Under unfavorable ground conditions, when the groundwater level is too high, or when there is a threat of flooding the construction site with surface groundwater, there is a need to organize water drainage and drainage.
For artificial lowering of the groundwater level in construction use the following methods:
- open drainage;
- needlepoint drainage;
- electroosmotic drainage;
- vacuum drainage;
- open water wells.
Open drainage is used in clay and sandy soils with good water permeability. This method is the most simple and economical, but at the same time leads to the dilution of the soil, the loss of part of the soil filtering water, resulting in a decrease in the natural strength of the base.
The main and most common method of artificial water reduction is an acupuncture filter. It is based on the use of needle filter units consisting of steel pipes with a filter element at the bottom (needle filter), a catchment collector on the ground surface and a vortex pump. The needle filters are immersed in the ground in one or two rows along the perimeter of the pit or trench, depending on the type of soil, the distance between the needles can be from 0.75 to 1.5 meters. With the help of needle filtering, it is possible to lower the level of groundwater by 4 – 5, and with a two-tiered arrangement of points, by 7 – 9 meters.
The method of drainage of soils using the phenomenon of electroosmosis is used in low-permeable soils with a filtration coefficient of less than 0.05 meters per day with a pit width up to 40 meters. The method of electroosmosis is based on the ability of water to move in the pores of the soil under the influence of direct electric current from the anode to the cathode. At the same time, along with needle filters, steel electrodes are immersed in the ground at a distance of 0.5 – 1 m from them in the direction of the pit. The needle filters are connected to the negative pole (cathode), the electrodes to the positive (anode). The electrodes are placed relative to each other in a staggered manner with a step in the range of 0.75 – 1.5 meters; under the influence of an electric current, the water contained in the pores of the soil moves towards the needle filters, and the filtration coefficient increases 5-25 times.
The vacuum method of water lowering is used in soils with a filtration coefficient of 0.01 – 3 meters per day. At the same time installations of vacuum water lowering with the easy iglofiltra equipped with air tubes are used. When the unit is working, a vacuum is created and groundwater is sucked in, after which the excess water is pumped out and drained by the pump. With this method, the reduction of groundwater reaches 20 – 22 meters.
Open water wells equipped with pumps are used in cases where the groundwater level needs to be lowered to a greater depth and then when the use of needle-filter units is difficult due to the large influx of water, the need to reduce large areas and constrained territory. The main working element of the system is a filter column, consisting of a filter, a settling tank, with the above-filter pipes inside which a pump is placed, usually an artesian one.