Entwicklung eines Bemessungsleitfadens für die Infiltration von Grundwasser mithilfe der Düsensauginfiltration

Koers, Henrik; Ziegler, Martin (Thesis advisor); Forkel, Christian (Thesis advisor); Treskatis, Christoph (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023

Abstract

Jet suction infiltration wells and systems have been used for more than a decade as an alternative method for infiltration of water into an aquifer. Infiltration systems are a component of groundwater management systems. Thereby, in addition to the extraction and potential treatment of contaminants, they represent one of the discharge methods available with any given man-made groundwater intervention. In addition to infiltration, groundwater from dewatering activities can be discharged into drainage ditches or sewage systems. If discharge into these systems is not permitted by the authorities or not wanted for financial or ecological reasons, the extracted water can only be re-infiltrated in some manner. Conventional infiltration methods such as seepage basins, infiltration shafts and wells as well as jet suction infiltration wells are all available for this purpose. Infiltration wells represent the method that comes closest to jet suction infiltration wells. In comparison, jet suction infiltration wells are installed with small drilling and filter diameters. Furthermore, they are only partially installed with slotted filter pipes in the aquifer. Infiltration wells are mostly installed over the full aquifer height with slotted filter pipes. The basics for determining the infiltration behaviour of jet suction infiltration wells are, on the one hand, the dynamics of pipeline flow, which determines flow behaviours in the supply line and further on into the nozzle inside the filter pipe. Here the principles of energy conservation and of the continuity equation describe the flow in terms of its velocity and pressure. On the other hand, the flow processes in the aquifer can be described analytically or numerically using Darcy's law. In the close vicinity of the infiltration well, the flow dynamics will not correspond fully with laminar conditions anymore. In practice, it has been shown that relatively small but widespread-increases in the height of the groundwater surface can be achieved with jet suction infiltration wells. The main reason for this is the merely partial infiltration of these wells. The aim is to infiltrate only into the most permeable or most efficient sections of the aquifer. The most permeable layers are detected while drilling a well with simultaneous testing of the aquifer response during the process of direct flush drilling. The depth and length of the slotted filter section will then be defined depending on the results of the aquifer response test. If the slotted filter section is only connected to the most permeable sections of the aquifer, this has advantages in terms of the infiltration rate which can theoretically be achieved. In the most permeable sections, extensive boundary conditions for the maximum infiltration rate and the three-dimensional pressure field in the infiltration area will prevail, due to the higher permeabilities there. The hydrogeological conditions are tested after the installation of a jet suction infiltration well in the form of an infiltration step test. By means of the testing, the practical maximum infiltration rate and the permeability in the infiltration layer can be tested and calculated. During well development before the infiltration step test and ongoing regeneration during the operating period, the aim is to bring the well into its needed condition for an optimal individual performance. In addition to the individual capacities, the group effect of infiltration wells and their possible vicinity to drawdown wells must be considered whilst designing a groundwater management system. From the designing perspective, this can be solved in simple cases with analytical multi-well methods, but in all other cases by groundwater modelling methods. Outside the close vicinity of the infiltration well, the flow behaviour of jet suction infiltration wells corresponds to the known laws. Until now, there has been a lack of knowledge regarding the pressure field and flow behaviour in the immediate vicinity of the slotted filter sections. In particular, the influence of the nozzle was unknown for a long time. Small and large-scale laboratory and field investigations were carried out to clarify this. In addition to the use of different filter materials, variations with different hydrogeological conditions, e.g. external groundwater flows, and infiltration techniques were carried out. The initial influence of the filter materials, slotted filter pipes and fillings was classified as very low compared to the influence of the permeability of the aquifer. External groundwater flows also had no direct influence on the flow conditions in the close vicinity of the well. Whilst using different infiltration techniques, their influence on the nearby well area became clear. Different pressure fields were found when comparing to closed systems without and with use of a nozzle. Further tests were carried out in which, in the case of infiltration without nozzle, a different change in the relative piezometer heights in the filter was detected across the length of the filter section. This caused a non-constant outflow from the filter into the aquifer. However, a constant outflow from the filter is optimal for the design conditions. In order to generate this, a new nozzle type, the so-called nozzle-register, was designed. With the nozzle-register, an almost constant pressure and outflow distribution could be proven experimentally. In comparison to tests with the previously used nozzles and an infiltration without nozzle, improved pressure and outflow conditions could be demonstrated with use of the nozzle-register. The test results with the three different infiltration techniques were modelled numerically for the aquifer. In addition, flow simulations for the flow behaviour within the filter pipe including the nozzle installation were carried out. With the knowledge of the non-constant outflow from the filter pipe and the corresponding approaches in the modelling, the test results in the aquifer could be validated. The flow simulations qualitatively reproduced the experimentally detected conditions when using the different infiltration techniques. The findings from the practical application, the further development of the drilling, measuring, infiltration and regeneration techniques as well as the laboratory tests and simulations carried out resulted in a design manual for jet suction infiltration systems. A distinction is made between design, installation and operational requirements, which must be considered when dimensioning jet suction infiltration system for projects.

Institutions

  • Chair of Geotechnical Engineering and Institute of Geomechanics and Underground Technology [314310]

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