Effects of riverbank erosion on the stability of surrounding infrastructure: A case study of the Nolhaga wastewater treatment plant
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2024
Författare
Theodorsson, Emil
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The impacts of climate change, such as more frequent and severe rainfall and longer
periods of drought, may heighten the likelihood and regularity of erosion along
riverbanks. This could result in negative outcomes for both ecosystems and human
activities in the vicinity. Most studies that analyse the effects of bank erosion do not
account for the influence of soil properties such as anisotropy or creep. They also
rarely investigate how surrounding structures are affected by the erosion process.
This thesis aims to use the data collected from the Nolhaga wastewater treatment
plant in Alingsås as a case study to assess these aspects. Regarding soil constitutive
models, a comparison between the use of simple to more complex models have
been considered in this thesis. The constitutive models considered include Mohr-Coulomb, Soft Soil Creep, and Creep-SCLAY1S. The Nolhaga test site is modelled in PLAXIS 2D finite element code as several 2D plane strain sections, using site
investigation data as a source to model the geometry and soil properties. A total of
five sections are modeled, the locations of which are based on a previously performed
stability analysis. The assumed bank erosion rate and patterns are simplified to
be equal across all five modeled sections, as well as evenly distributed over the
entire riverbed that is below water. The majority of the loads considered in the
sections are based on previous stability analyses. However, some have updated
values from more recent load estimations. The results show that Creep-SCLAY1S
generally predicts the highest vertical and horizontal displacements in the modeled
sections, with Soft Soil Creep predicting the second highest vertical displacements,
and Mohr-Coulomb predicting the second highest horizontal ones. The calculated
safety factors of the riverbanks decrease with time as a direct result of modelling
erosion, with some areas dropping below a safety factor of 1 within the studied
time frame, indicating a risk of failure. Based on a displacement comparison with
a non-erosion scenario, bank erosion has a large impact on predicted horizontal
displacements, while having significantly less impact on the vertical ones. Based on
a performed pipe tolerance assessment, the treatment plant pipelines are deemed to
be at risk of suffering damage by the calculated displacements, with the influence
of erosion on these risks being negligible. However, due to lack of relevant site data,
there are large uncertainties related to these results. Thus, further investigations
are recommended to gather more information and decrease these uncertainties.
Beskrivning
Ämne/nyckelord
groundwater modelling