University of Twente Student Theses
Assessing the hydraulic conductivity of the seepage reducing measure 'Sand bentonite' in diverse environments
Witteman, Joep (2024) Assessing the hydraulic conductivity of the seepage reducing measure 'Sand bentonite' in diverse environments.
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| Abstract: | In many regions of the Netherlands, the water level in waterways is higher than the surrounding groundwater level. This water level difference could result in seepage, which could lead to dike failure due to piping or uncontrolled saturation of the soil. Measures such as ZBM (Sand-Bentonite-Mixture or Zand-Bentoniet-Mengsel in Dutch) are applied to mitigate seepage. ZBM is applied as a soft liner at the bottom of waterways, functioning as a poorly permeable layer by increasing the hydraulic resistance and thereby reducing the conductivity. Joint research involving Rijkswaterstaat, Van Heteren Weg- en Waterbouw B.V and Deltares (knowledge institute in water and subsurface) showed that applying ZBM would increase the hydraulic resistance and could confidently be applied as a seepage control measure in the Twentekanaal, which was successfully applied in 2022 and 2023. Following this success, questions arose about whether the ZBM would also be applicable in different environmental contexts. This thesis assesses the influence of various environmental factors on the hydraulic conductivity of ZBMs used as a seepage control measure on the bottom of waterways. While existing literature offers valuable insights, it often focuses on specific characteristics such as swelling capacity, leaving a gap in knowledge about the factors influencing hydraulic conductivity. This makes it difficult to estimate the influences of the environment on the hydraulic conductivity of the ZBM. By conducting small-scale (5 litre) and large-scale (1000 litre) experiments under various environmental conditions while measuring the water flowing through the ZBM layer, the potential influence of the environment on the behaviour and hydraulic conductivity of the ZBM is assessed. The environmental factors studied include the coarseness of the surface layer on which the ZBM is applied and the chemical composition of the water in terms of salinity and acidity. Findings indicate that the mixture settles through coarse layers even with very fine gradings, with the separation of lighter and heavier particles observed during settling. Nevertheless, of all the experiments, the lowest discharge trend was observed during large-scale experiments with the coarse surface. Compared to fresh water, the experiment with water with increased salinity showed that the increased salt concentration accelerated the shrinkage of the ZBM layer, leading to the formation of cracks and increasing hydraulic conductivity. Furthermore, this study revealed the impact of ZBM on the pH of the surrounding water through an exchange of H+ ions that increased the pH of the water to that of the mixture itself. These results show that the hydraulic conductivity and behaviour of the ZBM can be strongly influenced by environmental factors. This indicates that it cannot be assumed that the ZBM could be applied in all environments, and results from the application of ZBM in other environments are not directly applicable to waterways with different water compositions or soil characteristics. Understanding these influences is critical to ensure the efficacy and applicability of ZBMs in different environmental contexts. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 56 civil engineering |
| Programme: | Civil Engineering and Management MSc (60026) |
| Link to this item: | https://purl.utwente.nl/essays/101747 |
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