## 2 Accurate Identification Method of Fractured Rock Structure
### The Concept of Fragmentation and Its Determination Method  
The fractured rock mass consists of blocks and discontinuous structural facets. Due to the different scales of discontinuous facets, structural bodies of different scales are cut, and there are smaller discontinuous facets in the larger structural bodies, which in turn cut smaller structural bodies belonging to the next level of structural bodies, and these smaller structural bodies can also be cut by the next level of discontinuous facets to form the next level of structural bodies. At the same time, there are many different types of structural faces according to their genesis, scale, and filling characteristics, and various types of structural faces and structural bodies and their combination characteristics are different, and the mechanical properties of the composed rock masses are different, thus constituting the complexity of the geometric and mechanical properties of the rock masses. Based on the investigation of the geometrical shape characteristics of the structure body formed by the cutting of the structure face of the broken rock body, the occlusion mode and the degree of occlusion between the structure bodies and the structural type of the broken rock body are studied and the degree of the brokenness of the broken rock body is quantitatively or semi-quantitatively described. At present, the degree of rock integrity is generally evaluated by a rock integrity index KV or structural surface spacing, and KV is the ratio of the velocity of rock and rock elastic longitudinal waves, but the relationship between KV taking value and the degree of rock integrity is an empirical relationship, which is difficult to give an intuitive concept. Further, the wave velocity test results will be affected by other factors in addition to the degree of structural surface development, which in turn will affect KV. When the number of structural faces within the rock mass is certain, the longer the structural face is, the smaller the measured spacing will be. For a rock mass with the same Jv, if the length of the structural face is larger, the number of structural faces within the rock mass will be smaller, so the integrity of the block formed by the corresponding cut is not the same, and thus the evaluation of the integrity and fragmentation of the rock mass used is also imperfect. By studying the characteristics of the blockiness of fractured rock masses and other characteristics, the fractured rock masses are further classified into more fractured rock masses, fractured rock masses, extremely fractured rock masses, and scattered rock masses, and the concept of fracture degree of fractured rock masses and an analysis method to obtain the fracture degree are proposed. The fragmentation degree mainly reflects the degree of fragmentation of the broken rock mass, which is mainly influenced by the rock structure type and the degree of complete cutting of the structural surface of the broken rock mass in the region. Considering that most of the broken rock masses are cut by three or more groups of structural faces with each other, the survey statistics reveal that the spacing between the mutually cut structural faces is 0.1-0.5 m (we mainly refer to the division of China's engineering practice and relevant codes), generally less than 0.5 m; the extension length of the main structural faces is mostly 1-3 m, generally less than 3 m; therefore, a block of 0.1 \(\times\) 0.1 \(\times\) 0.1 m, i.e., a volume of 0.001 m\({}^{3}\), and a block of 0.5 \(\times\) 0.5 \(\times\) 0.5 m, i.e., a volume of the block of 0.125 m\({}^{3}\) is taken as the standard block for evaluating the fragmentation degree, that is, the maximum block volume per unit volume is considered less than or equal to 0.125 m\({}^{3}\). The concept of fragmentation degree B is proposed, that is, the ratio of the sum of the volume of all blocks in a unit volume (1 m\({}^{3}\)) of broken rock between 0.001 m\({}^{3}\) and 0.125 m\({}^{3}\) to the unit volume.