## 1 Introduction  
The Yangtze River Delta urban agglomeration in China consists of Shanghai and three provinces, Jiangsu, Zhejiang, and Anhui. In recent years, to promote the regional integrated development and construct rail transit networks in Shanghai, Nanjing, Suzhou and other cities, the construction of rail transit within and between cities is being vigorously developed. For example, the Suzhou Metro Line S1 project connecting Shanghai and Suzhou is under construction [1, 2]. The Yangtze River Delta is located in the lower reaches of the Yangtze River in China, bordering the Yellow Sea and the East China Sea. Consequently, it is an alluvial plain formed before the Yangtze River enters the sea and is mainly composed of soft clay and sandy soil [3, 4]. Among soils, the mucky-silty clay is characterized by high moisture content and low strength coupled with high compressibility and sensitivity, which is one of the stratigraphic characteristics of the Yangtze River Delta and challenges underground engineering construction [5, 6]. For example, the shield has become the prevalent choice for tunneling activities in congested urban areas due to its safe working environment and small disturbance to the surrounding ground. However, when the shield tunnels in (very) soft clay, both the construction and post-construction period face the challenges of ground and tunnel settlement control, i.e., Shanghai Metro Line 1 has experienced a maximum settlement of 288 mm within 12.5 years [7], Nanjing Metro Line 10 has experienced a maximum settlement of 240 mm within 5.75 years after the track system was constructed [8], and Daiba tunnels suffered from excessive settlement due to the ongoing consolidation of the soft clay layer caused by adjacent construction [9]. This is mainly because the tunneling disturbance greatly reduces the strength of the soil with high sensitivity and aggravates the construction settlement. In addition, the deep and highly compressive soil may also produce larger consolidation settlements [10; 11]. Moreover, construction parameters, such as the grouting volume and the grouting pressure, have a great influence on the soil loss and the distribution of the pore water pressure, which also affects the short-term and consolidation settlement of the ground and tunnel [12; 13; 14]. Moreover, poor shield posture and segment posture always accompany shield tunneling in soft soil, which induces segment seal failure and increases post-construction settlement [15; 16; 17]. Scholars conducted extensive research to explore the ground and tunnel settlement in soft soil, including both construction period settlement [18; 19; 20; 21; 22; 23; 24; 25; 26] and long-term settlement [27; 28; 29; 30; 31; 32]. The short-term subsidence was studied mostly based on the Peck and modified Peck empirical formulas based on similar engineering experience, and also includes theoretical and numerical studies based on formation losses. The research on long-term settlement mainly focused on the effects of consolidation, secondary consolidation, and train loads, which were mostly studied using two-dimensional numerical simulations and on-site monitoring. However, field data were difficult to obtain and mostly used for qualitative analysis. Moreover, the modified Cambridge model, which is most suitable for describing the stress-strain relationship of soft clay, was rarely used in previous numerical simulation studies, especially in the three-dimensional numerical model of long-term settlement. In addition, long-term settlement is closely related to construction disturbance and parameters. However, it is rare to discuss the influence of construction parameters, such as grouting amount, grouting pressure, and segment leakage caused by poor construction, on the long-term settlement of the tunnel. Based on the project of Suzhou rail transit line S1, this paper presented a three-dimensional numerical model to evaluate the short-term and long-term displacement of the soft soil and tunnel when constructing shield tunnels in soft soil.