## 1 Introduction  
In recent years, with the rapid development of the Chinese economy and an increase in investment in infrastructure construction, all kinds of tunnel projects have been rapidly developed [1; 2; 3; 4; 5; 6]. The increasing number of long, large and deep buried tunnels has brought great challenges to the construction and operation of projects, in which large deformation of the soft rock mass is a prominent problem [7; 8; 9; 10; 11; 12; 13]. According to the literature reports, when complicated and difficult conditions have been encountered in tunnels, large deformation and failure phenomena have often occurred in tunnel projects including cross-section shrinkage, lining cracking, shotcrete spalling, steel arch distortion, etc. [14; 15; 16; 17; 18; 19]. This not only damages engineering equipment, and affects the construction progress, but also seriously threatens the safety of construction personnel. Therefore, large deformation of soft rock mass has always been one of the hotspots in tunnel research [20; 21; 22; 23; 24]. Currently, predecessors have done a lot of research work and achieved some results. Rocks containing a considerable amount of clay minerals intrude in the tunnel clearance slowly with an undetectable volume increase. This is the earliest description of large deformation of surrounding rock of Terzaghi [25]. The concept of large deformation of soft rock was proposed by the International Society of Rock Mechanics in 1995 [26]. It is a time-dependent deformation behavior, usually occurring around the excavation surface of underground space. It is generally caused by creep due to the instability of ultimate shear stress. This deformation may stop during excavation or last for a very long time. [PERSON] et al. [27] proposed that the mechanism of convergence deformation of surrounding rock should include five aspects: plastic wedge, flow deformation, swelling, dilatation, and deflection of the surrounding rock. [PERSON] [28] proposed that large deformation mainly depends on rock strength and overburden thickness. In principle, it can occur in any type of rock mass. [PERSON] et al. [29] pointed out that large deformation occurs on the premise of combining weak surrounding rock with high in situ stress. [PERSON] et al. [30] proposed a theoretical method for predicting the development of plastic zone and loosening pressure in soft rock tunnel and discussed the influence of mechanical properties of soft rock on loosening pressure. The causes of large deformation of soft rock mass are complex and can be generally classified into two categories: one is that the stress redistribution during excavation exceeds the strength of surrounding rock and causes plasticization; the other is that some minerals and water react and cause expansion [31; 32; 33; 34]. On the other hand, there are also many predecessors who have done a lot of research to provide solutions to these problems in terms of assessment and treatment. [PERSON] [35] obtained the design and construction of 12 tunnels driven in flysch in Northern Greece, to contribute to assessing tunnel behavior and support associated with the weak rock masses. [PERSON] et al. [36] proposed that the stability of the initial support system is the ultimate key to the stability of surrounding rock and support systems, using a convergence confinement method to evaluate the stability of an early support system of high-stressed soft rock. [PERSON] et al. [37] formed the collaborative bearing system of surrounding rock support to a large deformation of Mesozoic soft rock, and through field tests, the validity and rationality of the collaborative bearing system were also verified. However, up to now, due to the particularity of underground engineering, there has not been a unified understanding of the definition, classification, formation mechanism and displacement control of large deformations, which results in the theoretical research of large deformation of soft rock still lagging behind engineering applications.