# Experimental Study on the Soil-Structure Responses Induced by Tunnelling in Limited Space
## 1 Introduction  
Due to the sharp growth of the economy all over the world, the demands for tunnels in large cities are greatly increasing [1; 2]. Many studies have reported that metro systems could bring multiple benefits to urban development but can also induce new engineering challenges and risks [3; 4]. As the shield tunnelling approach has flexibility and could cause little negative influence on the environment, this construction technique has been widely adopted in many large cities. It is widely recognized that the construction of new tunnels in non-confined spaces could induce great soil stress release [5; 6; 7; 8; 9], which may have inevitably significant impact on the ground settlement and the tunnel. Based on many case histories, [PERSON] (1969) [10] and [PERSON] (1969) [11] first proposed an innovative pattern for ground settlement and used Gaussian shapes to represent this pattern. Subsequently, many scholars conducted long-term studies to investigate the ground settlement and tunnel deformation caused by tunnelling. Many scholars [12; 13; 14; 15; 16] used the field data to provide valuable references for the validation of the proposed prediction methods. Based on the reported findings [17; 18], tunnelling-induced soil movements are radial displacements towards the tunnel cavity and longitudinal displacements towards the advancing tunnel heading. Additionally, ground loss was the key factor that affected the range and maximum ground settlement [19]. [PERSON] et al. (2011) [20] investigated the factors affecting ground surface settlement due to shallow tunnel excavation and indicated that the buried depth and diameter of the tunnel could have a significant impact on the distribution of ground settlement. As the tunnel could deform distinctly during the construction process, the tunnel responses were also investigated extensively. When tunnels were excavated in non-confined spaces,Xue et al. (2020) [21] pointed out that the tunnel will be compressed vertically. Through field monitoring, model tests and numerical analysis [22; 23], the ground loss ratio and the shape of the tunnel could have a direct influence on the tunnel deformation and the internal forces in the linings of the tunnel. Based on the model test and the numerical analysis, many investigators [24; 25] concluded that the maximum positive bending moment of the tunnel was likely to appear at the tunnel crown and the maximum negative bending moment was at the waist of the tunnel. In actuality, as the underground spaces in urban areas are becoming more and more congested, new tunnels will be inevitably constructed near the adjacent existing underground infrastructures. Accordingly, the responses of the surrounding environment induced by close-proximity tunnelling have become a major concern of society [3; 26]. Many researchers have pointed out that the presence of the existing underground structures could have a non-negligible influence on the soil movement and deformation of tunnels [27; 28]. [PERSON] et al. (2012) [29] compared numerical simulation results and in situ monitoring data and concluded that the existing metro stations and surrounding buildings would affect the ground settlement pattern and that new tunnels would also experience uneven deformation. [PERSON] et al. (2022) [30] conducted a model test to study tunnel-pile interaction. The results showed that existing piles would affect the range of the ground settlement to some extent. [PERSON] et al. (2009) [31] focused on the shield tunneling and environment protection in Shanghai soft ground. The results revealed that existing buildings with large stiffness could greatly affect the distribution of the soil displacement and the tunnel deformation. By conducting model tests on close-proximity tunnelling, [PERSON] et al.