## 5 Discussion
An unexpected result was that the settlement rates predicted with VEPP during the reservoir water level raising process seemed to be higher than those observed in the dam, above all for control points located at an elevation of 300 m. It seems that the VEPP model provided a faster, quasi-instantaneous response of the dam deformation to variations in loading, while the observed behavior exhibited a slower response. An interesting fact is that, despite this difference, the total settlements estimated at the end of the impounding process were similar in most of the analyzed points at both elevations of 235 m and 300 m.  
The model presented has some limitations and areas for potential improvement that can be addressed in future research. One aspect is that the model does not consider variation in grain size distributions in time. How to implement such variation in \(d_{50}\) as the dam height and the water loading increase constitutes a field for future study. There are little data available regarding actual \(d_{50}\) variation in the high CFRDs built. The breakage phenomenon changes the grain size distribution curve, but there is little information available on how this change has impacted the \(d_{50}\) in high CFRDs. For instance, in the Xujixia Dam (China, CFRD, 121.5 m high), the particle gradation curve before compaction had a \(d_{50}\) of 100 mm and a maximum particle size of 800 mm. After compaction, the maximum particle size was reduced to 500 mm, and the \(d_{50}\) slightly increased to 110 mm [44]. The impact of such a small variation in the estimation of the plastic yield surface will be very small. As more information becomes available regarding the particle size distribution changes in high rockfill dams, the model estimations will likely be improved. Another area for improvement is the creep modeling approach. Although the authors have used a simplified creep model with satisfactory outcomes, further refinement in deformation prediction could likely be achieved through the development of more detailed and comprehensive creep models. Achieving this advancement would require implementing robust laboratory testing programs during the dam design phase, where sufficient time and resources would be allocated for long-duration creep tests that encompass a variety of loading and environmental conditions. These tests, such as triaxial creep tests, unconfined stress relaxation experiments, and multi-level loading tests, would capture the full range of time-dependent behaviors exhibited by the materials under operational stresses. This approach would enable a more accurate calibration of advanced creep models that could represent primary, secondary, and tertiary creep stages, reflecting real-world material responses over prolonged periods. Through these detailed laboratory insights, it would be  
Figure 6: Young’s modulus as a function of porosity for SBY CFRD [8]. possible to incorporate critical parameters such as strain hardening, visco-elastic response, and stress relaxation rates into the models. Additionally, the inclusion of parameters related to long-term viscosity and non-linear creep modulus adjustments would provide a nuanced understanding of how deformation rates evolve over time, especially under variable stresses and environmental influences such as temperature and moisture fluctuations. As a future improvement, the VEPP model may be implemented in 3D numerical modeling schemes, allowing for a more refined simulation of the construction sequence. However, 3D modeling of CFRDs presents significantly greater computational challenges compared to 2D models due to the added complexity and detail required. In 3D models, the need to account for the full construction sequence of the dam in three spatial dimensions increases the number of elements, leading to a substantial rise in computational resources and time. This dimensional increase results in a much larger system of equations, demanding more memory and processing power.