# Displacement Analyses of Main Structure of Parallel Pit Excavation and Analysis of Countermeasures
## 3 Parallel Pit Excavation Scheme
### Retaining Wall Deformation
#### 4.2.3 The Steel Pipe Structs' Horizontal Deformation
Under the condition of Case 2, with the excavation in Area C completed, the lateral deformation of the steel pipe structs is shown in Figure 16.  
As can be seen from Figure 16, after the completion of excavation in Area C, the overall horizontal deformation of the steel pipe structs decreases; the deformation direction of the steel pipe column Struct 1 and Struct 4 is opposite, and the deformation trend of the steel pipe structs is similar to that of Case 1; the structure of the adjacent excavation side (Struct 1 and Struct 4) is deformed to Area A and C, respectively; and the maximum deformation of steel pipe structs is 10.2 mm. After the completion of excavation in Area C, the soil pressure in Area B was distributed to Area A and C, respectively, which caused the deformation of the steel pipe structs to the excavation side, respectively; in addition, the deformation of the steel pipe structs in the opposite direction produced the mutual restraint effect. Compared with only the excavation in Area A, the maximum deformation of the steel pipe structs was reduced by 31%. Although the deformation of the structure is reduced after the excavation is completed in Area A and C, it still exceeds the design value by 25%. Therefore, such a construction plan should be avoided during the construction process. Under Case 3 conditions  
Controlling the staggered spacing of the pit excavation can significantly reduce the asymmetric external stresses acting on the steel pile structs by the asymmetric excavation. Figure 17 gives the horizontal deformation curves of the steel pile structs under Case 3. The deformation trends of the steel pipe structs is similar between Cases 3 and 1, which show the deformation of Struct 1, Struct 2, and Struct 3 to the excavation side of Area A, with the deformation of Struct 4 to the excavation side of the north side. The staggered spacing of the excavation in the A area and C area is controlled within 3 m, and the staggered spacing is small, and the additional stresses acting on the steel pipe structs are not obvious. It shows that a reasonable staggered spacing can reduce the influence of the asymmetric earth pressure on the structure. The smaller the staggered spacing, the smaller the asymmetric additional earth pressure and the smaller the horizontal deformation of the structure. Figure 17: Case 3: staggered excavation, steel pipe column structure horizontal deformation. Under Case 4 conditions  
As shown in Figure 18, the deformation of the steel pipe structs above the middle 1 slab in Area B is consistent and approximately a straight line after the middle 1 slab cast. In addition, the horizontal deformation of the steel pipe structs is only 3 mm; this indicates that the bottom plate, top plate, beam, and steel pipe column form a \"frame\", which effectively increases the overall stiffness of the main structure of Area B and resists the influence of additional external loading. The horizontal deformation of the steel pipe structs below the middle 1 slab is significantly reduced, with a maximum value of 5.8 mm; the trend of horizontal deformation of the steel pipe structs is similar in Cases 4 and 3, but the horizontal deformation of the structure is reduced by 30% compared with Case 3. Therefore, the early closure of the structure in Area B can effectively resist the additional stresses generated by the asymmetric excavation of the foundation pit, and the additional impact on the steel pipe column structure is minimal. Case 4 should be adopted as much as possible in the actual construction process.