Field Tests and Ecological Assessment of an Opencast Mine-Dewatering using a Horizontal Directional Drilled Well

摘要

Nowadays vertical filter wells are the main element of dewatering in opencast mines in Germany. An alternative - e.g. suitable in cases of limited water levels, reduced thickness of aquifers, or basin structures - are horizontal directional drilled wells (HDD wells). By the use of HDD wells with considerably longer filter screens in combination with free discharge of the drained water out of the pit slope, economies in costs, materials, and land use are anticipated.With respect to the dewatering effects using HDD wells, some questions remained unanswered so far. Therefore, field tests with a 200 m long HDD well combined with a vertical well interconnecting two hydraulically separated aquifers were realized within the central German lignite district in the south of Leipzig. Based on a structural model, details of the horizontal directional drilling as well as an appropriate position of the HDD well were investigated. For this purpose the information of 250 available exploratory drillings was evaluated. A numerical groundwater flow model was used to simulate the drainage using the software PCGEOFIM.Besides technical and economic issues an environmental assessment was made. On the basis of the information gathered in the field test, HDD wells and vertical wells were compared theoretically. Therefore a calculation model was set up to investigate the conventional dewatering method using vertical wells in comparison with HDD wells under environmental issues.