## 1 Introduction  
With the continuous advancement of urbanization, many large-diameter shield tunnels have been built in Shanghai, Nanjing, Wuhan and other cities in China. During the construction of shield tunneling, it's the support pressure that counteracts the effective earth pressure and water pressure. Ground deformation at the front of the tunnel face that occurs immediately before the shield tunnel's arrival is due to the imbalance of the support pressure at the tunnel face, which is approximately accounted for 10-20% of the total displacement induced by shield tunneling [1, 2]. The assessment of ground deformation induced by support pressure is still one of the keys to ensuring the control of excavation face especially in the urban area, where too large/small ground deformation can easily lead to accidents [3, 4, 5]. Therefore, it is of great significance to clarify the range of excavation face support pressure and its influence on ground deformation during shield tunneling [6, 7]. Over the decades, numerous studies including theoretical, experimental and numerical have been performed to investigate the stability of the excavation face and its influence on the ground deformation [8; 9; 10; 11; 12]. Since the experimental method is still an effective and intuitive way to study the phenomenon and failure mechanism of face stability, a lot of laboratory models have been conducted by researchers [7; 13]. An original laboratory reduced-scale model of earth pressure balanced shield was carried out by [14] to investigate the mechanisms of face collapse and blow-out of tunnels driven in soft grounds. Several centrifuge model tests and three-dimensional finite element analyses have been conducted to study the passive failure mechanisms of tunnel face for tunnels located at different cover over diameter (C/D) ratios [15; 16; 17]. In addition, the influence of the advanced status of EPBS machine [18], the steady state seepage [19], the soil density [20] and water content [21], etc., on the face failure mechanism and ground displacements were also investigated by conducting a series of the centrifuge or constant gravity tests. In parallel with these experimental studies, many analytical models for calculating the stability of the face have been proposed. Among these, limit analysis and limit equilibrium approaches are the most typical methods to predict the support pressure of face active/passive failure [22; 23; 24]. They have been used extensively and extended in many subsequent works. To further assess the capability of theoretical models, centrifuge tests were performed on a small-scale model in dry sand [25]. Additionally, some semi-analytical [26] or empirical [27] methods have been proposed to calculate the displacement induced by tunneling. Ref. [28] describes a new modified prediction method of surface settlement for Xi'an Metro, which can take into account the support pressure of the shield head at the tunnel face. Ref. [29] proposed an approach to estimate three-dimensional ground displacements induced by shield tunneling using the superposition method, advocating consideration of the support pressure during shield tunneling. As for numerical simulation, three-dimensional (3D) discrete element method (DEM) using PFC3D [30], the finite difference method based on FLAC3D [31; 32], the finite element method using PLAXIS 3D [33], COMSOL [34], etc. [35; 36], were applied to analyze the face stability and ground deformation. However, the validity of numerical analyses should be checked, either by in situ measurements or by laboratory model tests since it's generally difficult to adopt the proper constitutive model and parameters of the materials to model the real state of the tunnel.