Slope stability assessment of Longyeardalen, Svalbard
Master thesis
Permanent lenke
https://hdl.handle.net/11250/3092487Utgivelsesdato
2023Metadata
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Sammendrag
Slope stability assessment can represent a highly complex topic of investigation, requiring a considerable amount of field information in order to provide consistent predictions or to reconstruct historical events. In the Arctic regions, additional structural related components should be integrated into the stability analysis, due to the unique features encountered on the sites. A relevant influence can be connected to the active layer development starting from the end of freezing season until the final part of thawing period. The combination of thawed soil with significant infiltration events, in the form of powerful rainstorms or prolonged precipitation intervals, can considerably affect the structural integrity of a slope system. The complexity of the analysis can be further escalated by expanding the stability model from an individual slope case to a regional scale, because of the spatial variability characterizing the soil geotechnical properties.
The studied area in this paper is represented by Longyeardalen, Svalbard. A considerable amount of field measurements, laboratory testing results, analytical determinations were processed for the region, with the purpose of generating a suitable input configuration for the stability assessment model. Essential data, related to the landslide vulnerability of a slope system, can be divided generally into thermal parameters, mentioning soil heat capacity, thermal conductivity, grain density, unfrozen water content; hydrological parameters such as soil permeability, hydraulic diffusivity, SWCC properties, water table level, porosity; and strength parameters including soil cohesion, internal friction angle, specific weight, rigidity moduli.
A numerical thermal analysis was performed in PLAXIS V22, a finite element computational software, aiming to predict the evolution of active layer around Longyeardalen with respect to time. The numerical model was calibrated based on the existing thermal data series collected along the valley, the output was validated with thermal information from different projects conducted in the proximity of Longyearbyen between 2019-2022, along with the analytical solution proposed by modified Berggren equation. The last step of the thermal analysis was the prediction of soil thermal regime during the thawing season in 2016, important input for the stability assessment. Apart from thermal monitoring, PLAXIS was used to create a simplified hydrological model, targeting to identify the water table location along the slope profile. The implemented configuration was intended to reproduce the hydrological context on 14th of October 2016, when a significant mass movement event was recorded in Longyeardalen.
The stability assessment was conducted in TRIGRS, an infinite slope based computational software, with the intention of generating landslide susceptibility maps consisting of safety factors distribution for the zones surrounding Longyeardalen. The results interpreted from the thermal and hydrological numerical analysis were incorporated in the simplified stability model, providing a realistic initial setup to reconstruct the event in October 2016. In addition, a sensitivity analysis was performed for several input factors which manifest an influence over the structural integrity of the slope systems, including soil cohesion, soil friction angle, water table location. The variation of the computed safety factors was observed to be relatively proportional to the measured change on the assessed parameters, given that the values are referenced to the initial conformation. The stability model was created in a simplified form, and it is particularly sensible to the initial implemented data, nevertheless, the reconstruction process presents promising results. Slope stability assessment can represent a highly complex topic of investigation, requiring a considerable amount of field information in order to provide consistent predictions or to reconstruct historical events. In the Arctic regions, additional structural related components should be integrated into the stability analysis, due to the unique features encountered on the sites. A relevant influence can be connected to the active layer development starting from the end of freezing season until the final part of thawing period. The combination of thawed soil with significant infiltration events, in the form of powerful rainstorms or prolonged precipitation intervals, can considerably affect the structural integrity of a slope system. The complexity of the analysis can be further escalated by expanding the stability model from an individual slope case to a regional scale, because of the spatial variability characterizing the soil geotechnical properties.
The studied area in this paper is represented by Longyeardalen, Svalbard. A considerable amount of field measurements, laboratory testing results, analytical determinations were processed for the region, with the purpose of generating a suitable input configuration for the stability assessment model. Essential data, related to the landslide vulnerability of a slope system, can be divided generally into thermal parameters, mentioning soil heat capacity, thermal conductivity, grain density, unfrozen water content; hydrological parameters such as soil permeability, hydraulic diffusivity, SWCC properties, water table level, porosity; and strength parameters including soil cohesion, internal friction angle, specific weight, rigidity moduli.
A numerical thermal analysis was performed in PLAXIS V22, a finite element computational software, aiming to predict the evolution of active layer around Longyeardalen with respect to time. The numerical model was calibrated based on the existing thermal data series collected along the valley, the output was validated with thermal information from different projects conducted in the proximity of Longyearbyen between 2019-2022, along with the analytical solution proposed by modified Berggren equation. The last step of the thermal analysis was the prediction of soil thermal regime during the thawing season in 2016, important input for the stability assessment. Apart from thermal monitoring, PLAXIS was used to create a simplified hydrological model, targeting to identify the water table location along the slope profile. The implemented configuration was intended to reproduce the hydrological context on 14th of October 2016, when a significant mass movement event was recorded in Longyeardalen.
The stability assessment was conducted in TRIGRS, an infinite slope based computational software, with the intention of generating landslide susceptibility maps consisting of safety factors distribution for the zones surrounding Longyeardalen. The results interpreted from the thermal and hydrological numerical analysis were incorporated in the simplified stability model, providing a realistic initial setup to reconstruct the event in October 2016. In addition, a sensitivity analysis was performed for several input factors which manifest an influence over the structural integrity of the slope systems, including soil cohesion, soil friction angle, water table location. The variation of the computed safety factors was observed to be relatively proportional to the measured change on the assessed parameters, given that the values are referenced to the initial conformation. The stability model was created in a simplified form, and it is particularly sensible to the initial implemented data, nevertheless, the reconstruction process presents promising results.