# Low Carbon Optimization of Deep Foundation Pit Support in Undulating Strata
## 4 Calculation Results Comparison Analysis
### Analysis of Numerical Simulation Optimization
#### 4.2.1 Results of Foundation Pit Settlement  
The construction process for the deep foundation pit supported by bored piles involves first leveling the site and subsequently executing the pile support construction. After the supporting pile is added to the model, the displacement of the foundation pit unit soil is shown in Figure 7. The strata are uneven; the overlying soil layer is plain fill, and the lower soil layer is granite. As a result of the high elevation in the center of the foundation pit, after site leveling measures are taken, the gravitational stress of the soil is relieved, resulting in an upward displacement of the ground surface with a maximum settlement of 6.58 mm. After driving into the retaining pile, the soil settlement under the foundation pit changes slightly, and the maximum downward settlement displacement of the model is 5.26 mm.  
The excavation of the foundation pit adopts the NULL model, and the settlement of the first inner support is shown in Figure 8. From the side wall of the foundation pit, it can be seen that the settlement inside the foundation pit is almost unchanged due to the action of the supporting pile, which indicates that the supporting pile bears almost all the earth pressure. With the increase in excavation depth, it is obvious that the supporting pile alone cannot maintain the stability of the foundation pit. Therefore, it is necessary to apply internal support and an anchor rod to share the shear force of the supporting pile.  
Figure 6: The overall stability checking diagram of the deep foundation pit.  
Figure 7: Settlement diagram after pile driving.  
The addition of internal bracings significantly reduces the internal force of retaining piles and limits the horizontal displacement of excavation. When FLAC\({}^{\text{3D}}\) 6.0 simulation is carried out, the beam element is used to represent the internal support simulation. The displacement when the internal support is added is shown in Figure 9. Taking into consideration the analysis of the obtained results, it can be concluded that, in addition to the uplift caused by the previous site leveling, the maximum land subsidence is 5.26 mm.  
Finally, the supporting effect of the bolt is simulated. The bolt element is used to reduce the stress on the pile foundation and the inner support, and the durability of the supporting structure is increased. A prestress of 500 kN is applied to the bolt. The displacement settlement after adding the bolt is shown in Figure 10. The observation of Figure 10 reveals that the ground settlement does not change, and the bolt shares part of the shear force of the supporting pile.  
Monitoring points in numerical models are established in the center of the long side of the foundation pit, and Figure 11 illustrates the settlement changes observed throughout the entire construction process. The midpoint settlement of the foundation pit is gradually increasing with the excavation. As the settlement of the support structure is gradually  
Figure 8: Settlement of the pit without internal support after excavation.  
Figure 10: Ground subsidence after adding an anchor rod.  
Figure 9: Settlement diagram of foundation pit with internal support after excavation.  
improved by the side wall, the displacement curve becomes gentle. After the support is completed, the curve is stable, and the maximum surface settlement of the midpoint at the long side of the foundation pit is 2.12 mm.