## 1 Introduction  
Block-in-matrix-rocks (bimrocks) with high rock block proportions (RBPs) are considered problematic geological materials during engineering construction [1; 2; 3]. Figure 1 illustrates several types of geological formations in nature, which consist of higher RBPs and lower matrix contents. Due to the high block proportions, the physical and mechanical properties of the geological material can be rather different and heterogeneous, which may cause challenging problems for tunnel excavation, dam construction, and slope engineering. Thus, determination of the strength and elastic modulus of such geological materials is fundamental and crucial to guarantee the safety and stability of the aforementioned projects [4; 5; 6; 7; 8; 9; 10; 11]. Recently, some studies have been carried out to reveal the feasibility of predicting the strength of bimrocks with high RBPs based on laboratory experiments. [PERSON] [12; 13] conducted a uniaxial compression test on the bimrocks with high RBP ranging from 70% to 90%. The RBP was proven to be an effective parameter to predict the strength and deformation properties. However, the proposed model only considered a single influencing factor; other factors such as matrix strength and rock properties were ignored. Therefore, [PERSON]. et al. [14] suggested the use of empirical equations to predict the strength of bimrocks, which depends on multiple input parameters, e.g., RBP, repose angle of rock blocks, and the strength parameters of the matrix. Moreover, [PERSON] [15] calibrated the equations on the basis of experimental data from [PERSON] [16], [PERSON] [17], and [PERSON] [18]. The results showed that the empirical approach has high predictability with slightly conservative errors. Nevertheless, a series experiment process was required to obtain the input parameters. Other than empirical approaches, [PERSON] also introduced a back-propagation artificial neural network (BP-ANN) to predict the uniaxial compression strength (UCS) and the elastic modulus of bimrocks. However, an enormous database is required to train the network. Although the aforementioned approach provided effective prediction results under different conditions, a more convenient and practical method is preferred on construction sites. The widely used non-destruction test technology could be a promising solution to predict the strength of bimrocks in an accurate and rapid manner. [PERSON] et al. [19; 20] measured the velocity of ultrasonic waves of bimrocks with different RBPs and a multiple regression analysis was performed to correlate the UCS with the wave velocity. [PERSON] et al. [21; 22] obtained the complete stress-strain curves under uniaxial compression and the ultrasonic wave velocities of bimrocks with different RBP through indoor tests, and a simple damage constitutive equation of bimrocks was proposed based on the experimental data. Meanwhile, these tests also confirmed that applying ultrasonic testing technology to study the properties of bimrocks is feasible. [PERSON] et al. [23] investigated the damage characteristics and cracking state of bimrocks throughout the entire process of uniaxial compression using digital  
Figure 1: Samples of the bimrocks with high rock block proportions. (**a**) Ice-water accumulated bimrocks. (**b**) Bimrocks of misis fault breccia. (**c**) Bimrocks of gravel deposit. (**d**) Volcanic bimrocks. imaging technology. The results indicated that the damage state of bimrocks has a significant impact on their macro-mechanical properties. In conclusion, it is an effective and feasible to study the mechanical properties of welded bimrocks through combining the traditional compression test and nondestructive testing techniques, such as ultrasonic testing technology and digital imaging technology [19; 20; 21; 22; 23; 24]. These methods provide a reliable basis for quickly identifying the mechanical properties of bimrocks [24]. However, at present, few existing studies have linked the vibration attenuation signals of bimrocks to their mechanical properties.