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In some regions, groundwater is very close to the surface. So close that they threaten the integrity of buildings (their foundations) and prevent plantings from growing. All these problems are solved by the drainage of the site. In general, this event is costly both in terms of the amount of funds required and the necessary time costs. A lot of time is spent on planning. If you do everything wisely, then you need data from a hydrogeological study and a project drawn up by a specialist. But, as usual, only a few do this, most make the drainage system with their own hands.
What water is drained
Drainage of the site is a costly and time-consuming event that requires a large amount of land work. The best time for construction is the process of planning and arranging the site. Later deadlines lead to a lot of confusion, which is not everyone’s pleasure. However, if there is water on the site, you have to go for it.
There are several types of water on the site that interferes with us and needs to be diverted. They are different and require different measures.
surface water
They are formed during snowmelt and heavy rainfall, during work on the site (watering, washing paths), discharging water from the reservoir, etc. What all phenomena have in common is their one-time occurrence: surface waters appear after certain events. A more reasonable way to divert them is to install storm sewers. She copes with the task perfectly, and the cost of arrangement is much lower.
To divert surface water, mainly open channels are installed, water intake is point under storm pipes or linear along the entire roof overhang. From these receivers, water is taken by solid plastic (asbestos-cement) pipes into a sewer or dumped into a river or lake into a ravine. Sometimes let’s take it to the ground.
Groundwater
Those underground waters that have a seasonal level (higher in the spring after the flood, lower in the winter), have a feeding zone (where they come from) and outflow (where they go) are called groundwater. Usually, groundwater is present on sandy, sandy loamy soils, less often in loams with a small amount of clay.
The presence of groundwater can be determined using self-dug pits or several wells drilled with a hand drill. When drilling, a dynamic level is noted (when water appeared during drilling) and a steady level (some time after its appearance, its level stabilizes).
If we talk about the diversion of water from the building, then the drainage system is arranged if the groundwater level (GWL) is only 0,5 m below the foundation. If the groundwater level is high – above the freezing depth – then a monolithic slab foundation is recommended with water drainage measures taken. At a lower level, other options are possible, but this requires careful and multi-layer waterproofing. The need for drainage of the foundation should be assessed by specialists.
If high-standing groundwater (GWL above 2,5 meters) prevents plants from growing, site drainage is required. This is a system of channels or special drainage pipes laid in the ground at a certain level (below the GW level by 20-30 cm). The depth of laying pipes or ditches – below the GWL – so that water flows to lower places. Thus, the adjacent areas of the soil are drained.
Bleak
These underground waters are found on soils in highly located water-resistant layers, but their appearance is often the result of construction errors. Usually this is water, which, being absorbed into the soil, meets on its way layers with a low ability to absorb moisture. Most often it is clay.
If, after rain, puddles stand on the site and do not leave for a long time, this is perched water. If water accumulates in the dug ditches, this is also a perch. If a few years after the construction of a house on clay soils or loams in the basement, the walls begin to “cry” – this is also a perch. Water accumulated in rubble pockets under the foundation, in the blind area, etc.
The removal of the top water is easiest to do with the help of ditches, but it is better to prevent its appearance – to backfill the foundation not with crushed stone and sand, but with clay or native soil, carefully tamping it in layers. The main task is to exclude the presence of pockets in which water will accumulate. After such a backfill, it is required to make a blind area, which is wider than the backfill and an obligatory stroke – the removal of storm water.
If the site is sloping, consider terracing and retaining walls, with the obligatory installation of drainage ditches along the retaining wall. The most difficult thing to deal with perched water is in low areas that are lower in level than neighboring ones. Here a reasonable solution is to add earth, since there is usually nowhere to dump water. Another possible option is to drain the drain through neighboring areas or along the road to the point of a possible discharge. You have to decide on the spot, based on the existing conditions.
Not to drain
The installation of a drainage system is an expensive undertaking. If it is possible to get by with other measures, it is worth doing it. Other measures include the following:
- Storm sewer device.
- A blind area device (for heaving soils, an insulated blind area is desirable).
- In areas with a slope, the device of the upland ditch is a moat of sufficient depth, which is located on a slope higher than the house. From this ditch, water is diverted below the site, into the sewer, discharged into a ravine, river, lake, etc.
