Slope Stability Study at Lärjeån - A stability study to evaluate the risk of a landslide occurring for a part of Angeredsbanan located at Lärjeån

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Examensarbete för masterexamen
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2021
Författare
Magnusson, Irma
Johnsson, Alice
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Sammanfattning
The purpose of this Master’s thesis is to conduct a slope stability study regarding the risk of a landslide occurring, using different calculation methods and a sensitivity analysis. The calculations are performed using the Direct method and SLOPE/W. Historical research will be done on how the slope was constructed, together with its effect on the stability. Based on the slope stability as it is today, various factors that could affect the stability will be studied to find the most critical changes that could trigger a landslide. Additionally, actions that can be taken to secure the slope will further be evaluated. The slope stability is investigated for two sections (840/875 and 875/886) of Angeredsbanan which is located on a slope, leading down to Lärjeån. The data that is evaluated is retrieved from field tests conducted by Sweco at the request of Gothenburg city. For both the Direct method and SLOPE/W, the calculated factors of safety are compared with the required factors of safety which are set up by the Commission on slope stability. This is done to evaluate if the slope is safe or not. For the Direct method, three historical scenarios are set up as different models. The results show that the slope is unsafe for all scenarios. In SLOPE/W, five historical scenarios are set up. The results show that when excavating the natural slope it loses some of its stability, going from a stable to an unstable slope. Further piles were inserted and the slope increased its stability again, reaching the required values for the undrained analysis for both sections. Lastly, the construction of the embankment was per formed which resulted in a slight reduction of the stability, still reaching the required factor of safety for the undrained but not for the combined analysis. When performing a sensitivity analysis to see what possible changes that the slope stability is most sensitive towards, the natural changes: groundwater level, water level, erosion and the human changes: embankment height, slope angle, pressure bank and tram load were studied. The results show that the slope is most sensitive towards erosion when studying the factor of safety and the rate of change, meaning that this factor is most likely to trigger a landslide on the site. Comparing the different actions that could be done to secure the slope, the most profitable implementation would be to add a pressure bank. This is mainly due to the relatively easy implementation process connected with the flexible geometry and usage of material together with the high impact on the stability
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Slope stability, Angeredsbanan, Lärjeån, Direct method, SLOPE/W, Sensitivity analysis, factor of safety
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