## 3 Test of the Surrounding Rock
### Borehole Deformation Test of the Surrounding Rock  
After the borehole TV and acoustic wave test, according to the Standard for Engineering Rock Test Methods (GB/T50266-2013) and the Rock Test Procedure for Water Conservancy and Hydropower Engineering (SL/T264-2020), the borehole deformation test was conducted in the test range. A total of 42 deformation tests were carried out along the surrounding strata of the working shaft. The equipment used for the borehole deformation test is the Changjiang Academy of Sciences' CJBE91-I-type borehole elastic mode instrument. It is mainly composed of a pressurization system and a displacement testing system. In the test, two stiff pressure plates are pushed by four internal pistons to apply symmetrical strip stress to the borehole wall rock. The radial deformation of the borehole wall rock during loading is measured using displacement transducers installed in the pressure plates.  
The deformation displacement under various pressures is obtained in the test. The deformation or elasticity modulus (GPa) of the rock at the test site is determined using the following formula:  
\[E=A\cdot H\cdot D\cdot T(\
u,\beta)\cdot\frac{\Delta Q}{\Delta D} \tag{2}\]  
where \(A\) is the influence coefficient of the three-dimensional problem calculated by the two-dimensional formula, \(H\) is the pressure correction factor, \(D\) is the diameter of the borehole (mm), \(\Delta Q\) is the pressure (MPa), \(\Delta D\) is the deformation increment (mm), \(T(\
u,\beta)\) is the coefficient related to the size of the circumference and Poisson's ratio of rock mass when the bearing plate contacts the hole wall.  
The deformation modulus of the rock mass obtained from the borehole deformation and the pressure plate test are compared. The deformation modulus is more suitable for the project and the value is selected. The shear modulus for the engineering pressure on the test pressure-deformation curve corresponds to the deformation modulus. The tangent modulus for the engineering pressure on the rock borehole deformation test parameters corresponds to the elastic modulus. The NS-ZK-6 pressure-deformation curve is shown in Figure 5. The average values of the deformation and elastic modulus vary with depth and are shown in Figure 6. The results of the borehole deformation test can be used to convert the deformation and elastic modulus of six points of the surrounding rock at various depths. An analysis of the results of six borehole elastic deformation tests revealed that the rock in the working well has a deformation modulus from 0.4 GPa to 9.4 GPa, with an average value of 4.6 GPa. The elastic modulus ranges from 0.8 GPa to 11.3 GPa with an average value of 5.7 GPa. Figure 6 illustrates the overall depth dependence of the elastic and deformation modulus of the rock surrounding. The wave velocity of peolitic siltstone is related to porosity. High crustal stress can reduce rock porosity. So, the porosity decreases with the increase in depth, and the wave velocity increases with the increase in depth. Therefore, the modulus generally increases with the depth. Within the depth of 33 m (corresponding to the elevation above about 30 m), the deformation modulus of peolitic siltstone ranges from 0.4 to 2.3 GPa, while the deformation modulus below the elevation of about \(-\)30 m ranges from 3 to 9.4 GPa.