## 1 Introduction  
For large span tunnels excavated in the weak and broken surrounding ground, excessive deformation and potential damage may take place ahead of the excavation face. Pre-construction techniques have been extensively used to minimize pre-deformation and pre-failure of the rock mass. Pre-construction techniques can be divided into pre-support techniques and pre-reinforcement techniques. The core of pre-support techniques is transferring and bearing the rock load to prevent tunnel collapse, while the core of pre-reinforcement techniques is improving the strength and rigidity of surrounding rock to maintain tunnel stability. In tunnel engineering, the pipe roof and curtain grouting are commonly used as the representative techniques of pre-support and pre-reinforcement, respectively. Pipe roof pre-support (PRPS) consists of grouted steel pipes with large moment inertia. These pipes are circumferentially inserted from the tunnel face with the pipe diameter of 50-200 mm and the advanced length of 20-50 m. With the great stiffness of the steel pipe, the PRPS system could redistribute the stress state ahead of the tunnel face and eventually decrease the ground settlement [1]. Since its first application in Japan in 1971, the PRPS method has been successfully applied to minimize excavation interference and prevent ground collapse in the weak stratum or crossing projects. [PERSON] [2] found that PRPS could effectively control the ground settlements caused by metro tunnel excavation in the clayey ground. The PRPS method was approximately three times more efficient than the new Austrian tunneling method (NATM) in controlling surface settlement in the same geological ground. [PERSON] et al. [3] compared two pipe roof installation methods, including the cased-drilling method and the predrilling method. By on-site measurement with the horizontal inclinometer, they summarized that the cased-drilling method was preferred in strain sensitive ground owing to its better performance in preventing water saturation and flushing erosion. [PERSON] et al. [4] concluded that PRPS could significantly improve roof conditions by bearing and transferring the vertical pressure. They also noticed that with the increase of the diameter and amount of PRPS, the ground subsidence was considerably reduced. [PERSON] et al. [5] numerically modeled the pipe roof with beam elements, and they found that the bending moments of the pipe roof varied with different pipe diameter and pipe spacing. A design criterion for PRPS was put forward based on the numerical bending moment and the analytical bending stress derived by the flexure formula. Then, they suggested a broken rock mass that the pipe roof should hold up ranged from 1.5 to 3 m. [PERSON] et al. [1] proposed a double-parameter elastic beam model to analytically investigate the working mechanism of PRPS used in the tunnel entrance. The results showed that the load carried by PRPS greatly increased with the deterioration of the surrounding ground, and the load transferring capacity improved with the stiffness increase of primary lining. [PERSON] et al. [6] underlined that the PRPS was necessarily demanded in the excavation of the Laliki tunnel in the Carpathian flysch. Through field monitoring, they verified the important role of PRPS in preventing rock falling and reducing surface deformation. Curtain grouting pre-reinforcement (CGPR) is injecting cement-based slurry ahead of the tunnel face with the grouting thickness of 1-10 m and the diffusion distance of 10-25 m. Owing to the filling, permeating, compaction, and splitting effect of the CGPR, the broken rock mass could be reinforced, and the ground permeability could be reduced. The CGPR method has already been widely adopted in dam construction [7; 8] and slope stabilization [9; 10]. In complex tunneling engineering, the grouting method has also shown a significant effect in ground consolidation [11], settlement compensation [12], shear strength enhancement, and water tightness increment. [PERSON] et al.