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Qualitative assessment of soil permeability is important for designing drainage systems and waterworks. According to the research results, soil permeability factor depends on sample preparation, test method and conditions. The article summarizes the results of analyzing the factors that influence the permeability of sandy soils: filtration conditions (steady-state and non-steady-state), sample area, compaction method, and sample height. Water permeability of sand in field conditions was determined by filling a pit with water at a constant head and a stable flow rate. The soil surveyed was medium-grained sand of medium density located above the groundwater table. Permeability testing in laboratory conditions was carried out using filtration tubes with the area of 20 and 85 cm2. The height of the soil samples was 50 and 100 mm. The laboratory test results showed that the sand permeability factor greatly depends on the compaction method: layer-by-layer compaction, vibration compaction. Different permeability factor values for the surveyed soil were caused by non-uniform vertical compaction of the sample. With the standard test method, the deviation of laboratory test results from the field test results reached 16 to 28%. When using sand compaction by tamping, the results closest to the actual permeability can be achieved by selecting an optimum weight drop height and reducing the sample height. Meanwhile, filtration conditions and sample area have a negligible effect on sand permeability. The article demonstrates that selecting an optimal compaction method ensures the error of permeability factor determination in laboratory conditions within 5%.

The city of Arkhangelsk is located on a marshy plain, where the groundwater level used to coincide with the surface. The area preparation for construction consisted in filling a layer of sand over peat. Hence, the following characteristic geotechnical conditions of the newly developed areas: high groundwater level and long-term settlement of peat under sand embankment. That is why subsurface structures are protected by a drainage, and drains are installed over pile foundations. One problem developing in the course of drain operation and requiring expensive re-installation activities is clogging of drain filters with fine organic and clay particles carried over by groundwater flow. The article presents the results of a survey of a building erected more than 30 years ago, which suffered from groundwater table rising due to the reduction of drain system's water intake capacity. Clogging of crushed stone cover above the drainpipe resulted in the reduction of the permeability factor. Laboratory surveys were conducted to estimate the reliability of drains with the pipes wrapped in geotextile. Drains with a layer of geotextile surrounding the stone filtering cover were also investigated. To simulate clogging, humus and clay particles were added to the water running through the filtering tube. It turned out that the second geotextile arrangement – around the stone cover with sand backfillingwas the most effective.