## 2 Accurate Identification Method of Fractured Rock Structure
### Deformation Criterion of Underground Cavern Chamber Surrounded by Fractured Rock Body  
For the underground cavern surrounding the rock of the broken rock body, although its stability criterion is related to the deformation value and deformation rate, the determining factor should be the tendency of increasing or decreasing deformation rate, i.e., deformation acceleration. The ratio between the next and the previously measured value of the deformation rate indicates the tendency to increase or decrease the deformation rate of the surrounding rock. At the beginning of the support deformation, the rate ratio should not only be less than 1.0 (negative acceleration), and with the support of the layered application, this ratio should quickly drop to a threshold value below and gradually tend to zero.  
The measured deformation rate (or deformation value) of the surrounding rock is used to reflect the overall geological and construction conditions of the measured section of the tunnel, making full use of the measured \"ratio of surrounding rock deformation rate\" of each project for stability discriminations. On this basis, make full use of the deformation monitoring data of the typical tunnel project surrounding the rock support system to select several typical sections from the unstable state that have been transformed into a stable state, as typical mechanical problems of tunnel engineering using mathematical and statistical methods to derive the threshold value of the ratio of deformation rate judgment.  
Based on the above principles and known conditions, the deformation rate ratio criterion (empirical hypothesis) is proposed to be applied to the discriminatory method for the stability of the surrounding rock at the initial stage of the support of the fractured underground cavern, which is: the ratio of the deformation rate v of the surrounding rock within 24 h after the pre-designed initial support is fully applied and the maximum value of the measured deformation rate v\({}_{0}\) (usually the initial measurement value) of the surrounding rock in the section. If the ratio is less than the threshold value ([v/v\({}_{0}\)] = 5%) of the ratio derived from the typical measurement data of several sections that may be  
Figure 7: Inbound traffic cave rock vein collapse phenomenon.  
destabilized and indeed transformed into a stable state, the section is expected to stabilize the surrounding rock. Deformation rate ratio criterion as formula (5).  
\[\text{v}/\text{v}_{0}<[\text{v}/\text{v}_{0}]=5\% \tag{5}\]  
The rate of deformation, then the application of the criterion that the measured rate of deformation ratio of about 50% said that the rate of deformation is slightly reduced from the stability of the surrounding rock is far away; the ratio of about 20% said that the rate of deformation is significantly reduced and it needs to strengthen the support or there is still the possibility of turning into instability; the ratio of 5% to 10% will tend to stabilize, but construction should still pay attention to monitoring and measuring so that the ratio has been reduced to within 5% to prevent accidental rebound.  
Considering the complex and variable geological conditions, especially when the surrounding rock is obviously affected by groundwater conditions, the deformation rate ratio of less than 5% should continue to monitor and measure until the surrounding rock is completely stable in accordance with the specifications of the deformation rate ratio criterion of the initial measurement value of the supplementary criterion. When one of the following conditions occurs in the initial measurement, it should immediately strengthen the support: (1) the maximum value of measured deformation rate of surrounding rock v\({}_{0}\) > 20 mm/d; (2) the measured deformation value of one day reaches the allowed deformation value of 1/5 to 1/4 or more; and (3) the sprayed concrete appears a large number of obvious cracks.