University of Twente Student Theses
The risk assessment of incorrectly installed vinyl heave screens in dikes
Zagema, A.G. (2023) The risk assessment of incorrectly installed vinyl heave screens in dikes.
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| Abstract: | The Dutch River dikes are important to the country's flood protection infrastructure. However, these dikes are susceptible to a phenomenon known as piping, which can lead to their failure. Piping occurs when water seeps through the dike's soil, carrying small particles along with it. Over time, this can erode the soil and create channels, which weaken the dike's structure and ultimately cause it to fail. To prevent piping and protect the dikes, various measures can be taken. One effective approach is the use of heave screens, which are barriers placed in the soil to prevent heave and thus piping. These screens can be made from different materials and take various forms, depending on the specific needs of the dike and the site conditions. Among the different types of heave screens, vinyl sheet piling has been found to be an advantageous solution. Vinyl sheet piling consists of interlocking panels made from PVC, which are driven into the ground to create a screen in the dike. This material has several advantages, including its durability, corrosion resistance, and costs. However, the installation process of heave screens can be complex and carry risks. For example, if the screens are not installed properly, they may not function as intended, allowing heave to occur, and leading to piping. Additionally, the screens may be subject to damage during installation or over time, reducing their effectiveness. The goal of this research was to assess the failure risks due to the implementation of incorrectly installed vinyl heave screens against backward erosion piping in a dike. To determine what these failure risks are, a risk assessment can be used. The Wolferen - Sprok dike reconstruction project, in which Fugro is involved, is an innovative project in which large-scale plastic sheet pile walls have been inserted as a heave screen. This has been an important source for this study. The first part of this assessment is risk identification. Four different failure mechanisms of a heave screen are determined which are underpass, through pass, overpass, and backward pass. The study categorized potential causes of installation errors into seven groups, including incorrect placement, soil resistance, obstacles in the ground, unsuitable sheet pile type, unsuitable installation equipment, insufficient embedding of the screen, and damage to the sheet pile. Then, these are examined to see how installation errors affect those mechanisms. Next, we can look at what the probability is of a particular mechanism occurring and its effects on the hydraulic gradient which is a value that can be used to assess how critical the situation is in terms of heave. Failure due to incorrect installation poses a significant risk in terms of probability and impact. The impact of not reaching the required depth can lead to problems related to heave and backward erosion piping. The location and size of gaps in the heave screen affect the hydraulic gradient and flow paths, influencing the risk of piping and erosion. The study found that incorrect installation significantly affects the failure probability, with risks such as under-pass and over-pass having a substantial impact. The failure probability doubles or even triples when installation errors are considered, highlighting the need for mitigation measures. A comprehensive approach involving detection, preventative, and mitigation measures is necessary to mitigate the failure risks due to incorrect installation. Detection measures play a crucial role in identifying potential errors. Preventative measures address specific issues related to soil conditions, insertion speed, and strengthening the sheet pile system. The last step in the risk assessment is to provide recommendations for water boards and contractors. This thesis study has devoted an entire chapter to those recommendations, where also the Bowtie diagram is provided. The bowtie diagram is a visual representation tool used to communicate risks and measures and shows the relationship between the different components of the risk. The advice includes conducting site analysis, choosing appropriate plank types, assessing ground resistance, monitoring installation parameters, and performing post-installation checks. The main recommendation for further research based on this thesis study is that large-scale experiments are needed to reduce the knowledge gaps about the effects of a gap in the heave screen and the growth of the pipe. This step would increase the reliability of the vinyl heave screens. |
| 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/95139 |
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