Filter design impacton drainpipe water intake capacity

Abstract

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.