# Dewatering-Induced Stratified Settlement around Deep Excavation: Physical Model Study
## 4 Results
### Settlement of Tunnel  
In the graded dewatering stage, the ground settlement along the tunnel is approximately 57.0% of that in open space because of the constraint effect of the tunnel structure. When buildings are located around the tunnel, the ground settlement will be reduced by 3.0% again (Figure 6). As the key factor that affects tunnel safety, the uneven settlement between JS-1 and JS-5 measuring points is 1.7, 0.9, 0.9, and 2.1 mm, respectively. The maximum uneven settlement appears in the range of 45.0-90.0 m away from the central point of the tunnel (JS-3, perpendicular point to deep excavation), which is mainly affected by the frictional resistance of the diaphragm wall.  
The excavation will cause the displacement of walls and the reduction in earth pressure behind the walls, while to separately analyze the land settlement caused by dewatering, the PMMA tube is used to simulate the diaphragm wall, so the structural deformation caused by excavation is ignored. The value of earth pressure changes on the outer wall of the tunnel near the deep excavation is evidently greater than that under the tunnel (Figure 7), thus indicating that the tunnel is subjected to eccentric force during the vertical settlement process, thereby causing its horizontal movement and rotating to the side of the deep excavation [33]. In soft clay, more than 75% of the vertical ground movement may have occurred into the upper annulus of the oval-shaped gap due to the plastic flow of the yielded clay around the tunnel. Based on the oval-shaped gap geometry, the magnitude of the horizontal movement at the tunnel spring line is approximately half of the vertical movement at the tunnel crown [34]. Unfortunately, this phenomenon cannot be accurately measured because of the model size and the measurement methods [35]. When the groundwater level is recovered, the final settlement of each measuring point rebounds to 39.0-55.0% of the previous stage, and the uneven settlement between the JS-1 and JS-5 measuring points is 1.1, 1.5, 1.2, and 1.8 mm, respectively. The maximum uneven settlement appears around the deep excavation and the buildings, which is also influenced by the frictional resistance of the diaphragm wall and building foundations. After groundwater-level dewatering again, the final settlement increases by 13.0-20.0% compared with the first stage, and the maximum uneven settlement that appeared at the same location reached 2.1-3.0 mm.  
To control the tunnel's settlement, artificial groundwater recharging is added, as shown in Figure 8 groundwater level drawdown in the aquifer decreased to 13.0 m (recovery 35.8% at -60.0 m under the roof of layer ), 6.0 m (recovery 60.0% at -7.5 m under the roof of layer ), and 11.0 m (recovery 13.7% at -7.5 m under the roof of layer ). The final settlement of each measuring point in this stage is approximately 7.0-10.0 mm, which is rebounded to 70.0-80.0% of the previous stage, and the maximum uneven settlement is 2.4 mm near the buildings. Artificial groundwater recharging can protect the  
Figure 6: Vertical settlement along the tunnel.  
settlement of the tunnel and the surrounding strata. However, meeting the settlement control requirements is difficult because of its scope and amount.