## 4 On-Site Monitoring Results Analysis
### Determination of Surrounding Rock Loose Circle Thickness  
By measuring the thickness of the loose circle, the range and degree of influence of tunnel excavation activities on the surrounding rock could be grasped in detail. Based on this, the tunnel support parameters could be reasonably corrected, and lining construction could be adjusted in a timely and accurate manner, so as to achieve informed construction. At present, the commonly used loose circle thickness test methods are the acoustic method, the geological radar method, and the borehole camera method. However, these methods are complicated in terms of operation and are inconvenient for engineering applications [28]. Through data processing, the unit depth displacement rate curves of the surrounding rock at three sections within 10 m of the left and right sides of the main section were obtained, as shown in Figure 25. Through the analysis of the characteristics of the above curves, it could be judged whether the depth was in the loose circle. Therefore, the thickness of the surrounding rock loose circle was estimated. This method was very simple and convenient and enabled us to observe the changes in the surrounding rock loose circle with time.  
Figure 23: Time–displacement curve (left side).  
Figure 24: Time–displacement curve side (right side).  
From Figure 25, it can be seen that the displacement rate remained basically stable throughout the measurement period, and there was no mutation. The maximum displacement rates per unit depth on the left side of the section were 16.18 mm (0-1 m), 4.45 mm/d (1-5 m), and 4.37 mm/d (5-10 m) (Figure 25a), and the maximum displacement rates per unit depth on the right side of the section were 5.67 mm/d (0-1 m), 2.49 mm/d (1-5 m), and 2.38 mm/d (1-5 m) (Figure 25b). The displacement rate per unit depth in the 0-1 m interval was much higher than that in the 1-5 m and 5-10 m intervals. Therefore, it could be inferred that the depth of the surrounding rock loose zone of the 2# inclined shaft of the Muzhailing Tunnel was basically stable. At about 1 m, the beneficial effect of the NPR bolt harness coupling support in limiting the expansion of the surrounding rock loose circle was effectively verified. The displacement rate per unit depth on the left side of the section was much higher than that on the right side of the section. When measuring the depth of the loose circle, the number of measuring points could be appropriately increased to improve the accuracy of the measurement value.  
From the above analysis, the general law of radial displacement of surrounding rock after applying NPR bolt harness coupling support was obtained: the deformation was the largest in the shallow part of the wall, and gradually decreased along the radial direction to the deep part. After reaching a certain depth, the deformation became weak. This marked the maximum radius of the surrounding rock loose circle, \(R_{0}\). Without considering the influence of other processes, the displacement rate increased rapidly with time in the early stages, and then gradually decreased until the surrounding rock tended to stability, i.e., the displacement did not change.