## 1 Introduction  
Mechanical tunneling method has been widely employed in tunnel construction in recent decades. The tunnel boring machine, a.k.a. TBM, is a predominant choice in this tunneling method. The influence of traditional tunneling processes on surrounding environment, e.g., adjacent structures and stratum, cannot be neglected in the construction of underground infrastructure in congested urban areas [1]. TBM-driven processes and excavation of working shafts are two sources of the environment impact in tunnel construction. For TBM-driven-induced influence on adjacent environment, various research has been carried out using experiments [2; 3; 4; 5], numerical simulation [6; 7; 8; 9; 10; 11; 12; 13; 14; 15], analytical study [16; 17; 18; 19; 20; 21; 22; 23], and field observation [24; 25; 26; 27; 28; 29; 30; 31; 32]. The existing research reveals that the tunneling-induced influence is significantly related to particular tunneling variables, such as tunnel heading pressure and tail-grouting pressure [33; 34], especially for twin-tunneling activities in which the excavation of the second tunnel imposes remarkable effect on adjacent first tunnel [15; 25]. In addition, spacing between the twin tunnels notably affects both the soil movements and lining internal forces. Previous studies [10; 35] prove that the second tunnel construction reduces the bending moment of the first tunnel lining, while the first tunnel induces slight changes in the bending moment of the second tunnel lining. According to [PERSON], et al. [36], excavation of the first tunnel usually results in greater surface settlement than that of the second tunnel, and tunnel uplift can be minimized by optimizing the tail-grouting variables.  
In order to avoid influence of shaft excavation during traditional tunneling, the ultra -rapid under pass (URUP) TBM tunneling method was proposed initially for underground infrastructure in Japan [37; 38; 39]. The TBM is launched and received at the ground surface in the URUP tunneling process. Previous research has been carried out to analyze the ground responses during negative-overburden and shallow-overburden tunneling phases [33; 34] of the first demonstration work in China. The field monitoring and nonlinear finite element analyses (FEA) on this URUP demonstration work revealed that [33; 34]: (1) the grouting pressure should be considered as a non-uniform distribution during negative- and shallow-overburden tunneling phases; (2) a cover-diameter ratio of 0.55 can be considered as a critical magnitude under which the tunnel face cannot maintain stability; and (3) the Gaussian curve can be employed for the settlement prediction at the ground surface during shallow URUP tunneling under a C/D \(<\) 0.55 (C/D is cover-to-diameter ratio).  
Existing studies have been focused on the ground responses without detailed investigation on segment internal forces during URUP tunneling, especially for TBM launching of the second tunnel which is adjacent to the first URUP tunnel. The paper presents a comprehensive FEA investigation of the TBM-driven influence on adjacent first tunnel during twin-tunneling using the URUP method. The URUP demonstration work of Nanjing Metro [33] was selected as the tunnel prototype of the FEA. The paper is organized as follows. First, the URUP tunnel of Nanjing Metro is reviewed, and the field monitoring program on segment internal forces is introduced. Second, the FEA model for the URUP tunnel is validated for analyzing the segment internal forces (i.e., the bending moment) by comparing the numerical results with the monitoring data. Finally, the influence of TBM launching on the segment internal forces of adjacent first tunnel is explored by FEA parametric study.