So that the edges of the ditch do not sprinkle, it can be planted with moisture-loving plants with a powerful root system. - Foundation waterproofing. To eliminate capillary suction of moisture, several layers of waterproofing material are laid on top of the finished foundation, to eliminate problems with damp walls in the basement, external waterproofing of the foundation is made (dig out to the full depth and treated with waterproofing materials). For greater reliability from the inside, the walls of the basement and / or basement floor should be treated with penetrating waterproofing of the Penetron type.
If after all these activities the situation does not suit you, it makes sense to make a drainage system.
Types of drainage
Site drainage is a complex system with many nuances and features. By structure, it can be local (local) – to solve a problem in a particular area. Most often it is the drainage of the foundation, basement and semi-basement (basement) floors. Also, water drainage systems on the site are common – to drain the entire site or a significant part of it.
By installation method
According to the installation method, the drainage system can be:
- open. Concrete or stone trays are used, ditches are dug around the site. They remain open, but can be covered with decorative grilles to protect the system from large debris. If you need a simple solution for draining surface water in your country house, these are ditches along the perimeter of the site or in the lowest zone. Their depth should be sufficient so that at maximum flow the water does not overflow. So that the unreinforced walls of the drainage ditches do not collapse, they are made at an angle of 30 °,
The specific type of site drainage is selected based on site conditions. On clays and loams, an extensive gravel-sandy zone is needed, into which water will drain from the surrounding soil areas. On sands and sandy loams, there is no need for such a pillow – the soils themselves drain water well, but only a specialist in the results of geological research can specifically say.
By type of implementation
There are several types (schemes) of drainage devices on the site:
- Annular. Pipes are closed in a ring around the object. Usually they are the house. It is rarely used, since it is necessary to deeply deepen the drainage pipes – the pipe itself must be laid 20-30 cm below the groundwater level. This is expensive and difficult to implement.
- Wall drainage – to drain water from the walls. It is located at a distance of 1,6-2,4 m from the walls (in no case close). In this case, the drain is located 5-10 cm below the basement floor. If the floor is poured over a large crushed stone cushion, the drain is laid 5-10 cm below this level.
The right solution for drainage from the foundation – storm sewer system and drainage - Reservoir drainage. It is used in the construction of slab foundations in difficult situations. It is necessary for the removal of perched water, it is usually used together with wall water drainage. Reservoir drainage is layers poured into the pit – sand, crushed stone, waterproofing (as they are poured from bottom to top). Reinforcement is already laid on top of this pillow and the foundation slab is poured.
- Systematic and radiation. Used to dry areas. They differ in the way the drains are located relative to the central pipe. With a ray scheme, the system is similar to a Christmas tree (already existing plants can be taken into account), with a systematic scheme, drains are laid with a calculated step (usually arranged when planning a site).
Radiation drainage of the site
When draining the site, the central drain or collector is made of pipes of a larger diameter (130-150 mm versus 90-100 mm for conventional drains) – the volume of water here is usually larger. The specific type of drainage system is selected based on the tasks that need to be solved. Sometimes you have to use combinations of different schemes.
Site drainage – device
The drainage system consists of a network of interconnected pipes that are located along the perimeter (or area) of the territory protected from water. Drainage wells are placed at intersections or turns. They are necessary to monitor the condition of the system and clean silted pipes. From all drained areas, water enters the collector well, where it accumulates to a certain level. Then it can be dumped or used for irrigation and other technical needs. Discharge can go by gravity (if there is a place), and submersible drainage pumps are used for irrigation and other technical needs.
Drainage pipes and wells
Pipes for drainage are used special – with holes ranging in size from 1,5 to 5 mm. Water flows through them from the surrounding soil. Holes are located over the entire surface of the pipe. They come in different diameters, for private houses and plots the most used size is 100 mm, to divert large volumes of water, you can take a cross section of up to 150 mm.
They are now made mainly from polymers – HDPE, LDPE (low and high pressure polyethylene) and PVC (polyvinyl chloride). They are used for laying to a depth of 2 meters. There are also two and three-layer combined ones, which are made from combinations of these materials, they are buried to depths of up to 5 meters.
Pipes for drainage are selected taking into account the depth of occurrence. It is required to select according to the ring stiffness. It is indicated by the Latin letters SN and the numbers following them, displaying the ring stiffness (resistance to loads). For laying to a depth of up to 4 meters, the rigidity should be SN4, up to 6 meters – SN6.
The surface of the drain pipe is wrapped with filter materials. Filter layers can be from one to three. The number of layers is selected based on the composition of the soil – the smaller the particles, the more layers are required. For example, on clays and loams, pipes with three filter layers are used.
