## 5 Finite Element Modelling of the Two Embarments
### Numerical Models  
A plane strain finite element analysis was used for all the numerical predictions. The adopted finite element mesh and the boundary conditions are shown in Figures 5 and 6 for Embankments A and B, respectively. All numerical calculations were performed using PLAXIS 2D. A finite element fully coupled flow-deformation analysis (i.e., consolidation based on total pore water pressures) was used to perform numerical predictions. Fifteen-node triangular elements were used. The used elements provide a 4 th order interpolation for displacements, and the numerical integration includes twelve Gauss points (stress points) [40].  
Figure 3: Cross section of the embankment and key instrumentation points of Embankment A. (adapted from [6]).  
For both embankments, the horizontal displacements were fixed at the left and the right boundaries, while vertical displacements were allowed. Also, the horizontal and vertical displacements were fixed at the bottom boundary for both embankments.  
Figure 4: Cross section of the embankment and key instrumentation points of Embankment B. (adapted from [8]).  
Figure 5: Mesh and boundary conditions—Embankment A.  
Figure 6: Mesh and boundary conditions—Embankment B.  
Because both embankments are symmetrical, only one half of the embankment is modelled. The modelled area for Embankment A had a total horizontal width of 60 m and a vertical thickness of 22.5 m. The drainage boundaries for Embankment A were the ground surface and the bottom boundary (sand layer), while both left and right boundaries were modelled as impermeable. The modelled area for Embankment B had a total horizontal width of 94 m and a vertical thickness of 31.6 m. The impermeable boundaries for Embankment B were the bottom boundary (stiff clay) as well as the left boundary. The drainage boundaries for Embankment B were the ground surface and the right boundary. The right boundary was chosen as a completely permeable boundary for Embankment B in order to permit possible horizontal ground water flow across the boundary through the sand layer (drainage layer). The previously described boundary conditions for both embankments are the same ones as reported in [6,8].  
The domain chosen for numerical modelling must be wide enough in order to minimize the influence of the boundary effects on the obtained results, and more than three times the embankment width was selected. The modelled area for Embankment A was discretized into 1620 elements and for Embankment B into 2319 elements. Mesh sensitivity analyses were conducted to ensure that the adopted mesh was fine enough to produce accurate results.  
The first stage in the numerical calculations was to model the construction of both embankments. Embankment A was built up to a height of 2.5 m in 50 days, and Embankment B was built up to a height of 1.6 m in 69 days. Although the actual construction sequence of Embankment B consisted of multiple stages with rest periods in between [8], the results of an additional numerical analysis of Embankment B, with multiple construction stages, showed only small differences in the results compared to a linear evolution of the embankment height with time. It was decided to model the construction of both embankments in the same way. Computation is then continued up to four years after the end of embankment construction (up to the end of the measurements) in order to estimate the consolidation behavior. The results are given in terms of time (days) from the reference time (day zero)--the beginning of the embankment construction.  
The water table is assumed to be 1.0 m below the ground surface, and above this level the clay remains saturated and can sustain tensile pore water pressures--suction. This gives a finite value of the effective vertical stress and therefore the undrained strength at the ground surface [41]. The conducted fully coupled flow-deformation analysis takes into account suction in the saturated zone above ground water level table.