# The Future of Abandoned Shallow Mines as a Function of Precipitation Under Changing Climate
## 8 Discussion  
The numerical calculation provides many useful and interesting results: such as strain, displacement, stresses, failure zones, etc. To assess the influence of the geometry and water effect, we focus on analysing the horizontal and vertical stresses. The stress amplitude scale is constant across all the configurations (Figure 19). Figure 19 highlights the difference in stress distribution between the four configurations. The destressing zones, characterised by low horizontal compression stress and tensile stress, cover larger areas compared to the reference configuration. The position of the fault (configuration 3 to 5) influences the interaction between the slope, the mine and the fault. This is particularly visible in configuration 4, where the vertical stresses are affected. At this stage of the analysis, the configurations integrating mine, slope and fault are the most critical ones because they develop higher destressing zones.  
Figure 20 presents the results of configuration 5. The analysis of the numerical results in terms of stress distribution highlights an increase in the tensile stresses, and a reduction  
Figure 19: Horizontal and vertical stress distribution for the four configurations. Results show the effect of the geometry and the presence of fault on the stress distribution.  
in the normal compressive stresses. The increase in the tensile stresses and the decrease in the compressive stresses favour the sliding of the unstable mass of rock. On the other hand, the reduction in the chalk's strength reduces the bearing capacity of the underground chalk mine's pillars. This excavation, coupled with the degradation of the fault's properties due to the water effect (lubricification) and the saturation of the pillars, leads to an increase in the tensile stresses in the stiffer limestone and puddingstone beds of the roof (with the beds acting as beams). The plastic deformation of the pillars due to the saturation favours the development of tensile stress on the roof.  
The verification of the numerical modelling is based mainly on the reported observations and the rare photos. The numerical modelling results allow us to compare the different configurations and help us to identify a realistic mechanism. Based on both the in situ observations of the collapse and the numerical modelling results, Figure 21 summarises the main factors involved in the collapse. The collapse resulted from a combination of the internal factors (mine geometry, extraction ratio, slope and fault) and the external factors (heavy precipitation, raising and flooding of the underground mine, saturation of the strata and reducing the shearing strength of the fault). The external factors are closely related to climate parameters, particularly heavy rainfall, which triggered the collapse of the slope and the mine. Two scenarios are possible: the first one involves the sliding of the slope, where the sliding mass destabilised the weakened pillars and, finally, the mine collapsed. The second scenario suggests the collapse of the weakened pillars due to flooding, and then the mass of the slope, limited by the faults, followed by the sliding movement. The first scenario is more realistic due to the observed form of the collapse pattern (Figure 12).  
Figure 20: Distribution of the horizontal and vertical stresses for the four calculation phases for configuration 4. Results show the effect of the lubricification of the fault (decreasing of the friction angle) and the saturation of the chalk (water effect).  
The increase in rainfall due to climate change will certainly impact the stability analysis of underground mines. This influence will be particularly significant when the internal factors, such as the composition of the rock (e.g., chalk rock), are highly sensitive to the water. In such cases, the future of underground mines, especially those with these specific configurations, becomes uncertain, raising concerns about the safety and the security of the population, buildings and critical infrastructures.