# Research on Optimization Design of Tunnel Blasting Scheme Adjacent to Buildings
## 4 Optimal Design of Construction Parameters
### Exavation Feed Comparison  
Due to the presence of buildings adjacent to the tunnel, there will be a certain degree of damage to those above the tunnel as its excavation continues. The main problem is the differential settlement of the buildings caused by an uneven ground settlement. The building in this study is of a frame concrete structure with a strip foundation. In [PERSON]'s study [30], it was shown that the building settlement caused by the excavation of the upper half tunnel section accounted for more than 80% of the total settlement. In order to simplify the calculation, the upper section was excavated separately based on the numerical simulation to compare the effect of different working conditions on building settlement. The results recorded at the monitoring points during excavation with different  
Figure 8: Comparison of the vertical vibration velocity of different blasting schemes.  
Figure 9: The vibration velocity of the combined mechanical excavation and blasting scheme.  
feeds were compiled by considering the self-weight load of the building, and the settlement of its foundation under the two working conditions was plotted, as shown in Figure 10.  
Comparing the circular feeds of 0.5 m and 0.75 m, the maximum settlement value of the building foundation when excavating using a circular feed of 0.5 m was 18.53 mm at the upper section of circular feed excavation of 0.5 m, and 22.71 mm using that of 0.75 m. In the actual construction, the excavation of the lower section of the tunnel is also taken into account; therefore, the foundation settlement after the excavation of the upper section divided by 80% is used for the calculations, and the foundation settlement with a circular footage of 0.75 m reaches 28.38 mm. An uneven settlement occurred on the sides of the building near and facing away from the tunnel; thus, the tilt degree of the building should be considered. The building tilt rate was 0.099% at a cycle feed of 0.5 m, which reached 0.122% at a cycle feed of 0.75 m.  
Although the settlement and tilt degree of the building met the regulations in the Code for the Design of Building Foundations [31], the foundation settlement of the building reached 28.38 mm at the circular feed of 0.75 m, which was close to the limit value of the foundation settlement of the building in the Code. However, the construction tunnel is in a class V fenestration section [32] with poor geological conditions. [PERSON] [33] showed in his research that the damage area reduced with the increase in rock class. The stability of the fenestration rock needs to be compared. Figure 11 shows the surrounding rock plastic zone at a circular footage of 0.5 m and 0.75 m. By comparing the plastic zone of the surrounding rocks, it can be seen that the plastic zone at the shoulder of the tunnel arch increases significantly in extent at a cyclic feed of 0.75 m, which is not conducive to construction safety. Taking into account the settlement of the building foundation, the tilt degree and stability of surrounding rocks, the final determination on the cantilever boring machine excavation in the upper section of the tunnel is 0.5 m in a cycle.  
Figure 10: Building settlement under different working conditions: (**a**) circular footage of 0.5 m; (**b**) circular footage of 0.75 m.