## 1 Introduction  
The Tunnel Boring Machine (TBM) method allows tunnels to be constructed with considerable lengths in different geological environments [1; 2; 3]. This method has been widely used around the world [4; 5; 6; 7]; with the technique, it is possible to excavate a tunnel while simultaneously placing a primary lining based on segmental rings. This lining is formed by precast segments, generally of reinforced concrete, that work as temporary or permanent supports (Figure 1a). The TBM method is one of the most used in recent years for the construction of tunnels in soft soils [2; 5; 8; 9; 10; 11; 12]. With this construction technique, segmental rings are formed, which present joints and existing joints between segments (longitudinal joints or segment joints) (Figure 1b), as well as between rings (circumferential joints or ring joints) (Figure 1c). Therefore, this structure cannot be considered to be a continuous lining. In Figure 1, basic components of a typical segmental tunnel are depicted and details of a segment joint (Figure 1b) and a ring joint (Figure 1c) are indicated. The joints perform important structural functions which must be considered for the calculation of internal forces and displacements in the rings. These functions include loading transfer and moment distribution [2; 5; 13; 14; 15; 16]. The importance of the longitudinal joints has been analytically studied by several authors [17; 18; 19; 2; 13; 14; 2] who have obtained their mechanical behavior (moment-rotation constitutive equations). Other authors have conducted experimental research into these structural elements [2; 20; 21; 22; 23; 24; 25; 26]. Some conclusions of these studies are as follows:  
1. The number of longitudinal joints and their position relative to the loads are important factors in the stress level that acts in the ring. 2. The flexural moment and the acting forces in the segments decrease as the number of longitudinal joints in a ring increases. 3. The rotational stiffness of the longitudinal joint depends on the loads acting on it. 4. The mechanical behavior of the longitudinal joints depends not only on their geometry and material but also on the type of connection used and the applied loads in the ring. Figure 1: Basic components of a typical segmental tunnel: (a) lining, (b) longitudinal joint details, (c) circumferential joint details. It should be noted that the axial load \(N\) (Figure 1b) present at the joint, created by the radial pressure imposed by the soil in the tunnel, is not constant throughout the analysis because the load depends on the global stiffness of the lining, making it necessary to perform a series of iterations during the analysis to determine the structural response of the tunnel [2; 24]. However, these iterations are not necessary when using moment-rotation equations as they consider that the axial load \(N\) is variable throughout the analysis [2]. The constitutive equation used in this study was validated by [PERSON] et al. [2] wherein experimental scaled-down models of typical segment joints were tested considering a variable axial load with a constant eccentricity to avoid the iterations during the loading process. In addition, [PERSON] et al. [24] carried out two types of analysis in single rings considering that the axial load at the joint remained constant and variable, respectively, and were able to observe the importance of using equations which consider the variability of this force. Experimental research into circumferential joints has been carried out by some authors. These investigations were presented in the work by [PERSON] [27], where different friction coefficients were recommended depending on the packing material situated on the joint. The load-deformation behavior of this type of joint depends on the normal stress acting on it. On the other hand, there are few experimental (lab-based) research works that include the effect of the coupling between rings of a tunnel created by the construction process of the TBM.