The doctoral thesis of Francesco Raggi, entitled “Prediction of Deformation and Stability of Very High Concrete Face Rockfill Dams”, makes a significant contribution to the field of geotechnical engineering, with a focus on advancing the deformation control approach for the design of high and very high Concrete Face Rockfill Dams (CFRDs).

The research initiative was proposed by Dr. Ramon Pacheco, Technical Director at ELC Electroconsult, and carried out in collaboration with Prof. Luis Altarejos Garcia at UPCT. This achievement reflects the technical excellence of ELC’s team, gained through international collaboration and high-level academic programs.

In the following, the abstract of the thesis is reported:

“The research activity has focused on improving the prediction of the behavior of very high Concrete Face Rockfill Dams (200–250 m). One of the critical issues in high CFRDs is “deformation control” which, among other aspects, incorporates the prediction of rockfill deformation from the design phase. In fact, the first CFRDs that reached heights around 200 m experienced problems such as separation of the concrete face from the rockfill upstream slope, cracks, and fractures in the face slab, leading to watertightness capacity issues, significant leakage, and water loss. The direct cause was excessive settlements in the rockfill, sometimes far greater than those anticipated during the design phase. This is because the rockfill is a granular material with complex mechanical behavior, exhibiting high non-linearity, stress-path-dependent behavior, dilation, creep, degradation due to wetting, and particle breakage under high confining pressures, with significant scale effects.

In the context of improving “deformation control”, this research first developed two constitutive models for rockfill: VEPP (Viscous Elastic Perfectly Plastic model) and VEPHS (Viscous Elastic-Plastic Hardening Softening). Next, the ability of these models to accurately reproduce the behavior observed in real cases (back-analysis) has been verified using case studies of two CFRDs in China: Tianshengqiao-1 (178 m) and Shuibuya (233 m, currently the tallest CFRD in the world). The next step has been to use the VEPP to predict the behavior of the Shuibuya dam, now using only the information available during the design phase, before the dam was built (unlike the back-analysis). The prediction made with the VEPP closely matches the behavior observed after dam construction, the first reservoir filling, and the initial years of operation. In fact, prediction using VEPP significantly improves upon those made by other authors using more complex models.

 Moreover, these constitutive models, along with a cracking model developed for the concrete face slab (EPHS, Elastic Plastic Hardening Softening), have been applied to investigate the influence of different construction sequences and different compaction effort levels on rockfill deformations and cracking in the concrete face slab. For this purpose, a prototype CFRD, with a height of 238 meters, has been used as a case study. This allowed for the estimation of the relative influence of construction sequence and compaction intensity, providing valuable information for use in the design phase, optimizing construction methodologies, ensuring structural integrity, and reducing the risks associated with excessive unforeseen deformations in future very high CFRD projects.”

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