## 5 Recognition and Validation of Inadequate Grouting Section
### Application Effect Evaluation of Countermeasure by Field Monitor  
Through field monitor, the application effect of countermeasure of grouted engineering spoil backfill giant karst cave is analyzed. Figure 15 shows the monitoring results of the horizontal convergence of Yujingshan tunnel. Figure 15a shows the horizontal convergence on the upper step. It shows the tendency of gently increasing first, then rapidly increasing, and finally reaching a stable state. The maximum horizontal convergence is located at D3K279 + 885 section, with a value of 34.47 mm. The D3K279 + 896 section also has a large horizontal convergence, with a maximum value of 36.57 mm. In the rapid growth stage, the convergence velocity of the D3K279 + 885 and D3K279 + 896 are 0.91 mm/d and 1.25 mm/d, respectively. The results show that the maximum value and maximum velocity appear at D3K279 + 896 section, indicating that the grouting effect is not preferable. The horizontal convergences of most sections are only 8-13 mm, and the convergence  
Figure 14: The cores of D3K279 + 898 and D3K279 + 925 section. (**a**) D3K279 + 898 section 2–8 m. (**b**) D3K279 + 898 section 8–14 m. (**c**) D3K279 + 898 section 12–18 m. (**d**) D3K279 + 925 section 2–10 m. (**e**) D3K279 + 925 section 10–18 m.  
velocity is much lower than of the D3K279 + 885 and D3K279 + 896 sections, which is about 0.45 mm/d at the same stage.  
Figure 15: Horizontal convergence of Yujingshan tunnel on the (**a**) upper (**b**) middle and (**c**) lower steps.  
Figure 15b shows the monitor results of middle step excavation. The mileage D3K279 + 875-D3K279 + 925 produces horizontal convergence with 13 mm to 26 mm. Among them, D3K279 + 896 section maintains a large convergence with a value of 22.42 mm and a convergence velocity of 0.75 mm/d. The D3K279 + 875 section produces the maximum horizontal convergence of 24.05 mm and a convergence velocity of 0.78 mm/d. The monitoring results show that the horizontal convergences of D3K279 + 875-D3K279 + 925 section (7-9 mm) are larger than those of D3K279 + 935-D3K279 + 955 section. The deformation characteristic is that it increases slowly at first, then increases rapidly, and finally gradually tends to a stable state, similar to the excavation of upper step. However, it produces a shorter slow increasing stage and a longer rapid increasing stage than the upper step, and the maximum convergence velocity is 0.78 mm/d during rapidly increasing stage. All the monitor sections produce a controlled horizontal convergence which is smaller than 30 mm. The monitor results indicate that the penetration grouting can effectively reduce the horizontal convergence to allowable value, and improve the convergence velocity to a gentle state.  
As shown in Figure 15c, the maximum horizontal convergence of the lower step excavation occurs in D3K279 + 885 section with a value of 23.49 mm, and a convergence velocity is 0.78 mm/d. The horizontal convergences of other sections are less than 15 mm, and a convergence velocity of only 0.56 mm/d. The convergences of different sections show that after a short term rapid increasing stage, the horizontal convergence is in a stable state, and its value is less than the allowable value. The monitor results of lower step indicate that the lower step region is adequately reinforced by penetration grouting, its convergence value is low, and it reaches a stable state faster than the upper and middle steps. The variation law of displacement of surrounding rock show the similar tendency with previous literature [41; 42], which demonstrate the great grout effect is achieved.