## 1 Introduction  
Recently, with the continuous railway and highway construction in China, tunnel engineering has been developing in situations of long, large and deep burial [1; 2; 3; 4; 5; 6; 7]. It is inevitable more long tunnels will be built in soft and weak surrounding rock areas [8; 9; 10; 11; 12; 13; 14]. Large deformation of soft rock mass is one of the common geological hazards when a tunnel passes through soft rock mass [15; 16; 17], and is also a long-term problem plaguing tunnel construction [18; 19; 20; 21]. If the deformation of surrounding rock cannot be effectively controlled, the deformation will continue to grow and exceed the allowable value, which will often lead to the destruction of the rock mass structure and support structure of tunnel and bring great potential safety hazards and economic losses to the project [22; 23; 24; 25; 26]. With the continuous emergence of large deformation tunnels in soft rock mass, serious geological hazards are caused. Much attention has been paid to this and relevant research has been carried out. A lot of valuable data and experience have been accumulated in large deformation of soft rock mass at home and abroad,and there have been some achievements [27; 28; 29; 30; 31; 32; 33]. However, there is no unanimous and clear definition of large deformation of soft rock mass. Not only is there a lack of systematic research in theory, but in engineering practice also, the large deformation of soft rock mass has so far not been conclusively addressed in the design code. Therefore, the problem of large deformation of soft rock mass has always been one of the hotspots in tunnel research. Rocks containing a considerable amount of clay minerals intrude on the tunnel clearance slowly with an undetectable volume increase, as noted in the earliest description of large deformation of surrounding rock by [PERSON] [34]. The concept of large deformation of soft rock was proposed by the International Society of Rock Mechanics in 1995 [35]. It is a time-dependent deformation behavior, usually occurring around the excavation surface of an underground space and is generally caused by creep due to the instability of ultimate shear stress. The deformation may stop during excavation or last for a very long time. When defining large deformation of soft rock mass, most previous researchers have provided qualitative descriptions in terms of high in situ stress and weak surrounding rock. [PERSON] et al. [36] proposed that the mechanism of convergence deformation of surrounding rock should include five aspects: plastic wedge, flow deformation, swelling, dilatation and deflection of surrounding rock. [PERSON] [37] 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. [38] pointed out that large deformation occurs on the premise of weak surrounding rock combined with high in-situ stress. [PERSON] et al. [39] proposed a theoretical method for predicting the development of a plastic zone and loosening pressure in soft rock tunnels and discussed the influence of the mechanical properties of soft rock on loosening pressure. Numerous studies have been conducted to study the failure mechanism and law. In addition to the definition, numerous studies have been conducted to study on the failure mechanism and law. The characteristics of deformation and failure of a typical roadway were analyzed, and it was proposed that the fundamental reason for the failure was that traditional support methods and materials could not control the large deformation of deep soft rock. These studies are mainly based on the qualitative analysis of engineering cases. [PERSON] et al. [13] studied the mechanism of large deformation instability of deep soft rock. [PERSON] et al. [40] studied the large deformation and failure mechanism of deep soft rock tunnel in Xin'an Coal Mine. [PERSON] et al.