###### Abstract
[5] analyzed the macro-failure characteristics, micro-failure modes and micro-seismicity of a stress-structure controlled collapse and explained its evolution mechanism. With the methods of MS monitoring, conventional monitoring and a three-dimensional distinct element code (3 DEC), [PERSON] et al. [6] studied the effect of discontinuities and dynamic construction on the failure mechanism of surrounding rock mass and conducted a stability analysis of an underground powerhouse in a high geostress environment. [PERSON] et al. [7] investigated the failure mechanism of blocks in the collapse area of a tunnel by adopting a method of discontinuities' automatic identification and stability analysis based on terrestrial laser scanning. In regard to the rockburst hazard under high in situ stress, [PERSON] et al. [8] predicted an intense rockburst and identified the location at a deep-buried tunnel with complex geological structures by employing a MS monitoring system. [PERSON] et al. [9] predicted rockburst in an underground powerhouse with a new method based on the rough set theory and the extension theory. With respect to the stability assessment of surrounding rock mass, [PERSON] et al. [10] presented a practical flowchart of rock mechanics modeling for the steps in the evaluation process of an underground powerhouse. Based on the flowchart, stability analysis using the distinct element method (DEM) was conducted on three underground powerhouses. [PERSON] et al. [11] conducted a dynamic stability evaluation against the excavation-induced stress adjustment on a large underground powerhouse and identified potential risk zones. [PERSON] et al. [12] proposed a novel dynamic method for the stability evaluation of sidewall subjected to flexural toppling, which integrates stability criterion, continuum modeling and MS data. [PERSON] et al. [13] established a comprehensive safety evaluation method of surrounding rock mass, which combines a deformation stability prediction and evaluation method, a rapid prediction method of collapse and a comprehensive early-warning index system. [PERSON] et al. [14] developed a novel rock mass displacement back-analysis method considering the displacement loss and applied it in the caverns of the Jinping II hydropower station and the Taian pumped storage power station. In these studies, new techniques (including MS monitoring) were employed and a combination of multiple technical methods became a typical feature. According to actual engineering demands, previous research has explained the reasons and mechanisms of deformation and failure phenomena. In addition, the stability of surrounding rock mass in underground powerhouses has been comprehensively assessed via a variety of methods. Compared with other underground openings, the underground powerhouse of a hydropower station is characterized as large scale with a large span, a high sidewall and complex structures. In terms of excavation dimensions, some underground main powerhouses are more than 200 m long and more than 60 m high and have a span of over 25 m. As for spatial structure, the underground powerhouse has many caverns of different functions and sizes. Large caverns include the main powerhouse, the transformer chamber and the tailrace surge chambers. Relatively small caverns include diversion tunnels, omnibus bar caves, tailrace tunnels and auxiliary caverns, such as construction adits and access tunnels. These characteristics have an impact on the surrounding rock mass stability of an underground powerhouse. When the excavation dimension is large, the long-lasting excavation disturbance can increase the risk of surrounding rock mass deformation and failure. With the number of caverns increasing, a multi-cavern effect is likely to appear when adjacent or intersecting caverns are excavated simultaneously, leading to surrounding rock mass instability.