At the turning points and in places where several pipes are connected, revision wells are installed. They are needed for easier cleaning in case of blockage, as well as for the possibility of monitoring the condition of the pipes. As a rule, all pipes converge into one collector well, from where water is either sent by gravity to the discharge point, or pumped out forcibly.
There are special wells – for drainage systems, but it is quite possible to bury a concrete ring with a bottom and a lid of small diameter (70-80 cm) and bring pipes into it. Depending on the depth of laying the drainage rings, several rings may be required. Another option is to make a large manhole and drainage pipe, but in this case you will have to come up with something with the bottom. For example, you can fill the bottom with concrete.
Incline
In order for the collected water to drain on its own, it is necessary to observe a certain slope towards the direction of movement. The minimum slope is 0,002 – 2 mm per meter, the main one is 0,005 (5 mm per 1 meter of pipe). If the drainage is shallow, the slope of the pipe can increase to 1-3 cm per 1 meter, but it should be done as little as possible. At a flow velocity of more than 1 m/s, fine soil particles are “sucked in”, which contributes to a more rapid silting of the system.
The slope is changed (in relation to the “duty” of 5 mm per 1 meter) in two cases:
- If it is necessary to divert a larger amount of water per unit of time without increasing the diameter of the drain. In this case, the slope is increased.
- If you want to get away from the backwater (when the pipe laid with a given slope is below the GWL, i.e. water simply will not drain). In this case, the slope is reduced.
In the practical design of the system, questions may arise about how to provide a given slope. This can be done using a laser level (level), using a water level (not very convenient) or a flat board paired with a conventional building bubble level. Having leveled the bottom of the trench, a board is laid, a level is placed on it. Moving it along the board, they check and correct the slope of the bottom of the trench in a certain area.
Drain installation technology
Pre-dig trenches of a given width and depth. The bottom of the trench is leveled and compacted. Do not forget about the slope, but at this stage it makes no sense to withstand it exactly. Next, about 100 mm of coarse-grained washed river sand is poured, it is also rammed (spilled, then rammed), leveled. Sand is desirable fraction Dsr 1.5-2.5 mm.
Geotextiles with a density of not more than 200 g / m2 are laid on the sand. The edges of the canvas are lined along the walls of the trench. A layer of granite rubble is poured on top. The size of the crushed stone fraction is selected depending on the size of the holes in the drainage pipe. For the smallest holes, crushed stone with a grain of 6-8 mm is required, for the rest – larger. The thickness of the crushed stone layer is 150-250 mm, depending on the type of soil. On clays and loams, 250 mm is required, on soils that drain water better – sands and sandy loams – about 150 mm.
Crushed stone is rammed, leveling into a given slope. A drainage pipe is laid on the compacted gravel. Further, the pipe is sprinkled with gravel in layers, each layer is rammed. There should be at least 100 mm of gravel on top of the drain. After that, the ends of the geotextile are wrapped, their overlap should be 15-20 cm. A layer of sand with grains of 0,5-1 mm is poured on top. The thickness of the sand layer is 100-300 mm, also depending on the water permeability of the soil: the worse the water is drained, the thicker the sand layer. The “native” soil is laid on the compacted sand, and then plants can be planted.
A little about backfill materials
Crushed stone should be granite or other hard without calcareous rocks. Dolomite (lime) or marble are not suitable. Testing the existing one is simple: drip vinegar on it. If there is a reaction, it does not fit.
Once again, we pay attention: the crushed stone is laid washed – so that the new pipes do not immediately silt up.
Sand is required coarse-grained. Grain size from 0,5 mm to 1 mm. The sand must also be clean. Some part of the sand is poured with clean water, shaken up, they wait until the sand settles and evaluate the purity of the water. If the water is cloudy, with a lot of suspended particles, the sand needs to be washed.
Some nuances of construction
When draining the site, the central drain or collector is made of pipes of a larger diameter (130-150 mm versus 90-100 mm for conventional drains) – the volume of water here is usually larger.
The drainage device on the site starts from the lowest point and moves gradually up. First, a collector well is installed. With a high level of groundwater or with a perch that has not yet descended, water may accumulate in the ditches. This muddy slurry will roll down the well, clogging it. In addition, the presence of water in the ditch greatly interferes with work: drains must be laid in dry ditches. To drain them along the ditch, side pits (sumps) of greater depth are made. Crushed stone is poured at the bottom. The accumulated water is pumped out of these pits.