## 1 Introduction  
Particle breakage of granular materials usually occurs at high stress levels in high earth-rockfill dams [1]. Large deformation caused by rapid brittle breakage of particles usually leads to dam instability, even failure, causing serious accidents [2, 3, 4, 5]. Therefore, considerable effort has been devoted to particle breakage, as well as its affecting factors, and significant advancements have been achieved in recent years [6, 7, 8]. Mostly, the particle was considered to be an ideal sphere because the spherical particle has greater crushing strength [9]. Actually, almost all granular particles in nature exist in a non-spherical form. Compared with spherical particles, non-spherical particles need a higher coordination number to maintain a stable configuration due to a decrease in the number of strong force chains in numerical simulation [10]. Many experimental studies demonstrated that particle breakage could be significantly affected by the shape anisotropy of non-spherical particles [6, 10, 11].  
Particle shape parameters, such as sphericity, roundness, angularity, irregularity, were presented to describe particle shape [9, 12]. A lower degree of sphericity and higher flakiness index led to lower resistance to particle breakage [13, 14, 15]. Besides, the flat and elongated ratio and angularity index were recommended to describe the particle shape of the coarse-grained soil [16, 17, 18]. [PERSON] et al. [19] calculated the angularity index to eliminate the influence of particle size on the angularity of coarse aggregate. [PERSON] et al. [20] proposed particles' circularity value through image processing and analysis to describe the characteristics of particle shape. [PERSON] et al. presented a boundary-spheropolygon element method to simulate the interaction of particles and found the decrease in the circularity of particles increases the heterogeneity of the force chain and causes high tensile stress areas in certain particles, which would lead to more breakage and showed lower breakage resistance in the granular material [15].  
Meanwhile, particle size has a great influence on particle breakage. With the increase in particle size, the characteristic stress of a single particle decreases [21; 22; 23; 24; 25; 26; 27]. The possible explanation is that the increase in particle size increases the probability of larger flaws being present [27]. The characteristic stress of coral sand at the failure state and particle size has an exponential relationship under a single particle compression test [21]. Furthermore, the studies of non-spherical particle breakage are mostly for natural materials, and the quantitative analysis of particle shape on particle breakage is still scarce.  
This paper investigated the particle breakage of a kind of shape-anisotropic particle under normal load. The particles were molded as the cone-hemisphere with different sphere diameters, cone angles and contact diameters. The influences of these variables on particle breakage mode were elaborated by analyzing breakage processes, breakage modes and force-displacement curves. Furthermore, the breakage mode discrimination of cone-hemispherical gypsum based on particle shape was proposed. To eliminate the effect of fissures, high-strength gypsum was used as the molding material in this study due to its isotropy, flawlessness and ease of molding.