# New Perspectives on Excavation Disturbance Zones: Main Driving Forces
###### Abstract
Several researchers have reported that the formation of an EDZ is the result of a joint dominance of stress conditions, excavation methods, and other factors. They performed on-site monitoring, numerical calculations, and additional research on the EDZ. The research results revealed that the formation of the EDZ in underground caverns is mainly caused by stress redistribution and excavation damage, and a few studies have considered weathering or water-rock interactions [5; 21; 22]. To an extent, the above-mentioned research results provide an improved understanding of the concept and formation causes of the EDZ and can serve as a basis for excavation scheme design and safe construction in underground rock engineering. Furthermore, the results promote further research on the formation mechanism and support theory of the EDZ. In China, the EDZ is referred to as the broken rock zone. The concept and related support theory was first studied in the late 1970s. [PERSON] performed several ultrasonic tests in the Zhuxianzhuang coal mine and reported a sound wave velocity reduction zone around the roadway, which exhibited high regularity. Based on the mechanism analysis of the sound wave test, the sound wave velocity reduction zone was considered a fractured zone referred to as an EDZ. Subsequently, the support theory of the EDZ was established based on this test result. A significant amount of related research was conducted based on the consensus that stress is the fundamental cause of the formation of an EDZ. In terms of numerical calculations, several researchers have clarified the related mechanism of EDZ formation based on their predictions of the EDZ under different geostress states using numerical calculation software tools [23]. Furthermore, the significant influence of stress redistribution on an EDZ has been determined in several studies that simulated the entire process, from underground cavern excavation to the formation and gradual evolution of EDZs [24; 25; 26]. In terms of theoretical analysis, a criterion for determining the depth of the EDZ was proposed based on damage theory and a two-line damage model [27]. In terms of the combination of theoretical analysis and engineering practice, the depth of an EDZ is generally determined by stress calculation or using the fractal geometric theory. The theoretical results are thereafter compared with field measurement results [28; 29]. In addition, there are alternative perspectives on the causes of EDZ formation. For example, several researchers have reported that the formation of the EDZ is significantly influenced by geological conditions and excavation steps [30]. However, it has been highlighted that the ground stress magnitude, lateral coefficient, and support resistance considerably influence the formation of the EDZ [31]. Furthermore, several researchers have highlightedthat the excavation method is a significant contributing factor to the formation of the EDZ during tunnel excavation, particularly under low in-situ stress conditions [32, 33]. The above-mentioned research findings improve the understanding of the EDZ based on the discussion of the formation mechanism of an EDZ, the proposal of effective methods for detecting the depth of an EDZ, and the development of a relatively complete support theory of the EDZ, which have contributed significantly to underground geotechnical engineering. There is a consensus on the existence of the EDZ based on previous research. Although there are multiple descriptions of the EDZ, the underlying characteristics are the same. Generally, an EDZ is defined as a zone of surrounding rock fracture induced by stress adjustment. However, the formation mechanism and support theory of the EDZ require further clarification, which indicates that the above-mentioned studies are limited. For example, the formation process of the EDZ has time-dependent properties, and an EDZ and its actual depth under low confining pressure cannot be simulated using mechanical loading.