# New Perspectives on Excavation Disturbance Zones: Main Driving Forces
###### Abstract  
The support theory of the excavation disturbance zone (EDZ) cannot provide an accurate physical explanation or theoretical description of the time-dependent properties required for the development of an EDZ. Therefore, the primary factors that cause the formation of an EDZ should be determined to further improve the support theory of the EDZ and grasp the principle underlying the control of the long-term stability of rock masses. Considering the headrace tunnel and nuclear waste repository as the research background, this study aimed to understand the deformation damage evolution process of the surrounding rock after tunnel excavation under different working conditions using the self-developed realistic failure process analysis (RFPA2D) code. The simulation revealed the following. First, an EDZ is formed, although the deformation damage to the surrounding rock is relatively small under the action of environmental factors. Second, under the action of stress in the abovementioned case, the deformation speed, damage degree, and scope of the surrounding rock significantly increase, accelerating the formation and development of the EDZ. Therefore, the boundary of the EDZ expands significantly. Third, when environmental factors are blocked, the range of the EDZ is small due to the small deformation damage to the surrounding rock. Thus, the main factors responsible for the formation of the EDZ are environmental factors, whereas stress is only an auxiliary factor. A numerical simulation method that considers environmental factors can more accurately reproduce the formation of an EDZ. Therefore, a study of the internal mechanism of the EDZ phenomenon can provide a more in-depth understanding of the essential characteristics of an EDZ at the macro level. Furthermore, it can provide a scientific basis and method for the construction and support designs of underground excavation projects and widen the possibilities for further improving the support theory of the EDZ. EDZ; time-dependent deformation; main driving forces; environmental factors; numerical simulation +
Footnote †: journal: Medical  
stability of the rock mass around the excavation space. The depth of an EDZ is a critical parameter for the analysis of the stability of the surrounding rock, calculation of the rock mass load, and determination of the range and thickness of bolt-shotcrete, in addition to the lining support mode. Therefore, it is necessary to study the main driving forces and formation processes of an EDZ. Outside China, the EDZ is generally referred to as the range in which the surrounding rock caused by excavation is loosened. Research on EDZs was initiated in the early 20 th century. However, EDZs were comprehensively and systematically studied only in the 1980s, during which the HRL Lab, Sweden SKB, URL Lab of AECL, Canada [9], and JAEA, Japan, reported significant findings. Although several studies have investigated the causes of EDZ formation and reported significant results, their conclusions differ. Several researchers have reported that stress is the main cause of EDZ formation. Field measurement results demonstrate that the stress redistribution caused by excavation promotes the continuous initiation and expansion of microcracks and the gradual formation of a fracture network in the surrounding rock, which eventually leads to the formation of the EDZ. The influence of stress redistribution on the depth of an EDZ is greater than that of other factors [10; 11; 12]. Three regions generally exist around a cavern, and they are generally related to stress-induced damage, as detailed in several studies and monographs on EDZs; i.e., stress disturbance dominates the formation of these three regions [13; 14]. In addition, empirical methods [15; 16] or numerical simulations [17; 18; 19; 20] for predicting the depth of an EDZ in brittle rock masses have been used based on the damage range caused by the stress concentration.