## Materials and Methods
### Advance Numerical Model  
The commercial software PHASE2 v8.0 was used to develop a finite element analysis of the area under study. The geometry of the model corresponded to a cross-section of the embankment and the street, also including the Ebro River bank. Aside from the ground self-weight, two loads were considered: one representing the water column of the Ebro River, corresponding to the avenue that occurred in March 2015, which reached 5.7 m from the river bottom, and one representing the vehicle traffic at the street, with a uniform value of 10 kN. Boundary conditions were set as usual: fixed at the bottom and rollers at sides. Enough distance was left between the main area modeled and the boundaries to avoid any influence of them. This was set after a trial-and-error process.  
Two models were built. The first model considered the ground as a homogeneous mar-gypsum rocky substrate, defined by the Mohr-Coulomb behavior (properties are found in Table 2). A circular cavity of 5.3 m in diameter was introduced below the embankment simulating the possibility of the development of a sinkhole in that area, with an overburden thickness equal to 16 m (both the diameter of the cavity and the overburden thickness were based on the results obtained from the geotechnical investigation).  
The second model considered the ground following the geotechnical profile obtained in this work (see Figure 6 and Table 2 for their corresponding properties). The level found between a depth of 16 m and 21 m (from the embankment) was considered the location of the alteration and dissolution of the marl-gypsum rocky substrate, so one cavity of 5.3 m in diameter was located at various positions.  
Additionally, the deterioration of the karstic level was introduced as a progressive variable, evolving by incorporating increasingly unfavorable geotechnical parameters based on the common shear strength reduction technique usually used for computing the safety factor in finite element analyses.  
In both models, consolidation operations done before 2018 were considered, i.e., resin injections in the embankment done in 2015, mortar injections performed in the street in late 2016 (along with the installation of the high tensile strength geogrids) and an embankment regrowth of the embankment performed in 2017 (performed due to flooding issues and not directly related with the karstic phenomenon). Resin injections were treated as a \"new\" ground material (see Table 2). Mortar injections and geogrids were modeled as linear elastic materials with a Young modulus of 10 GPa and 2000 kPa, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Material** & **Unit Weight (\(\mathbf{k}\)/m\(\mathbf{{}^{3}}\))** & **Young Modulus (MPa)** & **Poisson Ratio (-)** & **Tensile Strength (KPa)** & **Cohesion (kPa)** & **Friction Angle (\(\mathbf{{}^{4}}\))** & **Permeability (m/s)** \\ \hline Embankment & 20 & 16 & 0.3 & 0 & 5.0 & 32 & 0.001 \\ \hline Artificial filling & 19 & 7 & 0.3 & 0 & 9.8 & 15 & 0.001 \\ \hline Marl-gypsum substrate & 22 & 36 & 0.3 & 250 & 96.1 & 33 & \(10^{-7}\) \\ \hline Alluvial material & 20 & 16 & 0.3 & 0 & 31.4 & 20 & 0.01 \\ \hline Material with resin injections & 14.2 & 20 & 0.3 & 0 & 6.5 & 41 & \(10^{-8}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Ground material properties.