## 1 Introduction
It is of little significance to discuss the supporting time of the tunnel in the hard rock, but the time effect of the surrounding rock deformation in the soft rock tunnel is obvious[PERSON] The determination of supporting time has a practical and positive significance for soft rock tunnel engineering. Based on many experiments, the researchers represented by [PERSON] put forward the shear strain control theory [12]. This theory holds that the maximum shear strain calculated by a certain theoretical formula is equal to the allowable shear strain of the stratum, which is the best support time, and gives the experimental formula to determine the best support time. [PERSON] et al. [13] introduced the global safety factor as the critical indicator to evaluate a tunnel's stability, established the comprehensive graphic relationship between the global safety factor and the distance to the tunnel face, and proposed a methodology to determine the appropriate timing of initial support installation. [PERSON] et al. [14] proposed the stress release law of the surrounding rock under support based on the displacement back analysis method and determined the optimal supporting time of the initial supporting structure by comparing the stress release ratio with surrounding rock displacement. [PERSON] et al. [15] studied the time-dependent deformation of a road tunnel in squeezing ground conditions and performed a series of 2D plane strain finite element analyses to reproduce the monitored time-dependent convergence. The results highlight the necessity of considering time-dependent phenomena in the selection of support systems. [PERSON] et al. [16] provided an analytical approach to estimating the influence of the compressible layer on the tunnel performance including the influences of the lining installation time. [PERSON] et al. [17] proposed an analytical model for the tunnel supported with a tangentially yielding liner in viscoelastic ground and analyzed the influence of the installation time of liner. [PERSON] et al. [18] proposed an analytical model to provide a good prediction of the time-dependent tunnel convergences in the Saint Martin La Porte access adit and studied the influence of the installation time of yielding lining. [PERSON] et al. [19] provided a semi-analytical approach to accurately address the elastic stress and displacement around shallow lined tunnelsinduced by tunnel excavation and lining installation. [PERSON] et al. [20] presented a theoretical solution to predict long-term tunnel convergence and long-term induced lining pressure and further studied the problem by numerical approach using FDM. The results show that the support installation time and the radius of the altered zone have remarkable effects on the output results. [PERSON] et al. [21] conducted a non-linear finite element analysis to reproduce the convergences measured focusing on time-dependent rock behavior. [PERSON] et al. [22] studied elastic-plastic solutions for frost heaving force of cold region tunnels and proposed that a proper supporting time is beneficial to the safety of construction and operation for tunnels in cold region. [PERSON] et al. [23] analytically built a mechanical model of a circular tunnel with a rock bolt-lining combined system, derived mathematical formulas for the stresses and displacements around the tunnel, and investigated the influence of the installation time of the rock bolts and the lining. In summary, the current research on the tunnel in the Xigeda stratum mainly focuses on its mechanical properties and deformation control. Few scholars have studied the influencing factors of tunnel deformation in the Xigeda stratum and the timing of support construction. In this paper, a longitudinal deformation formula considering the water content factor is proposed based on numerical simulation and numerical analytical methods. Then, the recommendations on the timing of tunnel support construction in Xigeda strata is given combining the convergence-constraint method.