## 1 Introduction  
By the end of the 13 th Five-Year Plan, the mileage of the subway lines built in China is expected to exceed the set target. With rapid infrastructure development in urban areas, there is an increasing demand for the construction of subway tunnels that are adjacent to existing ones due to limited underground space. In this context, it is essential to ensure the safety and stability of existing tunnels during adjacent construction activities. Conditions caused by the construction of the adjacent tunnel, such as temporary overloading on the ground, will adversely affect the existing tunnel, and the changing stress balance of the tunnel will result in uneven settlement. When the tunnel stress field reaches a certain threshold, segmental rupture, leakage, segmental joint opening, and varying degrees of other damage will occur. Some damage can even affect the structure and normal operation of the subway tunnel. Several scholars [1; 2; 3; 4; 5; 6; 7; 8; 9] have reported cases of tunnel structure damage caused by nearby ground surcharges. With the continuous increase in the mileage of subway lines, the development of surcharges along the subway tunnel will inevitably occur. The rapid and reliable prediction of the response of the existing tunnel structure to surface surcharge is an important subject to ensure the safe, stable, and normal operation of subways. Ground overloading changes the stress state of the existing stratum and causes stress release by the soil, thus resulting in the nonuniform settlement deformation of the existing tunnel. Domestic and foreign scholars have used different methods to conduct in-depth analyses of the responses of existing tunnels to ground surcharge [10; 11; 12; 13; 14]. [PERSON] et al. [15] used physical model tests to analyze the deformation response of an existing tunnel subjected to surcharge under different conditions, such as the spacing between the ground surcharge and the existing tunnel and the buried depth of the tunnel. [PERSON] et al. [13] carried out an equal-scale indoor model test to analyze the change in soil stress around the tunnel caused by ground surcharge. Their results show that the soil above the existing tunnel bears high pressure, and the earth pressure is positively distributed above the tunnel axis. As the distance from the tunnel axis increases, the earth pressure gradually decreases. [PERSON] et al. [16] carried out indoor model tests and demonstrated the applicability of the proposed theoretical method through indoor test simulations. The error between the model test results and the theoretical calculation results was less than 10%, which is within the allowable range. Finite element analysis software can be used to fully simulate the geological conditions of a construction site, and the construction step sequence is widely studied. [PERSON] et al. [13] used three-dimensional finite element software to simulate changes in the deformation and internal force of an existing tunnel subjected to ground overloading, and they verified the accuracy of the simulation by comparing the outputs with the results of indoor model tests. [PERSON] et al. [17] used finite element software to simulate the deformation responses of single and parallel tunnels under ground surcharge conditions and compared and analyzed them with published field data. Using the Port of Shanghai Small Lai channel fill project as the background, [PERSON] et al. [18] used 3D finite element software to simulate and analyze the ground using the Hardening Soil Model with small-strain Stiffness constitutive model (HSS model) of a soil-pile load response to an adjacent tunnel. They studied the influence of the relative positions of the pile and tunnel and the tunnel buried depth on the existing tunnel and observed that improving the soil stiffness could effectively reduce the action of the pile on tunnel deformation.