## 1 Introduction  
The compaction quality of earth-rock dam, especially in the region of dam core impervious material, is essential to dam safety [1]. Strengthening compaction quality control is an important measure to ensure the anti-seepage and strength performance of compacted materials and further prevents the appearance of cracks [2]. In the current specification of earth-rock dams [3], spot tests are chosen as the main control means. Spot tests are convenient to operate, but there are three shortcomings. First, these tests cannot be executed only after the whole working face is compacted, and the testing process can last for a day. Additionally, only after the inspection and evaluation are qualified can the next working face be constructed, which will delay construction progress. Second, the position of limited test pits is randomly chosen, which is unrepresentative and cannot fully reflect the whole working face [4]. When an unqualified test pit appears, it is rather ambiguous to define the scope of supplementary rolling. Third, the method is destructive and the test pits are usually of large size and need to be refilled and recompacted, which is harmful to the homogeneity and continuity of the properties of dam materials [5]. Therefore, in the last decade, real-time compaction monitoring (RTCM) technology for continuous compaction control is gradually introduced as a supplement to the quality evaluation of dam compaction, which integrates global position system (GPS), general packet radio service (GPRS) and personal digital assistant (PDA) technologies [6]. Based on the RTCM technology, the real-time evaluation for compaction quality has been developed, but there are still following main restrictions.  
1. Due to their simplicity and convenience, the physical indices of compacted dam materials (i.e., the compactness \(K\) and porosity \(n\)) are chosen as the evaluation indices for compaction quality. Physical indices are the indicators of the proportional relationship between the mass and volume of the three phases (i.e., the solids, liquids and gases) of earth-rock dam materials [7], which can help reflect the physical composition and seepage properties of compacted materials. Mechanical indices characterize the deformation and destruction morphology of earth-rock dam materials in the process of being subjected to external forces or other effects [7], which can help reflect the strength and stiffness performance. Due to the correlation between them, the physical properties are usually used to represent the mechanical properties. However, due to the uncertainties in material internal structure (i.e., the grain composition and moisture content), the relationship between the two properties is indeterminate [8]. Therefore, it is not enough to only assess the compaction quality with the physical indices.
2. For the current real-time compaction quality evaluation of dam materials, the inherent heterogeneity of the evaluation indices within the whole working face has been ignored. It is noteworthy that the compaction quality heterogeneity resulting from local under-compaction and over-compaction may lead to an uneven settlement and arch effect [3], which are major causes of dam damage.  
In allusion to these limitations, a comprehensive compaction quality evaluation method is proposed in this paper. In this method, real-time hybrid evaluation of compaction quality is carried out, integrating both the physical and mechanical properties of compacted dam materials and then analyzing the real-time compaction quality heterogeneity. This paper proceeds as follows: Section 2 gives a brief research background of compaction quality evaluation; Section 3 introduces the framework of this paper; Section 4 introduces the compaction quality evaluation system and relevant indices; Section 5 demonstrates the research methodology proposed in this paper; Section 6 is a case study to demonstrate the feasibility and advantages of the proposed method; Finally, conclusions and future research are summarized in Section 7.