## 1 Introduction  
Large deformations in tunnels frequently occur in soft rock strata under high geostress conditions. Large deformations in tunnels easily cause support structure failure and endanger the safety of construction personnel [1; 2; 3]. To effectively address the large deformation problem of tunnels, there are two fundamental problems to solve in advance: the confining pressure influence on the soft rock mechanical characteristics and the displacement field prediction and evaluation of surrounding rock considering the confining pressure influence [4; 5]. These two problems are the current research hotspots, which have significant meaning for the large deformation problem of tunnels [6; 7]. Therefore, numerous scholars have focused on the abovementioned problems and have had many achievements in recent decades. Regarding the mechanical characteristic variation of soft rock with confining pressure influence, the stress-strain curves of soft rock under different confining pressure conditions are obtained by triaxial experiments, and the confining pressure influence on the mechanical characteristics for soft rock has been investigated, including peak strength, failure pattern, and stress-strain curve pattern [8; 9; 10; 11; 12]. Moreover, a series of strength criteria have been proposed according to experimental results, such as the generalized Zhang-Zhu strength criterion (GZZ strength criterion), uniform strength criterion, etc. [10; 13; 14]. However, most previous studies only focus on the strength aspect of soft rock but neglect the deformation aspect. Therefore, the first purpose of this study is investigating the effect of confining pressure on the strength and deformation of soft rock. For the displacement field prediction and evaluation of surrounding rock considering the confining pressure influence, many scholars have proposed many new analytical solutions to calculate such a field [15; 16; 17]. However, there are two defects in these analytical solutions: (1) the assumptions of the analytical solutions are usually for circular tunnels, and the initial stress state is a hydrostatic stress state, and (2) the analytical solutions hardly consider the complex construction process of tunnels, which leads to solutions that are difficult to apply widely in practical soft rock tunnels. As an alternative, the numerical simulation method has been widely adopted in all aspects of engineering, with its advantages of low cost, time saving and repeatability [18; 19]. However, for tunnel engineering, the current conventional numerical simulation method for the displacement field of surrounding rock usually inputs mechanical parameters prior to calculation, and these parameters are regarded as constant during the calculation process, which leads the numerical simulation process not reflecting the confining pressure influence on mechanical characteristics and leads the numerical simulation results to clearly deviate from the in situ soft rock tunnel. Therefore, a series of new constitutive models have been established in numerical simulation methods to describe the confining pressure influence on the mechanical characteristics of soft rock; these models include the strain-hardening, Mohr-Coulomb, plastic-hardening, and Hoek-Brown constitutive models [20]. However, these constitutive models mostly focus on the confining pressure effect on strength aspects but neglect the deformation aspect. Meanwhile, the parameters of some new constitutive models are too complex to be generated widely. Therefore, another purpose of this study is proposing a numerical simulation method which can integrally consider the confining pressure effect on the strength and deformation aspects of soft rock, so that results of such a simulation can more realistically reflect the practical displacement field of surrounding rock for soft rock.