In the rapid development of the water conservancy and hydroelectricity project construction in recent years in China, the stability of tunnels has attracted more and more attention from Chinese and foreign specialists. However, most specialists give many efforts on the evaluation and control of stability of deep-buried tunnels and rather less efforts on the internal reasons-evolution and effect of stress fields. Based on the research for the stability problem of deep tunnels of a hydraulic power plant in Xinjiang, the relationships of stress fields of deep-buried tunnels during the excavation are analyzed in detail with a 3-D elastic and plastic finite element software. Firstly one numerical model is established in accordance with the geotechnical analysis, and several stress monitoring points are set at the stress concentration spots of each tunnel section; the step excavation function of the software is utilized to simulate the actual construction process of a tunnel, at the same time, the stress state of each monitoring point during the stepped excavation process is recorded in detail. Elaborate research has been done on these monitoring points to study the variation of stress fields of three adjacent tunnels during the excavation for this hydraulic plant. The findings show that the later construction of tunnel deteriorates the stress field of adjacent tunnel, i.e. intensifies the stress concentration effect in the tunnel excavated formerly; such a phenomenon is called "stress deteriorating effect in group tunnels". Meanwhile, the findings indicate that the later construction of tunnel optimizes the stress field of arch top, i.e. alleviates the stress concentration effect in arch top of the tunnel excavated.
With the rapid development of hydroelectric construction in China, the construction of group tunnels is often encountered, which has attracted more and more attention of Chinese specialists[1, 2]. The stability of group tunnels has been the focus in this area for many years. Initially, the engineering geological qualitative analysis method, combined with the Classification of Rock Mass Quality, is adopted to assess the stability of group tunnels. Subsequently, with the development of the geotechnical numeric modeling technologies, specialists utilize various numerical modeling softwares to do research on such a problem and get lots of effective findings in some projects [3,4,5,6]. At the same time, many research findings show that excavation sequence of group tunnels has an effect on the stability control, and then An Hong-Gang & Feng Xia-Ting[5,6] combined the numerical modeling technology with the artificial intelligence method to optimize the excavation sequences of tunnels to offer references for site construction and design. With the progress in this area, researchers cannot be satisfied with the exploration in one aspect, they begin to conduct systemic work on this problem, such as sensitivity of stability of group tunnels to rock mass parameters [7,8], classification of rock mass around group tunnels , optimization of construction sequence, selection of numerical modeling methods, etc.