## 1 Introduction  
Soil-rock mixture (S-RM) is a heterogeneous geotechnical material composed of coarse particles such as rock, gravel, and sand, and fine particles such as sand, clay, and silt. It is typically formed by seismic, collapse, landslide, and other actions during the Quaternary Period, and distributed in loose accumulations on steep slopes or beside ditches [1; 2; 3; 4]. For instance, the 2008 Wenchuan earthquake in China triggered numerous landslides and debris flows in the subsequent years due to secondary factors like aftershocks and heavy rainfall. This led to widespread S-RM slopes in the mountainous regions of southwestern China [5; 6]. S-RM formed by similar causes is also common in other areas [7; 8].  
S-RM offers numerous advantages, including its high strength, compactness, permeability, erosion resistance, and ability to utilize local materials [9]. Consequently, it is extensively utilized as a filler in subgrade engineering projects [10]. However, S-RM is a granular material that presents challenges in achieving a uniform mixing of particles with varying sizes, shapes, and material properties. Non-uniform mixing is a common occurrence in both natural and construction processes. For instance, during road construction, the coarse aggregates in S-RM tend to settle downwards due to their higher potential energy, resulting in layers with varying degrees of mixing [11; 12].  
The mixing degree is a measure of the heterogeneity of particle mixtures [13]. Current definitions primarily originate from the chemical, agricultural, construction, and medical fields, where they guide industrial production and quality evaluation. However, mixing degree indices are infrequently utilized in geotechnical engineering [14]. Previous research has demonstrated the significant influence of mixing degree on the local and global properties of granular materials [15]. However, limited studies have investigated its effect on the vibratory compaction of S-RM as a subgrade filler and the resulting negative effects on long-term road performance.  
Subgrade compaction involves the consolidation of soils through mechanical methods such as static pressure, dynamic compaction, or vibration compaction [16]. These methods apply external energy to the soil, causing particle movements and rearrangements. Energy is transformed and dissipated during this process, specifically in terms of particle potential energy. The compaction process is fundamentally driven by particle movements and the resulting energy conversions under loading conditions. Thus, conducting statistical analyses on particle motions and energy consumption during compaction can offer a more comprehensive understanding of the compaction mechanism of S-RM (specific road material) under vibration loads, in comparison to macro-scale observations.  
This paper employed numerical simulations using the discrete element method (DEM) to investigate the vibratory compaction process of S-RM with different degrees of mixing homogeneity. This study analyzed the relationships between changes in void ratio and particle movements, as well as energy dissipation during compaction. Furthermore, the effects of various vibration parameters on energy dissipation paths were examined. The findings will contribute to a deeper understanding of the vibration compaction mechanism for S-RM as a subgrade filler. This knowledge can serve as a more rational basis for selecting fillers, ensuring the quality and bearing capacity of compacted subgrades, and conducting stability assessments.