# Model Test Study on a Shield Tunnel Adjacent to Pile in the Sub-Clay of a Coastal Area
## 4 Test Results
### Surface Deformation  
The gap caused by shield tail prolapse was the main cause of surface deformation, and slurry filling was the main means of controlling surface deformation. According to the following formula, the free space and similar gap can be calculated as follows:  
\[V_{\text{gap}}=\pi\Big{[}R^{2}-\left(R-d\right)^{2}\Big{]}\cdot L=3.14\times \Big{[}4^{2}-\left(4-0.2\right)^{2}\Big{]}\times 2=9.8\Big{(}\text{cm}^{3}\Big{)} \tag{8}\]  
where: \(V\) is the volume of gap; \(R\) is the radius of the shield; \(d\) is the thickness of the shield; \(L\) is the movement distance. The filling coefficient of the grouting was stipulated 1.4-2.5 in the code of the specification for shield construction of Metro Tunnel Engineering (STB/DQ-010001-2007). Considering the silty clay characteristics of the surrounding layers in this test, the grouting filling coefficient of 1.2, 1.4, 1.6 and 1.8 were selected to analyze the law of ground settlement and the surface sedimentation when \(H/D=1\). When the grouting filling coefficient changes: 1.2\(\rightarrow\)1.4\(\rightarrow\)1.6\(\rightarrow\)1.8, the displacement change law of measuring points 1-5 during the shield process is given in Figure 14 and the maximum surface settlement is \(-0.985\rightarrow-0.422\rightarrow-0.213\rightarrow\)0.186 mm. The contours show that when the grouting filling coefficient reached 1.6, there was a certain degree of uplift in the soil layers, and when it reached 1.8, the surface uplift occurred. Figure 14: _Cont._  
Figure 13: Final state when \(H/D=3\). When the grouting filling coefficient was 2.0, surface slurry leakage occurred; the process is shown in Figure 15. At first, the grout around the grouting hole diffused unevenly (the infiltration trend was obvious); Then, the two grouting hole diffusion rings were combined; Finally, the slurry penetrated the soil layers between the grouting holes, raising the soil layers as a whole, and the slurry lifted up vertically at the weak position. Generally, the subway construction settlement should be controlled within 30 mm. The test settlement value should be controlled within 0.3 mm according to the test similar scale of 1:100. The surface heavy displacement with different grouting filling coefficients  
Figure 14: Displacement and contour of measuring point during shield tunneling: (**a**) Grouting filling coefficient 1.2; (**b**) Grouting filling coefficient 1.4; (**c**) Grouting filling coefficient 1.6; (**d**) Grouting filling coefficient 1.8. Figure 15: Grout flowing when grouting filling coefficient 2.0: (**a**) 1 hole; (**b**) 2 holes; (**c**) Grout diffusion; (**d**) Surface diffusion. is shown in Figure 16, where the grouting filling coefficient was 1.4-1.6, and the surface displacement was relatively uniform, meeting the control conditions. The influence of different filling factors on the vertical and horizontal displacement of piles is shown in Figure 17. The displacement of piles decreases with the increase in filling factor overall. The displacement of piles is sensitive to the filling coefficient in the range of 1.4-1.6. The horizontal displacement appeared to reverse increase in the range of 1.6-1.7 and upwarping deformation appeared. Based on the observed surface settlement and pile displacement, the recommended range of grouting filling coefficient in the silty clay layer was 1.4-1.6. The grouting filling coefficient of the gravel stratum test was given as 1.7-2.0 [7], and the grouting filling coefficient of the Shanghai shield project through muddy clay [8] was determined to be greater than 1.32. By comparing and analyzing the parameters obtained from relevant engineering cases, it could be concluded that the range of grouting filling coefficient given by this test relatively fluctuated near the above range.