# Roller-Integrated Acoustic Wave Detection Technique for Rockfill Materials
## 1 Introduction  
Effective control of compaction quality is critical to ensure the safety of rockfill dams [1]. Many researchers have attempted to develop compaction detection techniques and methods for soil. Based on whether or not the detection equipment is in contact with the material, these detection techniques and methods can be classified into contact and non-contact techniques and methods. Contact techniques and methods include the water-filling method, the falling weight deflectometer (FWD), the lightweight deflectometer (LWD), the dynamic cone penetrometer (DCP), the California bearing ratio (CBR), the nuclear density gauge, the resistivity test method, and so on. Non-contact techniques and methods include the roller-integrated compaction monitoring (RICM) techniques, intelligent compaction (IC) techniques, the ground penetrating radar (GPR) techniques, the Rayleigh wave techniques, the near-infrared and microwave resonance sensing technique, and so on. Contact techniques and methods are utilized to detect the compactness of rockfill materials by measuring the density and moisture content of the materials. [PERSON] et al. [2] studied compaction control of highway materials using the sand cone method, which is time-consuming. In order to improve this disadvantage of the sand cone method, [PERSON] et al. [3] and [PERSON] et al. [4] further investigated compaction control of pavement layer materials and coarse-grained soil using the LWD, FWD, DCP,and soil stiffness gauge (SSG). [PERSON] [5] and [PERSON] et al. [6] studied compaction control of recycled aggregate and cohesive soil and fly ash using the CBR test. [PERSON] et al. [7] utilized the DCP to research quality control of mining tailing dams. [PERSON] et al. [8] developed the LWD for estimating the surface stiffness of lateritic soil. Subsequently, [PERSON] et al. [9] utilized the LWD to study compaction control of pavement layers. To further simplify the operating process and improving efficiency, [PERSON] et al. [10] and [PERSON] et al. [11] investigated soil compaction using the nuclear density gauge. Although contact techniques and methods have the advantages of high accuracy and wide application range, they also have obvious disadvantages of point sampling and destructive measurements, low efficiency, and higher requirements for operators. In order to avoid the disadvantages of contact techniques and methods, lots of researchers have developed non-contact techniques and methods. [PERSON] et al. [12] and [PERSON] [13] stated that the vibration acceleration amplitude and harmonic amplitude were correlated with the soil density and the underlying stiffness. [PERSON] et al. [14] extracted the stiffness of the soil based on the vibration acceleration and phase difference. With in-depth research, a relative measurement index value (RICMMV) based on RICM was proposed to determine the compactness of the soil [15; 16; 17; 18; 19; 20]. RICMMV is defined in various ways, including compaction meter value (CMV) used by Geodynamic [15], \(K_{b}\) used by Ammann [16], machine drive power (MDP) used by Caterpillar [17; 18; 19], and OMEGA used by Bomag [20]. Furthermore, [PERSON] et al. [21; 22] pointed out that total harmonic distortion (THD) was a highly sensitive index for evaluating the compaction status of soil, and [PERSON] et al. [18] introduced \(E_{vib}\) as a vibration modulus. Related studies have demonstrated that these indexes are closely correlated to the stiffness or modulus of compacted materials, and the non-contact techniques and methods based on RICMMV can be used to detect the compactness and evaluate the compaction quality of soil. By combining AFC techniques, some researchers have developed IC for road compaction control, and IC is currently widely used in Europe, Japan, and the United States [23; 24; 25]. Moreover, wave techniques have been used to the detect compactness of subgrade [26; 27]. However, the law and mechanism theory of wave propagation in various soils have been not yet been well studied.