# Research on Construction Sequencing and Deformation Control for Foundation Pit Groups
## 4 Discussion  
### Comparison of Segmented Foundation Pit Deformation Under Different Exaxation Sequences  
The experimental findings on segmented pit deformation align with and extend previous research on excavation sequencing effects. [PERSON] et al. [13], studying large-scale zoning excavation in Hangzhou soft soil, similarly emphasized the significant reduction in overall deformation achievable through sectional excavation but highlighted the critical need for sequence optimization to balance support forces. Our results quantitatively demonstrate this optimization: Figure 20 compares the maximum horizontal displacements of the diaphragm walls under the three different construction sequences. The maximum positive displacement of the shared wall 2# occurs under the shallow-to-deep construction sequence, measuring 0.394 mm. For the shared wall 2#, the maximum positive displacement is observed in the shallow-to-deep construction sequence, reaching 0.278 mm. The maximum positive displacement of wall 3# is found in the shallow-to-deep construction sequence, at 0.406 mm. As shown in the figure, compared to the other two construction sequences, the \"shallow-to-deep\" sequence results in the largest deformation of the retaining walls. In contrast, the \"deep-to-shallow\" construction method demonstrates some effectiveness in controlling the deformation of the exterior walls (1# and 3#), reducing their maximum horizontal displacements by 0.132 mm and 0.286 mm, respectively, compared to the \"shallow-to-deep\" condition. Additionally, synchronous excavation, due to the simultaneous unloading of soil on both sides, proves highly beneficial for controlling the deformation of the shared wall 2#. Compared to sequential excavation, the lateral displacements are reduced by 0.178 mm and 0.286 mm, respectively. This suggests that prioritizing deeper section excavation mitigates the impact on the exterior walls of the shallower pit, a strategy less explicitly quantified in previous case studies like those reviewed by [PERSON] et al. [38]. Additionally, synchronous excavation, due to the simultaneous unloading of soil on both sides, proves highly beneficial for controlling the deformation of the shared wall 2#. Compared to sequential excavation, the lateral displacements are reduced by 0.178 mm and 0.286 mm, respectively. This significant reduction (18-25%) underscores the efficiency of bilateral symmetrical stress relief, a mechanism less emphasized in the existing literature focused primarily on sequential methods. Figure 19: Active earth pressure on the retaining structure. The excavation sequence results in varying degrees of deformation in the retaining structure of the foundation pit due to changes in the stress path and stress state of the soil. In the case of \"deep-to-shallow\" construction sequence, the soil within Pit A initially undergoes vertical unloading caused by the excavation of Pit A, followed by lateral unloading induced by the excavation of Pit B. Conversely, in the case of excavating the shallower section first followed by the deeper section, the soil within Pit A first experiences lateral unloading due to the excavation of Pit B, followed by vertical unloading resulting from the excavation of Pit A. The differing stress paths under these two scenarios lead to distinct developments of plastic deformation in the soil, which in turn modifies soil parameters such as stiffness. Consequently, this results in variations in the deformation of the retaining structure and the ground surface. It is evident that, compared to conventional single-pit excavation, the stress paths in segmented foundation pit excavation are more complex and diverse due to the multiple unloading effects and varying unloading methods. This complexity, highlighted as a research gap in the Introduction, is systematically addressed here through controlled model tests.