## 1 Introduction  
As urbanization accelerates and the density of surface buildings and transportation facilities continues to rise, surface transportation is no longer able to meet the growing demand for travel, and underground tunnels are therefore being constructed more and more frequently. However, the tunneling process is often accompanied by ground settlement, which can adversely affect surface buildings and the existing railroad system. For this reason, ensuring the safety of tunnel construction and effectively controlling the ground settlement are key tasks [1, 2]. To this end, effective reinforcement means must be used to minimize the impact of tunnel excavation on the amount of ground settlement [3, 4]. More and more scholars have begun to focus on what can be performed to better reduce the impact of surface subsidence to control the impact of surface subsidence. Many scholars have revealed the settlement mechanism of shield tunnels in conjunction with urban shield tunnels: the construction of double-lane tunnels causes huge settlement on the surface above the centerline of the tunnel, and scholars have reduced changes in surface settlement by reinforcing the soil body, and some of these strategies are methods with which to optimize grouting pressure, soil bin pressure, and so on. However, there are still many great challenges, such as the improvement of prediction models for specific structural settlement criteria and for complex crossing geometries in soft soils. Some scholars have analyzed the theory of changes in surface settlement caused during shield tunnel excavation and found that surface settlement during shield tunnel excavation is symmetrically distributed and conforms to [PERSON]'s theoretical formula [5; 6; 7; 8]. Recent research by some scholars has revealed the critical impact of shield tunneling and some reinforcement methods, such as the reinforcement of bridges, as well as the control of groundwater in the subsoil layer to reduce the impact of surface settlement [9; 10; 11; 12]. Some scholars have explored the key shield boring mechanism, where double tunneling induces asymmetric settlement, as well as the destruction of asymmetric center columns. Some scholars have reduced surface settlement in soft soils by 50% through a two-fluid system, while controlling grouting parameters to minimize soil disturbance. This was verified with numerical simulation, which was consistent with the field data and confirmed the effectiveness of structural reinforcement [13; 14; 15; 16]. Other reinforcement strategies have also been used, such as the use of UHPG for reinforcement in the case of diagonal tunneling, and the use of rubble-cement composites for soil reinforcement, both of which have been effective in reducing changes in surface settlement [17; 18; 19; 20]. Some scholars also adjust the digging attitude, as well as change the shape of the shield machine to reduce the impact of the shield tunnel excavation process brought about by changes in surface settlement; these methods are also certainly effective, but there are some shortcomings that need to be remedied, such as the integrity of the predictive model of complex terrain and other issues [21; 22; 23; 24; 25]. Some scholars have also studied the new SCJB construction method (shaft-roofed box combination) for underground stations to control surface settlement within 15 mm; a reinforcement study has been carried out on the settlement of small-radius curved tunnels [26; 27]. However, with urban planning, space constraints mean that many railways must cross existing railways. The impact caused by trains cannot be equated with static loads. To take into account the real situation of the actual project, the abovementioned reinforcement is not very suitable for construction under such working conditions, and a new reinforcement method must be found to reinforce the subsoil layer to avoid impacting, as much as possible, the operational safety of the existing railway.