter and is devoid of side branches, then the distance between inspection wells can be increased to 50 m.
Inspection wells perform the function of monitoring the performance of drainage systems
This article provides general data for calculating drainage. However, it should be borne in mind that any drainage system is unique in its own way. Therefore, in order for the drainage system on the site to work as efficiently as possible, design and installation issues must be resolved by specialists.
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