## 5 Conclusions  
In this paper, the ground surface settlement and lateral deformation of a diaphragm wall induced by rectangular pedestrian underpass excavations with the PPM were investigated using 3D finite element analysis. According to the analysis results, the following conclusions were reached:  
1. For the south and north sides of the diaphragm wall, the errors between the analysis values and the monitoring values of the surface settlement after the construction of each stage were between 0.3 and 0.78 mm. The results showed that the constructed numerical analysis model had considerable accuracy. 2. The lateral displacement of monitoring point 2 was much larger than the values of monitoring point 1 and monitoring point 3. It was assumed that the main reason for this was that part of the lateral support in the launching shaft was removed for the convenience of personnel operations and the space requirements for equipment placement before the construction of the pipe roof. In this area, only the supports of the first stage and the foundation plate were left to resist the lateral soil pressure outside the diaphragm wall, which in turn affected the lateral displacement of the diaphragm wall. 3. Numerical analysis results showed that the use of the pipe-roof preconstruction method combined with a box culvert structure to form the pedestrian underpass could effectively control the surface displacement above the box culvert. For the four different aspect ratios, the final subsidence of the ground surface was within 2 cm, which was in line with past construction experience. 4. With the increase in the aspect ratio, the excavation would cause the surface subsidence above the underpass to gradually decrease. In other words, under the condition of the same sectional area, the smaller the width of the pipe-roof structure, the more the impact on the ground surface was reduced. 5. As the aspect ratio increased, the maximum positive bending moment and the maximum negative bending moment gradually decreased. The results showed that the maximum positive bending moment and the maximum negative bending moment on the pipe roof produced by excavation in each stage were roughly inversely related to the aspect ratio. 6. The shallow-buried box culvert was more sensitive to the subsidence caused by construction than the deep-buried box culvert. 7. The shallow-buried box culvert was affected by the buoyancy of groundwater, and on the other hand, the overall weight of the culvert decreased with the excavation, so the vertical displacements of the observation points tended to decrease. 8. The simulation analysis showed that under different overburden depths, the vertical displacement trends of the shallow-buried box culvert at the observation point on the top or bottom in each excavation stage were roughly the same. According to the analysis results, the maximum lateral displacement of the diaphragm wall caused by the excavation of the launching well was 27.95 mm, which was caused by the removal of part supports, and its value was very close to the design warning value (30 mm). Therefore, it is suggested that in actual engineering, more attention should be paid to the lateral displacement of the diaphragm wall caused by the removal of part supports for the convenience of personnel operations or the space requirements for equipment placement before the construction of the pipe roof. In addition, for the surface subsidence around the excavation area, the maximum subsidence value on the north side and south side was about \(-7\) mm and \(-10\) mm, respectively, the difference from the on-site monitoring data was within 1 mm, and the subsidence influence range was about three times the excavation depth. From this point of view, the model boundary was set to 5 times the excavation depth, which was sufficient to cover the impact of excavation in each stage on surface subsidence. and S.-W.C.; resources, S.-L.C. and X.-L.Z. ; data curation, C.-W.T. and S.-W.C.; writing--original draft preparation, C.-W.T. ; writing--review and editing, C.-W.T.