## 1 Introduction  
A Concrete Face Rockfill Dam (CFRD) is a type of dam that consists of a compacted rockfill body, with a thin concrete slab built in the upstream face as an impervious element. CFRD dams are recognized as an effective and efficient alternative to other types of dams such as impervious core or concrete dams [1; 2; 3; 4]. In the last three decades, the height increase of a CFRD has developed constantly, up to more than 200 m, which has been driven by the increasing demand in hydropower energy and supported by enhanced construction and design methods [5; 6; 7]. CFRD dams with heights close to, or higher than, 200 m have experienced several problems related to excessive, higher than predicted, deformations [8]: These include Tiangshenquiao-1 (China, 1998, 178 m)--2.05 m predicted and 3.47 m measured; Sanbaxi (China, 2005, 185 m)--0.8 m predicted and 1.56 m measured; and Shuibuya (China, 2006, 233 m)--1.92 m predicted and 2.5 m measured. Other dams with excessive settlement include Aguanilpa (Mexico, 1993, 187 m), Barra Grande (Brazil, 2005, 185 m), and Campos Novos (Brazil, 2006, 202 m). To successfully build and operate CFRD dams higher than 200 m, it is necessary to put the focus on deformation control through all the phases of the dam life cycle [9]. During the design phase, deformation control involves deformation prediction. During construction, reservoir impoundment, and operation, deformations are observed, and numerical model parameters to simulate past deformations and predict future deformations can be calibrated through back-analysis. The prediction of rockfill deformation at the design phase is constrained by the limitations of laboratory testing programs and by the scale effect, which means that rockfill parameters are assessed using samples with smaller grain sizes than those used in the dam. Rockfill is a loose granular material with polyhedral particles mainly obtained by quarry blasting exploitation, which lead to an extremely variable gradation that can further change during compaction due to very high contact forces that develop at the particle-particle interface. The compaction results not only in a change of the specific volume due to particle rearrangement but also in a change of the distribution of solid matter among the particle size range (primary breakage). As the height of the dam increases, the compacted rockfill layers can undergo a secondary breakage and the rearrangement of broken particles. Grain size distribution and porosity control the mechanical behavior of rockfill [9; 10; 11; 12; 13; 14; 15; 16]. This complex mechanics is responsible for non-linear stress-dependent stiffness, creep, hardening, and irreversible strain. An approach for deformation prediction incorporating the breakage and scale effect based on the critical breakage energy concept has been proposed by [PERSON] et al. [17] with a continuum model whose parameters can be obtained from laboratory tests. The model incorporates a linear elasticity law, which does not consider pressure-dependent elasticity nor porosity as an explicit parameter. Another approach for deformation prediction in practical applications is also based on continuum mechanics models, but with non-linear elastic, elasto-plastic constitute laws, that try to incorporate the particle breakage linking it to a state variable that has an influence on the plastic flow. Examples of such models are the Duncan-Chang hyperbola model [18], modified Naylor K-G model [19], Lade-Duncan model [20], [PERSON] model [21], Daouadji model 84 [22], Barcelona-type models [23] and Kohgo model [24]. Sometimes creep is also considered using empirical models that may have a relatively large number of parameters (from five to nine). As creep tests take a long time, parameters are estimated in practice from back-analyses of similar dams [17]. The parameters of these models are obtained from laboratory tests that do not capture the breakage or scale effect phenomena witnessed in high dams.